Article

Effect of different duration isometric contraction on tendon elasticity in human quadriceps muscles

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Abstract

1. The present study aimed to investigate the influence of isometric training protocols with long- and short-duration contractions on the elasticity of human tendon structures in vivo. The elasticity was assessed through in vivo determination of the elongation (L) of the tendons and aponeuroses using ultrasonography, while the subjects performed ramp isometric exercise up to maximum voluntary contraction (MVC). 2. Eight young males completed 12 weeks (4 days per week) of a unilateral isometric training programme on knee extensors, which consisted of two different combinations of contraction and relaxation times at 70 % MVC: one leg was trained using a short-duration protocol (3 sets of 50 repetitions of contraction for 1 s and relaxation for 2 s), and the other leg was trained using a long-duration protocol (4 sets of a combination of contraction for 20 s and relaxation for 1 min). The training volume per session, expressed as the integrated torque, was the same for the two protocols. 3. Both protocols resulted in a significant increase in MVC: 31.8 +/- 17.2 % for the short-duration protocol and 33.9 +/- 14.4 % for the long-duration protocol. Moreover, the training produced significant increases in the muscle volume of the constituents of the quadriceps femoris, with similar relative gains for the two protocols: 7.4 +/- 3.9 % for the short-duration protocol and 7.6 +/- 4.3 % for the long-duration protocol. 4. The short-duration protocol produced no significant change in L values at any of the force production levels. For the long-duration protocol, however, the L values above 550 N were significantly shorter after training. Analysis revealed that the group x test time interaction effect on tendon stiffness was significant. Stiffness increased significantly for the long-duration protocol, but not for the short-duration protocol. 5. The present study demonstrates a greater increase in stiffness of human tendon structures following isometric training using longer duration contractions compared to shorter contractions. This suggests that the changes in the elasticity of the tendon structures after resistance training may be affected by the duration of muscle contraction.

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... Dynamic movements incorporating the stretch-shortening cycle comprise the overwhelming majority of resistance training programs (179). However, isolated concentric, eccentric and isometric contractions have specific advantages when improving musculoskeletal properties and neuromuscular function (58,185,219), and are increasing in popularity (86). Isometric contractions (where the muscle-tendon unit remains at a constant length) and their role as a training option provide the focus of this chapter. ...
... Training variations outside of joint position or contraction intensity were also included. These variations include; 1) intent of contraction which included "progressive" vs "rapid" (216,389) and "explosive" vs "sustained" (32,225,354) contractions (Table 3); 2) total volume (231); 3) contraction duration (185,314); 4) rest period duration (385); and 5) periodization schemes (362) (Table 4). (32,35,49,164,205,216,225,250,335,344,353,354,389,396). ...
... While most methods of progressive resistance training can result in increased muscular size, it is important to understand how to optimally alter variables including intensity, frequency, and duration of each training method for maximal efficiency. Isometric resistance training has been demonstrated to induce significant hypertrophy (9,32,164,185,188,231,250,314). ...
Thesis
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Muscle structure and function are important to quality of life and physical performance. With eccentric and isometric resistance training established for improving muscle size and strength, eccentric quasi-isometric (EQI) contractions, defined as “holding a position until isometric failure and maximally resisting the subsequent eccentric phase”, are the focus of this thesis. The primary aims were to answer the overarching research question: “What are the acute, and long-term effects of EQI loading on muscle form and function?”. Systematic and narrative reviews were conducted, followed by the evaluation and optimization of testing methods, culminating in acute and short-term experimental studies. Reviews of the literature established that isometric training at longer muscle lengths produced greater hypertrophy than volume-equated shorter muscle length training (0.1-1.0%·week-1, effect size (ES) = 0.05-0.2·week-1), and transferred better to full range of motion (ROM) performance. Ballistic intent resulted in greater increases in rate of torque development (RTD) and neuromuscular activation (-1.5-3.6%·week-1, ES = 0.03-0.28·week-1). Hypertrophy and strength improvements were not related to isometric training intensity, however, contractions ≥ 70% were likely required to improve tendon qualities. While there is a lack of studies directly examining EQIs, they may provide a practical means of increasing metabolic and hormonal factors, while safely applying large quantities of mechanical tension. EQI training appears to be effective for improving musculotendinous morphological and performance variables with low injury risk. To be confident in the primary findings of the PhD, it was important to test and determine an optimized assessment battery for the acute and long-term effects and adaptations to EQI loading. Repeated between-day testing determined that ultrasound derived muscle thickness (MT) and subcutaneous fat corrected echo intensity (EI) had low variability in all quadriceps muscles and regions. Pennation angle (PA) and extended field-of-view fascicle length (FL) could only be reliably assessed in the vastus lateralis. Concentric torque and impulse were reliable between 90-20° of knee-flexion. Maximal voluntary isometric torque (MVIT), and RTD and impulse from 0-200 ms can be confidently assessed regardless of joint angle. Correlational analysis revealed that the isometric length-tension relationship was minimally associated with regional architecture and that the middle and distal architecture were the strongest predictors of MVIT. When comparing impulse-equated bouts of EQI and isokinetic eccentric loading (ECC), physiological responses were similar in 21/56 variables. EQIs resulted in greater vastus intermedius swelling (7.1-8.8%, ES = 0.20-0.29), whereas ECC resulted in greater soreness at the distal and middle vastus lateralis and distal rectus femoris (16.5-30.4%, ES = 0.32-0.54) and larger echogenicity increases at the distal rectus femoris and lateral vastus intermedius (11.9-15.1%, ES = 0.26-0.54). Furthermore, ECC led to larger reductions in concentric (8.3-19.7%, ES = 0.45-0.62) and isometric (6.3-32.3%, ES = 0.18-0.70) torque and RTD at medium-long muscle lengths. There were substantial differences in the number of contractions required to impulse-match the conditions (ECC: 100.8 ± 54 vs EQI: 3.85 ± 1.1). Mean contraction velocity over four contractions was 1.34º·s-1 with most (62.5 ± 4.9%) impulse produced between 40-70º. Most between-contraction changes in total angular impulse, contraction velocity, and time-under-tension occurred between 30-50º (ES = 0.53 ± 0.31, 60 ± 52%), while kinetics and kinematics relatively constant between 50-100º (ES = 0.10 ± 0.26, 14.3 ± 24.6%). Findings suggest that EQI loading could be an alternative to traditional resistance-training, possibly for individuals suffering from, or susceptible to musculoskeletal injury. Practitioners could shift the loading distribution to longer muscle lengths by prescribing a greater number of contractions, reducing rest periods, or implementing EQI contractions towards the end of a traditional training session where fatigue may be present. Although extensive future research is required to understand underlying mechanisms and long-term adaptations, the thesis provided novel and original information on the biomechanics and physiological effects of EQI loading. With the benefits of time-efficiency and minimal negative effects, EQI training is likely best applied in rehabilitation, general preparatory, unloading, or transition periods of the periodized plan.
... The authors suggested that the higher metabolites concentration and lower muscle pH during the longer sustained contraction protocol was most likely the reason for the increase muscle hypertrophy. However, Kubo et al. [34] who compared 2 methods of isometric leg extension training protocol, 3 × 50 repetitions of non-sustained contraction vs. 4 × 20 s sustained contraction, at 70 % MVC for a total of 50 training sessions, found similar magnitude of muscle hypertrophy (7.4 vs. 7.6 %) and strength gain (31.8 vs. 33.9 %) in both protocols. ...
... The difference in findings on muscle hypertrophy could be due to the difference in method of measuring muscle hypertrophy. Schott et al. [58] measured muscle size using computer tomographic scans at one-and 3-quarter of femur length, while Kubo et al. [34] measured muscle cross sectional area using magnetic resonance imaging. Possible reason for the conflicting findings in isometric strength improvement could be because Schott et al. [58] equalized the training volume between the 2 protocols while Kubo et al. [34] did not. ...
... Schott et al. [58] measured muscle size using computer tomographic scans at one-and 3-quarter of femur length, while Kubo et al. [34] measured muscle cross sectional area using magnetic resonance imaging. Possible reason for the conflicting findings in isometric strength improvement could be because Schott et al. [58] equalized the training volume between the 2 protocols while Kubo et al. [34] did not. In fact, the non-sustained contraction protocol in the study by Kubo et al. [34] induced a greater total contraction duration than the sustained contraction protocol (150 vs. 80 s). ...
Article
This review used a narrative summary of findings from studies that focused on isometric strength training (IST), covering the training considerations that affect strength adaptations and its effects on sports related dynamic performances. IST has been shown to induce less fatigue and resulted in superior joint angle specific strength than dynamic strength training, and benefited sports related dynamic performances such as running, jumping and cycling. IST may be included into athletes’ training regime to avoid getting overly fatigue while still acquiring positive neuromuscular adaptations; to improve the strength at a biomechanically disadvantaged joint position of a specific movement; to improve sports specific movements that require mainly isometric contraction; and when athletes have limited mobility due to injuries. To increase muscle hypertrophy, IST should be performed at 70–75% of maximum voluntary contraction (MVC) with sustained contraction of 3–30 s per repetition, and total contraction duration of>80–150 s per session for>36 sessions. To increase maximum strength, IST should be performed at 80–100% MVC with sustained contraction of 1–5 s, and total contraction time of 30–90 s per session, while adopting multiple joint angles or targeted joint angle. Performing IST in a ballistic manner can maximize the improvement of rate of force development.
... On the other hand, for isometric contractions, the doseresponse is not so clear. Several studies present interesting results focusing on dose-response volume and intensity of isometric contractions (3,15,27,30,34). Tillin and Folland (30) reported a sustained contraction protocol involving 3-sec of isometric contractions at 75%MVC resulted in greater strength improvement than a protocol involving 1-sec of isometric ballistic contraction at 80-90%MVC. ...
... Tillin and Folland (30) reported a sustained contraction protocol involving 3-sec of isometric contractions at 75%MVC resulted in greater strength improvement than a protocol involving 1-sec of isometric ballistic contraction at 80-90%MVC. Kubo et al., (15) observed a greater total contraction duration than the sustained contraction protocol (150-sec or 80-sec). Schott et al. (27) reported that longer sustained contractions (4x30-sec) presented greater responses in isometric strength and hypertrophy than shorter sustained contractions (4x10x3-sec) with the same intensity. ...
... Schott et al. (27) reported that longer sustained contractions (4x30-sec) presented greater responses in isometric strength and hypertrophy than shorter sustained contractions (4x10x3-sec) with the same intensity. Kubo et al., (15) indicated that when the intensity of training is equalized, the magnitude of strength and hypertrophy gained could more likely be determined by the total contraction duration per training session rather than per repetition. Authors suggested that the higher metabolites concentration and lower muscle pH during the longer sustained contractions might be the reason for muscle hypertrophy in isometric contractions (27). ...
Article
Full-text available
International Journal of Exercise Science 15(6): 676-685, 2022. The primary purpose of this study was to evaluate the acute effects of different durations of the isometric forearm plank exercise (IFPE) on peak force, echo intensity, muscle thickness, and perception of effort in recreationally-trained participants. Fifteen resistance-trained participants (23±3years, 76.4±6.5kg, 173.3±6.5cm) performed the IFPE with bodyweight in one of three durations in a randomized order: a). 1-min, b). 2-min, and c). 3-min. Muscle thickness (MT), echo intensity (EI), peak force (PF), and rating of perceived exertion (RPE) were measured pre-test and post-test. Two-way repeated-measures ANOVAs (2x3) were used to test differences between tests (pre-test and post-test) and treatment (1-min, 2-min, and 3-min) for PF, MT, and EI. One-way ANOVA was used to compare RPE between treatments (1-min, 2-min, and 3-min). There was a significant increase between pre-and post-test only for 3-min IFPE (p=0.008). For EI, there was a significant increase between pre-and post-test only for 3-min IFPE (p<0.001). For PF, there were observed significant reductions on post-test between 1-min vs. 3-min (p<0.001) and 2-min vs. 3-min IFPE (p<0.001). For RPE, there were statistical differences between 1-min vs. 2-min (p<0.001), 1-min and 3-min (p<0.001), 2-min and 3-min (p=0.001). In conclusion, only 3-min IFPE induced an increase in MT and EI and a reduction in PF when compared to 1-min and 2-min (during the post-test). RPE increased with the increase in the duration of the IFPE.
... properties, and this may have implications for performance and injury (Bohm et al., 2015). For example, tendons become more extensible (Kubo et al., 2001b(Kubo et al., , 2009Kay and Blazevich, 2009;Burgess et al., 2009;Joseph et al., 2014) and smaller in thickness (Wearing et al., 2007(Wearing et al., , 2014Grigg et al., 2009;Kristiansen et al., 2014) when subjected to acute load, and become stiffer (Kubo et al., 2012(Kubo et al., , 2001a(Kubo et al., , 2006 and may hypertrophy (Arampatzis et al., 2007;Couppé et al., 2008;Bohm et al., 2014;Geremia et al., 2018;Kongsgaard et al., 2007) when loaded over long-term periods (>12 weeks). The mechanisms responsible for tendon adaptation to load are currently unclear. ...
... Kubo et al. (2009) compared short-(1 s, 5 sets×50 repetitions) and long-duration (15 s, 1 set×17 repetitions) highintensity isometric contractions and found an immediate increase in AT elongation only after the long-duration contraction. Previous studies by the same group showed that long-duration and highintensity isometric contractions over 12 weeks resulted in a greater increase in tendon stiffness compared with shorter-duration contractions (Kubo et al., 2001a(Kubo et al., , 2006. However, none of these studies linked changes in mechanical properties (i.e. ...
... increased stiffness and tendon hypertrophy) compared with lower levels of load duration and intensity. In this context, Kubo et al. (2001a) found that tendon stiffness remarkably increased after 12 weeks of high-intensity isometric training with a longer-duration contraction versus a shorter duration. ...
Article
The Achilles tendon (AT) exhibits volume changes related to fluid flow under acute load which may be linked to changes in stiffness. Fluid flow provides a mechanical signal for cellular activity and may be one mechanism that facilitates tendon adaptation. This study aimed to investigate whether isometric intervention involving a high level of load duration and intensity could maximize the immediate reduction in AT volume and stiffness compared to interventions involving a lower level of load duration and intensity. Sixteen healthy participants (12 males, 4 females; age= 24.4±9.4 y; body mass= 70.9±16.1 kg; height= 1.7±0.1 m) performed three isometric interventions of varying levels of load duration (2 s and 8 s) and intensity (35% and 75% MVICs) over a 3-week period. Freehand 3D ultrasound was used to measure free AT volume (at rest) and length (at 35%, 55%, and 75% of maximum plantarflexion force) pre and post interventions. The slope of force-elongation curve over these force levels represented individual stiffness (N/mm). Large reductions in free AT volume and stiffness resulted in response to long-duration high-intensity loading whilst less reduction resulted with a lower load intensity. In contrast, no change in free AT volume and a small increase in AT stiffness occurred with lower load duration. These findings suggest that the applied load on the AT must be heavy and sustained for a long duration to maximize immediate volume reduction, which might be an acute response that enables optimal long-term tendon adaptation via mechanotransduction pathways.
