ArticleLiterature Review

Altering the Length-Tension Relationship with Eccentric Exercise

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Abstract

The effects of eccentric exercise on muscle injury prevention and athletic performance are emerging areas of interest to researchers. Of particular interest are the adaptations that occur after a single bout, or multiple bouts of eccentric exercise. It has been established that after certain types of eccentric exercise, the optimum length of tension development in muscle can be shifted to longer muscle lengths. Altering the length-tension relationship can have a profound influence on human movements. It is thought that the length-tension relationship is influenced by the structural makeup of muscle. However, the mechanism responsible for the shift in optimum length is not readily agreed upon. Despite the conflict, several studies have reported a shift in optimum length after eccentric exercise. Unfortunately, very few of these studies have been randomised, controlled training studies, and the duration of the shift has not yet been established. Nonetheless, this adaptation may result in greater structural stability at longer muscle lengths and consequently may have interesting implications for injury prevention and athletic performance. Both contentions remain relatively unexplored and provide the focus of this review.

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... Whereas, when muscle velocity is only at 17% of maximal velocity muscle force is just 50% of maximum, (Lieber, 2010). The magnitude of force a muscle can generate depends on its length, velocity and stimulation (Brughelli and Cronin, 2007). The force-length relationship of a muscle is an 'inverted U' (Figure 2.7), and is dependent on the cross-bridge theory, in which muscle tension is proportional to the number of cross bridges in the zone of overlap of the thick and thin filaments (Ter Keus, Iwazumi and Pollack, 1978;Brughelli and Cronin, 2007). ...
... The magnitude of force a muscle can generate depends on its length, velocity and stimulation (Brughelli and Cronin, 2007). The force-length relationship of a muscle is an 'inverted U' (Figure 2.7), and is dependent on the cross-bridge theory, in which muscle tension is proportional to the number of cross bridges in the zone of overlap of the thick and thin filaments (Ter Keus, Iwazumi and Pollack, 1978;Brughelli and Cronin, 2007). At the optimal length, where actin-myosin interactions are maximal, muscles generate a high level of force (Gordon, Huxtey and Jitliant, 1966;Brughelli and Cronin, 2007;Lieber and Ward, 2011). ...
... The force-length relationship of a muscle is an 'inverted U' (Figure 2.7), and is dependent on the cross-bridge theory, in which muscle tension is proportional to the number of cross bridges in the zone of overlap of the thick and thin filaments (Ter Keus, Iwazumi and Pollack, 1978;Brughelli and Cronin, 2007). At the optimal length, where actin-myosin interactions are maximal, muscles generate a high level of force (Gordon, Huxtey and Jitliant, 1966;Brughelli and Cronin, 2007;Lieber and Ward, 2011). As sarcomere length increases, force decreases owing to the decreasing number of interactions between actin and myosin myofilaments (Gordon, Huxtey and Jitliant, 1966;Brughelli and Cronin, 2007;Lieber and Ward, 2011). ...
... Lower shear modulus could be attributed to reduced collagen content, decreased collagen linking, decreased tissue fluid, reduced cell swelling, and lower tissue pressure (Kovanen et al., 1984), but this might not be true after resistance training protocol. Moreover, accentuated eccentric training increases vastus lateralis fascicle length and, concurrently, lowers the fascicle pennation angle (Brughelli & Cronin, 2007). Changes in the pennation angle of the vastus lateralis impacts shear modulus results, as it influences the velocity of shear waves propagation (Miyamoto et al., 2015;Sarto et al., 2021). ...
... It is possible that the overall muscle length (from origin to insertion) increased following the training protocol in our study. This change may result from adaptations in both contractile and non-contractile elements of the muscle-tendon unit after heavy resistance training with an emphasized eccentric component (Brughelli & Cronin, 2007;Douglas et al., 2017b). These adaptations could also mean that the 20° knee angle position induced higher muscletendon resting tension before measurements compared to after. ...
Article
This study aimed to investigate the effects of an 8-week resistance training using flywheel (FW) device on countermovement jump (CMJ) performance and resting stiffness of the vastus lateralis (VL) muscle. Physically active adults were randomly assigned to a training intervention group (T; n = 18) and a control group (C; n = 13), which received no intervention. Jump performance variables and ultrasound- assessed resting VL shear modulus were measured before and after the intervention. Analysis of covariance revealed statistically significant group differences in jump height (T = +9%; C = -3%), rate of force development (T = +32%; C = +4%), peak power (T = +9%; C = -1%), and peak force (T = +7%; C = -1%). Jump performance improved only in the training group (all CMJ variables p < 0.05). Conversely, no significant changes within groups were observed in the resting shear wave modulus results (p > 0.05). VL stiffness decreased in the training group (−4%) and increased in the control group (+6%). Our results suggest that resistance training using FW device with individually allocated high-load FW inertia induces significant improvements in jump performance, which are not underpinned by changes in VL muscle stiffness.
... Though the contributions of different potential stimuli of skeletal muscle hypertrophy during RT are not fully understood, it is clear that mechanical overload/tension plays a prominent role in initiating the hypertrophic response (Roberts et al., 2023). Within the context of RT, mechanical tension can further be subcategorized into active tension and passive tension (Brughelli & Cronin, 2007). Both active and passive tension appear to stimulate muscle hypertrophy, potentially via different mechanisms (Warneke et al., 2022). ...
... The degree of active and passive tension experienced is dependent on muscle length, which has been coined the length-tension relationship. The length to active tension relationship begins with an ascending limb, followed by a plateau at optimal muscle lengths, and terminates in a descending limb (Brughelli & Cronin, 2007). Passive tension, on the other hand, begins increasing as muscle length increases beyond resting length. ...
... Additionally, shifts in the hamstrings eccentric angle of peak torque towards shorter lengths following soccer match-play exertions may potentially increase players' vulnerability to ACL injury (Cohen et al., 2015;Sanna & O'Connor, 2008). These shifts implicates that the peak torque generation may be suboptimal, as more of the muscle operating range would be on the descending aspect of the length-tension curve (Brughelli & Cronin, 2007) and implicate a compromised knee stability and increased ACL injury risk ). More recent publications by Steffen et al. (2016), argued that peak lower extremity strength parameters was not associated with an increased ACL injury risk and cannot be used to screen athlete for injury risk prediction. ...
... According to Brughelli and Cronin (2007), It was stated that the muscles are prone to operate at the descending limb of the length-tension curve if their peak torque output is affected by a reduction in muscle length. With a combination of greater knee extension during single-legged task landings (Greig, 2009;Raja Azidin et al., 2015c;Sanna & O'Connor, 2008), a decreased angle of peak Hecc torque, and a decreased Hecc peak torque (Small et al., 2010), the muscles are pushed to perform in a lengthened stat e (Garrett, 1990) during later phases of match-play, which is outside of the muscles' preferred range, possibly explaining the higher occurrence of injuries in these stages. ...
Thesis
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Anterior Cruciate Ligament (ACL) injury persists to be one of the dominant and dreaded injury in soccer. With costly implications to players, teams, and practitioners, injury prevention exercises and training programmes have been researched specifically with the intention to reduce the likelihood of ACL injury. However, the implementation, adherence, understanding of injury prevention training programmes in Malaysia have been underwhelming. Several factors to the issue include a lack of injury prevalence documentation and a lack of knowledge of injury risk and prevention, among coaches, practitioners, and the players themselves. In the first part of this study, injury rates and conditions were documented from several elite soccer teams in Malaysia across different age groups to get an illustration of the injury prevalence in elite soccer. It was found that most of the injuries that occur in Malaysian elite soccer occurs in the lower limb, specifically in the knee and ankle joints. Coaches, players, and practitioners from soccer teams across various soccer competition levels were then surveyed for their knowledge, attitude, and practices of injury prevention exercise programmes. It was generally agreed that injury prevention was very important, however, the practice of evidence-based injury prevention was reported by just over a third of respondents. Only half of the responding players admitted to being well informed about injury risk factors most players admitted practicing a combination of exercises both proven and unproven efficacy towards preventing injury. This finding suggests a better player education and maintenance of injury prevention programmes as irregular sessions and monotonous sessions were the most common barriers to proper implementation of such programmes. In the second and third part of the study, several selected overground soccer match simulations were reviewed in pursuit of developing an ecologically valid soccer match simulation with the incorporation of ball utility tasks, where similar physiological responses in the newly developed Ball-Oriented Soccer Simulation (BOSS) were similar to a previously existing overground soccer match-play simulation (OSMS; HR: BOSS = 156 ± 5 bpm, OSMS = 160 ± 7 bpm; RPE: BOSS = 14 ± 1, OSMS = 15 ± 2). Exertions in the BOSS revealed discrepancies between the left and right peak knee abduction moments during bipedal landings, as well as reductions in hamstrings eccentric peak torques, as well as functional hamstrings to quadriceps ratios, suggested a higher risk of injuries. Following a multicomponent injury prevention exercise program (IPEP), it was found that IPEP participants displayed improved tolerance to BOSS exertions. Biomechanical responses in the control group showed more extended knee and hip joint angles compared to the IPEP participants. The findings suggest that the BOSS may replicate similar responses to actual soccer match-play. The BOSS was then used as a fatigue protocol during the investigation towards the temporal efficacy of a multicomponent injury prevention training programme on biomechanical markers of ACL injury. It was found that a multicomponent injury prevention programme improved participants’ landing mechanics and allowed a sustained landing kinematic throughout the accumulation of fatigue from soccer-specific exertions.
... In healthy young adults, muscle proprioception rather than vision is the basis of postural control (Kiefer et al., 2013;Henry & Baudry, 2019;Brughelli & Cronin, 2007;Macefield & Knellwolf, 2018;Błaszczyk et al., 2020a). In particular, the calf muscles play an important role by stabilizing the ankle joints and providing the most relevant proprioceptive inputs (Błaszczyk et al., 1994;Henry & Baudry, 2019;Macefield & Knellwolf, 2018;Honeycutt et al., 2012). ...
... The joint hypermobility challenges, however, the postural control and affects the movement-posture interaction. In particular, the increased range of ankle joint motion leads inevitably to a shift of length-tension characteristics in the ankle stabilizers and this can have a profound impact on both motor and postural control (Bennell et al., 1999;Brughelli & Cronin, 2007). This might be just the case in ballet students' training where the tip-toe standing position increases the ankle range of motion and all training-related alternations in postural control are fully compensated by visual feedback. ...
Article
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The stability of human upright posture determines the range and dynamics of movements performed. Consequently, the repertoire and quality of the movements performed by a dancer are mainly determined by the efficiency of postural control. This is of particular importance in professional dance training that should focus on shaping optimal movement‑posture interaction. To get a deeper insight into this problem, the impact of the training on postural sway characteristics during quiet stance was analyzed in 16 female students in the seventh grade of a ballet school and compared with the size‑ and age‑matched group of secondary school students. Center of pressure trajectories were recorded for 25.6 s while standing quiet with eyes open (EO) and then with eyes closed (EC). The assessment of postural control was based on novel normalized sway parameters including sway vector (SV), sway anteroposterior (AP) and mediolateral (ML) directional indices (DIAP and DIML), and sway ratios (SRAP and SRML). The results document a significant contribution of vision to postural stability control in ballet students, which seems to compensate for training‑related changes in joint mobility and altered activity ranges of the legs’ muscles. In the control group standing with EC, SV amplitude increased only by 18% whereas in the ballet students tested in the same conditions, the increase exceeded 72%. Under full control of standing posture (EO test), the training‑related increase of leg muscle forces allows dancers to maintain balance with lesser effort as documented here by 21% reduced SRAP. Additionally, the dancers while tested with their EC exhibited a 12% increase in the anteroposterior sway with a concomitant reduction of the mediolateral sway. The resulting changes in the postural control asymmetry were documented by both DIAP/DIML and SV azimuth. In conclusion, our novel analysis of postural sway seems a useful tool in monitoring the effects of trainingas well as the proper course of postural control development in children and adolescents.
... Therefore, the weight to be carried or lifted is closely associated with the length of the muscles involved. Compared to bilateral knuckle-to-shoulder lifting and bilateral shoulder-to-overhead lifting, bilateral carrying and bilateral floor-to-knuckle lifting are less demanding and are easier action modalities, and they have also been shown to have the greatest improvement after the work hardening training [25][26][27]. ...
... This study was limited by the small number of participants, which is why we grouped the five load grades of the six strength subtests into two categories. In addition, although evidence supports the importance of workhardening [25][26][27], we did not find associations between any post-training strength subtest result and successful RTW. Other factors necessary for successful RTW that require additional investigation include resolution of chronic pain and recovery of muscle endurance. ...
Article
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Background Occupational accidents may lead laborers to lose their working capacities, affecting their physical and mental health. Occupational rehabilitation helps improve the ability of patients with occupational accidents and suggests appropriate jobs to avoid second injuries. This study aimed to identify whether any of the functional capacity evaluation (FCE) strength subtests predicted successful return to work. Methods Data were collected of 84 patients receiving government-subsidized occupational rehabilitation between September 2016 and December 2018. A structured questionnaire was employed for pre- and post-training assessment, including basic information, information of the occupational accident, status of the laborer at the opening of the injury case, physical requirement for the job, and physical capacity. Eight subtests of strength were included in the physical capacity evaluation, i.e., carrying, lifting to several levels, power grip, and lateral pinch, to explore the association between the strength tests and return to work. Results The unadjusted model showed that for every additional kilogram in bilateral carrying strength before work hardening training, the odds of successful return to work increased (crude odds ratio [OR] = 1.12, 95% confidence interval [CI] = 1.01–1.24, p = 0.027). After adjustment for basic demographic information and pre-accident physical functional elements of work, the odds of successful return to work increased (adjusted OR = 1.27, 95% CI = 1.04–1.54, p = 0.02) for every additional kilogram in the pre-training bilateral carrying strength. There were no statistically significant differences observed in the other seven subtests. Conclusion Through thorough evaluation and work hardening training provided in the occupational rehabilitation, patients’ physical capacity can be understood and improved. However, a full evaluation of functional capacities is prolonged and time-consuming. This study provides evidence that pre-work-hardening bilateral carrying strength may be a promising predictor of return to work and we recommend to consider it as a prioritized test to assist in determining appropriate advice regarding return to work.
... Serial sarcomere number specifically has been implicated in the shape of the whole muscle active force-length relationship (12,29), maximum shortening velocity (30), mechanical work (31), power output (32), and passive properties of muscle (33). Longitudinal fascicle growth has been advocated in clinical settings for hamstring strain injury prevention in athletes (34,35), and as therapy for sarcopenia (36), and spastic muscle (5,37,38). Therefore, the functional impact of interventions promoting longitudinal fascicle growth is of both basic and clinical interest. ...
... Due to longitudinal muscle fascicle growth's potential to increase the range for active force production, increase optimal muscle length, and reduce passive tension at longer muscle lengths, interventions promoting longitudinal fascicle growth may be beneficial in certain clinical settings (e.g., muscle strain injury prevention, sarcopenia, muscle spasticity) (5,34,36). ...
Article
Skeletal muscle has the remarkable ability to remodel and adapt, such as the increase in serial sarcomere number (SSN) or fascicle length (FL) observed after overstretching a muscle. This type of remodelling is termed longitudinal muscle fascicle growth, and its impact on biomechanical function has been of interest since the 1960s due to its clinical applications in muscle strain injury, muscle spasticity, and sarcopenia. Despite simplified hypotheses on how longitudinal muscle fascicle growth might influence mechanical function, existing literature presents conflicting results partly due to a breadth of methodologies. The purpose of this review is to outline what is currently known about the influence of longitudinal muscle fascicle growth on mechanical function and suggest future directions to address current knowledge gaps and methodological limitations. Various interventions indicate longitudinal muscle fascicle growth can increase the optimal muscle length for active force, but whether the whole force-length relationship widens has been less investigated. Future research should also explore the ability for longitudinal fascicle growth to broaden the torque-angle relationship's plateau region, and the relation to increased force during shortening. Without a concurrent increase in intramuscular collagen, longitudinal muscle fascicle growth also reduces passive tension at long muscle lengths; further research is required to understand whether this translates to increased joint range of motion. Lastly, some evidence suggests longitudinal fascicle growth can increase maximum shortening velocity and peak isotonic power, however, there has yet to be direct assessment of these measures in a neurologically intact model of longitudinal muscle fascicle growth.
... Eccentric force-velocity relationships differ from the concentric muscle actions [18,19] first devised in Hill's muscle model [20]. During eccentric muscle lengthening, higher forces are attained alongside high velocity [13,14,16,[20][21][22][23][24][25][26][27][28]. However, this statement only holds true to a certain degree; for example, if tension (force and velocity) is too great, then an individual would not be able to produce enough force to decelerate and would continue to displace through a motion [23,27,29]. ...
... These findings are in agreement with the review by Kellis and Baltzopoulos [70], who explained that the eccentric IKD is not velocity specific. The increased torque values are expected as eccentric torque values are enhanced or maintained when velocity increases [21,[71][72][73]. Therefore, participants will increase the force production and overall strength capacity of the muscle through physiological factors, e.g., increasing motor unit recruitment [3,71]. ...
Article
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Eccentric training as a method to enhance athletic performance is a topic of increasing interest to both practitioners and researchers. However, data regarding the effects of performing the eccentric actions of an exercise at increased velocities are limited. This narrative review aimed to provide greater clarity for eccentric methods and classification with regard to temporal phases of exercises. Between March and April 2021, we used key terms to search the PubMed, SPORTDiscus, and Google Scholar databases within the years 1950–2021. Search terms included ‘fast eccentric’, ‘fast velocity eccentric’, ‘dynamic eccentric’, ‘accentuated eccentric loading’, and ‘isokinetic eccentric’, analysing both the acute and the chronic effects of accelerated eccentric training in human participants. Review of the 26 studies that met the inclusion criteria identified that completing eccentric tempos of < 2 s increased subsequent concentric one repetition maximum performance, velocity, and power compared with > 4 s tempos. Tempos of > 4 s duration increased time under tension (TUT), whereas reduced tempos allowed for greater volume to be completed. Greater TUT led to larger accumulation of blood lactate, growth hormone, and testosterone when volume was matched to that of the reduced tempos. Overall, evidence supports eccentric actions of < 2 s duration to improve subsequent concentric performance. There is no clear difference between using eccentric tempos of 2–6 s if the aim is to increase hypertrophic response and strength. Future research should analyse the performance of eccentric actions at greater velocities or reduced time durations to determine more factors such as strength response. Tempo studies should aim to complete the same TUT for protocols to determine measures for hypertrophic response.
... To assess the torque-angle curve, the angle-specific averaged knee flexor torque of each participant was measured every 10 from 10 to 60 of knee flexion. The peak torque of torque-angle curve was also determined by fitting to a fourth-order polynomial curve (Brughelli & Cronin, 2007;Yeung & Yeung, 2008). Four conditions (concentric at 60 /sec (CON60) and 300 /sec (CON300), eccentric at 60 /sec (ECC60) and eccentric at 300 /sec (ECC300) were analyzed. ...
... The reason for these differences remains unclear. Any change in knee flexor torque development, such as the torque-angle curve, is caused by the change in musculotendinous stiffness as well as neuromuscular function (Brughelli & Cronin, 2007). In the present study, hamstring viscoelastic properties were not investigated. ...
Article
Objectives To investigate the knee flexor torque-angle curve after hamstring strain injury using different muscle action types and angular velocities. Design Cross-sectional. Setting Controlled laboratory. Participants Thirteen collegiate athletes injured hamstring strain (21.0 ± 0.8 years; 173.9 ± 6.5 cm; 70.1 ± 10.5 kg). Main outcome measures Concentric and eccentric knee flexor torque was measured at 60 & 300°/sec. Peak torque and average torque every 10° were determined from torque-angle curve and injured side was compared with non-injured side. Results No significant differences were found in the concentric muscle actions. However, the eccentric peak torque was significantly lower on the injured side at 60°/sec (p = 0.048) and at 300°/sec (p = 0.002). The average eccentric torque was significantly lower on the injured side at 60°/sec from 10° to 20° of knee flexion (p = 0.012–0.018) and at 300°/sec from 10° to 60° of knee flexion (p = 0.005–0.049). Conclusion The knee flexor torque-angle curve changes with eccentric muscle action after hamstring injury. Eccentric torque declines were close to full knee extension at 60°/sec and a wide range of knee flexion at 300°/sec. The assessment and rehabilitation of eccentric hamstring strength may be important to consider the effect of the angular velocity after hamstring strain injury.
... It has been shown that chronic use of eccentric contractions results in increased eccentric strength and increased fascicle length [39], often concomitantly with a rightward shift in the optimal operating angle on the length-tension curve [40]. The chronic use of isometric exercise at long musculotendinous unit lengths has been shown to increase isometric strength, pennation angle and fascicle length, and cause hypertrophy [41]. ...
... The potential benefits of a contraction mode that incorporates an eccentric stimulus, resulting in an enhanced isometric steady-state force at a reduced metabolic cost [53], are intriguing. Evidence suggests that with chronic use of eccentric contractions, increased eccentric strength and increased fascicle length [39] often occur concomitantly with a rightward shift in the optimal operating angle on the length-tension curve [40]. These changes to the structure and behaviour of the muscle have been found to increase the resilience of the hamstring to strain injury [61]. ...
Article
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Residual force enhancement (rFE) is observed when isometric force following an active stretch is elevated compared to an isometric contraction at corresponding muscle lengths. Acute rFE has been confirmed in vivo in upper and lower limb muscles. However, it is uncertain whether rFE persists using multiple, consecutive contractions as per a training simulation. Using the knee flexors, 10 recreationally active participants (seven males, three females; age 31.00 years ± 8.43 years) performed baseline isometric contractions at 150° knee flexion (180° representing terminal knee extension) of 50% maximal voluntary activation of semitendinosus. Participants performed post-stretch isometric (PS-ISO) contractions (three sets of 10 repetitions) starting at 90° knee extension with a joint rotation of 60° at 60°·s−1 at 50% maximal voluntary activation of semitendinosus. Baseline isometric torque and muscle activation were compared to PS-ISO torque and muscle activation across all 30 repetitions. Significant rFE was noted in all repetitions (37.8–77.74%), with no difference in torque between repetitions or sets. There was no difference in activation of semitendinosus or biceps femoris long-head between baseline and PS-ISO contractions in all repetitions (ST; baseline ISO = 0.095–1.000 ± 0.036–0.039 Mv, PS-ISO = 0.094–0.098 ± 0.033–0.038 and BFlh; baseline ISO = 0.068–0.075 ± 0.031–0.038 Mv). This is the first investigation to observe rFE during multiple, consecutive submaximal PS-ISO contractions. PS-ISO contractions have the potential to be used as a training stimulus.
... Similarly, performing acute and chronic eccentric exercise (including the reverse Nordic) has been shown to increase the optimal length of the quadriceps muscles (+6.58) (12) and muscle fascicle length of the rectus femoris (+9.5%), vastus lateralis (+3.4%), and vastus medialis (+2.4%) (3,4). These adaptations theoretically support injury mitigation by allowing peak torque to occur at Exercise Technique VOLUME 00 | NUMBER 00 | MONTH 2025 longer muscle lengths (15,28), extending the physiological range of muscle contractions (11,32), and reducing the strain experienced by muscles during athletic tasks at long muscle lengths (70,78). Although the effect of the reverse Nordic on quadriceps femoris flexibility has not been explicitly studied, the S&C practitioner should consider the potential of this exercise for injury mitigation, especially in highrisk athletes. ...
Article
The reverse Nordic is a single joint (knee), controlled open kinetic chain exercise with a predominantly eccentric focus. This review summarizes the reverse Nordic, including exercise benefits, muscles involved, exercise technique, progressions, regressions, and programming strategies. Furthermore, this review outlines how strength and conditioning coaches can use the reverse Nordic within a training program to improve athletic performance and mitigate injury risk.
... Hamstring muscles operate differently across different lengths in response to changing exercise stimuli [43] and studies have suggested that injury is associated with a left-ward shift of peak torque to shorter angle lengths in the hamstrings [44]. The evaluation of the torque-angle relationship may be a useful tool for predicting hamstring strain injuries and as a return-to-play measure [45] and therefore standardized, controlled technique of exercises that measure torque-angular data are important, as a deviation of form can alter the intended nature of the exercise, impacting the desired adaptations, whether for training, angle-specific testing, performance optimisation, injury prevention or rehabilitation. Specifically, in the NHE, maintaining a neutral 0° hip position minimises variability in torque production, allowing for a more consistent and targeted training effect in the knee flexor muscles, however, whether this enhances the overall training effect depends on the specific adaptation being targeted, and further research is required [46,47]. ...
Article
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Purpose A wealth of research exists for the Nordic hamstring exercise and several devices provide real-time feedback on torque profiling. However, none currently offer feedback on technique execution. This study investigated the effect of verbal and software feedback on Nordic exercise kinetic and kinematic metrics. Methods 24 recreational participants completed two sets of three bilateral repetitions on a hamstring testing device. In a crossover design, one set was performed with verbal feedback, while the other set used software-based feedback. Hamstring strain injury risk metrics (peak torque, break-torque angle, and bilateral limb percentage difference) and exercise technique metrics (relative trunk-to-thigh angle and angular velocity of the knee) were recorded for analysis. Results The feedback type significantly affected eccentric knee flexor peak torque, by a mean decrease of 7.1 Nm when performed with software feedback (Cohen’s d = 0.238, p < 0.01). Altering feedback had no significant effect on bilateral limb difference percentage (Cohen’s d = 0.068, p = 0.578) or break-torque angle (Cohen’s d = 0.159, p = 0.115). Software feedback significantly decreased the mean of both the relative-trunk-to-thigh angle at peak torque by 5.7° (Cohen’s d = 0.514, p < 0.01) and the angular velocity of the knee at peak torque by 8.7 deg·s⁻¹. Conclusions An integrated software feedback system significantly improves acute Nordic exercise technique, benefitting individuals initially exhibiting poorer technique the most.
... These adaptations are likely the result of an increase in the number of sarcomeres in series and in parallel (47). Such muscle adaptations contribute to enhanced muscular strength, particularly at greater muscle lengths (48), by improving the tension-length relationship of the muscle (48,49). Moreover, ET, which involves lengthening the muscle while producing force, is particularly effective in the context of stroke rehabilitation. ...
Article
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Spastic paresis, a frequent consequence of stroke, is characterized by both neurological and muscular alterations, leading to decreased muscle strength, increased passive muscle stiffness, and subsequently, diminished functional capacity. Although conventional rehabilitation programs are effective in enhancing muscle strength, they often fail to yield clinically significant improvements in functional capacities. Eccentric Training (ET) has shown promise in addressing the shortened muscle fascicle lengths and joint contractures commonly observed in stroke survivors. Despite the prevalence of contractures and rigidity in this population, the effects of ET on the structural and mechanical properties of muscles remain underexplored. This study aims to investigate the impact of ET on gait speed in sub-acute stroke patients compared to conventional therapy. Additionally, we aim to explore the effects of ET on the mechanical properties, structural characteristics, and neuromuscular parameters of the plantar flexors. A randomized controlled trial will be conducted, adhering to CONSORT guidelines, with participants assigned to either a Conventional Therapy Group or an Eccentric Training Group. Assessments will be conducted at baseline, and after ET intervention, encompassing clinical, biomechanical, and functional evaluations. This study seeks to provide empirical evidence on the efficacy of ET in improving motor outcomes in sub-acute stroke patients, thereby informing more effective rehabilitation strategies.