... The analysis of human Achilles tendon (AT) mechanical properties in vivo using ultrasonography combined with dynamometry has established itself as a non-invasive, affordable, and easily applied valid measure. The application of the ultrasound method has provided relevant information with respect to tendon adaptation [1,2], tendon injury [3], and tendon function [4] across different populations and age groups. For example, repeated exposure to specific mechanical loading (e.g., resistance training) can increase tendon stiffness along with muscle strength gains [1,2], whereas tendinopathic as well as aging tendons demonstrate lower stiffness and higher tendon strains at given Sensors 2022, 22, 2549 2 of 10 force levels [3,5,6]. ...
... The application of the ultrasound method has provided relevant information with respect to tendon adaptation [1,2], tendon injury [3], and tendon function [4] across different populations and age groups. For example, repeated exposure to specific mechanical loading (e.g., resistance training) can increase tendon stiffness along with muscle strength gains [1,2], whereas tendinopathic as well as aging tendons demonstrate lower stiffness and higher tendon strains at given Sensors 2022, 22, 2549 2 of 10 force levels [3,5,6]. Recent observations indicate that due to discrepancies between the time frames of muscle and tendon adaptation, imbalances between muscle force generation and tendon resistance may occur through periods of exercise, potentially increasing the demand of the tendon and its risk to overuse injuries [7]. ...
... AT elongation during muscular contraction is usually estimated by choosing a tissue landmark (e.g., myotendinous junction or muscle fascicle insertion) using ultrasonography and digitizing that landmark frame by frame [1,3,8]. Based on the generated force-length relationship, AT stiffness is commonly assessed by linear regression using intervals from 50% to 100% [8], 80% to 100% [9], or from 90% to 100% of the calculated AT force [10]. ...
Article
Full-text available
The assessment of the force–length relationship under mechanical loading is widely used to evaluate the mechanical properties of tendons and to gain information about their adaptation, function, and injury. This study aimed to provide a time-efficient ultrasound method for assessing Achilles tendon mechanical properties. On two days, eleven healthy young non-active adults performed eight maximal voluntary isometric ankle plantarflexion contractions on a dynamometer with simultaneous ultrasonographic recording. Maximal tendon elongation was assessed by digitizing ultrasound images at rest and at maximal tendon force. Achilles tendon stiffness index was calculated from the ratio of tendon force-to-strain. No within- and between-day differences were detected between the proposed method and manual frame by frame tracking in Achilles tendon maximal force, maximal elongation, maximal strain, and stiffness index. The overall coefficient of variation between trials ranged from 3.4% to 10.3% and average difference in tendon tracking between methods was less than 0.6% strain. Furthermore, an additional assessment demonstrated significant differences between elite athletes, healthy young, and older adults in Achilles tendon force and stiffness index. Hence, the analysis has the potential to reliably and accurately monitor changes in Achilles tendon mechanical properties due to aging and altered mechanical loading in a time-efficient manner.
... eccentric, fascicle, force, mechanical loading, muscle, stiffness, strength, tendon contractions have specific advantages when improving musculo-skeletal properties and neuromuscular function [11][12][13] and are increasing in popularity. 14 Isometric contractions (where the muscle-tendon unit remains at a constant length) and their role as a training option provide the focus of this paper. ...
... 44 Training variations outside of joint position or contraction intensity were also included. These variations include the following: (a) intent of contraction which included "progressive" vs "rapid" 48,66 and "explosive" vs "sustained" 43,47,67 contractions (Table 3); (b) total volume 39 ; (c) contraction duration 13,34 ; (d) rest period duration 68 ; and (e) periodization schemes 69 (Table 4). ...
... by 0.84%/week and 0.043 ES/week. 13,[30][31][32]34,43,44,67,69 Maximal isometric force significantly increased in 14 studies (8%-60.3%, ES = 0.34-3.26) ...
Article
Full-text available
Isometric training is used in the rehabilitation and physical preparation of athletes, special populations and the general public. However, little consensus exists regarding training guidelines for a variety of desired outcomes. Understanding the adaptive response to specific loading parameters would be of benefit to practitioners. The objective of this systematic review, therefore, was to detail the medium to long‐term adaptations of different types of isometric training on morphological, neurological and performance variables. Exploration of the relevant subject matter was performed through MEDLINE, PubMed, SPORTDiscus and CINAHL databases. English, full‐text, peer‐reviewed journal articles and unpublished doctoral dissertations investigating medium to long‐term (≥3 weeks) adaptations to isometric training in humans were identified. These studies were evaluated further for methodological quality. Twenty‐six research outputs were reviewed. Isometric training at longer muscle lengths (0.86‐1.69%/week, ES = 0.03‐0.09/week) produced greater muscular hypertrophy when compared to equal volumes of shorter muscle length training (0.08‐0.83%/week, ES = ‐0.003‐0.07/week). Ballistic intent resulted in greater neuromuscular activation (1.04‐10.5%/week, ES = 0.02‐0.31/week vs. 1.64‐5.53%/week, ES = 0.03‐0.20/week) and rapid force production (1.2‐13.4%/week, ES = 0.05‐0.61/week vs. 1.01‐8.13%/week, ES = 0.06‐0.22/week). Substantial improvements in muscular hypertrophy and maximal force production were reported regardless of training intensity. High‐intensity (≥ 70%) contractions are required for improving tendon structure and function. Additionally, long muscle length training results in greater transference to dynamic performance. Despite relatively few studies meeting the inclusion criteria, this review provides practitioners with insight into which isometric training variables (e.g. joint angle, intensity, intent) to manipulate to achieve desired morphological and neuromuscular adaptations.
... In vivo tendinous tissue stiffness is typically determined from force-elongation relationships acquired by combining tissue elongation visualized via ultrasonography with estimates of tendon force during ramp isometric contractions. In response to a constant rate of increase in contractile force, elongation of the free tendon [between proximal and distal osteotendon junction's (Kongsgaard et al., 2007;Seynnes et al., 2009)] and elongation of the distal tendon-aponeurosis complex (i.e., aponeurosis and free tendon) via the displacement of a musclefascicle aponeurosis intersection (Kubo et al., 2001(Kubo et al., , 2006cArampatzis et al., 2007) can be used to determine stiffness of both these structures. During muscle contraction the free tendon experiences tensile loading and positive longitudinal strain, whereas the radial expansion of muscle fascicles during force-generation and shortening causes the aponeurosis to also undergo transverse elongation and positive strain (Azizi and Roberts, 2009;Raiteri et al., 2016). ...
... The mechanical stiffness of the tendon-aponeurosis complex has been repeatedly found to increase following strength training with sustained contractions at high loads (≥2 s duration with loads of >70% maximum: Bohm et al., 2015;Wiesinger et al., 2015), e.g., 16-54% after 12-14 weeks (Kubo et al., 2001(Kubo et al., , 2006bArampatzis et al., 2007). Interestingly, two recent studies reported that strength training with brief explosive-contractions (<1 s) characterized by maximum/near maximum rate of force development up to a high level of force produced increases in stiffness after merely 4 (34%; Tillin et al., 2012) and 6 weeks (62%; Burgess et al., 2007) of training. ...
... In contrast to the free tendon, the tendon-aponeurosis complex stiffness measured at high force levels (i.e., 70-80% pre-training MVT) increased only after SCT, but not ECT. The increased tendon-aponeurosis complex high force stiffness after SCT is consistent with previous findings (Kubo et al., 2001;Arampatzis et al., 2007Arampatzis et al., , 2010Bohm et al., 2014) and the greater increase after SCT than ECT may be attributable to the substantially longer loading duration in SCT. Previous work has shown greater increases in tendon-aponeurosis complex stiffness after strength training with long vs. short duration contractions (Kubo et al., 2001;Arampatzis et al., 2007). ...
Article
Full-text available
The effect of different strength training regimes, and in particular training utilizing brief explosive contractions, on tendinous tissue properties is poorly understood. This study compared the efficacy of 12 weeks of knee extensor explosive-contraction (ECT; n = 14) vs. sustained-contraction (SCT; n = 15) strength training vs. a non-training control (n = 13) to induce changes in patellar tendon and knee extensor tendon–aponeurosis stiffness and size (patellar tendon, vastus-lateralis aponeurosis, quadriceps femoris muscle) in healthy young men. Training involved 40 isometric knee extension contractions (three times/week): gradually increasing to 75% of maximum voluntary torque (MVT) before holding for 3 s (SCT), or briefly contracting as fast as possible to ∼80% MVT (ECT). Changes in patellar tendon stiffness and Young’s modulus, tendon–aponeurosis complex stiffness, as well as quadriceps femoris muscle volume, vastus-lateralis aponeurosis area and patellar tendon cross-sectional area were quantified with ultrasonography, dynamometry, and magnetic resonance imaging. ECT and SCT similarly increased patellar tendon stiffness (20% vs. 16%, both p < 0.05 vs. control) and Young’s modulus (22% vs. 16%, both p < 0.05 vs. control). Tendon–aponeurosis complex high-force stiffness increased only after SCT (21%; p < 0.02), while ECT resulted in greater overall elongation of the tendon–aponeurosis complex. Quadriceps muscle volume only increased after sustained-contraction training (8%; p = 0.001), with unclear effects of strength training on aponeurosis area. The changes in patellar tendon cross-sectional area after strength training were not appreciably different to control. Our results suggest brief high force muscle contractions can induce increased free tendon stiffness, though SCT is needed to increase tendon–aponeurosis complex stiffness and muscle hypertrophy.
... The potential for aponeurosis hypertrophy in response to resistance training has also had limited research attention. 32,33 Short-term functional overload with resistance training (up to 14 weeks) utilizing high load contractions consistently increases "free" tendon 22,24,34,35 and tendon-aponeurosis complex 23,25,26,[36][37][38] stiffness. The increased tendon stiffness after short-term resistance training is typically ascribed to the approximately parallel increases in tendon Young's modulus (material stiffness 24,35 ) rather than substantive changes in tendon size, as mentioned above. ...
... This finding is in contrast to previous reports of greater knee extensor tendon-aponeurosis complex stiffness assessed with repeated measures before and after short-term resistance training. 26,36,37 It is possible that a cross-sectional design lacks the sensitivity to detect relatively modest differences in tendon-aponeurosis stiffness. Alternatively, previous studies have commonly measured stiffness at different absolute forces pre-and post-training, which may have accentuated the scale of this training adaptation. ...
... Error bars indicate the within-group SD for stress (y-axis bar) and strain (x-axis bar). B and C, Group comparisons of the PT strain at the common stress level of 40 MPa, and PT Young's modulus (gradient of curves in A over 80%-100% common stress level[32][33][34][35][36][37][38][39][40]). Bars are mean AE SD. ...
Article
Aim: The potential for tendinous tissues to adapt to functional overload, especially after several years of exposure to heavy resistance training is largely unexplored. This study compared the morphological and mechanical characteristics of the patellar tendon and knee-extensor tendon-aponeurosis complex between young men exposed to long-term (4 years; n=16), short-term (12 weeks; n=15) and no (untrained controls; n=39) functional overload in the form of heavy resistance training. Methods: Patellar tendon cross-sectional area, vastus-lateralis aponeurosis area and quadriceps femoris volume, plus patellar tendon stiffness and Young's modulus, and tendon-aponeurosis complex stiffness, were quantified with MRI, dynamometry and ultrasonography. Results: As expected long-term trained had greater muscle strength and volume (+58% and +56% vs untrained, both P<0.001), as well as a greater aponeurosis area (+17% vs untrained, P<0.01), but tendon cross-sectional area (mean and regional) was not different between groups. Only long-term trained had reduced patellar tendon elongation/strain over the whole force/stress range, whilst both short-term and long-term overload groups had similarly greater stiffness/Young's modulus at high force/stress (short-term +25/22%, and long-term +17/23% vs untrained; all P<0.05). Tendon-aponeurosis complex stiffness was not different between groups (ANOVA, P = 0.149). Conclusion: Despite large differences in muscle strength and size, years of resistance training did not induce tendon hypertrophy. Both short-term and long-term overload, demonstrated similar increases in high force mechanical and material stiffness, but reduced elongation/strain over the whole force/stress range occurred only after years of overload, indicating a force/strain specific time-course to these adaptations. This article is protected by copyright. All rights reserved.
... Dört ve 8 haftalık kuvvetlendirme eğitiminin kas sıkılığına etkisi araştırıldığında 8 haftalık eğitimin tendo-apenöroz yapı üzerinden sıkılığı arttırdığı bulunmuştur (94). ...
... Neden aşırı kullanım sendromu olan bir tendonun, ağır egzersiz eğitimiyle iyileştiği tam olarak aydınlatılamamıştır. Fakat sonuçta ilgili bölgede kollajen tip I'in önemli ölçüde arttığı gösterilmiştir (89)(90)(91)(92)(93)(94)(95)(96)(97)(98)(99)(100). ...
Chapter
İntramusküler konnektif dokunun güç aktarımında rolünün anlaşılması ve ilerleyen teknolojiyle birlikte inceleme tekniklerindeki gelişmelere bağlı olarak matriks aktivitesi de önem kazanmıştır. Ekstraselü- ler matriks doku mekaniğinin temelidir ve çevreyle etkileşerek mekanik olayları biyokimyasal aktiviteye dönüştüren canlı ve son derece dinamik bir ağ sistemidir. Ekstraselüler matriksin işleyişini ve değişken yüklere tepkilerini anlamak klinik bakış açısına yön verebilir. Fizyoterapi ve rehabilitasyon yöntemlerinin etki mekanizmalarını açıklayıcı nitelikte olan ekstraselüler matriksle ilgili gelişmeler, aynı zamanda tedavi programları için yönlendirici de olacaktır. Hastalıkların açığa çıkmasında ve/veya klinik bulgularında matriks maddelerinin de çok önemli olduğu bilinmektedir. Bu nedenle ekstraselüler matriksin genel olarak yüke verdiği cevapları bilmek, klinikte kullanılan yöntemlerin etkinliğinin arttırılması ve izlenecek yol haritasının belirlenmesine de katkı sağlayacaktır.
... However, the HFS diet combined with exercise was associated with a reduction in the Young's modulus of the tail tendon compared to that obtained in LFD control animals. Exercise in normal weight animals has beneficial effects on tendon morphology and function (Kubo et al., 2001;Langberg et al., 2001;Langberg et al., 1999;Narici et al., 1996). It has been shown that chronic exercise induces collagen fiber formation (Langberg et al., 2001;Langberg et al., 1999), and an increased cross sectional area and stiffness in weight bearing tendons of humans (Kubo et al., 2001;Narici et al., 1996), horses (Birch et al., 1999), and pigs (Woo et al., 1981). ...
... Exercise in normal weight animals has beneficial effects on tendon morphology and function (Kubo et al., 2001;Langberg et al., 2001;Langberg et al., 1999;Narici et al., 1996). It has been shown that chronic exercise induces collagen fiber formation (Langberg et al., 2001;Langberg et al., 1999), and an increased cross sectional area and stiffness in weight bearing tendons of humans (Kubo et al., 2001;Narici et al., 1996), horses (Birch et al., 1999), and pigs (Woo et al., 1981). However, little is known about the effects of chronic exercise on non-weight bearing tendons in young and old animals. ...