... 50 Given the potential for hamstring injury during eccentric actions (late swing and early stance), there has been a focus on accentuated eccentric training when training the hamstrings. [51][52][53] It is suggested this mode of training results in superior adaptations compared with conventional resistance training. 53,54 Flywheel training-where athletes create inertial torque by pulling a cable attached to a flywheel during the concentric phase of the exercise, which they must resist as it pulls against them during the eccentric portion of the movement 55,56 -is a popular mode of loading the eccentric phase of a movement. ...
Article
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Purpose: The optimal approach to hamstring training is heavily debated. Eccentric exercises reduce injury risk; however, it is argued that these exercises transfer poorly to improved hamstring function during sprinting. Some argue that other exercises, such as isometric exercises, result in better transfer to running gait and should be used when training to improve performance and reduce injury risk. Given the performance requirements of the hamstrings during the terminal swing phase, where they are exposed to high strain, exercises should aim to improve the torque production during this phase. This should improve the hamstrings' ability to resist overlengthening consequently, improving performance and limiting strain injury. Most hamstring training studies fail to assess running kinematics postintervention. Of the limited evidence available, only eccentric exercises demonstrate changes in swing-phase kinematics following training. Studies of other exercise modalities investigate effects on markers of performance and injury risk but do not investigate changes in running kinematics. Conclusions: Despite being inconsistent with principles of transfer, current evidence suggests that eccentric exercises result in transfer to swing-phase kinematics. Other exercise modalities may be effective, but the effect of these exercises on running kinematics is unknown.
... Hamstring muscles operate differently across different lengths in response to changing exercise stimuli [45] and studies have suggested that injury is associated with a left-ward shift of peak torque to shorter angle lengths in the hamstrings [46]. The evaluation of the torque-angle relationship may be a useful tool for predicting hamstring strain injuries and as a return-to-play measure [47]. Therefore, standardized, controlled technique of exercises that measure torque-angular data is important, as a deviation of form can alter the intended nature of the exercise, impacting the desired adaptations in the knee exors, whether for training, angle-speci c testing, performance optimisation, injury prevention or rehabilitation. ...
Preprint
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Purpose A wealth of research exists for the Nordic hamstring exercise, and several devices provide real-time feedback on torque profiling. However, none currently offer feedback on technique execution. This study investigated the effect of verbal and software feedback on Nordic exercise kinetic and kinematic metrics. Methods 24 recreational participants completed 3 bilateral repetitions per feedback condition on a hamstring testing device. Hamstring strain injury risk metrics (peak torque, break-torque angle, bilateral limb percentage difference) and exercise technique metrics (relative trunk-to-thigh angle, angular velocity of the knee) were recorded for analysis. Results Feedback type significantly affected eccentric knee flexor peak torque, by a mean decrease of 7.1 Nm when performed with software feedback (Cohen’s d = 0.238, p < 0.01). Altering feedback had no significant effect on bilateral limb difference percentage (Cohen’s d = 0.068, p = 0.578) or break-torque angle (Cohen’s d = 0.159, p = 0.115). Software feedback significantly decreased the mean of both the relative-trunk-to-thigh angle at peak torque by 5.7° (Cohen’s d = 0.514, p < 0.01) and the angular velocity of the knee at peak torque by 8.7 deg·s-1. Conclusions An integrated software feedback system significantly improves acute Nordic exercise technique, benefitting individuals initially exhibiting poorer technique the most.
... As eccentric contractions require less energy and muscle activity for equivalent force production, eccentric exercise has received considerable attention over the past decades to rehabilitate injuries, to improve athletic performance, and to help manage neuromuscular diseases (9)(10)(11)(12)(13). Accordingly, many training studies aimed to determine the specific adaptations of the muscle-tendon unit (MTU) to eccentric exercise compared with concentric exercise. ...
Article
Whether eccentric exercise involves active fascicle stretch is unclear due to muscle-tendon unit (MTU) series elasticity. Therefore, this study investigated the impact of changing the activation timing and level (i.e., pre-activation) of the contraction on muscle fascicle kinematics and kinetics of the human tibialis anterior during dynamometer-controlled maximal voluntary MTU-stretch-hold contractions. B-mode ultrasound and surface electromyography were employed to assess muscle fascicle kinematics and muscle activity levels, respectively. While joint kinematics were similar among MTU-stretch-hold contractions (~40° rotation amplitude), increasing pre-activation increased fascicle shortening and stretch amplitudes (9.9-23.2 mm, p ≤ 0.015). This led to increasing positive and negative fascicle work with increasing pre-activation. Despite significantly different fascicle kinematics, similar peak fascicle forces during stretch occurred at similar fascicle lengths and joint angles regardless of pre-activation. Similarly, residual force enhancement (rFE) following MTU stretch was not significantly affected (6.5-7.6%, p = 0.559) by pre-activation, but rFE was strongly correlated with peak fascicle force during stretch ( r rm = 0.62, p = 0.003). These findings highlight that apparent eccentric exercise causes shortening-stretch contractions at the fascicle level rather than isolated eccentric contractions. The constant rFE despite different fascicle kinematics and kinetics suggests that a passive element was engaged at a common muscle length among conditions (e.g., optimal fascicle length). Although it remains unclear whether different fascicle mechanics trigger different adaptations to eccentric exercise, this study emphasizes the need to consider MTU series elasticity to better understand the mechanical drivers of adaptation to exercise.
... The previous literature has reported that the posture of the hips and spine affects the activation patterns of the surrounding musculature due to altered length-tension relationships [11,12]. Specifically, an LEO DB can alter the resting hip position while standing [7], resulting in a significant anterior rotation and increased lumbar lordosis, especially when the belt is loaded anteriorly [6]. ...
Article
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Sixty percent of all law enforcement officers (LEOs) experience low back pain (LBP), with the LEO duty belt (LEODB) commonly reported to be a contributing factor. The primary purpose of the study was to investigate the LEODB’s effect on muscular activity and compare it to a tactical vest, which is a commonly used alternative to an LEODB. In total, 24 participants (13 male, 11 female; mass, 73.0 ± 11.1 kg; height, 169.0 ± 10.0 cm; age, 24.0 ± 5.8 years) completed a progressive series of hip hinge tasks in a single testing session. All participants completed four conditions (no belt, leather belt, nylon belt, and weight VEST) in a randomized order. Surface electromyography (sEMG) sensors were placed bilaterally on the rectus abdominus, multifidus, biceps femoris, and rectus femoris. Across all tasks, no significant effects of load on muscle activity were found for any of the muscles. Participants rated the VEST condition as more comfortable (p < 0.05) and less restrictive (p < 0.05) than either LEODB. The findings suggest an LEODB does not alter muscle activity during bodyweight hip hinging or lifting objects from the ground. Future research should examine whether changes in muscle activity occur with durations of LEODB wear more similar to an actual work shift duration for LEOs (≥8 h).
... gradually lean forward at the slowest possible speed, whilst keeping the shoulders, hips and knees in line with one another throughout the full range of motion), the NHE will elicit an increase in muscle fascicle length (FL) through the addition of more sarcomeres in series [53][54][55]. This is thought to correspond to a longer muscle length at failure and a modification of the hamstring length-tension relationship acting to alleviate the potential risk of HSI [56]. Despite this being the focus of previous research, investigations have noted improvements in sprint speed, COD and jumping following an NHE intervention in youth athletes [57][58][59]. ...
Article
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The aim of this systematic review was to critically appraise the effects of eccentric resistance training on measures of physical performance (i.e. muscular strength, jump, sprint and change of direction) in youth athletes 18 years of age and under
... Interestingly, gastrocnemius shear modulus however decreased after a drop-jump training intervention (Ando et al. 2021b), without concomitant changes in RFD. Considering the participants in that study were not trained athletes, the authors suggested that drop jump training could enforce lengthening of muscles fascicles, which could result in decreased shear modulus at a given muscle length by altering the lengthtension relationship and thus leading to less passive tension at a given muscle length (Brughelli and Cronin 2007). The associations between shear modulus and jumping performance may be significantly affected by the length-tension relationship and the associated muscle slack length, which were not measured in the present study (Van Hooren and Zolotarjova 2017). ...
Article
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This study explored the relationships between passive muscle stiffness (shear modulus) and vertical jumping performance, countermovement utilization ratio (CUR) and rate of force development (RFD) in an attempt to unravel the mechanism that may explain the association between shear modulus and performance. 32 recreationally active participants (16 males, 16 females; age: 22.4 ± 5.1 years) participated. Shear modulus was assessed for the lateral and medial gastrocnemius (GL and GM), and vastus medialis (VM) and lateralis (VL) muscles using shear wave elastography. Squat jump (SJ) and countermovement (CMJ) jump were determined, with CUR being expressed as the ratio between the two. RFD in ankle and knee extension tasks was measured using isometric dynamometers. Our results suggest that within a heterogeneous group of recreational athletes, passive muscle stiffness is not related to RFD and jump performance, but positively related to CUR. In males, shear modulus of the GL was positively related to SJ height (r = 0.55). We also found inverse moderate correlations between VL and VM shear modulus and RFD in females only (r = –0.50 to –0.51), but this relationship was possibly affected by age and body fat content. Different mechanisms may underpin the association between shear modulus and performance depending on the muscle, task and population investigated.
... Il convient de souligner qu'un travail mécanique à haute(s) intensité(s) de contraction, haut volume, grande(s) longueur(s) musculaire(s) et/ou la combinaison de ces facteurs, peut exacerber la sévérité des EIMD et par conséquent, les changements de la mécanique contractile du muscle et/ou du groupe musculaire étudié (BRUGHELLI et CRONIN, 2007). ...
Thesis
La survenue d’altérations neuromusculaires et musculo tendineuses lors d’épreuves de course à pied de fond s’avère être délétère sur la capacité de performance d’endurance et la période de récupération des athlètes. Par ailleurs, la sévérité de ces perturbations peut être exacerbée par les caractéristiques du terrain, et plus particulièrement par la présence de dénivelé négatif. En course à pied de descente, l’amplitude plus importante de ces altérations est sous-tendue par la prédominance du régime de contraction excentrique à l’exercice. Dès lors, la course à pied de descente constitue un challenge pour les coureurs dans leur quête d’excellence athlétique, aussi bien à l’entraînement que lors d’épreuves compétitives. L’exploration de stratégies préventives, ayant pour objectif de mieux tolérer les sections de course à pied en descente, apparaît donc pleinement justifiée dans le domaine de l’optimisation des réponses adaptatives en course à pied. Dans ce contexte, une première analyse prospective de la littérature a focalisé sur l’exploration des stratégies de répétitions de sessions (c.-à-d., usage chronique de la course à pied en descente) et du port in situ de textiles vestimentaires à visée ergogénique (e.g., textiles de compression et réflecteurs de rayons infrarouges lointains). Étant donné que l’usage chronique de la course à pied en descente pourrait également permettre l’instauration d’adaptations bénéfiques sur la capacité de performance des athlètes, il convenait au préalable de préciser les adaptations neuromusculaires et musculo-tendineuses à l’entraînement de course à pied en descente. Ainsi, les objectifs du travail de thèse étaient de caractériser les adaptations neuromusculaires et musculo-tendineuses à l’entraînement de course à pied en descente d’une part, et d’enrichir nos connaissances sur l’apport de stratégies préventives dans le domaine de la course à pied de fond, d’autre part. Les résultats de ce travail ont montré que : (i) l’entraînement de course à pied en descente (4 semaines) peut instaurer de rapides adaptations neuromusculaires (e.g., gains de force, hypertrophie musculaire) et tendineuses (par exemple, augmentation de la raideur du tendon patellaire), sans pour autant atténuer la sévérité des perturbations neuromusculaires à l’issue d’une session de course à pied en descente ; (ii) que le port de textiles de compression à l’exercice peut exercer un « effet protecteur dynamique » sur les groupes musculaires compressés, sans pour autant atténuer les perturbations de la capacité de performance d’endurance des athlètes ; et (iii) que le port de textiles réflecteurs de rayons infrarouges à l’exercice pourrait générer certains effets ergogéniques mais que la compréhension de leurs effets reste à ce jour globalement limitée.
... Al., (9) (5,11,12) . Brughelli e Cronin (13) (14) . ...
Article
Introdução: O Exercício Nórdico dos Isquiotibiais (ENI) tem sido objeto de polêmicas relativas à sua utilização; alguns pesquisadores afirmam que ele pode contribuir para lesões nos isquiotibiais, outros preconizam os efeitos terapêuticos do ENI. Objetivo: discutir a partir de um modelo biomecânico simples, as forças isométricas exercidas pelos isquiotibiais (Fisq) e a resultante sobre o joelho (Rj) que atuam, em isometria, sob diferentes ângulos de inclinação do tronco. Métodos: Foi construído o modelo mimetizando o ENI representando um sujeito ajoelhado com os tornozelos fixados de modo a impedir a movimentação das pernas. O tronco inclinado com a horizontal sob ângulos de 80, 75, 70, 65, 60 e 55 graus com a vertical. Nessas seis inclinações foi considerado o ângulo médio de ação dos isquiotibiais de 7º com a linha longitudinal do tronco. A estatura (entre 1,60 e 2,00m) e a massa corporal (entre 50 e 120 Kg) foram variáveis consideradas. Foram aplicadas as condições de equilíbrio de um corpo extenso da mecânica clássica. Foram consideradas as localizações dos centros de massa de cada segmento corporal para a identificação do ponto de aplicação de forças gravitacionais no modelo, posteriormente, com o software Origin 9.0®, foram calculadas as forças resultantes exercidas pelos isquiotibiais (Fisq) e as forças resultantes exercidas sobre os joelhos (Rj); os cálculos estatísticos realizados onde foram aplicados testes de normalidade, homoscedasticidade, comparações e correlações, todos com p<0,05. Resultados: a normalidade dos dados foi confirmada pelos testes de Kolmogorov-Smirnov e a homogeneidade das variâncias pelo teste de Levene. A associação entre a Fisq e a estatura foi significante para com h2=0,988 em todas as angulações do tronco, por sua vez, a força resultante que atua sobre o joelho apresentou associação com a estatura com h2=0,923. As comparações foram significantes entre todos os ângulos de inclinação do tronco considerados com p de Bonferroni <0,001. Todas as correlações entre Fisq e Rj foram significantes com r>0,980. Conclusão: o modelo evidenciou a complexidade do ENI e que novos estudos que considerem outras forças devem ser realizados.
... As for jumping performance, a compliant musculo-tendon system can store high amounts of elastic energy, while a stiffer one can transmit energy at a higher rate. Both adaptations of the musculo-tendon system may improve athletic performance, optimally by being more compliant at the start and stiffer towards the completion of the elongation (Brughelli & Cronin, 2007). However, stiffer individuals were found to be subjected to greater loading, as they could not resist large eccentric loadings (Walshe & Wilson, 1997). ...
Article
This study examined whether analysing kinetic features of drop jumps (DJ) as one-dimensional biomechanical curves can reveal specific patterns that are consistent and can cluster DJ performance. Hierarchical clustering analysis on DJ from 40 cm data performed by 128 physically active male participants (23.0 ± 4.5 yrs, 1.84 ± 0.07 m, 79.1 ± 10.8 kg) was performed on the derived time-normalised force, power and vertical stiffness curves to unmask the underlying patterns and to explore the dissimilarities identified from the subgroup (cluster) analysis. Results revealed poor, average and top DJ performers. Top performers exhibited larger peak force, power and vertical stiffness compared to the other two groups, and the poor performers had lower values compared to the average performers (p < .05). The time curves of force, power and vertical stiffness exhibited between cluster dissimilarities from ~25% to ~70%, and ~20% to 40% plus ~55% to 70% from the beginning of the ground contact, respectively. The force and power time-curves distinguished DJ ability similarly since they shared 69% of the cases in the top performers’ cluster. The content of cases (membership) for vertical stiffness was different from the membership for the force and power time-curve clusters. In conclusion, stiffness should be considered during plyometric training, but does not distinctly define DJ performance.
... Their benefits to physical performance have been clearly described to develop strength and increase the cross-sectional area of the muscle (Dudley et al. 1991). However, the intensity and duration of eccentric muscle contractions can acutely induce muscle damage, considering that high levels of force performed at higher levels of muscle stretching are one of the main causes of damage to the contractile and connective elements of muscles (Brughelli and Cronin 2007). ...
Article
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Studies comparing the two classes of stimuli (concentric and eccentric) have shown differences in the improvement of cardiovascular, metabolic, and muscle strength gain. This is an experimental, quantitative, and prospective study that aimed to verify the effect of eccentric exercise on glycolytic consumption and kinetics. The blood glucose kinetics of 17 male subjects was evaluated during a treadmill exercise with a 10% declined floor and velocity that required a 60% metabolic activity of VO2max, for 30 minutes. Seventy-two hours later, the same subjects exercised on the treadmill with a 10% inclined floor and 60% VO2max, for 30 minutes. To quantify glucose, blood samples were collected before the exercise, every three minutes along the 30 minutes of physical activity, and five and 10 minutes after finishing the exercise. For the downward slope, there was a homogeneous group behavior for blood glucose dynamics during the exercise, which was characterized by a monotonic decrease of glucose levels until reaching a minimum value at experimental times between 20 and 30 min, followed by a progressive recovery toward initial values. For the acclivity condition, blood glucose dynamics did not follow such a homogeneous behavior. A set of different types of dynamics could be identified. Experimental data showed that the type of dynamics could be predicted, to some extent, by the basal blood glucose level of subjects. The type of floor slope (upward or downward) directly affected glycolytic consumption and kinetics for the individuals analyzed.
... Previous studies have demonstrated that during forearm and leg extension muscle actions, there is an increase in antagonist activation at longer muscle lengths, due to the joint being more susceptible to injuries such as hyperextension (Aagaard et al., 2000;Babault et al., 2003;Komi et al., 2000;Solomonow et al., 1988). The current study, which resulted in no changes in EMG AMP, analyzed the middle 1/3 of the range of motion, when agonist force production is highest (Brughelli & Cronin, 2007). It is possible that when examined at longer muscle lengths, there would be similar fatigue-induced antagonist activation responses as reported in rested a state. ...
Article
Background Antagonist activation may contribute to fatigue-induced decreases in torque while assisting in the maintenance of joint stability. This study utilized a reciprocal, slow velocity (60°·s⁻¹) forearm flexion and extension fatiguing task to examine the contributions of coactivation to torque production at slow and moderate (180°·s⁻¹) velocities, as well as during a maximal voluntary isometric contraction (MVIC). Methods Twelve recreationally active men (mean ± SD: age = 21.7 ± 1.6 years; body mass = 83.5 ± 8.8 kg; height = 179.4 ± 5.2 cm) completed isokinetic (60 and 180°·s⁻¹) and isometric pre-testing of forearm flexion and extension, followed by 50 maximal, reciprocal, isokinetic muscle actions at 60°·s⁻¹, followed by post-testing. The amplitude (AMP) of the electromyographic (EMG) signals from the biceps and triceps brachii were simultaneously recorded. Torque and EMG AMP were normalized to the corresponding values from the pre-testing peak torque movements. Repeated measures ANOVAs and pairwise comparisons were used to identify mean changes in torque, EMG AMP, and coactivation ratios. Results The torque analyses indicated greater (p < 0.03) decreases for 180°·s⁻¹ (24%) and MVIC (23%) than 60°·s⁻¹ (14%) for forearm flexion. For forearm extension, there were no differences (p > 0.05) in fatigability between velocities. For EMG AMP there were no changes (p > 0.05) from pre- to post-testing for any velocity or movement. There were no changes (p > 0.05) in the coactivation ratio for forearm flexion, but significant increases (13.6 ± 6.6 to 16.9 ± 6.0; p = 0.003) for forearm extension, collapsed across Velocity. Conclusions There was velocity- and movement-specific fatigability for forearm flexion and extension. The parallel, fatigue-induced EMG AMP responses indicated that coactivation did not contribute to the decreases in torque and would not affect elbow joint stability.
... Early studies suggested that hamstring injury was associated with a shift of peak torque at shorter angle lengths [20], which suggests that evaluation of the torque-angle relationship may be useful as a hamstring injury risk predictor and a return to play measure [21]. A more recent review, however, has raised doubts about the use of angle of peak torque [22], naming several limitations of knee flexion--angle curve assessment, which relate to the potential influence of muscle architecture, neural activation, and moment arms as well as experimental limitations. ...
Article
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Temporal biomechanical and physiological responses to physical activity vary between individual hamstrings components as well as between exercises, suggesting that hamstring muscles operate differently, and over different lengths, between tasks. Nevertheless, the force-length properties of these muscles have not been thoroughly investigated. The present review examines the factors influencing the hamstrings’ force-length properties and relates them to in vivo function. A search in four databases was performed for studies that examined relations between muscle length and force, torque, activation, or moment arm of hamstring muscles. Evidence was collated in relation to force-length relationships at a sarcomere/fiber level and then moment arm-length, activation-length, and torque-joint angle relations. Five forward simulation models were also used to predict force-length and torque-length relations of hamstring muscles. The results show that, due to architectural differences alone, semitendinosus (ST) produces less peak force and has a flatter active (contractile) fiber force-length relation than both biceps femoris long head (BFlh) and semimembranosus (SM), however BFlh and SM contribute greater forces through much of the hip and knee joint ranges of motion. The hamstrings’ maximum moment arms are greater at the hip than knee, so the muscles tend to act more as force producers at the hip but generate greater joint rotation and angular velocity at the knee for a given muscle shortening length and speed. However, SM moment arm is longer than SM and BFlh, partially alleviating its reduced force capacity but also reducing its otherwise substantial excursion potential. The current evidence, bound by the limitations of electromyography techniques, suggests that joint angle-dependent activation variations have minimal impact on force-length or torque-angle relations. During daily activities such as walking or sitting down, the hamstrings appear to operate on the ascending limbs of their force-length relations while knee flexion exercises performed with hip angles 45–90° promote more optimal force generation. Exercises requiring hip flexion at 45–120° and knee extension 45–0° (e.g. sprint running) may therefore evoke greater muscle forces and, speculatively, provide a more optimum adaptive stimulus. Finally, increases in resistance to stretch during hip flexion beyond 45° result mainly from SM and BFlh muscles.
... Such a shift has been linked to a decreased risk of injury, as a longer optimal skeletal muscle length would mean that less of the muscle's functional range would be along the more unstable descending limb of the length-tension curve. Conversely, T allele carriers may be susceptible to injuries [20,33]. The importance of the TTN gene for muscle properties and injury risk was confirmed by Vera et al., who showed the association between connective tissue disorders (CTDs) and genetic variants within this gene [26]. ...
Article
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TTN encodes the third myofilament, titin, which plays structural, mechanical, regulatory, and developmental roles in sarcomeres. The aim of this research was to determine the interaction between novel and previously described TTN variants and athletic performance, as well as competition level, in Caucasians. Firstly, 100 athletes and 47 controls were recruited, and whole-genome sequencing was performed. Secondly, 348 athletes (108 endurance, 100 sprint/power, 140 mixed-sport athletes) and 403 volunteers were included, and real-time PCR was performed. We found a significant overrepresentation of the rs10497520 CT and TT genotypes in the sprint/power athlete group (95% CI, 1.41–3.66, p = 0.0013). The rs10497520 T carriers were 2.17 times more likely to become sprint/power athletes (95% CI 1.35–3.49, p = 0.0021). We also found that the likelihood of having the TT genotype was higher for the highly elite and sub-elite sprint/power athletes. Possessing at least one TAA (rs10497520, rs55837610, rs72648256) haplotype resulted in an increase in the log-odds ratio by 0.80 (p = 0.0015), 1.42 (p = 0.003), and 0.77 (p = 0.044) for all, highly elite, and sub-elite sprint/power athletes, respectively. We demonstrated that harbouring the rs10497520 T allele, individually and in a haplotype combination, increased the chance of being an elite sprint/power athlete, indicating that this allele may be favourable for sprint/power performance.
... Several authors have reported that a potential disadvantage of the NHE is that it is difficult to perform this exercise using the optimal form required for achieving the complete benefit. [5][6][7] Athletes who are not strong enough to descend to a fully extended knee position may not be able to take the full advantage of this exercise. Therefore, the conventional NHE may not be optimal for preventing strain to the hamstrings in athletes of all levels. ...
Article
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# Background Previous studies have shown that performing the Nordic hamstring exercise (NHE) with different board slope angles can affect hamstring activation. However, changes in muscle length with different board slopes can alter joint angles leading to the moment arm (MA) at the knee changing during the NHE. # Purpose This study aimed to investigate the influence of changing muscle length on hamstring electromyographic activity during an isometric NHE, while maintaining an equal moment arm. # Study Design A crossover study design # Methods Sixteen male volunteers performed two types of conventional NHE, one with knees on the floor (NHE) and one with the legs placed upon an incline slope of a lower leg board (NHEB). To compare between the conventional and inclined NHE, the moment arm at the knee was calculated to be equal by an examiner holding the lower legs at points marked at 77% and 94% of the length of the lower leg. The four sub-groups comprised of: 1) NHE-77%, 2) NHE-94%, 3) NHEB-77%, and 4) NHEB-94%. The hamstring EMG activity was measured at the biceps femoris long head (BFlh) and at the semitendinosus (ST) and related compensatory muscles. The RMS data were normalized as a percentage of the maximum isometric values (normalized EMG nEMG). Significant main effects findings were followed up with Tukey's post-hoc test using SPSS software and statistical significance was set at the p \< 0.05 level. # Results The BFlh EMG activity values for NHE-77% were significantly higher than those for NHE-94% (p= 0.036) and NHEB-77% (p \< 0.001), respectively, while ST during NHE-77% was significantly higher only in NHEB-77% (p \< 0.001). In addition, NHEB-94% was significantly greater than NHEB-77% for both BFlh (p \< 0.001) and ST (p \< 0.001). # Conclusion These results indicate that hamstring electromyographic activity is decreased when the hamstring muscle is lengthened during the Nordic hamstring exercise. # Level of Evidence 3
... The increased inherent stiffness of the muscles that may result from coactivation helps to increase the ability of the lower extremities to absorb shocks and protect the knee from injury [48]. In this study, DJs50 at DJH50 may enhance the CMJ landing phase muscle activation in the lower extremities and reduce the risk of injury by changing the muscles' mechanical properties and stabilizing with the longer muscles' stretch length [49]. However, the right and left TA, SOL, QF and GA muscle activation during CMJs100, CMJs150 and CMJs200 at DJH50 are smaller than at DJH40 and DJH30 in the CMJ landing phase. ...