Article
The worldwide trajectory of increasing obesity rates is a major health problem precipitating a rise in the prevalence of a variety of co-morbidities and chronic diseases. Tendinopathy, in weight and non-weight bearing tendons, in individuals with overweight or obesity has been linked to metabolic dysfunction resulting from obesity. Exercise and dietary fibre supplementation (DFS) are common countermeasures to combat obesity and therefore it seems reasonable to assume that they might protect tendons from structural and mechanical damage in a diet-induced obesity (DIO) model. The purpose of this study was to determine the effects of a DIO, DIO combined with moderate exercise, DIO combined with DFS (prebiotic oligofructose), and DIO combined with moderate exercise and DFS on the mechanical and biochemical properties of the rat tail tendon. Twenty-four male Sprague-Dawley rats, fed a high-fat/high-sucrose diet were randomized into a sedentary, a moderate exercise, a DFS, or a moderate exercise combined with DFS group for 12 weeks. Additionally, six lean age-matched animals were included as a sedentary control group. DIO in combination with exercise alone and with exercise and DFS reduced the Young’s Modulus but not the collagen content of the rat tail tendons compared to lean control animals. However, no differences in the mechanical and biochemical properties of the rat tail tendon were detected between the DIO and the lean control group, suggesting that DIO by itself did not impact the tail tendon. It seems that longer DIO exposure periods may be needed to develop overt differences in our DIO model.
... It is unclear why increased variation is observed but speculatively may be a consequence of altered tendon composition after exercise, muscle stiffness or muscle bulk, which may affect the measurement protocol. Kubo et al. [55] previ- ously suggested that increased activity through long contraction training causes changes in the internal structure of the tendon resulting in increased stiffness. Stiffer tendon may affect variation and future studies are required to investigate the relationship between increased activity levels and measurement variability, and its clinical significance. ...
... Stiffer tendon may affect variation and future studies are required to investigate the relationship between increased activity levels and measurement variability, and its clinical significance. Meanwhile, this association may be a significant limitation in the future application of SE in quadriceps tendon, particularly as extensor weakness has been indicated as a risk factor in the development of knee osteoarthritis [56], and previous association of increased activity levels and quadriceps tendon stiffness have been reported [55]. SE application in MSK imaging is currently restricted by limited pathological understanding and lack of standardisation [18]. ...
Article
Objectives To explore the associations between participant characteristics and magnitudes of difference in paired elastography measures of knee tendon from different ultrasound systems, and to compare strain elastography pattern description. Materials and Methods Quadriceps and patellar tendons of 20 healthy volunteers (40 tendons) were examined by an experienced operator employing two ultrasound systems (GE S8 and Esaote MyLab 70XVG). Pearson/Spearman correlations explored the influence of participant characteristics (BMI, body fat %, leg circumference, activity level) on the magnitude of differences between measures. Paired-sample t test or Wilcoxon signed rank test were performed to compare repeated measures of individual ultrasound systems. Results The quadriceps tendon was characteristically stiffer than the patellar tendon. Participant characteristics were associated with within machine differences of the distal quadriceps tendon (BMI; r = 0.49, p = 0.028–0.03 and body fat %; r = 0.43, p = 0.05–0.056) ER measures. Conclusions Anthropometric and body composition parameters were associated with within machine differences for elasticity measures, where high BMI and body fat % contribute to paired measurement variance at the distal quadriceps tendon. Strain elastography protocols should be standardised, repeated ER measures performed using the same US system and patient characteristics considered for future clinical applications.
... These studies had a limited number of patients for the reliability analysis (6 and 7 patients) and reliability was estimated only for a single rater. Furthermore, we are aware of only one study reporting test-retest reliability for patellar tendon CSA using MRI (Kubo et al. 2001). In addition, to the best of our knowledge, only studies by Brushøj et al. (2006) and Kruse et al. (2017) have reported reliability estimates of USI and MRI for measurement of lower limb tendon dimensions from the same set of patients. ...
... In the present data, the corresponding values were 3.4% and 6.6% for the experienced and inexperienced raters, respectively. Kubo et al. (2001) reported a coefficient of variation of 1.6% for patellar tendon CSA measurement for repeated measures performed 12 wk apart. In our study, these values were 4.1% and 6.0% for the experienced and inexperienced raters, respectively. ...
Article
This study investigated the reliability of Achilles and patellar tendon cross-sectional area (CSA) measurement using ultrasound imaging (USI) and magnetic resonance imaging (MRI). Fifteen healthy adults were imaged twice on two occasions, interrupted by a tendon loading protocol. Tendon CSA segmentations were conducted by an experienced and an inexperienced rater blinded to information regarding subject, session and loading status. USI provided good test-retest reliability (intra-class correlation coefficient [ICC] 2,1 > 0.85, standard error of measurement [SEM] 5%-6%), while with MRI it was excellent (ICC 2,1 > 0.92, SEM 4%) for the experienced rater. This study suggests that MRI provides superior reliability for tendon CSA measurements compared with USI. However, the difference in reliability between the methods was small, and the results were inconclusive regarding objectivity and sensitivity to change when assessed based on the effect of loading. We concluded that both methods can be used for reliable CSA measurements of the Achilles and patellar tendons when using a highly standardized measurement protocol and when conducted by an experienced rater.
... Cette sous-estimation influence grandement la relation force-élongation, et donc la valeur de la raideur calculée à partir de Pour le groupe J55, la raideur de l'aponévrose du muscle VL est augmentée suite à l'entrainement dans notre étude. Certaines études ont montré des résultats similaires mais avec des valeurs de gains plus élevés (~+60%) (Kubo et al. 2001a;Kubo et al. 2001b;Kubo et al. 2006b;Kubo et al. 2009), ou une raideur inchangée (Kubo et al. 2001a;Kubo et al. 2003b;Kubo et al. 2006d;Kubo et al. 2006a;Kubo et al. 2006b;Kubo et al. 2009). Comme évoqué précédemment, il est difficile de pouvoir comparer ces différents résultats car le protocole d'entrainement est différent pour chaque étude. ...
... Cette sous-estimation influence grandement la relation force-élongation, et donc la valeur de la raideur calculée à partir de Pour le groupe J55, la raideur de l'aponévrose du muscle VL est augmentée suite à l'entrainement dans notre étude. Certaines études ont montré des résultats similaires mais avec des valeurs de gains plus élevés (~+60%) (Kubo et al. 2001a;Kubo et al. 2001b;Kubo et al. 2006b;Kubo et al. 2009), ou une raideur inchangée (Kubo et al. 2001a;Kubo et al. 2003b;Kubo et al. 2006d;Kubo et al. 2006a;Kubo et al. 2006b;Kubo et al. 2009). Comme évoqué précédemment, il est difficile de pouvoir comparer ces différents résultats car le protocole d'entrainement est différent pour chaque étude. ...
Thesis
Un des problèmes majeurs contribuant à la réduction de la mobilité chez la personne âgée est la hausse de l’occurrence des chutes. La capacité à maintenir l’équilibre ou la stabilité posturale a été précédemment associée à la structure et aux propriétés mécaniques des tendons du membre inférieur. Cette étude fut menée afin d’évaluer les effets de l’intensité d’entrainement et de l’âge sur les changements de l’architecture tendineuse et ses propriétés mécaniques ainsi que sur les adaptations musculaires du membre inférieur. Ce projet avait ainsi pour objectif de comparer les effets de deux conditions d’entrainement pour un volume équivalent (intensité modérée (55% d’une répétition maximale (1RM) vs élevée (80% de 1RM)) sur deux groupes musculaires différents (quadriceps vs triceps sural), sur les adaptations des tendons d’Achille et patellaire associés aux adaptations de ces groupes musculaires respectifs. Enfin, le dernier objectif de cette étude était de montrer si des changements de la balance posturale et de la capacité de mouvement pouvaient s’expliquer par les évolutions de l’architecturale et de propriétés mécaniques des structures musculaires et tendineuses avec l’âge. Dix hommes jeunes (Age : 24.8 ± 3.6) et 27 séniors (Age : 69.9 ± 4.5) sédentaires ont été recrutés et ont participé à un programme d’entrainement en résistance de 12 semaines (3 fois/semaine) sur les muscles du triceps sural et du quadriceps. Le groupe de jeunes (n=10) ainsi qu’un groupe de séniors (n=13) ont participé à un programme d’entrainement modéré correspondant à 55% de 1RM, tandis qu’un deuxième groupe de seniors s’est vu imposer une intensité d’entrainement de 80% de 1RM (n=14). Chaque groupe a reçu exactement le même volume d'entraînement sur les muscles quadriceps et triceps sural en utilisant des machines de musculation guidées : la presse à jambes, l'extension des jambes et la machine à mollets assis. Afin de pouvoir obtenir les paramètres nécessaires à cette étude, l’utilisation d’ergomètres, d’images échographiques et IRM et d’un système de capture de mouvement ont été nécessaires. En comparant deux populations de jeunes et de séniors, cette étude a ainsi permis de quantifier une diminution de la force, couplée ou non suivant le tendon considéré à une diminution des propriétés intrinsèques du matériau tendineux. L’obtention de l’architecture musculaire a permis de construire les courbes d’évolutions de la section de chacun des muscles du quadriceps et du triceps sural pour les populations jeunes et séniors. Les deux conditions d’entrainement nous ont permis de mettre en évidence une amélioration des propriétés mécaniques des tendons d’Achille et patellaire, et plus sensiblement le tendon d’Achille, sur les deux populations jeunes et séniors sans toutefois observer de gain supplémentaire pour une intensité élevée. Des gains similaires suite à la période d’entrainement ont pu être observés chez les séniors sur les volumes des muscles du triceps sural et du quadriceps sans distinction de l’intensité considérée. L’analyse du mouvement nous a permis de mettre en évidence l’amélioration de la stabilité posturale et une évolution de la stratégie de flexion du tronc lors d’un lever de chaise suite à l’entrainement chez les séniors sans bénéfice supplémentaire entre une intensité modérée et élevée. De plus, les effets de l’âge sur les propriétés mécaniques des tendons ont pu être corrélés avec les performances liées aux exercices de stabilité posturale, de saut et de lever de chaise. Ce travail a donc permis de quantifier les effets de l’âge sur les capacités musculaires, tendineuses et de mouvement. Cette étude nous a également permis de mettre en évidence un seuil d’intensité d’entrainement (55% de 1RM) à partir duquel les personnes âgées ne semblent pas montrer de gain additionnel pour les systèmes musculaires et tendineux. Ce travail permet donc de proposer une optimisation de l’activité physique prescrite à la personne âgée ou vieillissante.
... Furthermore, isometric contraction of lumbar and postural muscles may improve internal stabilization (Kisner et al., 2017). Acute and chronic exposure to isometric contractions may modulate muscle stiffness and augment muscular activity allowing the spine to maintain proximal stability while under load (Kibler et al., 2006, Burgess et al., 2007, Kubo et al., 2001, Lee and McGill, 2017. While MVIC appears to elicit improvements in muscle force-generating attributes, the effect of an MVIC on postural stability and lumbar motion has not been thoroughly investigated (McGill, 2001). ...
... Therefore, an effective warm-up strate-gy targeting neuromuscular efficiency prior to axial-loaded exercise may offer application for injury-mitigation, stabil-ity, and performance. A pre-exercise MVIC may modulate muscle stiffness and augment muscular activity allowing the spine to maintain proximal stability while under load (Kibler et al., 2006, Burgess et al., 2007, Kubo et al., 2001, Lee and McGill, 2017. For example, Lee and McGill (2017) recent-ly showed that isometric training exercises could induce immediate changes in core stiffness, which may transiently influence performance and injury resilience. ...
Article
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Background: Post-activation potentiation (PAP) is a neuromuscular phenomenon that has been shown to augment muscular force generating attributes as well as neural and sensory recruitment. While PAP has demonstrated to acutely enhance muscular performance during high-intensity activities, the effect of PAP on lumbopelvic kinematics under load remains unknown. Objectives: The purpose of this study was to examine the potential PAP effect of a hip abduction maximal voluntary isometric contraction (MVIC) on lumbar motion and power output during the barbell back squat. Methods: Nine resistance-trained men (22.9±2.3 y; 85.0±13.8 kg; 174.3±5.1 cm) performed a set of 5 repetitions of the barbell back squat using 80% one-repetition maximum with and without a hip abduction MVIC prior to performance. Experimental and control trials were randomized and counterbalanced among participants. MVIC was carried out via manual long-lever hip abduction. During the back squat exercise, lumbar motion analysis was performed using wireless motion-sensor technology, and power output was assessed via an accelerometer. Results: No significant differences were observed between trials for lumbar flexion range of motion (ROM) (p=0.32), lumbar flexion maximum deviation (p=0.32), lumbar lateral flexion ROM (p=0.81), lumbar lateral flexion maximum deviation (p=0.98), lumbar rotation maximum deviation (p=0.70), average peak power (p=0.98), or average mean power output (p=0.99) during the squat protocol. Conclusions: Implementation of a manual long-lever hip abduction MVIC prior to the back squat exercise did not significantly alter lumbar motion or augment power output in resistance trained males.
... During isometric contractions, the rate of skeletal muscle contractile force production is slowed by the necessity of the muscle to shorten in order to stretch the elastic components that transmit muscle force (Hill, 1951;Edman & Josephson, 2007). The mechanical stiffness (resistance to elongation) of the muscle-tendon unit (MTU) and particularly its tendinous tissue components (external "free" tendon and aponeurosis) are therefore widely hypothesised to influence in vivo RTD (Wilson et al. 1994;Kubo et al. 2001;Reeves et al. 2003). Stiffer tissues are thought to provide greater mechanical resistance that can constrain muscle shortening during the initial stages of contraction thereby permitting muscle fibers to operate in the higher force region of the force-velocity relationship (Wilson et al. 1994). ...
... Yet MTU stiffness has typically been measured over a high torque increment (e.g. [Bojsen-Møller et al. 2005]; 50-100%MVT [Kubo et al. 2001;Wang et al. 2012]) even though RTD is usually measured from the lowest possible torque -rest (e.g. 0-50% MVT). ...
Article
The influence of musculotendinous tissue stiffness on contractile rate of torque development (RTD) remains opaque. This study examined the relationships between both patellar tendon (PT) and vastus lateralis (VL) muscle-tendon unit (MTU) stiffness, and voluntary and evoked knee extension RTD. Fifty-two healthy untrained males completed duplicate laboratory sessions. Absolute and relative RTD was measured at 50 Nm/25%MVT increments from onset and sequentially during explosive voluntary and evoked octet (supramaximal stimulation: [8 pulses at 300 Hz]) isometric contractions. Isometric maximum voluntary torque (MVT) was also assessed. PT and MTU stiffness were derived from simultaneous force and ultrasound recordings of the PT and VL aponeurosis during constant RTD ramp contractions. Absolute and relative (to MVT and resting tissue length) stiffness (k) was measured over identical torque increments as RTD. Pearson's correlations tested relationships between stiffness and RTD measurements over matching absolute/relative torque increments. Absolute and relative PT k was unrelated to equivalent voluntary or evoked RTD (r = 0.020.255, P = 0.069–0.891). Absolute MTU k was unrelated to voluntary or evoked RTD (r ≤ 0.191, P ≥ 0.184), however some measures of relative MTU k were related to relative voluntary/evoked RTD (e.g. RTD25-50%MVT r = 0.374/0.353, P = 0.007/0.014). In conclusion, relative MTU k explained a small proportion of the variance in relative voluntary and evoked RTD (both ≤19%), despite no association of absolute MTU k or absolute/relative PT k with equivalent RTD measures. Therefore the muscle-aponeurosis component, but not free tendon was associated with relative RTD, although it seems an overriding influence of MVT negated any relationship of absolute MTU k and absolute RTD. This article is protected by copyright. All rights reserved
... Tendons therefore modulate the movement output response for a given muscular input, with this influence being governed by the tendon's mechanical properties (Ettema, 1996;Bobbert, 2001;Lichtwark and Wilson, 2007). It is well-accepted that a tendon's properties adapt in response to chronic changes in loading volume and intensity (Kubo et al., 2001;Arampatzis et al., 2007;Kongsgaard et al., 2010). The possibility therefore exists to manipulate loading in order to elicit specific adaptive responses in the tendon and control (i.e., optimize) the muscle inputmovement output relationship. ...