Article
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Background: The study explored the influence of repeated drop jumps (DJs) from different drop heights on the lower extremity bilateral asymmetry and muscle activation of countermovement jumps (CMJs). Methods: Eighteen male athletes performed 200 drop jumps (DJs200) from three drop jump height (DJH30, 40 and 50 cm). The CMJs were performed before the first DJ and after the 50th, 100th, 150th and 200th DJs, recording them as pre-CMJ, CMJs50, CMJs100, CMJs150 and CMJs200. One-way repeated measures ANOVA was used to compare differences among the three drop heights at pre-CMJ, CMJs50, CMJs100, CMJs150 and CMJs200, respectively. Results: The peak ground reaction forces (PGRF) of CMJs100, CMJs150 and CMJs200 at DJH50 were greater than at DJH30 and DJH40 (all p < 0.05). The muscle activation during CMJs50 at DJH50 was greater than at DJH30 and DJH40 (all p < 0.05). The muscle activation during CMJs100, CMJs150 and CMJs200 at DJH50 was smaller than at DJH40 and DJH30 (all p < 0.05). The PGRF had no significant difference among the three different drop heights during CMJs50 (p > 0.05). Conclusions: The DJs50 at DJH50 had no effect on the bilateral asymmetry and increased muscle activation of CMJs. The excessive DJs100 at DJH50 increased bilateral asymmetry and decreased CMJ muscle activation during CMJs.
... The ROM was regulated according to Figure 1, obeying the angles of 20° and 90° of flexion for the beginning and end of the concentric actions, respectively. Thus, we assume that the CNS [17], the substrate reserves [18], and the tension-length curve [19] of the hamstrings muscles would be functionally preserved. That is, these ...
... In contrast, greater changes are observed in pennation angle following concentric-only resistance training [60][61][62]. This likely reflects the differential addition of serial sarcomeres following eccentric resistance training, which has notable implications for performance and injury prevention, due to a concurrent shift in the 'optimum' force-length and force-velocity relationships of the working musculature, which subsequently alter their function [63][64][65]. In the context of high-velocity eccentric contractions, the evidence regarding physiological adaptation is limited. ...
Article
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High-intensity horizontal decelerations occur frequently in team sports and are typically performed to facilitate a reduction in momentum preceding a change of direction manoeuvre or following a sprinting action. The mechanical underpinnings of horizontal deceleration are unique compared to other high-intensity locomotive patterns (e.g., acceleration, maximal sprinting speed), and are characterised by a ground reaction force profile of high impact peaks and loading rates. The high mechanical loading conditions observed when performing rapid horizontal decelerations can lead to tissue damage and neuromuscular fatigue, which may diminish co-ordinative proficiency and an individual’s ability to skilfully dissipate braking loads. Furthermore, repetitive long-term deceleration loading cycles if not managed appropriately may propagate damage accumulation and offer an explanation for chronic aetiological consequences of the ‘mechanical fatigue failure’ phenomenon. Training strategies should look to enhance an athlete’s ability to skilfully dissipate braking loads, develop mechanically robust musculoskeletal structures, and ensure frequent high-intensity horizontal deceleration exposure in order to accustom individuals to the potentially damaging effects of intense decelerations that athletes will frequently perform in competition. Given the apparent importance of horizontal decelerations, in this Current Opinion article we provide considerations for sport science and medicine practitioners around the assessment, training and monitoring of horizontal deceleration. We feel these considerations could lead to new developments in injury-mitigation and physical development strategies in team sports.
... A 27% increase was observed in concentric hamstring ND strength in TG (Table 1). Since there are concerns that bilateral exercises like Nordic might provide a lower stimulus for the weaker leg leading to asymmetries [26], we implemented a unilateral hamstring exercise which can be performed without any equipment or assistance and induces high hamstring activation [22]. The observation of greater gains to the ND leg is in line with previous studies [25,27] who also reported increased PT in the ND leg after eccentric hamstring training. ...
Article
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Soccer teams integrate specific exercises into their typical workout programs for injury prevention. The purpose of this study was to investigate whether the incorporation of a brief and supplementary training program that involves eccentric, balance, and core exercises into the weekly soccer schedule can cause positive neuromuscular adaptations. Twenty-one soccer players were randomly allocated to either a training (n = 11) or a control group (n = 10). All players followed their teams' typical program, consisting of 4-5 soccer-specific sessions plus 1 match, weekly. Training group players additionally performed biweekly, hamstring eccentric, balance, and core stability exercises for 8 weeks. Isokinetic concentric and eccentric peak torque (PT) of the hamstrings and quadriceps, changes in the center of pressure (COP) during a 30 s single-leg stance, and a supine bridge (trunk stability) test were assessed before and after the intervention. After the intervention, a 27% increase in hamstring concentric PT and a 33% reduction in COP sway in the stance test, were observed for the training group only (p < 0.05). These improvements were significant only for the non-dominant leg. Furthermore, the control group displayed an increase in COP sway during the bridge test compared to baseline values (p < 0.05), which reflects a deterioration in postural balance over time. Consequently, incorporating small doses of hamstring eccentric, proprioception, and core stability exercises into a typical training program of youth soccer players improves strength and postural balance in the non-dominant leg, as well as core muscle performance.
... 5 Despite the high proportion of injuries attributed to contact mechanisms, these findings support the rationale to engage in targeted initiatives aimed at reducing the incidence of overuse or noncontact injuries in the hip/groin region. 26,27 Precise measurements of exposure time and workload are needed to examine this paradigm more comprehensively. Given that the NCAA ISP captures aggregated exposure information at the team level, it is difficult to further expand on these findings using data captured within the NCAA ISP. ...
Article
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Context: The National Collegiate Athletic Association (NCAA) has sponsored women's ice hockey championships since 2001, and sponsorship has grown over time. Background: Routine examinations of injuries sustained by athletes are important for identifying and understanding patterns that can be used to inform sport safety practices. Methods: Exposure and injury data collected in the NCAA Injury Surveillance Program from 2014-2015 through 2018-2019 were analyzed. Injury counts, rates, and proportions were used to describe injury characteristics, and injury rate ratios were used to examine differential injury rates. Results: The overall injury rate was 5.89 per 1000 athlete-exposures; preseason injury incidence rose sharply during 2016-2017 through 2018-2019. Head/face injuries (15.2%), knee injuries (13.2%), and shoulder injuries (12.9%) were the most commonly injured body parts, and injuries were most often classified as contusions (18.9%), strains (18.7%), and sprains (15.5%). Concussion (11.9%) was the most commonly reported specific injury, and concussion rates notably increased during 2017-2018 through 2018-2019. Summary: Study findings were generally consistent with the existing epidemiological evidence. Injury incidence in preseason and the etiology of strains warrant further attention in this population.
... In theory, individuals with the CC genotype with longer skeletal muscle fascicles would have a rightward shift in their length-tension relationship and greater optimal joint angles for maximal torque production. Such the shift has been associated with a decrease in injury occurrence, as a longer optimal skeletal muscle length would provide that less of the muscle's functional range would be along the more unstable descending limb of the length-tension curve (Brughelli & Cronin, 2007). For this reason, knowledge of the TTN genotype in populations at higher injury risk, such as physically active people, would help to predict the consequences of performed exercises (Stebbings et al., 2017). ...
Article
A titin, encoded by a TTN gene, is a third most abundant sarcomere component. Although, this myofilament plays a wide range of key roles in muscle tissue such as structural, developmental, mechanical, and regulatory functions, it is a usually missed aspect of the muscle properties formation. At first, the TTN gene variants was described in development of skeletal and cardiac muscle diseases. Recently, the gene is also considered a very promising genetic marker for sport performance which may underlie differences in the potential to be an elite athlete. The aim of the present study is to provide the comprehensive update of the titin protein and the TTN gene variants role in formation of skeletal and cardiac muscle properties. We review function and structure of the protein, the gene, and the isoforms, as well as molecular mechanisms, disease-causing mutations, associated phenotypes, and their implications for human health, physical performance, adaptive changes of muscles in response to training, and injury risk.
... This increase in sarcomere compliance, is demonstrated by acute and long-term shifts in the length-tension relationship (135). These shifts are proposed to reduce injury potential, and joint-angle-specific performance (55,211). ...
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.
... For determination of maximal voluntary torque during bilateral flexion and extension of the knee, the subject was seated (with 90 • and 60 • flexion at the hips and knees, respectively) on an isometric knee dynamometer (S2P Ltd., Ljubljana, Slovenia) with tight straps across the pelvis, above the knees and behind the distal leg to ensure fixation. This positioning of the joints was chosen to allow the knee flexors/extensors to develop maximal knee torque (Brughelli and Cronin, 2007;Brughelli et al., 2010). This testing procedure has been reported to yield highly reproducible results . ...
Article
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The ground reaction forces (GRF) associated with competitive alpine skiing, which are relatively large, might be asymmetric during left and right turns due to asymmetries in the strength of the legs and torso and the present investigation was designed to evaluate this possibility. While skiing a symmetrical, 20-gate slalom course, the asymmetries of 9 elite alpine skiers were calculated on the basis of measurements provided by inertial motion units (IMU), a Global Navigation Satellite System and pressure insoles. In addition, specialized dynamometers were utilized to assess potential asymmetry in the strength of their legs and torso in the laboratory. In total, seven variables related to GRF were assessed on-snow and eight related to strength of the legs and torso in the laboratory. The asymmetries in these parameters between left and right turns on snow were expressed in terms of the symmetry (SI) and Jaccard indices (JI), while the asymmetries between the left and right sides of the body in the case of the laboratory measurements were expressed as the SIs. The three hypotheses to be tested were examined using multivariable regression models. Our findings resulted in rejection of all three hypotheses: The asymmetries in total GRF (H1), as well as in the GRF acting on the inside and outside legs (H2) and on the rear- and forefeet GRF (H3) during left and right turns were not associated with asymmetries in parameters related to muscular strength. Nevertheless, this group of elite slalom skiers exhibited significant asymmetry between their right and left legs with respect to MVC during ankle flexion (0.53 ± 0.06 versus 0.60 ± 0.07 Nm/kg, respectively) and hip extension (2.68 ± 0.39 versus 2.17 ± 0.26 Nm/kg), as well as with respect to the GRFs on the inside leg while skiing (66.8 ± 7.39 versus 76.0 ± 10.0 %BW). As indicated by the JI values, there were also large asymmetries related to GRF as measured by pressure insoles (range: 42.7–56.0%). In conclusion, inter-limb asymmetries in GRFs during elite alpine skiing are not related to corresponding asymmetries in muscular strength. Although our elite athletes exhibited relatively small inter-limb asymmetries in strength, their asymmetries in GRF on-snow were relatively large.
... An observed peak torque shift in the direction of more extended angles during long musclelength chronic-training interventions is attributed to an increase in fascicle length, assumed to reflect more sarcomeres in series (Morgan, 1990;Potier et al., 2009;Oranchuk et al., 2019). It is proposed that in the NHE this would result in a larger breakpoint angle (where 180 • is full extension), corresponding to a longer muscle length at failure (Brughelli and Cronin, 2007) thus potentially leading to greater increases in muscle fascicle length, and modifying the length-tension relationship of the hamstrings which may reduce injury risk. ...
Article
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The Nordic hamstring exercise (NHE) has been shown to reduce hamstring injury risk when employed in training programs. This study investigates a novel device to modify the NHE torque-length relationship of the knee flexors, as targeting the hamstrings at a more extended length may have benefits for hamstring strain injury prevention and rehabilitation. Eighteen recreational male participants completed three bilateral NHE repetitions at a conventional 0° flat position, a 10° incline, and a 10° decline slope on a novel device (HALHAM°). Measures of peak torque and break-torque angle explored the effect of inclination on the knee flexors' length-tension relationship. Relative thigh-to-trunk angle and angular velocity of the knee joint were used to assess influence of inclination on technique and exercise quality. Break-torque angle increased when performed at an incline (134.1 ± 8.6°) compared to both the decline (112.1 ± 8.3°, p <0.0001, g = 2.599) and standard flat NHE positions (126.0 ± 9.8°, p = 0.0002, g = 0.885). Despite this, altering inclination did not affect eccentric knee flexor peak torque (decline = 132.0 ± 63.1 Nm, flat = 149.7 ± 70.1 Nm, incline = 148.9 ± 64.9 Nm, F = 0.952, p = 0.389), angular velocity of the knee joint at break-torque angle (decline = 23.8 ± 14.4°, flat = 29.2 ± 22.6°, incline = 24.5 ± 22.6°, F = 0.880, p = 0.418) or relative thigh-to-trunk angle at break-torque angle (decline = 20.4 ± 10.4°, flat = 16.7 ± 10.8°, incline = 20.2 ± 11.2°, F = 1.597, p = 0.207). The report recommends the use of arbitrary metrics such as break-torque angle that can be replicated practically in the field by practitioners to assess proxy muscle length changes i.e., the angular range over which the torque can be produced. Inclination of the Nordic hamstring exercise leads to hamstring muscle failure at longer muscle lengths without reductions in the maximal force exuded by the muscle. Therefore, the NHE performed on an incline may be a more effective training intervention, specific to the proposed mechanism of hamstring strain injury during sprinting that occurs whilst the muscle is rapidly lengthening. Using a graded training intervention through the inclinations could aid gradual return-to-play rehabilitation.
... Thus, the observed increased knee joint flexion during landing indicates that EIMD may be another condition that can lead to a similar strategy, in an attempt to increase safety [44]. Moreover, given that the optimum length of tension development in muscle can be shifted to longer muscle lengths following EIMD [45], the increased peak knee flexion angle 48 h post-exercise may be a compensating strategy to achieve optimal muscle length for torque production. However, a greater flexion of the lower joints during absorption may increase the risk of overuse injuries by increasing the energy absorption of the musculotendinous units that are in a lengthened position [46]. ...
Article
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Limited research exists in the literature regarding the biomechanics of the jump-landing sequence in individuals that experience symptoms of muscle damage. The present study investigated the effects of knee localized muscle damage on sagittal plane landing biomechanics during drop vertical jump (DVJ). Thirteen regional level athletes performed five sets of 15 maximal eccentric voluntary contractions of the knee extensors of both legs at 60°/s. Pelvic and lower body kinematics and kinetics were measured pre- and 48 h post-eccentric exercise. The examination of muscle damage indicators included isometric torque, muscle soreness, and serum creatine kinase (CK) activity. The results revealed that all indicators changed significantly following eccentric exercise (p < 0.05). Peak knee and hip joint flexion as well as peak anterior pelvic tilt significantly increased, whereas vertical ground reaction force (GRF), internal knee extension moment, and knee joint stiffness significantly decreased during landing (p < 0.05). Therefore, the participants displayed a softer landing pattern following knee-localized eccentric exercise while being in a muscle-damaged state. This observation provides new insights on how the DVJ landing kinematics and kinetics alter to compensate the impaired function of the knee extensors following exercise-induced muscle damage (EIMD) and residual muscle soreness 48 h post-exercise.
... In this study, the knee flexors' peak torque angle curve shifted toward longer muscle lengths for both groups. It has been proposed that eccentric training results in sarcomerogenesis (Douglas et al., 2017) and shifts the peak of the torque-angle curve toward longer muscle lengths, which can prove important for injury prevention and improvement of athletic performance (Brughelli & Cronin, 2007). In our study, the peak-torque angle curve shift may be attributed to the different pattern of knee flexors' activation during running on sloping surfaces. ...
Article
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We examined changes in selected muscle performance parameters after 8 weeks of interval training using two opposite running inclinations. We hypothesized that the uphill training will affect endurance muscle performance outcomes, whereas the downhill training will affect power muscle performance outcomes. Fourteen physically active volunteers were randomly assigned into either the Uphill group (UG; n = 7; uphill interval running at +10% incline) or the Downhill group (DG; n = 7; downhill interval running at −10% incline) and completed 16 training sessions. Each session consisted of ten 30 s treadmill runs at 90% of maximum aerobic speed (MAS) with a work to rest ratio of 1:2. Vertical jump performance, isometric (MVC) and isokinetic torque of knee extensors and flexors, and fatigue of knee extensors were evaluated pre and post-training. Moreover, body composition (via bioimpedance) and vastus lateralis muscle architecture (via ultrasonography) were assessed pre and post-training. Relative lean tissue mass, relative fat mass, and squat jump (cm) significantly (p < .05) changed from baseline values by +4.5 ± 4.0%, −11.5 ± 9.6%, and +9.5 ± 11.7%, respectively, only in the DG. Similarly, DG improved absolute values of knee extension rate of torque development and impulse (p < .05), whereas knee flexion peak torque angle significantly decreased in both groups (p < .05). On the other hand, the UG increased the number of repetitions achieved during the fatigue
... Shortened hamstring optimum length (OL) is considered as another HS risk factor (13). OL is the length that muscle demonstrates peak torque (14). Shorter the OL shifts, more susceptibility to the HS (15). Overall, isokinetic dynamometry needs technical expertise and is difficultly accessible in athletic centers because ...
... For example, a change in fascicle length can shift the optimum length-tension relationship and maximum shortening velocity of the muscle, with notable effects on performance and injury prevention. 28 Variability in architectural characteristics at different regions of the muscle is also of particular importance when trying to model and predict the behavior of a specific muscle, as large intra-muscular differences can have a considerable effect on estimated force-velocity properties of muscles 23 and whole muscle force. 25 Although some research has been focused on architectural responses to ECC training, fewer studies have compared isolated CON vs isolated ECC exercise in terms of both architectural and regional changes in the muscle. ...
Article
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The different architectural adaptations and the regional changes that occur with eccentric (ECC) vs concentric (CON) muscle actions are not fully understood. The purpose was to investigate regional changes in vastus lateralis muscle (VL) after ECC and CON training. Sixteen males (23 ± 3 years) performed ECC or CON training twice weekly over 5 weeks, using a single‐leg design. Both training modalities caused similar increases in knee extensor strength (measured with dynamometry) (10%‐13%) and muscle volume (8%) (measured with 3D ultrasound) after 5 weeks of training. Anatomical cross‐sectional area at the mid‐point of the muscle was greater after CON training (9%), but greater at the distal end after ECC training (8%). CON training increased fascicle angle at the mid‐point (8%), with little change at the distal end (2%). There was a small increase in fascicle length at the mid‐point after CON training (3%). Conversely, ECC training caused a greater variation in regional and architectural adaptations. Fascicle length increased at both the mid‐point (6%) and distal ends (8%) after ECC training, and similar changes in fascicle angle were also observed in both regions (3%‐4%). Different region‐specific changes are evident after CON and ECC training, with implications for performance and injury risk.
Preprint
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The aim of this systematic review and meta-analysis was to examine how mean muscle length during resistance training (RT) influences regional muscle hypertrophy. We included studies that manipulated muscle length through range of motion (ROM) or exercise selection and evaluated regional muscle hypertrophy (i.e., changes at proximal, mid-belly, and/or distal sites). After systematically searching through three databases with additional secondary searches 12 studies were included in a meta-analysis. The meta-analysis was performed within the Bayesian meta-analytic framework. Standardized mean changes indicated trivial hypertrophic effects estimated with relatively high precision between proximal (25% muscle length; SMD: 0.04 [95%QI: -0.07, 0.15]; Exponentiated lnRR: 0.48% [95%QI: -1.99%, 3.13%]), mid-belly (50% muscle length; SMD: 0.07 [95%QI: -0.02, 0.15]; Exponentiated lnRR: 1.14% [95%QI: -0.84%, 3.13%]), and distal (75% muscle length; SMD: 0.09 [95%QI: -0.01, 0.19]; Exponentiated lnRR: 1.8% [95%QI: -0.52%, 4.26%]) sites. While the effects of training at longer muscle lengths showed an increasing trend from proximal to distal sites, the percentage of posterior distributions falling within ROPE was high from proximal to distal sites suggesting that effects are practically equivalent when contrasting “shorter” and “longer” mean muscle lengths at the typical differences employed in the current body of literature (i.e., an average difference of 21.8% mean muscle length). In summary, our results indicate that training at longer mean muscle length does not seem to produce greater regional muscle hypertrophy compared to shorter mean muscle lengths. However, due to small contrast in muscle lengths employed between conditions/groups, our findings should be considered limited to the contrasts typically employed in the literature.
Article
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Background The benefit of performing the Nordic Hamstring Exercise (NHE) on an inclined board has been described, however, isometric hamstring activation in different knee and hip angles has not yet been thoroughly explored. Purpose This study investigated the effect of variations in knee and hip angles during the isometric performance of the NHE on electromyographic activity of the hamstring muscles. Study design Crossover study Methods Thirteen male volunteers performed isometric contractions during the NHE with the knee (30°, 50°, 60°) and the hip (0°, 30°, and 45°) in various angles of flexion on a leg support platform which was inclined at 30°. An electrical goniometer was used to monitor the knee and hip joint angles during 5-s isometric contractions. A multivariate analysis of variance with repeated measures was used to compare normalized electromyographic values of each muscle across different knee and hip angles, followed by pairwise comparisons. Results The electromyographic activity of the biceps femoris, semitendinosus, and semimembranosus at a knee angle of 30° and hip angle of 0° were significantly higher than those observed with a knee angle of 50° and hip angle of 0°, or a knee angle of 60° and hip angle of 0° (p<0.05). The electromyographic activity of the semimembranosus at a knee angle of 60° and hip angle of 45° was significantly higher than values obtained with knee and hip angles of 60° and 0°, respectively (p<0.05). Conclusions The results indicate that using a knee flexion of 30° and a hip flexion of 0°, while isometrically performing the NHE on a platform inclined at 30°, may optimize electromyographic activity of the hamstrings. Level of Evidence 3
Article
Traumatic muscle injury represents a collection of skeletal muscle pathologies caused by trauma to the muscle tissue and is defined as damage to the muscle tissue that can result in a functional deficit. Traumatic muscle injury can affect people across the lifespan and can result from high stresses and strains to skeletal muscle tissue, oftendue to muscle activation while the muscle is lengthening, resultingin indirect and non-contact muscle injuries (strains or ruptures), orfrom external impact, resulting in direct muscle injuries (contusionor laceration). At a microscopic level, muscle fibres can repair focal damage but must be completely regenerated after full myofibrenecrosis. The diagnosis of muscle injury is based on patient history andphysical examination. Imaging may be indicated to eliminate differentialdiagnoses. The management of muscle injury has changed within thepast 5 years from initial rest, immobilization and (over)protection toearly activation and progressive loading using an active approach.One challenge of muscle injury management is that numerous medicaltreatment options, such as medications and injections, are often usedor proposed to try to accelerate muscle recovery despite very limitedefficacy evidence. Another challenge is the prevention of muscle injuryowing to the multifactorial and complex nature of this injury.
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Whether there is an optimal range of motion (ROM) to induce muscle hypertrophy remains elusive, especially for gastrocnemius. This study aimed to compare the changes in gastrocnemius muscle thickness between calf raise exercise performed with full ROM (FULLROM), partial ROM performed in the initial (INITIALROM), and final (FINALROM) portions of the ROM. Forty-two young women performed a calf training program for 8 weeks, 3 d·wk–1, with differences in the calf raise ROM configuration. The calf raise exercise was performed in a pin-loaded horizontal leg-press machine, in 3 sets of 15–20 repetitions maximum. The subjects were randomly assigned to 1 of the 3 groups: FULLROM (ankle: -25º to +25º), INITIALROM (ankle: -25º to 0º), and FINALROM (ankle: 0º to +25º), where 0º was defined as an angle of 90º of the foot with the tibia. The muscle thickness measurements of medial and lateral gastrocnemius were taken via B-mode ultrasound. INITIALROM elicited greater medial gastrocnemius increases than FULLROM and FINALROM (INITIALROM = +15.2% vs. FULLROM = +6.7% and FINALROM = +3.4%; P ≤ 0.009). Furthermore, INITIALROM elicited greater lateral gastrocnemius increases than FINALROM (INITIALROM = +14.9% vs. FINALROM = +6.2%; P < 0.024) but did not significantly differ from FULLROM (FULLROM = +7.3%; P = 0.060). The current results suggest that calf training performed at longer muscle lengths may optimize gastrocnemius muscle hypertrophy in young women. Therefore, when prescribing hypertrophy-oriented training, the inclusion of the calf raise exercise performed with partial ROM in the initial portion of the excursion should be considered.
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Purpose: To compare the effects of variable resistance complex training (VRCT) versus traditional complex training (TCT) on muscle architecture in rugby league players during a 6-week mesocycle. Methods: Twenty-four rugby league players competing in the BUCS Premier North Division were randomised to VRCT (n=8), TCT (n=8) or control (n=8). Experimental groups completed a 6-week lower-body complex training intervention (2x/week), which involved alternating high-load resistance exercise with plyometric exercise in the same session. The VRCT group performed resistance exercises at 70% of 1RM + 0-23% of 1RM from band resistance with a 90 second intra-contrast rest interval (ICRI), whereas the TCT group performed resistance exercise at 93% of 1RM with a 4-minute ICRI. Muscle thickness (MT), pennation angle (P¬¬ang) and fascicle length (Lf) were assessed for the vastus lateralis (VL) and gastrocnemius medialis (GM) using ultrasound imaging. Results: Both TCT and VRCT groups significantly improved VL MT and VL Lf compared to control (all p<0.05). Standardised within-group changes in MT and Lf (Cohen’s dav ± 95% confidence interval) were moderate for TCT (dav = 0.91±1.0; dav = 1.1±1.1) and unclear for VRCT (dav = 0.44±0.99; dav = 0.47±0.99), respectively. Differences in change scores between TCT and VRCT were unclear. Conclusions: VRCT and TCT can be utlilised during the competitive season to induce favourable MT and Lf muscle architecture adaptations for the VL. TCT may induce greater muscle architecture adaptations of the VL whereas, VRCT may be of more practical value given the shorter ICRI between resistance and plyometric exercises.
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Egzersize bağlı iskelet kası hipertrofisinin doğası, günümüzde hâlâ tartışmalı bir olgu olarak karşımıza çıkmaktadır. Kas hipertrofisi ölçüm yöntemleri ve kullanılan antrenman metotları gibi sürecin merkezinde yer alan çeşitli faktör ve limitasyonlar, geçmişte hipertrofik adaptasyon ve mekanizmaların doğru bir şekilde tanımlanmasına engel olmuştur. Spor biliminde yaşanan yenilik ve gelişmelerle birlikte çeşitli antrenman yöntemlerinin farklı ölçüm teknikleriyle karşılaştırıldığı uzun vadeli çalışmalar, önceki kaynaklarda yer alan hipertrofi tanımlamalarının doğruluğu konusunda şüphe uyandırmaktadır. Bu tanımlamalarla ilgili dikkat çeken en büyük eksiklik ise serial hipertrofi olgusuyla ilgilidir. Bu açıdan bu derleme, iskelet kası hipertrofisini etkileyen birçok faktörü inceleyerek bu faktörlerin serial hipertrofi üzerindeki etkilerini derlemeyi amaçlamaktadır. Bu derleme ile, hipertrofi tanımı ve hipertrofik adaptasyonlara literatür eşliğinde yeni ve güncel bir yaklaşım getirilmeye çalışılmıştır. Bu doğrultuda, 1969 ve 2020 yıları arasında yapılmış 62 çalışma ve kaynak taranmıştır. Sonuç olarak, tam hareket açıklığı, eksantrik antrenmanlar ve hızlı eksantrik antrenmanların, lif ve fasikül uzunluğundaki artışlar kapsamında daha fazla serial hipertrofiye neden olduğu, kısmi hareket açıklığı, konsantrik antrenmanlar ve yavaş eksantrik antrenmanların ise lif çapında daha fazla artışlar ortaya koyduğu vurgulanmıştır. Araştırmalar, direnç eğitimi dönemlerinde kas lifi hipertrofisi ile farklı morfolojik adaptasyonların ortaya çıkabileceğini göstermektedir.