... These findings are of great interest because they not only indicate that a tendon's elastic energy storage and release potential during a movement may be influenced by loading rate, but because they indicate that a tendon's loading rate might influence its chronic adaptation (Arampatzis et al., 2007(Arampatzis et al., , 2010. It may be speculated, therefore, that increases in strain magnitude (i.e., loading magnitude) might stimulate increases in tendon stiffness but that increases in the strain rate (i.e., loading rate) may reduce this adaptive response (Roeleveld et al., 1993;Kubo et al., 2001;Arampatzis et al., 2007Arampatzis et al., , 2010Bohm et al., 2014). However, to our knowledge no studies have directly compared tendon adaptation when external load is fixed and tendon strain is manipulated by varying movement velocity. ...
Article
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Introduction: Tendon dynamics influence movement performance and provide the stimulus for long-term tendon adaptation. As tendon strain increases with load magnitude and decreases with loading rate, changes in movement speed during exercise should influence tendon strain. Methods: Ten resistance-trained men [squat one repetition maximum (1RM) to body mass ratio: 1.65 ± 0.12] performed parallel-depth back squat lifts with 60% of 1RM load at three different speeds: slow fixed-tempo (TS: 2-s eccentric, 1-s pause, 2-s concentric), volitional-speed without a pause (VS) and maximum-speed jump (JS). In each condition joint kinetics, quadriceps tendon length (LT), patellar tendon force (FT), and rate of force development (RFDT) were estimated using integrated ultrasonography, motion-capture, and force platform recordings. Results: Peak LT, FT, and RFDT were greater in JS than TS (p < 0.05), however no differences were observed between VS and TS. Thus, moving at faster speeds resulted in both greater tendon stress and strain despite an increased RFDT, as would be predicted of an elastic, but not a viscous, structure. Temporal comparisons showed that LT was greater in TS than JS during the early eccentric phase (10–14% movement duration) where peak RFDT occurred, demonstrating that the tendon's viscous properties predominated during initial eccentric loading. However, during the concentric phase (61–70 and 76–83% movement duration) differing FT and similar RFDT between conditions allowed for the tendon's elastic properties to predominate such that peak tendon strain was greater in JS than TS. Conclusions: Based on our current understanding, there may be an additional mechanical stimulus for tendon adaptation when performing large range-of-motion isoinertial exercises at faster movement speeds.
... Stiffness of the muscle-tendon as a unit increased in response to isometric exercise (Klinge 1997) but adding flexibility exercises did not change this increase in stiffness. Exploring further, Kubo (2001) found similar increases in tendon stiffness with quadriceps exercise with/without flexibility exercise, but the stretching reduced hysteresis of the tendon, leading him to conclude that stretching changed tissue velocity but not elasticity. While both 1 second and 20 second isometric contractions of plantar flexors increased muscle strength, only the 20 second training increased tendon stiffness (Kubo 2001). ...
... Exploring further, Kubo (2001) found similar increases in tendon stiffness with quadriceps exercise with/without flexibility exercise, but the stretching reduced hysteresis of the tendon, leading him to conclude that stretching changed tissue velocity but not elasticity. While both 1 second and 20 second isometric contractions of plantar flexors increased muscle strength, only the 20 second training increased tendon stiffness (Kubo 2001). ...
Article
Physical therapists and osteopaths want to know the quantitative force transmitted in the tissues during resistance exercise and also the relationship between tissue strength and the specific type of resistance exercise of the skeletal muscles. This paper uses the strain energy function for large deformations associated with the active and passive response of transversely isotropic skeletal muscle tissue to evaluate muscle strength and force transmitted in tissues during resistance exercises for the quadriceps muscle at the knee during isometric training exercise at different knee angles in vivo. It is found that after an exercise program, the muscle stiffness is halved when the bending angle of the knee increases from 50° to 100°. The muscle strength generated is marginally greater at 100° than at 50°. The stress transmitted in the lateral direction for 100° bending is double that for 50°.
... Tendon stiffness has been shown to decrease with age (34,35), thus assuming constant activity levels, older adult tendon would experience higher strains compared to the same load on younger adult tendons. Stiffening of tendon in response to tendon training has been reported in numerous studies (36)(37)(38)(39)(40). Mechanisms such as tendon hypertrophy and changes in material properties of tendon have often been postulated as the underlying causes of this phenomenon (41,42). ...
Article
The composition of extracellular matrix (ECM) in tendon depends on the secretion profile of resident cells known as tenocytes. For tissues with a mechanical role like tendon, mechanical strain is known to play an important role in determining the secretion profile of resident cells. Previously we explored the idea of estimating average concentrations of ECM molecules as a function of tendon strain magnitude and number of loading cycles. Specifically, we developed a model of the mechanical fatigue damage of tendon collagen fibers and introduced elementary cell responses (ECRs) by which local cellular-level responses to the strain environment, combined with the fatigue damage model, were scaled up to predict tissue-level responses. Using this approach, we demonstrated that the proposed model is capable of estimating average concentrations of ECM molecules that qualitatively accord with experimental observations. In this study, we increase model realism by extending this approach to consider the implications of a non-uniform collagen fiber distribution, and the influence of time delay on repair of damaged collagen fibers. Using this approach, we focus the study on the average tenocyte secretion profile for active transforming growth factor beta (TGF-β), and discover that increasing fiber length dispersion and/or increasing repair delay leads to increasing active TGF-β concentrations, and reduced sensitivity of average concentration profile of TGF-β to tendon strain.
... These have not been examined in children or adolescents. Tendinous stiffness has been demonstrated to increase following RT in adults (Kubo et al. 2001;Kubo et al. 2002;Reeves et al. 2003), reducing the electromechanical delay in the muscle and increasing the rate of force development. Although musculo-tendinous stiffness has been reported to be lower in children compared with adults in some (Lambertz et al. 2003) but not all studies (Cornu & Goubel 2001), the effect of RT on tendinous stiffness in children and adolescents has not been investigated. ...
... Increases in plantarflexor strength have been shown with various forms of plyometric training (McCann and Higginson, 2008;Saunders et al., 2006;Spurrs et al., 2003;Storen et al., 2008), and isometric strength training (Arampatzis et al., 2007;Fletcher et al., 2010;Kubo et al., 2002Kubo et al., , 2001 or resistance training (Albracht and Arampatzis, 2013). These training protocols have been shown to increase AT stiffness (~16%) and reduce the energy cost of running (~4%) following training. ...
Article
We have recently demonstrated that the triceps surae muscles energy cost (ECTS) represents a substantial portion of the total metabolic cost of running (Erun). Therefore, it seems relevant to evaluate the factors which dictate ECTS, namely the amount and velocity of shortening, since it is likely these factors will dictate Erun. Erun and triceps surae morphological and AT mechanical properties were obtained in 46 trained and elite male and female distance runners using ultrasonography and dynamometry. ECTS (J·stride-1) at the speed of lactate threshold (sLT) was estimated from AT force and crossbridge mechanics and energetics. To estimate the relative impact of these factors on ECTS, mean values for running speed, body mass, resting fascicle length (Lf), Achilles tendon stiffness and moment arm and maximum isometric plantarflexion torque were obtained. ECTS was calculated across a range (mean ± 1 sd) of values for each independent factor. Average sLT was 233 m·min-1. At this speed, ECTS was 255 J·stride-1. Estimated fascicle shortening velocity was 0.08 Vmax and the level of muscle activation was 84.7% of maximum isometric torque. Compared to the ECTS calculated from the lowest range of values obtained for each independent factor, higher AT stiffness was associated with a 39% reduction in ECTS, 81% reduction in fascicle shortening velocity and a 31% reduction in muscle activation. Longer AT moment arms and elevated body masses were associated with an increase in ECTS of 18% and 23%, respectively. These results demonstrate that a low ECTS is achieved primarily from a high AT stiffness and low body mass, which is exemplified in elite distance runners.
... However, it should be noted that a similar result in terms of greater hypertrophy of RF than the vasti has been reported after single-joint knee extension training using a conventional weight lifting/lowering model (ie, involving both CON and ECC contractions), 28,29 or even after CON-only knee extension training, 30 but not after ISO knee extension training (ie, equivalent hypertrophy among QF muscles). 31,32 These findings and the current result together imply that (a) dynamic (ECC and/or CON) but not static (ISO) knee extension training results in pronounced hypertrophy in RF and (b) an ECC stimulus is not a requisite but promotes muscle hypertrophy. Importantly, while increasing/maintaining muscle size is a fundamental factor for achieving high athletic performance or quality of life, 33 we acknowledge the possibility that muscle hypertrophy per se may not have any protective effect against muscle strain injuries. ...
Article
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Eccentric contraction‐induced quadriceps strains, particularly in the rectus femoris (RF), frequently occur in sports. By using MRI‐based transverse relaxation time (T2) as an index of exercise‐induced muscle edema, previous studies found pronounced damage in RF after an acute single‐joint eccentric knee extension exercise. This study examined whether single‐joint eccentric knee extension training would preferentially train RF, resulting in greater hypertrophy of RF than the other quadriceps muscles. Twelve males conducted work‐matched single‐joint isokinetic (180°/s) maximal eccentric contractions of the knee extensors in one leg (ECC‐leg) and concentric in the other (CON‐leg), 6 sets/session (3−5 sets in the initial 1−3 sessions), 2 sessions/week for 10 weeks. Muscle volume of each quadriceps was measured pre‐ and post‐training. T2 of each muscle was assessed weekly throughout the training period and pre‐ and post‐training. Muscle volume significantly increased in all muscles in ECC‐leg only, with a greater degree for RF (+7.3%) than the vasti (2.9−3.7%). T2 did not change in all muscles throughout. These results suggest that RF can be preferentially trained by single‐joint eccentric knee extension training. Cooperatively with the potential repeated bout effect (i.e. protective effect) in eccentric exercise, this training modality would have positive implications for strain injury prevention of RF. This article is protected by copyright. All rights reserved.
... Tendons are viscoelastic structures, possessing both viscous (rate-dependent) and elastic (rateindependent) properties. During muscular contraction, tendons lengthen in direct proportion to the loading magnitude due to their elastic properties (11, 23,28), but this lengthening may be reduced as the rate of tendon loading increases due to viscous properties (4). During rapid human movements, the addition of external load to the body or limb increases both the magnitude and rate of tendon loading making it difficult to predict the influence of external loading on tendon strain (8). ...
Article
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Purpose: The influence of external loading on muscle and tendon dynamics during maximal vertical jumping was explored. Methods: Ten resistance-trained men performed parallel-depth, countermovement vertical jumps with and without additional load (0%, 30%, 60% and 90% of maximum squat lift strength), while joint kinetics and kinematics, quadriceps tendon length (LT) and patellar tendon FT and RFDT were estimated using integrated ultrasound, motion analysis and force platform data and muscle-tendon modelling. Results: Estimated FT and RFDT, but not peak LT, increased with external loading. Temporal comparisons between 0% and 90% loads revealed that FT was greater with 90% loading throughout the majority of the movement (11-81% & 87-95% movement duration). However, RFDT was greater with 90% load only during the early movement initiation phase (8-15% movement duration) but was greater in the 0% load condition later in the eccentric phase (27-38% movement duration). LT was longer during the early movement (12-23% movement duration) but shorter in the late eccentric and early concentric phases (48-55% movement duration) with 90% load. Discussion: External loading positively influenced peak FT and RFDT but tendon strain appeared unaffected, suggesting no additive effect of external loading on patellar tendon lengthening during human jumping. Temporal analysis revealed that external loading resulted in a large initial RFDT that may have caused dynamic stiffening of the tendon and attenuated tendon strain throughout the movement. These results suggest that external loading influences tendon lengthening in both a load- and movement-dependent manner.
... Previous studies on male adults revealed that growth 9,16,20 and resistance training 21,22,23 increase tendon (structure) stiffness. In recent years, similar results have also been observed in children. ...
Article
This study aimed to compare the morphological/mechanical characteristics of muscle‐tendon unit (MTU) in children affected by Osgood‐Schlatter disease (OSD) and healthy children. The morphological/mechanical properties of MTU were investigated in fifteen subjects (21 legs) who were affected by OSD (OSD group) and 15 subjects (28 legs) found to have no OSD (CON group). Tendon structure stiffness, elongation, and strain of knee extensors were measured using ultrasonography. In addition, we calculated the ratio of fascicle to femur length. Tendon structure stiffness was significantly higher in the OSD group than in the CON group (p = 0.0008). Maximum elongation (p = 0.0006) and maximum strain (p = 0.0003) were significantly lower in the OSD group than in the CON group. There was no significant difference in the MVC values of the knee extensors between the two groups (p > 0.05), nor was there a significant difference in the ratio of fascicle to femur length between the two groups (p > 0.05). These results indicate that a mechanical properties of tendon structure are related to the presence of OSD and that an imbalance in the morphological development of muscles and bones has little association with the presence of OSD. This article is protected by copyright. All rights reserved.
... In their study including elder individuals Reeves et al., (2003) reported that 14-week long weightlifting trainings do not cause an increase in the cross sectional area of patellar tendon. Kubo et al., (2001) and Kubo et al., (2002) also reported that following 8-12-week long isometric force trainings do not lead an increase in the cross sectional areas of patellar and AT. Moreover, the researchers Urlando and Hawkins (2007) noted that there is a positive correlation between hypertrophic development in AT and force parameters. ...
Article
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Objectives: The study aims to investigate the Achilles tendon thickness of men, women athletes in Olympic weightlifting and sedentary individuals.Methods: This research study was conducted on 4 groups, comprising of athletes in Olympic weightlifting (n= 25 men, n=25 women) and sedentary individuals (n=25 men, n=25 women), aged 18-19 years. Ultrasonography was performed on the Achilles tendon of the two limbs of 100 individuals. Results: The mean thickness of the Achilles tendon was significantly larger in the athletes than in the sedentary individuals. No correlation was found between the age, height, body weight of the athletes and the thickness of the Achilles tendon.Conclusion: In conclusion, we state that in addition to the following hypertrophic development of the Achilles tendon in athletes in weightlifting, future studies including force parameters may be beneficial.
... In healthy individuals, Arampatzis, Bohm, and colleagues demonstrated that when a high load-intensity is used (i.e., 90% of MVC), a low loading frequency (i.e., 0.17 Hz, 3 s loading/3 s relaxation) was superior when compared to a high loading frequency (i.e., 0.5 Hz, 1 s loading/1 s relaxation) [42], whereas the high loading rate (i.e., one-legged jumps) and high loading duration (i.e., a single 12 s isometric plantar flexion contraction per set) yielded inferior adaptive results compared to the reference protocol (4 × 6 s isometric contractions at 90% of MVC) [44]. Beyond the Achilles, it appears that conflicting evidence exists as to the effect of loading rate [150] and duration [151,152] on tendon adaptation. Given the impact of rest duration on collagen organization [103], more research into this factor may be warranted. ...