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PURPOSE: The purpose of this study was to compare the vastus lateralis (VL) architecture and exercise biomechanics indices during drop landing in young football players.METHODS: Fifteen young football players were divided into a long vastus lateralis muscle fascicle length group (LFG, n=8) and short vastus lateralis muscle fascicle length group (SFG, n=7). All of the participants performed drop landing onto the ground reaction force plate from a platform 30 cm high. The muscle activities of the VL, tibialis anterior (TA), and gastrocnemius (GCM), angular velocity, and ground reaction force in the ankle, knee, and hip joints were measured during drop landing.RESULTS: The VL muscle activity (p=.032), ankle ground contact angle (p=.027), ankle maximum flexion angle (p=.014), knee maximum flexion angle (p=.007), and ground reaction force per body weight (p=.032) were significantly higher in the LFG than in the SFG. Muscle activity of the TA (p=.017), ankle (p=.033), and hip (p=.045) time to stability and the ground reaction force time to stability (p=.043) were significantly lower in the LFG than in the SFG. Muscle activity of the GCM (p=.053) and knee time to stability (p=.057) tended to be lower in the LFG than in the SFG.CONCLUSIONS: These results confirmed that muscle activity, angular velocity, and ground reaction force variables during drop landing are affected by the VL muscle fascicle length in young football players.
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Five women and three men (aged 24-43 yr) performed maximal eccentric contractions of the elbow flexors (for 20 min) on three occasions, spaced 2 wk apart. Muscle pain, strength and contractile properties, and plasma creatine kinase (CK) were studied before and after each exercise bout. Muscle tenderness was greatest after the first bout and thereafter progressively decreased. Very high plasma CK levels (1,500-11,000 IU/l) occurred after the first bout, but the second and third bouts did not significantly affect the plasma CK. After each bout the strength was reduced by approximately 50% and after 2 wk had only recovered to 80% of preexercise values. Each exercise bout produced a marked shift of the force-frequency curve to the right which took approximately 2 wk to recover. The recovery rate of both strength and force-frequency characteristics was faster after the second and third bouts. Since the adaptation occurred after the performance of maximal contractions it cannot have been a result of changes in motor unit recruitment. The observed training effect of repeated exercise was not a consequence of the muscle becoming either stronger or more resistant to fatigue.
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1. The effect of muscle length on the development of muscle pain and fatigue has been studied. 2. Eight normal young adults performed maximal eccentric contractions of the elbow flexors. The muscles of one arm were exercised at short length, and the contralateral muscle at long length. Each contraction lasted approximately 1 s, and was repeated once every 10 s for 30 min. 3. Muscle strength and frequency-force characteristics were measured from isometric contractions before, immediately after and at 24 h intervals for the next 4 days. Muscle tenderness was assessed daily. 4. The muscle strength was reduced by approximately 10% by exercise at short length, and by 30% by exercise at long length. 5. The 20:100 ratio (force generated by stimulation at 20 Hz/force generated at 100 Hz) fell by 30% after exercise at short length and had recovered after 24 h. Exercise at long length reduced this ratio by 65% and the muscles had not fully recovered 4 days later. 6. Muscle pain developed after both exercise regimens, but was slightly worse after that at long length. 7. It is concluded that there is a length-dependent component in the development of pain and fatigue after eccentric exercise, which had previously been thought to be caused solely by high force generation.
Article
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Five women and three men (aged 24-43 yr) performed maximal eccentric contractions of the elbow flexors (for 20 min) on three occasions, spaced 2 wk apart. Muscle pain, strength and contractile properties, and plasma creatine kinase (CK) were studied before and after each exercise bout. Muscle tenderness was greatest after the first bout and thereafter progressively decreased. Very high plasma CK levels (1,500-11,000 IU/l) occurred after the first bout, but the second and third bouts did not significantly affect the plasma CK. After each bout the strength was reduced by approximately 50% and after 2 wk had only recovered to 80% of preexercise values. Each exercise bout produced a marked shift of the force-frequency curve to the right which took approximately 2 wk to recover. The recovery rate of both strength and force-frequency characteristics was faster after the second and third bouts. Since the adaptation occurred after the performance of maximal contractions it cannot have been a result of changes in motor unit recruitment. The observed training effect of repeated exercise was not a consequence of the muscle becoming either stronger or more resistant to fatigue.
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1. Normal subjects performed a step test in which the quadriceps of one leg contracted concentrically while the contralateral muscle contracted eccentrically. 2. Maximal voluntary force and the force:frequency relationship were altered bilaterally as a result of the exercise, the changes being greater in the muscle which had contracted eccentrically. Recovery occurred over 24 h. 3. Electromyographic studies using three sites on each muscle showed an increase in electrical activation during the exercise only in the muscle which was contracting eccentrically. Recovery followed a time course similar to that of the contractile properties. 4. Pain and tenderness developed only in the muscle which had contracted eccentrically. Pain was first noted approximately 8 h after exercise and was maximal at approximately 48 h after exercise, at which time force generation and electrical activation had returned to pre-exercise values. 5. Eccentric contractions cause more profound changes in some aspects of muscle function than concentric contractions. These changes cannot be explained in simple metabolic terms, and it is suggested that they are the result of mechanical trauma caused by the high tension generated in relatively few active fibres during eccentric contractions.
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Biopsies, taken up to 1 week postexercise, from the soleus muscles of 5 healthy males (20--34 years old) suffering from pronounced exercise-induced delayed muscle soreness were analyzed morphologically. There was no evidence for ischemic tissue injury or mechanical fibre disruption. However, at the subcellular level frequent myofibrillar disturbances, especially with regard to the Z-bands, were noted. Thus, the contractile machinery of overloaded muscle fibres seemed to be partially distorted several days following exercise.
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Delayed onset muscle soreness (DOMS) is a sensation of discomfort that occurs 1 to 2 days after exercise. The soreness has been reported to be most evident at the muscle/tendon junction initially, and then spreading throughout the muscle. The muscle activity which causes the most soreness and injury to the muscle is eccentric activity. The injury to the muscle has been well described but the mechanism underlying the injury is not fully understood. Some recent studies have focused on the role of the cytoskeleton and its contribution to the sarcomere injury. Although little has been confirmed regarding the mechanisms involved in the production of delayed muscle soreness, it has been suggested that the soreness may occur as a result of mechanical factors or it may be biochemical in nature. To date, there appears to be no relationship between the development of soreness and the loss of muscle strength, in that the timing of the two events is different. Loss of muscle force has been observed immediately after the exercise. However, by collecting data at more frequent intervals a second loss of force has been reported in mice 1 to 3 days post-exercise. Future studies with humans may find this second loss of force to be related to DOMS. The role of inflammation during exercise-induced muscle injury has not been clearly defined. It is possible that the inflammatory response may be responsible for initiating, amplifying, and/or resolving skeletal muscle injury. Evidence from the literature of the involvement of cytokines, complement, neutrophils, monocytes and macrophages in the acute phase response are presented in this review. Clinically, DOMS is a common but self-limiting condition that usually requires no treatment. Most exercise enthusiasts are familiar with its symptoms. However, where a muscle has been immobilised or debilitated, it is not known how that muscle will respond to exercise, especially eccentric activity.
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The time course of muscle contractile and cellular properties was studied in rabbit ankle flexor muscles after injury produced by eccentric exercise. Cyclic eccentric exercise was produced by increasing the tibiotarsal angle of the rabbit while activating the peroneal nerve by use of transcutaneous electrodes. Muscle properties were measured 1, 2, 3, 7, 14, and 28 days after exercise to define the time course of muscle changes after injury. A control group receiving only isometric contraction was used to study the effect of cyclic activation itself. The magnitude of the torque decline after 1 day was the same with use of isometric or eccentric exercise, but eccentric exercise resulted in a further decrease in torque after 2 days, at which time isometrically exercised muscles had fully recovered. The most prominent morphological changes in the injured muscle fibers were the loss of antibody staining for the desmin cytoskeletal protein and deposition of intracellular fibronectin, even when the injured muscle fibers retained their normal complement of contractile and enzymatic proteins. The presence of fibronectin inside the myofibers indicated a loss of cellular integrity. Invasion by inflammatory cells was apparent on the basis of localization of embryonic myosin. Thus eccentric exercise initiates a series of events that results in disruption of the cytoskeletal network and an inflammatory response that could be the mechanism for further deterioration of the contractile response.
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Unaccustomed eccentric exercise, in which a muscle is lengthened while generating tension, is well known to cause injury and pain. A rapid training effect has been demonstrated in a number of eccentric exercises. The mechanism for both the damage and the training has been unknown. Morgan proposed that the damage is caused by sarcomere length instabilities during operation on the descending limb of the sarcomere length-tension curve and that the training effect is an increase in the number of sarcomeres connected in series in a muscle fiber, thus avoiding the descending limb (Biophys. J. 57: 209-221, 1990). We tested this proposal by exercising rats on a treadmill set at either an incline or a decline of 16 degrees, an exercise that has previously been shown to cause damage in untrained rats and a training effect. The vastus intermedius muscles were fixed and were digested in acid, and the fiber and sarcomere lengths of representative fibers were measured. From these measurements, the mean number of sarcomeres per fiber was found for the different training regimes. A clear and repeatable difference was found, supporting Morgan's prediction of more sarcomeres after decline running, although with some differences in response that depended on the age of the rats.
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It has been proposed that lengthening of active muscle at long lengths is nonuniformly distributed between sarcomeres, with a few being stretched beyond overlap and most hardly being stretched at all. A small fraction of the overstretched sarcomeres may fail to reinterdigitate on subsequent relaxation, leading to progressive changes in the muscle's mechanical properties. Sartorius muscles of the toad Bufo marinus were subjected to repeated lengthening (eccentric) contractions at long lengths, while controls were passively stretched and then contracted isometrically or stretched at short lengths. The muscles undergoing eccentric contractions showed a progressive shift to the right of the length-tension curve, a fall in the yield point during stretch, an increase in slope of the tension response during stretch, and a fall in isometric tension. In control muscles, changes, if any, were significantly less. In electron micrographs, muscle fibers that had been subjected to a series of eccentric contractions showed sarcomeres with A bands displaced toward one half-sarcomere, leaving no overlap in the other half. Adjacent regions often looked normal. These results are all in agreement with the predictions of the nonuniform stretch of sarcomeres hypothesis.
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1. Histological evidence suggests that the force deficit associated with eccentric contraction-induced muscle injury is due to structural damage to contractile elements within the muscle fibre. Alternatively, the force deficit could be explained by an inability to activate the contractile proteins. It was the objective of this study to investigate the latter possibility. 2. Mouse soleus muscles were isolated, placed in an oxygenated Krebs-Ringer buffer at 37 degrees C, and baseline measurements were made. The muscle then performed one of three contraction protocols: (1) twenty eccentric (n = 10 muscles); (2) ten eccentric (n = 12); or (3) twenty isometric (n = 10) contractions. At the end of the injury protocol, measurements were made during performance of a passive stretch, twitch and tetanus. Next, force was recorded during exposure of the muscle to buffer containing 50 mM caffeine. 3. Decrements in maximal isometric tetanic force (P0) observed for muscles in the twenty eccentric, ten eccentric, and twenty isometric contraction protocols were 42.6 +/- 4.2, 20.0 +/- 2.3 and 3.9 +/- 2.4%, respectively. However, the caffeine-elicited forces in muscles from the three protocols were not different when corrected for initial differences in P0 (64.9 +/- 1.3, 64.2 +/- 2.1 and 68.9 +/- 2.5% of pre-injury P0). The peak caffeine-elicited force was 118.4 +/- 8.6% of post-injury P0 for the muscles in the twenty eccentric contraction protocol, which was significantly different from that observed for the other protocols (71.8-80.2% post-injury P0). These findings indicate that the force deficit in this muscle injury model results from a failure of the excitation process at some step prior to calcium (Ca2+) release by the sarcoplasmic reticulum. 4. In an attempt to locate the site of failure, intracellular measurements were made in injured muscles to test whether injury to the sarcolemma might have resulted in a shift of the resting membrane potential of the muscle fibre. However, microelectrode measurements of resting membrane potential for muscles in the twenty eccentric contraction protocol (-74.4 +/- 0.6 mV) were not different from muscles in the twenty isometric contraction protocol (-73.4 +/- 1.0 mV). These data suggest that membrane resting conductances were normal and are compatible with the idea that the ability of the injured fibres to conduct action potentials was probably not impaired.
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Electron microscopy of toad (Bufo marinus) muscle fixed without relaxing after a single eccentric contraction at muscle lengths greater than optimum showed over-stretched half-sarcomeres in sufficient numbers to account for more than half of the imposed stretch. Such sarcomeres were absent in another muscle fixed without relaxing after an isometric contraction at the same length and largely absent in a third muscle that underwent eccentric contraction at muscle lengths less than optimum. This provides direct evidence in support of the hypothesis that lengthening of muscles at long length involves lengthening of a few half sarcomeres to beyond filament overlap, while most half sarcomeres are extended much less than in proportion to muscle extension.