Article
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Therapeutic exercise is widely considered a first line fundamental treatment option for managing tendinopathies. As the Achilles tendon is critical for locomotion, chronic Achilles tendinopathy can have a substantial impact on an individual’s ability to work and on their participation in physical activity or sport and overall quality of life. The recalcitrant nature of Achilles tendinopathy coupled with substantial variation in clinician-prescribed therapeutic exercises may contribute to suboptimal outcomes. Further, loading the Achilles tendon with sufficiently high loads to elicit positive tendon adaptation (and therefore promote symptom alleviation) is challenging, and few works have explored tissue loading optimization for individuals with tendinopathy. The mechanism of therapeutic benefit that exercise therapy exerts on Achilles tendinopathy is also a subject of ongoing debate. Resultingly, many factors that may contribute to an optimal therapeutic exercise protocol for Achilles tendinopathy are not well described. The aim of this narrative review is to explore the principles of tendon remodeling under resistance-based exercise in both healthy and pathologic tissues, and to review the biomechanical principles of Achilles tendon loading mechanics which may impact an optimized therapeutic exercise prescription for Achilles tendinopathy.
... However, our meta-analysis failed to show a significant effect of IST after a short-to-medium period of concurrent training, suggesting that the lack of specificity of this training mode could attenuate the improvement of RE in endurance athletes. It should, however, be pointed out that so far only two studies used IST and, in addition, such a training method only appears to be effective in improving both MTS and RE after a long period of training [15,19,48]. ...
Article
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Background Several strategies have been used to improve running economy (RE). Defined as the oxygen uptake required at a given submaximal running velocity, it has been considered a key aerobic parameter related to endurance running performance. In this context, concurrent strength and endurance training has been considered an effective method, although conclusions on the optimal concurrent training cannot yet be drawn. Objective To evaluate the effect of concurrent training on RE in endurance running athletes and identify the effects of subject characteristics and concurrent training variables on the magnitude of RE improvement. Methods We conducted a computerized search of the PubMed and Web of Science databases, and references of original studies were searched for further relevant studies. The analysis comprised 20 effects in 16 relevant studies published up to August 2015. The outcomes were calculated as the difference in percentage change between control and experimental groups (% change) and data were presented as mean ± 95 % confidence limit. Meta-analyses were performed using a random-effects model and, in addition, simple and multiple meta-regression analyses were used to identify effects of age, training status, number of sessions per week, training duration, type of strength training, and neuromuscular performance on % change in RE. ResultsThe concurrent training program had a small beneficial effect on RE (% change = −3.93 ± 1.19 %; p < 0.001). In addition, explosive (% change = −4.83 ± 1.53; p < 0.001) and heavy weight (% change = −3.65 ± 2.74; p = 0.009) training programs produced similar improvements in RE, while isometric training (% change = −2.20 ± 4.37; p = 0.324) in selected studies did not induce a significant effect. The multiple linear meta-regression analysis showed that all the differences between % changes could be explained by including the above-mentioned characteristics of subjects and weight training program elements. This model showed that the magnitude of the % change in RE was larger for longer training duration (β = −0.83 ± 0.72, p = 0.02). Conclusion Explosive training and heavy weight training are effective concurrent training methods aiming to improve RE within a few weeks. However, long-term training programs seem to be necessary when the largest possible improvement in RE is desired.
... Optimal performance requires the efficient transfer of force from muscle to bone (101,114), necessitating transmission by a tendon that is sufficiently stiff to minimize electromechanical delay while avoiding rupture (101). Properly executed dynamic, eccentric, and isometric training can improve tendon structure and function (11,12,81,82,85,86,90,101,127). ...
Article
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Eccentric quasi-isometric (EQI) resistance training involves holding a submaximal, yielding isometric contraction until fatigue causes muscle lengthening, then maximally resisting through a range of motion. Practitioners contend that EQI contractions are a powerful tool for the development of several physical qualities important to health and sports performance. Additionally, several sports involve regular quasi-isometric contractions for optimal performance. Therefore, the primary objective of this review was to synthesize and critically analyze relevant biological, physiological and biomechanical research and develop a rationale for the value of EQI training. Additionally, this review offers potential practical applications and highlights future areas of research. While there is a paucity of research investigating EQIs, the literature on responses to traditional contraction types is vast. Based on relevant literature, EQIs may provide a practical means of increasing total volume, metabolite build-up and hormonal signalling factors while safely enduring large quantities of mechanical tension with low levels of peak torque. Conversely, EQI contractions likely hold little neuromuscular specificity to high velocity or power movements. Therefore, EQI training appears to be effective for improving musculotendonous morphological and performance variables with low injury risk. Although speculative due to the limited specific literature, available evidence suggests a case for future experimentation.
... A common method used to assess AT stiffness is B-mode ultrasound. This method involves measuring the displacement of the medial gastrocnemius (MG) muscleÀtendon junction (MTJ) in relation to an echogenic skin marker during ramped isometric plantar flexion (PF) contraction (Kubo et al. 2001;Magnusson et al. 2003aMagnusson et al. , 2003bArya and Kulig 2010;Child et al. 2010;Geremia et al. 2018). The gradient of the relationship between tendon force (N) and corresponding MGÀMTJ elongation (mm) represents AT stiffness (N/mm). ...
Article
Achilles tendon (AT) stiffness is an important property of both human locomotor performance and injury mechanics. Freehand 3-D ultrasound (3-DUS) is a promising method for measuring stiffness of the Achilles tendon, particularly the free AT (2–6 cm proximal to calcaneus), which is commonly injured. The aim of this study was to investigate the test–retest reliability of freehand 3-DUS in measuring free AT stiffness in humans. The free Achilles tendon length of healthy participants (n = 10) was scanned on the same day on two consecutive occasions (1 h apart) during rest and isometric plantar flexion contractions at 20%, 40% and 60% of maximum force. The slope of the force–elongation curve over these force levels represented individual stiffness (N/mm). Relative reliability was assessed using the intra-class correlation coefficient (ICC), and absolute reliability was estimated with the standard error of measurement (SEM) and smallest detectable change. Systematic bias in stiffness measures was explored by comparing test and retest distributions and Bland–Altman plots. The test–retest reliability of free AT stiffness measured using freehand 3-DUS was excellent [ICC = 0.994, 95% confidence interval [CI]: 0.978–0.999)]. The mean stiffness values at test (361.83 N/mm [170.77]) and retest (364.98 N/mm [168.57]) did not significantly differ (p = 0.72), and the smallest detectable change was 52.14 N/mm. The Bland–Altman plot indicated the absence of systematic bias (95% CI: –22.18 to 15.88). Freehand 3-DUS provides reliable and precise measures of tendon stiffness and can be used to detect small changes in free AT stiffness in response to load or tendon pathology.
... Three papers from Fouré et al. reported duplicate data for AT CSA and two reported duplicate stiffness measures [49][50][51]. Two papers from Kubo et al. reported duplicate data for QT CSA and VL aponeurosis stiffness [52,53]. Two papers from Waugh et al. [54,55] and Werkhausen et al. [56,57] reported duplicate data for Achilles stiffness. ...
Article
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Background Exposure to increased mechanical loading during physical training can lead to increased tendon stiffness. However, the loading regimen that maximises tendon adaptation and the extent to which adaptation is driven by changes in tendon material properties or tendon geometry is not fully understood. Objective To determine (1) the effect of mechanical loading on tendon stiffness, modulus and cross-sectional area (CSA); (2) whether adaptations in stiffness are driven primarily by changes in CSA or modulus; (3) the effect of training type and associated loading parameters (relative intensity; localised strain, load duration, load volume and contraction mode) on stiffness, modulus or CSA; and (4) whether the magnitude of adaptation in tendon properties differs between age groups. Methods Five databases (PubMed, Scopus, CINAHL, SPORTDiscus, EMBASE) were searched for studies detailing load-induced adaptations in tendon morphological, material or mechanical properties. Standardised mean differences (SMDs) with 95% confidence intervals (CIs) were calculated and data were pooled using a random effects model to estimate variance. Meta regression was used to examine the moderating effects of changes in tendon CSA and modulus on tendon stiffness. Results Sixty-one articles met the inclusion criteria. The total number of participants in the included studies was 763. The Achilles tendon (33 studies) and the patella tendon (24 studies) were the most commonly studied regions. Resistance training was the main type of intervention (49 studies). Mechanical loading produced moderate increases in stiffness (standardised mean difference (SMD) 0.74; 95% confidence interval (CI) 0.62–0.86), large increases in modulus (SMD 0.82; 95% CI 0.58–1.07), and small increases in CSA (SMD 0.22; 95% CI 0.12–0.33). Meta-regression revealed that the main moderator of increased stiffness was modulus. Resistance training interventions induced greater increases in modulus than other training types (SMD 0.90; 95% CI 0.65–1.15) and higher strain resistance training protocols induced greater increases in modulus (SMD 0.82; 95% CI 0.44–1.20; p = 0.009) and stiffness (SMD 1.04; 95% CI 0.65–1.43; p = 0.007) than low-strain protocols. The magnitude of stiffness and modulus differences were greater in adult participants. Conclusions Mechanical loading leads to positive adaptation in lower limb tendon stiffness, modulus and CSA. Studies to date indicate that the main mechanism of increased tendon stiffness due to physical training is increased tendon modulus, and that resistance training performed at high compared to low localised tendon strains is associated with the greatest positive tendon adaptation. PROSPERO registration no.: CRD42019141299.
... For all contraction forms, substantial increases in quadriceps force and hypertrophy were found, whereas no significant differences between the contraction forms (P > 0.05) were reported. Kubo et al. (2001) addressed the influence of isometric contraction durations on the elasticity of human tendon structures in vivo. Therefore, eight young men (22.6 ± 2.8 years) were recruited and a within-subject design was used whereby one leg was assigned to a long-and the other leg to a short-duration contraction protocol. ...
Article
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Skeletal muscle is one of the most important tissues of the human body. It comprises up to 40% of the body mass and is crucial to survival. Hence, the maintenance of skeletal muscle mass and strength is pivotal. It is well-established that resistance exercise provides a potent anabolic stimulus to increase muscle mass and strength in men and women of all ages. Resistance exercise consists of mechano-biological descriptors, such as load, muscle action, number of repetitions, repetition duration, number of sets, rest interval between sets, frequency, volitional muscular failure, and range of motion, which can be manipulated. Herein, we discuss the evidence-based contribution of these mechano-biological descriptors to muscle mass and strength.
... La variabilidad observada en los sujetos se corresponde a una disminución del rango hacia el valgo de rodilla y del recorrido articular en el eje anteroposterior, así como del rango de rotación externa del complejo tibio-femoral registrados en el eje axial (Tabla 1). Estos hallazgos podrían explicarse a que la posición de cuclillas ha mostrado ser capaz de aumentar la rigidez del complejo aponeurosis-tendón (8,9), al igual que la coactivación de musculatura agonista-antagonista (10), pudiendo influir de esta manera en la limitación de los rangos articulares observados (11), protegiendo a la rodilla con un control postural dinámico eficiente en estos ejes en sujetos sanos. ...
Conference Paper
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Propiedades cinemáticas de rodilla en respuesta a la posición de cuclillas: Implicancias para la rehabilitación. Resumen Este trabajo estudia las propiedades cinemáticas de la articulación de rodilla mediante sistema optoelectrónico de captura de movimiento 3D para la grabación y el análisis de movimiento en respuesta a un protocolo de carga. Se valoró el perfil cinemático de la rodilla derecha e izquierda en diez sujetos sanos, antes y después de un protocolo de carga basado en la mantención de la posición de cuclillas por 10 minutos. La aplicación del protocolo de carga se asoció a una disminución en el valgo y del recorrido articular en el plano frontal de la rodilla derecha. En el eje axial se asoció a una disminución del rango de rotación externa sólo para la rodilla derecha, pero no para el segmento contrario (p > 0.05). No se observaron variaciones en el eje transversal posterior a la aplicación del protocolo de carga. Abstract This pilot work studies the kinematic properties of the knee joint using the 3D Optoelectronic motion capture system to record and analyze movement in response to a loading protocol. The right and left knee kinematic profile was assessed in ten healthy subjects before and after a loading protocol based on maintaining the squatting position for 10 minutes. The application of the loading protocol was associated with a decrease in valgus and joint travel in the frontal plane of the right knee. The axial axis was associated with a reduction in the range of external rotation only for the right knee but not for the opposite segment (p > 0.05). No variations were observed in the transverse axis after the application of the loading protocol.
... A common method used to assess AT stiffness is B-mode ultrasound. This method involves measuring the displacement of the medial gastrocnemius (MG) muscleÀtendon junction (MTJ) in relation to an echogenic skin marker during ramped isometric plantar flexion (PF) contraction (Kubo et al. 2001;Magnusson et al. 2003aMagnusson et al. , 2003bArya and Kulig 2010;Child et al. 2010;Geremia et al. 2018). The gradient of the relationship between tendon force (N) and corresponding MGÀMTJ elongation (mm) represents AT stiffness (N/mm). ...
... Some reports refer to changes in stiffness under the influence of sports training (e.g., plyometric or isometric). However, they take into account the stiffness of local structures (e.g., tendon) [36][37][38][39][40][41][42][43][44][45][46]; the determination of which may be more complicated than the discussed values of leg, vertical, and joint stiffness. Several reports analysed the relationships between mechanical (leg, vertical, or joint) stiffness and movement performance (e.g., during biomechanical types of jumps) before and after the applied training program. ...
Article
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Stiffness, the resistance to deformation due to force, has been used to model the way in which the lower body responds to landing during cyclic motions such as running and jumping. Vertical, leg, and joint stiffness provide a useful model for investigating the store and release of potential elastic energy via the musculotendinous unit in the stretch-shortening cycle and may provide insight into sport performance. This review is aimed at assessing the effect of vertical, leg, and joint stiffness on running performance as such an investigation may provide greater insight into performance during this common form of locomotion. PubMed and SPORTDiscus databases were searched resulting in 92 publications on vertical, leg, and joint stiffness and running performance. Vertical stiffness increases with running velocity and stride frequency. Higher vertical stiffness differentiated elite runners from lower-performing athletes and was also associated with a lower oxygen cost. In contrast, leg stiffness remains relatively constant with increasing velocity and is not strongly related to the aerobic demand and fatigue. Hip and knee joint stiffness are reported to increase with velocity, and a lower ankle and higher knee joint stiffness are linked to a lower oxygen cost of running; however, no relationship with performance has yet been investigated. Theoretically, there is a desired “leg-spring” stiffness value at which potential elastic energy return is maximised and this is specific to the individual. It appears that higher “leg-spring” stiffness is desirable for running performance; however, more research is needed to investigate the relationship of all three lower limb joint springs as the hip joint is often neglected. There is still no clear answer how training could affect mechanical stiffness during running. Studies including muscle activation and separate analyses of local tissues (tendons) are needed to investigate mechanical stiffness as a global variable associated with sports performance.
... In agreement, increases in Achilles tendon-aponeurosis stiffness (+36.0%), elastic modulus (~18.2%) and region-specific hypertrophy were found after 14 weeks of high-strain, but not low-strain IT (Arampatzis et al., 2007), supporting the results of previous studies (Kubo et al., 2001a(Kubo et al., , 2006a. Arampatzis et al. (2010) also showed that a higher tendon strain duration per contraction may evoke superior adaptational responses. ...
Article
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Treatment strategies and training regimens, which induce longitudinal muscle growth and increase the muscles’ length range of active force exertion, are important to improve muscle function and to reduce muscle strain injuries in clinical populations and in athletes with limited muscle extensibility. Animal studies have shown several specific loading strategies resulting in longitudinal muscle fiber growth by addition of sarcomeres in series. Currently, such strategies are also applied to humans in order to induce similar adaptations. However, there is no clear scientific evidence that specific strategies result in longitudinal growth of human muscles. Therefore, the question remains what triggers longitudinal muscle growth in humans. The aim of this review was to identify strategies that induce longitudinal human muscle growth. For this purpose, literature was reviewed and summarized with regard to the following topics: (1) Key determinants of typical muscle length and the length range of active force exertion; (2) Information on typical muscle growth and the effects of mechanical loading on growth and adaptation of muscle and tendinous tissues in healthy animals and humans; (3) The current knowledge and research gaps on the regulation of longitudinal muscle growth; and (4) Potential strategies to induce longitudinal muscle growth. The following potential strategies and important aspects that may positively affect longitudinal muscle growth were deduced: (1) Muscle length at which the loading is performed seems to be decisive, i.e., greater elongations after active or passive mechanical loading at long muscle length are expected; (2) Concentric, isometric and eccentric exercises may induce longitudinal muscle growth by stimulating different muscular adaptations (i.e., increases in fiber cross-sectional area and/or fiber length). Mechanical loading intensity also plays an important role. All three training strategies may increase tendon stiffness, but whether and how these changes may influence muscle growth remains to be elucidated. (3) The approach to combine stretching with activation seems promising (e.g., static stretching and electrical stimulation, loaded inter-set stretching) and warrants further research. Finally, our work shows the need for detailed investigation of the mechanisms of growth of pennate muscles, as those may longitudinally grow by both trophy and addition of sarcomeres in series.
... Each study must have included a measure of direct or indirect lower body stiffness, taken both prior to and after the intervention period. Lower limb stiffness can be assessed using either laboratory measures, such ultrasonography, to directly quantify muscle and tendon stiffness 28,30 , or field-related measures such as vertical hopping stiffness 11 . In the present study, when methods are used to quantify muscle and/or tendon stiffness, the resultant term "tissue stiffness" is used. ...
Article
Objectives: To examine the effects of plyometric jump training (PJT) on lower limb stiffness. Methods: Systematic searches were conducted in PubMed, Web of Science, and SCOPUS. Studies included healthy males and females who undertook a plyometric jump training programme, isolated from any other training type. Results: There was a small effect size (ES) of PJT on lower limb stiffness (0.33 [0.07, 0.60], Z = 2.47, p = 0.01). Untrained individuals exhibited a larger ES (0.46 [0.08, 0.84], p = 0.02) than trained (0.15 [-0.23, 0.53], p = 0.45). Those interventions with a greater number of weeks (>7 weeks) had a larger ES (0.47 [0.06, 0.88], p = 0.03) than those with fewer weeks (0.22 [-0.12, 0.55], p = 0.2). Two sessions or fewer per week exhibited a larger ES (0.39 [0.01, 0.77], p = 0.04) than programmes which incorporated more than two sessions (0.20 [-0.10, 0.50], p = 0.18). Fewer than 250 jumps per week (0.50 [0.02, 0.97], p = 0.04) showed a larger ES than 250 to 500 jumps (0.36 [0.00, 0.72], p = 0.05) which, in turn, was larger than the negative ES for more than 500 jumps per week (-0.22 [-1.10, 0.67], p = 0.63). More than 7.5 jumps per set showed a larger effect size (0.55 [0.02, 1.08], p = 0.04) than fewer than 7.5 jumps (0.32 [0.01, 0.62], p = 0.04). Conclusions: PJT enhances lower body stiffness which can be optimised with lower volumes (<250 jumps per week) over a relatively long period of time (>7 weeks).
... Kada je mišić u stanju manje krutosti mišićno-tetivne jedinice, više rada je direktno pretvoreno u spoljašnji rad. U aktivnostima poput vožnje bicikla, klizanja i plivanja, uglavnom, koriste se pokreti u kojima dolazi do generisanja sile u toku skraćenja mišića, tako da je prisutna mala mogućnost apsorpcije određene količine energije tokom kretanja (Biewener, Corning, & Tobalske, 1998 (Kubo et al., 2001) utvrđuju da izometrijski trening takođe povećava krutost tetivnih struktura mišića opružača u zglobu kolena. ...
Article
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A large number of human movement studies have focused on functioning of complex biological systems. These systems can be observed as one muscle-tendon unit or one muscle fiber, one limb or joint, or a whole locomotor system presented as a kinetics chain. A muscletendon unit may generate forces in two distinctly different ways: as an elastic-like spring in stretch-shortening motion and as converters of metabolic energy into mechanical work. Furthermore, during movement a muscle-tendon unit can be stiff or compliant. Understanding these conditions during movement would provide important information that could be used for sports performance improvement and injury prevention planning.
... For example, isometric training at different quadriceps muscle lengths (Kubo et al., 2006) and long-vs. short-duration (Kubo et al., 2001) influences the adaptations to tendon stiffness and maximal torque levels. Isometric training at longer muscle lengths for longer durations has shown to result in significant increases in tendon stiffness and maximal strength levels across a spectrum of joint-angles. ...
Article
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Athletic performance is determined by numerous variables that cannot always be controlled or modified. Due to aesthetic requirements during sports such as dance, body alignment constrains possible movement solutions. Increased power transference around the ankle-joint, coupled with lower hip-joint power, has become a preferential strategy in dancers during leaps and may be considered a dance-specific stretch-shortening cycle (SSC) demand. Newell's theoretical model of interacting constraints includes organismic (or individual), environmental, and task constraints describing the different endogenous and exogenous constraints individuals must overcome for movement and athletic performance. The unique task constraints imposed during dance will be used as a model to justify an isolated joint, single-targeted block progression training to improve physical capacity within the context of motor behavior to enhance dance-specific SSC performance. The suggested ankle-specific block progression consists of isometrics, dynamic constant external resistance, accentuated eccentrics, and plyometrics. Such programming tactics intend to collectively induce tendon remodeling, muscle hypertrophy, greater maximal strength, improved rate of force development, increased motor unit firing rates, and enhanced dynamic movement performance. The current perspective provides a dualistic approach and justification (physiological and motor behavioral) for specific strength and conditioning programming strategies. We propose implementation of a single-targeted block progression program, inspired by Newell's theoretical model of interacting constraints, may elicit positive training adaptations in a directed manner in this population. The application of Newell's theoretical model in the context of a strength and conditioning supports development of musculoskeletal properties and control and is conceptually applicable to a range of athletes.
... VL muscle was chosen because previous studies (Alkner et al., 2000;Place et al., 2007) showed that this muscle is representative of the muscle quadriceps. Moreover, studies showing decreases in muscle stiffness by assessing aponeurosis or muscle tendon junction displacements or by SWE after repeated isometric contractions were made exclusively in the VL muscle (Kubo et al., 2001a;Morel et al., 2019;Siracusa et al., 2019), allowing comparisons with the present study. ...
Article
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We investigated the in vivo effects of voluntary fatiguing isometric contractions of the knee extensor muscles on the viscoelastic properties of the vastus lateralis (VL). Twelve young males (29.0 ± 4.5 years) performed an intermittent voluntary fatigue protocol consisting of 6 sets × 10 repetitions of 5-s voluntary maximal isometric contractions with 5-s passive recovery periods between repetitions. Voluntary and evoked torque were assessed before, immediately after, and 20 min after exercise. The shear modulus (µ) of the VL muscle was estimated at rest and during a ramped isometric contraction using a conventional elastography technique. An index of active muscle stiffness was then calculated (slope from the relationship between shear modulus and absolute torque). Resting muscle viscosity (η) was quantified using a shear-wave spectroscopy sequence to measure the shear-wave dispersion. Voluntary and evoked torque decreased by ∼37% (P < 0.01) immediately after exercise. The resting VL µ was lower at the end of the fatigue protocol (−57.9 ± 5.4%, P < 0.001), whereas the resting VL η increased (179.0 ± 123%, P < 0.01). The active muscle stiffness index also decreased with fatigue (P < 0.05). By 20 min post-fatigue, there were no significant differences from the pre-exercise values for VL η and the active muscle stiffness index, contrary to the resting VL µ. We show that the VL µ is greatly reduced and η greatly enhanced by fatigue, reflecting a more compliant and viscous muscle. The quantification of both shear µ and η moduli in vivo may contribute to a better understanding of the mechanical behavior of muscles during fatigue in sports medicine, as well as in clinical situations.
Thesis
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Abstract The Chinese internal martial arts of Tai Chi Chuan, Hsing Yi Chuan and Pa Kua Chang are sister arts philosophically built upon Taoist foundations. They have been practiced in mainland China for hundreds of years, building a reputation as superb health practices and self-defence methods. Although the physical approaches to self-defence and expression of power differ, all three arts devote a major part of training on solo posture work, both static and dynamic, where different postures are performed in a slow, flowing and meditative manner. Furthermore, all three martial arts lay their foundations on the same basic principles of standing, which can then be applied into literally hundreds of shapes or postures making up the backbone of a particular martial art. This thesis sought to investigate scientifically each dissected pillar on which the basic internal martial art posture is based, in order to explore deeply and understand better the potential utility of these internal martial arts. Scientific studies dealing with human anatomy in the standing position, psychology of posture, breathing, meditative movement and mindfulness, relaxation and the energetic biofield, were searched and evaluated for their relevance to posture in the internal martial arts. The results from the analyzed data reveal a surprising alignment of the principles of posture training in the Chinese internal arts to emerging scientific discoveries on health and human potential. This has profound implications for modern society’s evidence-based health practices, whether preventive, palliative or even curative. An advantage of the Chinese internal martial arts is that they can be readily practiced in a small floor area, without the need for equipment, and whenever one can spare even a few minutes in private. In today’s hectic lifestyle, such a practice can yield profound health rewards, both physically and psychologically. Other implications are the contribution of these arts to the further development of human potential and sports science, especially in psychology, myofascial biomechanics and biofield energetics, a new and exciting field of study.
Article
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BACKGROUND: There is currently limited evidence available to support the use of the isometric mid thigh pull (IMTP) within professional soccer. The aim of this study was to analyse the association between IMTP variables, with common markers of athletic performance capability. METHODS: Eleven professional development soccer players (age: 20 ± 2 years, stature: 1.82 ± 0.10 m, mass: 76.4 ± 12.8 kg) performed IMTP, 5 m and 10 m accelerations, maximal sprint speed (MSS), countermovement jump (CMJ), and the 505 change of direction test (COD). RESULTS: Relative and absolute Peak force (PF) and force at 50, 100, 150 and 200 ms values were measured during the IMTP. Relative F150, F200, PF displayed large to very large correlations with MSS (r = 0.51, r = 0.66, and r = 0.76 respectively), while absolute PF also displayed a large correlation with MSS (r = 0.57). Relative and absolute PF showed large correlations with CMJ height (r = 0.54 and r = 0.55 respectively). Relative F150 and F200 highlighted large correlations with COD ability (r = -0.68 and r = -0.60 respectively). Relative F200 and PF had a large negative correlation with 10m acceleration (r = -0.55 and r = -0.53 respectively). CONCLUSIONS: This study provides an important contribution to knowledge within the area of IMTP testing in professional soccer by evidencing the prominence of the isometric force generating capacity as an underpinning factor in relation to athletic capability. KEY WORDS: Football; Force; Strength; Training
Chapter
The traditional domain of fatigue failure analysis has been in the analysis of the fatigue life of engineering materials such as metals, plastics, and composite materials. As complicated as the fatigue failure process can be in inert materials when one adds dynamic biological materials to the mix, an entirely new dimension of complexity is introduced. There are substantial differences in stress response when comparing inert materials with musculoskeletal tissues. Of all the differences between inert and biological materials, probably the most significant difference is the ability of biological tissues to self‐heal. To maintain musculoskeletal health a balance must be maintained between the damage kinetics imposed on a tissue and the healing kinetics. Unsurprisingly, individuals of increased age may have a wound healing response that takes a significantly longer time than that of individuals of a younger age. The rate of collagen synthesis is a critical factor in the healing of musculoskeletal tissues.
Article
Effects of life-long physical activity on tendon function have been investigated in cross-sectional studies, but these are at risk of "survivorship" bias. Here, we investigate if life-long side-specific loading is associated with greater cross-sectional area (CSA), mechanical properties, cell density (DNA content) and collagen cross-link composition of the male human patellar tendon (PT), in vivo. Nine seniors and six young male life-long elite badminton players and fencers were included. CSA of the PT obtained by 3-tesla MRI, and ultrasonography-based bilateral PT mechanics were assessed. Collagen fibril characteristics, enzymatic cross-links, non-enzymatic glycation (autofluorescence), collagen and DNA content were measured biochemically in PT biopsies. The elite athletes had a ≥15% side-to-side difference in maximal knee extensor strength, reflecting chronic unilateral sport-specific loading patterns. The PT CSA was greater on the lead extremity compared with the non-lead extremity (17 %, p=0.0001). Furthermore, greater tendon stiffness (18 %, p=0.0404) together with lower tendon stress (22 %, p=0.0005) and tendon strain (18 %, p=0.0433) were observed on the lead extremity. No effects were demonstrated from side-to-side for glycation, enzymatic cross-link, collagen, and DNA content (50%, p=0.1160). Moreover, tendon fibril density was 87±28 fibrils/μm ² on the lead extremity and 68±26 fibrils/μm ² on the non-lead extremity (28%, p=0.0544). Tendon fibril diameter was 86±14 nm on the lead extremity and 94±14 nm on the non-lead extremity (-9%, p=0.1076). These novel data suggest that life-long side-specific loading in males yields greater patellar tendon size and stiffness possibly with concomitant greater fibril density but without changes of collagen cross-link composition.
Chapter
Tendinopathy is one of the most common overuse injuries in basketball players, with patellar and Achilles tendinopathy occurring most frequently. In athletic populations, these injuries typically result from excessive load (acute or chronic) placed upon the tendon with inadequate time for recovery. A variety of non-invasive treatment options are available for tendinopathy, but controlled tendon loading is supported by the highest level of evidence. In this chapter, we will describe key tendinopathy rehabilitation principles. Furthermore, we will describe how these principles are applied to patellar and Achilles tendinopathy.