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The purposes of this study were to assess the presence of 99mTc-labeled white blood cells (WBC) in exercised muscle compared with nonexercised muscle over time and to determine the time course of delayed onset muscle soreness (DOMS) and eccentric torque in 10 female subjects. A pretest was followed by 300 eccentric repetitions of the right quadriceps. DOMS and eccentric torque were measured at 2, 4, 20, 24, 48, and 72 h postexercise. Eccentric torque was also tested at 0 h. Radionuclide images of both quadriceps were taken at 2, 4, 20, and 24 h postexercise. The presence of 99mTc-WBC in the exercised muscle was significantly greater (P < 0.001) than in the nonexercised muscle. Eccentric torque declined at 0 and 24 h postexercise. DOMS peaked at 24 h postexercise. The presence of 99mTc-WBC in the exercised muscle in the first 24 h suggests that acute inflammation occurs as a result of exercise-induced muscle injury. The bimodal pattern of eccentric torque supports the hypothesis that more than one mechanism is involved.
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Rats were trained for 5 days by running on either an inclined or declined treadmill. Three days later, the rats were anesthetized, and angle-torque curves were plotted for the vastus intermedius muscles. The maximum active torque was generated at significantly greater muscle lengths for muscles from decline-trained rats compared with incline-trained rats. Sixteen muscles were then fixed and acid digested, and fiber lengths and sarcomere lengths were measured. The estimated average number of sarcomeres in series was greater in muscle fibers from decline-trained animals. Fourteen other muscles underwent a test series of lengthening contractions, all from the same knee angle. Torque fell less and the optimum angle shifted less for muscles from decline-trained animals, showing that the decline-trained muscles were more resistant to changes in mechanical parameters that indicate damage. These results support but do not prove the proposal that the lesser damage from a series of eccentric contractions seen in muscles trained by prior eccentric contractions is due to a greater number of sarcomeres in series.
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The objectives of this research were to determine the contribution of excitation-contraction (E-C) coupling failure to the decrement in maximal isometric tetanic force (Po) in mouse extensor digitorum longus (EDL) muscles after eccentric contractions and to elucidate possible mechanisms. The left anterior crural muscles of female ICR mice (n = 164) were injured in vivo with 150 eccentric contractions. Po, caffeine-, 4-chloro-m-cresol-, and K+-induced contracture forces, sarcoplasmic reticulum (SR) Ca2+ release and uptake rates, and intracellular Ca2+ concentration ([Ca2+]i) were then measured in vitro in injured and contralateral control EDL muscles at various times after injury up to 14 days. On the basis of the disproportional reduction in Po (approximately 51%) compared with caffeine-induced force (approximately 11-21%), we estimate that E-C coupling failure can explain 57-75% of the Po decrement from 0 to 5 days postinjury. Comparable reductions in Po and K+-induced force (51%), and minor reductions (0-6%) in the maximal SR Ca2+ release rate, suggest that the E-C coupling defect site is located at the t tubule-SR interface immediately after injury. Confocal laser scanning microscopy indicated that resting [Ca2+]i was elevated and peak tetanic [Ca2+]i was reduced, whereas peak 4-chloro-m-cresol-induced [Ca2+]i was unchanged immediately after injury. By 3 days postinjury, 4-chloro-m-cresol-induced [Ca2+]i became depressed, probably because of decreased SR Ca2+ release and uptake rates (17-31%). These data indicate that the decrease in Po during the first several days after injury primarily stems from a failure in the E-C coupling process.
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Background The injury risk in football is high, but little is known about causes of injury. Purpose To identify risk factors for football injuries using a multivariate model. Study Design Prospective cohort study. Methods Participants were 306 male football players from the two highest divisions in Iceland. Before the 1999 football season started, the following factors were examined: height, weight, body composition, flexibility, leg extension power, jump height, peak O2 uptake, joint stability, and history of previous injury. Injuries and player exposure were recorded throughout the competitive season. Results Older players were at higher risk of injury in general (odds ratio [OR] = 1.1 per year, P = 0.05). For hamstring strains, the significant risk factors were age (OR = 1.4 [1 year], P < 0.001) and previous hamstring strains (OR = 11.6, P < 0.001). For groin strains, the predictor risk factors were previous groin strains (OR = 7.3, P = 0.001) and decreased range of motion in hip abduction (OR = 0.9 [1°], P = 0.05). Previous injury was also identified as a risk factor for knee (OR = 4.6) and ankle sprains (OR = 5.3). Conclusions Age and previous injury were identified as the main risk factors for injury among elite football players from Iceland.
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Delayed onset muscle soreness (DOMS) is a sensation of discomfort that occurs 1 to 2 days after exercise. The soreness has been reported to be most evident at the muscle/tendon junction initially, and then spreading throughout the muscle. The muscle activity which causes the most soreness and injury to the muscle is eccentric activity. The injury to the muscle has been well described but the mechanism underlying the injury is not fully understood. Some recent studies have focused on the role of the cytoskeleton and its contribution to the sarcomere injury. Although little has been confirmed regarding the mechanisms involved in the production of delayed muscle soreness, it has been suggested that the soreness may occur as a result of mechanical factors or it may be biochemical in nature. To date, there appears to be no relationship between the development of soreness and the loss of muscle strength, in that the timing of the two events is different. Loss of muscle force has been observed immediately after the exercise. However, by collecting data at more frequent intervals a second loss of force has been reported in mice 1 to 3 days post-exercise. Future studies with humans may find this second loss of force to be related to DOMS. The role of inflammation during exercise-induced muscle injury has not been clearly defined. It is possible that the inflammatory response may be responsible for initiating, amplifying, and/or resolving skeletal muscle injury. Evidence from the literature of the involvement of cytokines, complement, neutrophils, monocytes and macrophages in the acute phase response are presented in this review. Clinically, DOMS is a common but self-limiting condition that usually requires no treatment. Most exercise enthusiasts are familiar with its symptoms. However, where a muscle has been immobilised or debilitated, it is not known how that muscle will respond to exercise, especially eccentric activity.
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Objective: To describe and analyse injuries and illness occurring in Australian cricket at first class level. Methods: Injuries occurring to the state and national teams were surveyed prospectively between the seasons 1998/1999 and 2000/2001, and the three preceding seasons were surveyed retrospectively. The definition of an injury was detailed and generally required the player to miss playing time in a major match. Results: Average injury match incidence in the seasons studied prospectively varied from a low of 19.0 injuries per 10 000 player hours in first class domestic matches to a high of 38.5 injuries per 10 000 player hours in one day internationals. The average seasonal incidence was 19.2 injuries per squad (25 players) per season (20 matches). Injury prevalence (the percentage of players missing through injury at any given time) was 14% for pace bowlers, 4% for spin bowlers, 4% for batsmen, and 2% for wicket keepers. The most common injuries were hamstring strains, side strains, groin injuries, wrist and hand injuries, and lumbar soft tissue injuries. Bowlers who had bowled more than 20 match overs in the week leading up to a match had an increased risk of sustaining a bowling injury (risk ratio 1.91, 95% confidence interval (CI) 1.28 to 2.85). A further risk for bowling injury is bowling second in a match—that is, batting first (risk ratio 1.62, 95% CI 1.04 to 2.50). A risk factor for injury in fielding is colliding with the boundary fence. Conclusions: Further study is required to determine ways to minimise the risk of injury in fast bowlers. Cricket grounds should mark a boundary line on the playing field to prevent players colliding with fences in the field.
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Eccentric exercise has been shown to have a measurable effect on the force-length relationship(FLR), as peak force is shifted to longer muscle lengths following exercise. Recently, this shift in the FLR has been proposed as a ''simple, reliable indicator'' for assessing contractile element damage following eccentric exercise. However, eccentric exercise causes fatigue and damage, and there is evidence that fatigue alone may also cause a shift in the FLR. The purpose of this paper was to assess the role of fatigue on the FLR (as measured by a torque-joint angle relationship) following isometric and eccentric exercise in the New Zealand white (NZW) rabbit. Six NZW rabbits were divided into two groups for eccentric or isometric contractions of the hindlimb dorsiflexor muscles. Pre- and post-exercise torque-joint angle relationships were measured, and the shift from the pre- to the post-exercise relationship was measured as the change in joint angle at which peak torque was produced. Eccentric exercise resulted in a rightward shift of seven degrees; isometric exercise, which is thought to not cause damage, resulted in a shift of four degrees. Furthermore, torque production was reduced to a greater extent at short compared to long muscle lengths for the eccentric and isometric exercise, resulting in a post-exercise torque-joint angle relationship that was altered in shape. We conclude from these results, that the shift in peak torque may not be a simple and reliable indicator of muscle damage, but is caused by a combination of damage and post- exercise fatigue. r 2004 Elsevier Ltd. All rights reserved.
Article
Objectives: Although previous research shows that the hamstring length–tension relationship during eccentric contractions plays a role in hamstring injury, training methods to promote beneficial adaptations are still unclear. The purpose of this pilot study was to determine whether an eccentric hamstring specific training programme results in favourable adaptations. Design: Eccentric training consisting of the Nordic hamstring exercise performed twice a week for four weeks. Pre-and post-training concentric/concentric isokinetic testing of peak torque (PT) and position of peak torque (POS) was performed for both the quadriceps and hamstrings of both legs at 608 s K1 . Vertical jump height was also assessed. Participants: Nine athletic, male subjects with no previous strength training experience. Results: There was a significant increase in vertical jump height (preZ51.0G4.8 cm, postZ54.4G6.3 cm, pZ0.04), a significant reduction in quadriceps PT (preZ204.6G21.9 N.m., postZ181.5G19.9 N.m., pZ0.01), a significant decrease in hamstring POS from full knee extension (preZ32.5G7.48, postZ26.2G8.68, pZ0.01) and a significant hamstring POS difference between limbs (dominantZ33.8G9.58, non-dominantZ24.9G6.58, pZ0.01). Conclusion: Nordic hamstring exercise training may produce favourable neuromuscular adaptations for the possible prevention of hamstring injuries while enhancing performance in athletic, untrained males.
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We measured titin and nebulin content in muscle biopsies from the vastus lateralis before and 24 h after one bout of high-intensity eccentric knee extensor resistance exercise in seven men (26 ± 3 years). Titin and nebulin content were significantly (P < 0.05) reduced after exercise by 30 and 15%, respectively. These results suggest that the structural components of the myofibrillar apparatus are degraded following high-intensity eccentric resistance exercise in humans. Loss of these proteins may have important implications for the mechanisms regulating the adaptive response of skeletal muscle to resistance exercise. © 2002 John Wiley & Sons, Inc. Muscle Nerve 25: 289–292, 2002 DOI 10.1002/mus. 10037
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W was found to produce low specific contact resistance (ρ c ∼8.0×10-5 Ω cm2) ohmic contacts to n+‐GaN (n=1.5×1019 cm-3) with limited reaction between the metal and semiconductor up to 1000 °C. The formation of the β–W 2 N and W–N interfacial phases were deemed responsible for the electrical integrity observed at these annealing temperatures. No Ga out‐diffusion was observed on the surface of thin (500 Å) W contacts even after 1000 °C, 1 min anneals. Thus, W appears to be a stable contact to n+‐GaN for high temperature applications. © 1996 American Institute of Physics.
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The purpose of this investigation was to evaluate changes in myosin heavy chain (MyHC) and titin isoforms after using various loads during explosive jump squat training. Twenty-four male athletic subjects were recruited for this study. Two experimental groups performed 8-weeks of jump squats using either 30% (n = 9) or 80% (n = 9) of their previously determined 1 repetition maximum. A third group served as controls (n = 6). Muscle biopsies were obtained before and after 8 weeks from vastus lateralis. The analysis of titin within these subjects confirmed that human skeletal muscle contains 2 isoforms of titin. There was no significant group x time interaction for MyHC or titin isoform expression. The data from this investigation indicates that a relatively short period of explosive resistance training results in negligible changes in the expression of MyHC or titin isoforms.
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1. Integrated electromyogram (e.m.g.) from the vastus lateralis muscles, and steady-state rates of oxygen uptake, were measured simultaneously during the performance of set rates of positive (concentric) and negative (eccentric) work at 50 rev/min on a motorized bicycle ergometer. 2. Similar experiments were also carried out at other pedalling rates and using other leg muscles. 3. The relationships between each of the variables (integrated e.m.g., oxygen consumption) and mean torque on pedals were found to be linear (r greater than 0-98) with a remarkable degree of reproducibility in surface e.m.g. for each subject over several months. 4. The ratio of the e.m.g. slopes at 50 rev/min (positive/negative) was 1-96 +/- 0-12 while the same ratio for the oxygen uptake slopes was 6-34 +/- 0-82. The discrepancy between the ratios suggests that not only is less muscle fibre activity required to maintain the same exerted force during negative work exercise, but there is also a substantial reduction in the oxygen uptake when the fibres are stretched. This was observed for all speeds of pedalling.
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To explore the role of titin filaments in muscle elasticity, we measured the resting tension-sarcomere length curves of six rabbit skeletal muscles that express three size classes of titin isoform. The stress-strain curves of the split fibers of these muscles displayed a similar multiphasic shape, with an exponential increase in tension at low sarcomere strain followed by a leveling of tension and a decrease in stiffness at and beyond an elastic limit (yield point) at higher sarcomere strain. Significantly, positive correlations exist between the size of the expressed titin isoform, the sarcomere length at the onset of exponential resting tension, and the yield point of each muscle. Immunoelectron microscopic studies of an epitope in the extensible segment of titin revealed a transition in the elastic behavior of the titin filaments near the yield point sarcomere length of these muscles, providing direct evidence of titin's involvement in the genesis of resting tension. Our data led to the formulation of a segmental extension model of resting tension that recognizes the interplay of three major factors in shaping the stress-strain curves: the net contour length of an extensible segment of titin filaments (between the Z line and the ends of the thick filaments), the intrinsic molecular elasticity of titin, and the strength of titin thick filament anchorage. Our data further suggest that skeletal muscle cells may control and modulate stiffness and elastic limit coordinately by selective expression of specific titin isoforms.