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The purpose of this study was to quantify the effect of the contraction duration of two isometric exercise protocols on the post-activation potentiation of 14 well-trained males (age: 22.6±2.8 yrs., height: 180.3±5.9 cm, body mass: 72.3± 37.9 kg). The protocols consisted of 4x6 maximal plantar flexions, of 3 s (P3) or 6 s (P6) duration, performed in random order, with a 2 minute and 15 s intervals between the sets and repetitions, respectively. The torque during maximal isometric voluntary contraction (MIVC), the peak twitch torque (TT), and the rate of torque development (RTD) after each MIVC were analyzed, for the first and the last trial of each set, the average of all trials of each set, and the trials within each set that had the highest peak TT. The MIVC had an overall greater reduction during P6 compared to P3 (P3: -4.6±2.3% vs. P6: -16.0±1.9%). P6 showed higher potentiation in TT during the initial repetitions of the first 2 sets (p<0.05) in contrast to the P3, which revealed a lower potentiation but for a longer period along the exercise session. However, both protocols had on average the same potential for potentiation (P3: 81.6±6.1% vs. P6: 79.8±6.3%). The twitch RTD presented no systematic difference between the two protocols (p>0.05). These data demonstrate the dependence of the TT potentiation on the conditioning stimulus and verify the cumulative effect of potentiation, suggesting the implementation of longer contractions to achieve maximal but temporal TT potentiation and shorter contractions for less variable but prolonged potentiation.
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The economy of running has traditionally been quantified from the mass-specific oxygen uptake; however, because fuel substrate usage varies with exercise intensity, it is more accurate to express running economy in units of metabolic energy. Fundamentally, the understanding of the major factors that influence the energy cost of running (Erun) can be obtained with this approach. Erun is determined by the energy needed for skeletal muscle contraction. Here, we approach the study of Erun from that perspective. The amount of energy needed for skeletal muscle contraction is dependent on the force, duration, shortening, shortening velocity, and length of the muscle. These factors therefore dictate the energy cost of running. It is understood that some determinants of the energy cost of running are not trainable: environmental factors, surface characteristics, and certain anthropometric features. Other factors affecting Erun are altered by training: other anthropometric features, muscle and tendon properties, and running mechanics. Here, the key features that dictate the energy cost during distance running are reviewed in the context of skeletal muscle energetics.
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The influences of age on muscle architectural characteristics, i. e., muscle thickness, pennation angle, fascicle length, were studied in 121 men and 229 women aged 17 to 85 yrs. The subjects were divided into three age groups (younger : 17-39 yrs, middle-aged : 40-59 yrs, elderly : 60-85 yrs) for both genders. Muscle thickness and pennation angle of the vastus lateralis (VL), medial gastrocnemius (MG), and long head of triceps brachii (TB) muscles were measured using B-mode ultraso-nography, and fascicle length was estimated. In all age groups, men had significantly greater relative muscle thickness (to limb length) in VI, and TB than women, but not in MG. Relative muscle thickness of VL was significantly lower in elderly than in younger and middle-aged subjects. Ilowever, the corresponding differences in MG and TB were insignificant. The pennation angle of VL was significantly lower in elderly than in younger and middle-aged subjects, although there were no significant differences in pennation angles of MG and TB among the three groups. These results suggest that the decrease in thickness of vastus lateralis muscle with aging is significant, but not significant for medial gastrocnemius and triceps hrachii muscles.
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The purpose of present study was to investigate site differences in the effects of strain rate on tendon properties between knee extensors and plantar flexors. Elongation of tendon structures (L) in vastus lateralis and medial gastrocnemius muscles was measured by ultrasonography while participants performed ramp and ballistic contractions to their voluntary maximum, followed by ramp and sudden relaxation. The relationship between muscle force (Fm) and L was fit to linear regression, the slope of which was defined as stiffness of tendon structures. Hysteresis of tendon structures was calculated as ratio of area within Fm-L loop to area beneath loading portion of curve. In knee extensors and plantar flexors, L values at all force levels were significantly lower during ballistic than ramp contractions. However, no significant differences were observed in stiffness of tendon structures between two contractions at both measured sites. Hysteresis of tendon structures was significantly higher during ballistic than ramp contractions for knee extensors and plantar flexors. In conclusion, elongation of tendon structures was lower and hysteresis was greater during ballistic than ramp contractions. Furthermore, site differences in the effects of strain rate on tendon properties were not found between knee extensors and plantar flexors.
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Eight men and eight women trained 3 days/wk for 16 wk by doing attempted ballistic unilateral ankle dorsiflexions against resistance that either rendered the resultant contractions isometric (one limb) or allowed a relatively high-velocity (5.23 rad/s on an isokinetic dynamometer) movement (other limb). Training sessions consisted of five sets of 10 contractions of each type. Training produced the same high-velocity-specific training response in both limbs (P < 0.001). Peak torque increased most at 5.23 rad/s (38%) in comparison to lower velocities (0, 0.26, 0.52, 1.04, 1.55, 3.02, and 4.19 rad/s). Both limbs also showed similar increases in voluntary isometric rate of torque development (26%) and relaxation (47%) and in evoked tetanus rate of torque development (14%). A similar decrease in evoked twitch time to peak torque (6%) and half-relaxation time (11%) was also observed. Thus, all of these training responses, previously associated specifically with high-velocity resistance training, were produced by a training regimen that prevented an actual rapid movement through a range of movement. The results suggest that the principal stimuli for the high-velocity training response are the repeated attempts to perform ballistic contractions and the high rate of force development of the ensuing contraction. The type of muscle action (isometric or concentric) appears to be of lesser importance.
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Wallaby tail tendons fail after repeated application of stresses much lower than would be needed to break them in a single pull. We show that this a fatigue phenomenon, distinct from the creep rupture that occurs after prolonged application of a constant stress. The two phenomena are disctinguished by experiments in which tensile stress is cycled at different frequencies, ranging from 1 to 50 Hz.
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The aim of this study was to measure the effects of hindlimb suspension on mechanical properties of the rat Achilles tendon. Adult male Wistar rats were randomly assigned to groups to be either suspended, or a control. After 21 days, Achilles tendons were removed for mechanical analysis. Classical tests of tensile performance were made, and mechanical parameters were derived from a stress-strain relationship. The tendons of animals that had been suspended presented values for maximal stress and tangent modulus which were 37.5% (P < 0.01) and 41% (P < 0.01), respectively, lower than the tendons of the control rats. In a similar way, the energy absorption capacity had largely decreased in animals that had been suspended. However, the maximal strain was similar in the two groups. These results showed that hindlimb suspension in rats has an important detrimental effect on mechanical properties of the Achilles tendon. Differences in tendon stiffness obtained here, along with those found by other investigators, encourage the hypothesis that homeostatic responses of soft tissues are due to changes in limb loadings. This study may be useful in providing a better understanding of the adaptation of human skeletal muscle when exposed to microgravity.
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The purpose of this study was to investigate the influences of static stretching on the viscoelastic properties of human tendon structures in vivo. Seven male subjects performed static stretching in which the ankle was passively flexed to 35 degrees of dorsiflexion and remained stationary for 10 min. Before and after the stretching, the elongation of the tendon and aponeurosis of medial gastrocnemius muscle (MG) was directly measured by ultrasonography while the subjects performed ramp isometric plantar flexion up to the maximum voluntary contraction (MVC), followed by a ramp relaxation. The relationship between the estimated muscle force (Fm) of MG and tendon elongation (L) during the ascending phase was fitted to a linear regression, the slope of which was defined as stiffness of the tendon structures. The percentage of the area within the Fm-L loop to the area beneath the curve during the ascending phase was calculated as an index representing hysteresis. Stretching produced no significant change in MVC but significantly decreased stiffness and hysteresis from 22.9 +/- 5.8 to 20.6 +/- 4.6 N/mm and from 20.6 +/- 8.8 to 13.5 +/- 7.6%, respectively. The present results suggest that stretching decreased the viscosity of tendon structures but increased the elasticity.
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The aim of this study was to investigate local muscle O(2) consumption (muscV(O(2))) and forearm blood flow (FBF) in resting and exercising muscle by use of near-infrared spectroscopy (NIRS) and to compare the results with the global muscV(O(2)) and FBF derived from the well-established Fick method and plethysmography. muscV(O(2)) was derived from 1) NIRS using venous occlusion, 2) NIRS using arterial occlusion, and 3) the Fick method [muscV(O(2(Fick)))]. FBF was derived from 1) NIRS and 2) strain-gauge plethysmography. Twenty-six healthy subjects were tested at rest and during sustained isometric handgrip exercise. Local variations were investigated with two independent and simultaneously operating NIRS systems at two different muscles and two measurement depths. muscV(O(2)) increased more than fivefold in the active flexor digitorum superficialis muscle, and it increased 1.6 times in the brachioradialis muscle. The average increase in muscV(O(2(Fick))) was twofold. FBF increased 1.4 times independent of the muscle or the method. It is concluded that NIRS is an appropriate tool to provide information about local muscV(O(2)) and local FBF because both place and depth of the NIRS measurements reveal local differences that are not detectable by the more established, but also more global, Fick method.
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The purpose of this study was to observe the effect of training on morphological properties in the collagen fibers of tendons. Wistar strain rats at 7 weeks old were assigned to high speed endurance (H), moderate speed endurance (M), jump training (J) and control (C) groups. The amount of exercise for H group (speed at 30m/min for 60 minutes) and M group (speed at 17m/min for 75 minutes) was equalized according to the amount of oxygen consumed during training. As for the anaerobic training (J group), rats made high jumping form the standing position, wearing jacket with 50% of body weight, 50 times/day, which lasted for 4-5 minutes. The training period was designed for 5 days per week for 16 weeks.The follwing is a summary of the results obtained:1) Increases in fiber areas of both Slow-Twitch (ST) and Fast-Twitch (FT) fibers were observed in the H, M and J groups. The ST fiber area of H group was significantly larger than that of C group. Significant increase in FT fiber area was observed in both M and J groups.2) Hypertrophy of collagen fiber in gastrocnemius muscle tendon was observed in Hand M groups; especially, M group showed much larger increase than H group. It tended to be greater for J group as compared with C group.3) Collagen fiber area and diameter of tendon in plantar muscle were slightly larger for H and M groups relative to C group, but these differences were not significant.These results suggested that both types of aerobic training induced hypertrophy in the collagen fibers of the tendons and increased the tensile strength; especially, the group which trained longer hours induced the higher effect.
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Forty-eight volunteer males were randomly assigned to one of three groups. Group I trained with isokinetic exercises, Group II trained with plyometric exercises, and Group III was the control. Subjects in the training groups trained three times per week for 8 weeks. The isokinetic group performed three sets of 10 repetitions per set of leg presses each training session. The plyometric group performed three sets of 10 repetitions per set of depth jumps from a height of 34 inches, with added resistance beginning with weeks 3, 5, and 7 of 10, 15, and 20 pounds, respectively. Prior to and at the end of the training period, all subjects were given a vertical jump-and-reach test. Covariance analysis was used to compare posttest scores with the effect of pretest differences removed. Results showed both training groups improved significantly in vertical jump capacity; however, no significant difference existed between training groups.
Article
The purpose of this study was to determine the effects of strength improvement on vertical jump ability. Eighty-nine male college students participated in four different training programs. Group I (N = 29) trained with the 10-RM, Group II (N = 20) with 50 to 60 percent of the 10-RM for ten repetitions of jumping squats, Group III (N = 21) trained statically, and Group IV (N = 19) trained by jumping vertically. Training occurred three times weekly for seven weeks. Vertical jumping height was determined before and after the seven-week training period. The groups that trained dynamically improved significantly more in vertical jump than the groups that trained statically or trained strictly by jumping vertically.
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Using either a bone-ligament-bone or a muscle-tendon-bone preparation, numerous investigators have demonstrated that the usual site of separation is in the transitional zone between the ligament (or tendon) and bone; hence, the term junction strength or load at separation is used to describe functional changes in these preparations. Junction strength is decreased with inactivity (immobilization) and increased with chronic activity (training) provided that the exercise program is of an endurance nature. Training also increases junction strength in thyroidectomized and hypophysectomized rats. Besides in junction strength, training results in heavier ligaments and higher ligament weight/length ratios. However, water content, collagen concentrations/dry weight or collagen concentration per weight/length unit are not significantly influenced by repeated bouts of exercise. Although immobilization is associated with lower elastic stiffness values (kg/mm), training appears to have little influence on this measure in normal animals. Rats and dogs with surgically repaired ligaments are weaker and the strength results are markedly lower if the leg is immobilized. Exercise training improves the repair strength of ligaments but does not result in normal values twelve weeks after the surgery. Exogenous administration of ICSH or testosterone results in higher repair strength whereas TSH, thyroxine, ACTH and growth hormone decreases this measure. It was concluded that the mechanical stress produced by chronic exercise is an important determination of the strength of repaired ligaments and of the junctions between ligaments (or tendons) and bones.
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In order to ascertain the effect of 2 contrasting speeds of isokinetic training programs upon performance of women in the vertical jump, 48 varsity and second team intercollegiate volleyball players from 4 universities were randomly assigned to either a control or isokinetic training group. After performing 3 sets of 10 leg press repetitions maximum, 3 days/wk for 8 wks, on isokinetic speed controlled machines, the groups were compared on a strength measure and on vertical jump performance. According to the group to which they were assigned (control, fast speed, or slow speed) subjects from all schools were combined according to treatment effect for comparison purposes on the vertical jump. For the strength measure, the combined slow or fast speed subject groupings formed an experimental treatment group which was compared to a combined control group. A 2-way ANOVA with repeated measures on 1 factor was applied to data obtained on the jump and on each of the strength measures. Results indicated that: the slow and fast speed isokinetic groups were significantly superior to the control group on vertical jump performance; the slow speed isokinetic group improved significantly more in strength than did the control group.
Article
Rat soleus muscles were overloaded with intent to induce a relative increase in fast fibres and modifications in muscular stiffness. The overloading technique was a training period consisting of an 11-week vertical jump programme. The method of controlled releases was used to obtain tension/extension curves characterizing the elastic behaviour of the soleus. Fibre typing was made by myofibrillar adenosine 5'-triphosphatase staining. With regard to a control group, training resulted in a relative decrease in type I fibres for the benefit of type II fibres. Training also induced a decrease in muscle stiffness as attested notably by significant differences in maximal extension. These results are interpreted in terms of modifications occurring in the active fraction of the so-called series elastic component.
Lengths of muscle tendon complexes of the quadriceps femoris muscle and some of its heads, biceps femoris and gastrocnemius muscles, were measured for six limbs of human cadavers as a function of knee and hip-joint angles. Length-angle curves were fitted using second degree polynomials. Using these polynomials the relationships between knee and hip-joint angles and moment arms were calculated. The effect of changing the hip angle on the biceps femoris muscle length is much larger than that of changing the knee angle. For the rectus femoris muscle the reverse was found. The moment arm of the biceps femoris muscle was found to remain constant throughout the whole range of knee flexion as was the case for the medial part of the vastus medialis muscle. Changes in the length of the lateral part of the vastus medialis muscle as well as the medial part of the vastus lateralis muscle are very similar to those of vastus intermedius muscle to which they are adjacent, while those changes in the length of the medial part of the vastus medialis muscle and the lateral part of the vastus lateralis muscle, which are similar to each other, differ substantially from those of the vastus intermedius muscle. Application of the results to jumping showed that bi-articular rectus femoris and biceps femoris muscles, which are antagonists, both contract eccentrically early in the push off phase and concentrically in last part of this phase.
Article
The mechanical properties of 3, 15 and 25 month-old rat tail tendons were investigated in relation to proximal-distal sampling location along the fibre length. For the 15 and 25 month-old tendons maximum load as well as collagen content per mm fibre length (unit collagen) increased markedly from the proximal to the distal location. A linear regression analysis of the collagen content and mechanical parameters (maximum load, maximum slope of the load-strain curve and energy absorption) showed that these parameters were linearly correlated to the collagen content. However, normalization of the mechanical parameters with regard to the collagen content did not cancel the dependency of the parameters on proximal-distal sampling location. Normalized load and energy values for the 3 month-old tendons and normalized slope values for the 15 and 25 month-old tendons were found to decrease from proximal to distal location. These findings showed that tail tendons are heterogeneous along their length in respect to mechanical strength. The regression analysis also indicated the existence of an inverse relationship between unit collagen and mechanical quality of the collagen. Alternatively, the mechanical properties of tendon fibres might be influenced by other components than collagen.
Article
Eleven male subjects (20-32 years) accustomed to strength training went through progressive, high-load strength training for 24 weeks with intensities ranging variably between 70 and 120% during each month. This training was also followed by a 12-week detraining period. An increase of 26.8% (P less than 0.001) in maximal isometric strength took place during the training. The increase in strength correlated (P less than 0.05) with significant (P less than 0.05-0.01) increases in the neural activation (IEMG) of the leg extensor muscles during the most intensive training months. During the lower-intensity training, maximum IEMG decreased (P less than 0.05). Enlargements of muscle-fibre areas, especially of fast-twitch type (P less than 0.001), took place during the first 12 weeks of training. No hypertrophic changes were noted during the latter half of training. After initial improvements (P less than 0.05) no changes or even slight worsening were noted in selected force-time parameters during later strength training. During detraining a great (P less than 0.01) decrease in maximal strength was correlated (P less than 0.05) with the decrease (P less than 0.05) in the maximum IEMGs of the leg extensors. This period resulted also in decreases (P less than 0.05) of the mean muscle-fibre areas of both fibre types. It was concluded that improvement in strength may be accounted for by neural factors during the course of very intensive strength training. Selective training-induced hypertrophy also contributed to strength development but muscle hypertrophy may have some limitations during long-lasting strength training, especially in highly trained subjects.
Article
This study was designed to gain more detailed morphological information on skeletal tendons in the course of adaptation to physical loading. The effect on collagen fibrils was investigated in 6-week-old mice by means of electron microscopy. Physical loading was performed on a treadmill 5 days a week for 1, 3, 5, 7 and 10 weeks. Morphometric analysis of collagen fibrils revealed the mean diameter, the diameter distribution, the number and the cross-sectional area. The principal observations included:1. After one week of physical loading an increase in mean fibril diameter (30%, p≦0.01), in number (15%, p≦ 0.05), and in cross-sectional area (15%, p≦0.05), as well as a change in mean fibril diameter distribution. 2. From the third to the seventh week a fall under the level of the controls in mean diameter (26%, p≦0.01), in number (26%, p≦0.01), and a reduced cross-sectional area (17%, p≦0.01), accompanied by signs of splitting of individual collagen fibrils. 3. In the long-term study an increase in fibril number (29%, p≦0.01), a fall in mean diameter from 189 nm in the controls to 179 nm (p≦0.05) but no statistically significant change in the relative cross-sectional area (32%) per unit in comparison to unloaded tendons. The possible physiological implications of the findings are discussed in the light of several regulatory mechanisms known to appear during the course of physical loading in connective tissues.
Article
Immobilization of the knee joint for 9 weeks results in a reduction of the mechanical properties in the lateral collateral ligament. Specifically, ligament stiffness is reduced in this tissue. No statistical change in collagen mass was detected for the medial collateral ligament (MCL) or patellar tendon. An increase in collagen turnover (synthesis and degradation) was, however, found in the immobilized medial collateral ligament and patellar tendon. It is thus proposed that stiffness reduction is due to a change in the ligament substance itself, rather than a result of tissue atrophy.
Article
In addition to the utilization of muscle's elastic energy enhancement of performance in exercise involving stretch-shortening cycle might be also due to simultaneous increase of myoelectrical activity. This hypothesis was tested by examining three athletes during jumping exercise on force-platform. Vertical jumps were performed with and without preliminary counter-movement, and the jumps were called counter-movement jump (CMJ) and squatting jump (SJ), respectively. In both conditions several jumps were performed also with extra loads on the shoulders (15–220% of b. wt.). Additional droppingjumps (DJ) were executed from different heights (20–100 cm). During jumping exercise myoelectrical activity of selected muscles from the quadriceps femoris was monitored with surface electrodes. The results obtained were similar to those reported in isolated muscle and as expected, the prestretch in CMJ shifted the force-velocity curve of concentric work to the right. In two cases enhancement of performance was attributed primarily to restitution of elastic energy because myoelectrical activity was similar to that observed in SJ. In one subject increased myoelectrical activity was observed during the concentric phase of CMJ. In DJ condition the EMG activity during eccentric phase was much higher than in SJ. Therefore the high performance in this condition was attributed to both elastic energy and reflex potentiation. In eccentric work of CMJ the average force decreased with the increase of stretching speed. This phenomenon was associated with a light increase of EMG activity. The observed results emphasize that both elastic energy and reflex potentiation may operate effectively during stretch-shortening cycle activity.
Article
The digital flexor tendons of the miniature swine were studied after 12 mo of running exercise. Using a newly developed methodology whereby the properties of tendon substance and tendon-bone composite are measured simultaneously, it was found that training augments the strength of the tendon insertion site, but has minimal effect on the tendon substance. Biochemical analyses also showed that the collagen concentration in the tendon substance remains unchanged following exercise. There was also moderate, but not significant, tendon hypertrophy. The present results on flexor tendon differ from those previously obtained for the swine digital extensors [6]. Such difference in response to functional stress may be attributed to the biochemical composition and mechanical properties of these tissues.
Article
Different age groups of male Wistar rates were submitted to intense strength training, swim training or no training. It was found that the tetanic of the m. soleus decreased with age. This was counteracted by strength training, whereas swim training had no effect on tetanic tension. Force at ultimate failure and yield point in the Achilles tendon decreased with age, but were not influenced by strength training. Swim training, on the other hand, appeared to compensate for the ageing process in the tendon. We conclude that tendon strength decreases with age and that tendon strength does not reflect muscle strength. The absolute tensile strength of tendons appears to be influenced by physical activity of endurance-type exercise. However, it is not known whether the tissue responds to the number of mechanical muscle contractions or physiological factors connected with endurance training. Although it is questionable to extrapolate from the rat to humans, it is speculated that intensive muscle strength training should be accompanied by endurance exercise in order to prevent the muscles from damaging connective tissue structures, such as the tendons and ligaments.
Article
This study was performed to determine which of three theoretically optimal resistance training modalities resulted in the greatest enhancement in the performance of a series of dynamic athletic activities. The three training modalities included 1) traditional weight training, 2) plyometric training, and 3) explosive weight training at the load that maximized mechanical power output. Sixty-four previously trained subjects were randomly allocated to four groups that included the above three training modalities and a control group. The experimental groups trained for 10 wk performing either heavy squat lifts, depth jumps, or weighted squat jumps. All subjects were tested prior to training, after 5 wk of training and at the completion of the training period. The test items included 1) 30-m sprint, 2) vertical jumps performed with and without a countermovement, 3) maximal cycle test, 4) isokinetic leg extension test, and 5) a maximal isometric test. The experimental group which trained with the load that maximized mechanical power achieved the best overall results in enhancing dynamic athletic performance recording statistically significant (P < 0.05) improvements on most test items and producing statistically superior results to the two other training modalities on the jumping and isokinetic tests.
Article
Quadriceps muscle and fibre cross-sectional areas (CSA), torque and neural activation were studied in seven healthy males during 6 months of weight training on alternate days with six series of eight unilateral leg extensions at 80% of one repetition maximum. After training, the quadriceps cross-sectional area increased by 18.8 +/- 7.2% (P < 0.001) and 19.3 +/- 6.7% (P < 0.001) in the distal and proximal regions respectively, and by 13.0 +/- 7.2% (P < 0.001) in the central region of the muscle. Hypertrophy was significantly different between and within the four constituents of the quadriceps. Biopsies of the vastus lateralis at mid-thigh did not show any increase in mean fibre cross-sectional area. Maximum isometric voluntary torque increased by 29.6 +/- 7.9%-21.1 +/- 8.6% (P < 0.01-0.05) between 100 degrees and 160 degrees of knee extension, but no change in the optimum angle (110 degrees-120 degrees) for torque generation was found. A 12.0 +/- 10.8% (P < 0.02) increase in torque per unit area together with a right shift in the IEMG-torque relation and no change in maximum IEMG were observed. Time to peak isometric torque decreased by 45.8% (P < 0.03) but no change in time to maximum IEMG was observed. In conclusion, strength training of the quadriceps results in a variable hypertrophy of its components without affecting its angle-torque relation. The increase in torque per unit area, in the absence of changes in IEMG, may indicate changes in muscle architecture. An increase in muscle-tendon stiffness may account for the decrease in time to peak torque.
Article
The purpose of this study was to determine the fatigue behaviour of human tendons in vitro. The testing was accomplished with the use of specially designed grips and the local measurement of tendon cross-sectional area. Ninety specimens prepared from Extensor digitorum longus (EDL) tendons of the foot were subjected to a cyclic square tension-tension stress waveform at physiological frequencies. The maximum tensile stress was normalised to values corresponding to prescribed levels between 10% and 90% of the calculated ultimate tensile strength (UTS) of 100 MPa. The minimum stress was set at 1% of the UTS. A replication of 10 specimens per stress level allowed the use of statistical models for the distribution of fatigue life. Results followed a linear model, of form S = 101.3 - 14.8 log(N), relating the normalised stress to the median number of cycles to failure, therefore suggesting the absence of an endurance limit. The Weibull distribution was found to describe adequately the probability of failure at each stress level. A model which takes into account in vivo healing was proposed. This model was able to explain the presence of intact tendons throughout the lifetime of an individual.
Article
The purpose of this study was to quantify the elastic properties of tendon structures in vivo and to investigate the influence of the tendon properties on jump performance with and without countermovement. Elongation of the tendon and aponeurosis of vastus lateralis muscle (dL) was directly measured by ultrasonography while subjects (n = 31) performed ramp isometric knee extension up to the voluntary maximum (MVC). The relationship between muscle force and dL was fitted to a linear regression above 50% MVC, the slope of which was defined as stiffness of the tendon structures. Statistical analysis revealed no significant difference between duplicated measurements of stiffness, with an interday reliability of r = 0.88 and a coefficient of variance of 6.1%. Although the stiffness was not significantly related to absolute jump height in either vertical jump, it was inversely correlated with the difference in jump height between the vertical jumps performed with and without countermovement. The results suggested that the stiffness of tendon structures has a favorable effect on stretch-shortening cycle exercise, possibly due to adequate storage and recoil of elastic energy.
Article
The purpose of this study was to investigate the elastic properties of muscle-tendon complex (MTC) in knee extensor muscles and the capacity for elastic energy utilization in long-distance runners (LDR) by comparing with data obtained from untrained individuals (CON). The elongation (L) of the tendon and aponeurosis of vastus lateralis muscle during isometric knee extension was determined by real-time brightness mode ultrasonography, while the subjects developed a gradually increasing torque from 0 (relaxed) to maximal effort (MVC) within 7 s. In addition, performances in two kinds of maximal vertical jumps, i.e. squatting (SJ) and counter-movement jumps (CMJ), were measured. The relationship between L muscle and force (F ) was curvilinear and consisted of an initial region (toe region), characterized by a large increase in L with increasing F, immediately followed by a linear region. The slope of the regression equation for the L-F relationship in the range 50%–100% of MVC was defined as an index of MTC compliance, where the rate of the changes in L to that in muscle F at every 10% of MVC became almost constant. The maximal L (L max) and MTC compliance were significantly lower in LDR than in CON: 29.9 (SD 3.9) mm in LDR compared to 33.3 (SD 5.5) mm in CON for L max and 1.55 (SD 0.25) × 10−2 mm · N−1 in LDR compared to 1.88 (SD 0.82) × 10−2 mm · N−1 in CON for MTC compliance. Also, LDR showed significantly less elastic energy absorption (E e) than CON, defined as the area below the L-F relationship curve from 0 to 100% of MVC. Not only jump heights but also the differences between the heights in SJ and CMJ, expressed as the percentage of the height in SJ, were significantly lower in LDR than in CON. The augmentation with counter-movement was significantly correlated to either MTC compliance (r = 0.554, P < 0.05) or E e (r = 0.563, P < 0.05). Thus, the present results would indicate that MTC of vastus lateralis muscle is less compliant and its potential for energy storage during MTS lengthening is lower in LDR than untrained individuals. These elastic profiles of vastus lateralis muscle in LDR may be associated with their lower performances during CMJ.
Article
The present study aims to investigate the elasticity of tendon structures of the lower limbs in sprinters and its relation with sprint performance. Subjects were 10 male sprinters and 14 controls whose anthropometric variables and isometric maximum strength were similar. The elongation (L) of the tendon and aponeurosis of vastus lateralis (VL) and medial gastrocnemius muscles (MG) during isometric knee extension and planter flexion, respectively, were determined using a real-time ultrasonic apparatus in vivo, while the subjects developed a gradually increasing torque from zero (relax) to maximal effort (MVC) within 5 s. While sprinters compared with controls showed significantly greater L above 500 N (about 50% of MVC) and higher dL/dF for VL at less than 20% of MVC during knee extension, there were no significant differences between the two groups in L and dL/dF for MG at every 10% of MVC during plantar flexion. Moreover, the average value of dL/dF above 50% of MVC, proposed as the compliance of tendon structures, did not significantly differ between sprinters and controls in either VL or MG. In a regression analysis within sprinters, the compliance of VL was negatively correlated to 100-m sprint time, r=-0.757 (P < 0.05), but that of MG was not, r=0.228 (P > 0.05). Thus the present results indicate that the elasticity of tendon structures of VL and MG at high force production levels, which might be assumed to associate with the storage and subsequent release of energy during exercises involving the stretch-shortening cycle, are similar in both sprinters and controls. For sprinters, however, the tendon structures of VL are more compliant than that for controls at low force production levels, and its elasticity at high force production levels may influence sprint performance.
Article
The purpose of this study was to investigate the changes in the elastic properties of tendons in humans in relation to fatigue of knee extensor muscles. The muscle fatigue test (MFT) consisted of maximal isometric contractions performed 50 times. The decline in peak moment was 43.6 (SD 19.5)%. After MFT, the muscle thickness and pennation angle of the vastus lateralis muscle (VL) significantly increased 1.5 (SD 0.7) mm (5%) and 1.7 (SD 1.8) degrees (11%), respectively. Before and after MFT, the elongation (l) of the tendon and aponeurosis of VL was directly measured by ultrasonography, while the subjects performed ramp isometric knee extensions up to maximal voluntary contraction. The l tended to be greater after MFT than before MFT. This difference in the l was statistically significant (P < 0.05) at force developments beyond 220 N. Furthermore, the compliance increased significantly from 2.0 (SD 0.6).10(-2) mm.N-1 before MFT to 2.6 (SD 0.7).10(-2) mm.N-1 after MFT (22.7%). In addition, the electromechanical delay was significantly increased from 60.6 (SD 5.9) ms before to 70.0 (SD 4.4) ms after MFT. These results suggested that the repeated muscle contractions made the tendon structures more compliant.