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Effect of 8-Week High-Intensity Stretching Training on Biceps Femoris Architecture

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Sandro R. Freitas at University of Lisbon
Sandro R. Freitas
Pedro Mil-Homens at University of Lisbon
Pedro Mil-Homens
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Previous studies have reported no changes on muscle architecture after static stretching interventions; however, authors have argued that stretching duration and intensity may not have been sufficient. A high-intensity stretching intervention targeting the knee flexors with an 8-week duration was conducted to observe the effects on biceps femoris long head (BF) architecture.Participants (n=5) performed an average of 3.1 assisted-stretching sessions per week, whereas a control group (n=5) did not perform stretching. The knee extension passive maximal range of motion (ROM), and BF fascicle length (FL), fascicle angle, and muscle thickness were assessed before and after the intervention.A significant increase was observed for FL (+12.3 mm, p=0.04) and maximal ROM (+14.2°, p=0.04) for the stretching group after the intervention. No significant changes were observed for the control group in any parameter.A 8-week high-intensity stretching program was observed to efficiently increased the BF fascicle length, as well as the knee extension maximal ROM. Stretching intensity and duration may play an important role on muscle architecture adaptation.
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RESEARCH NOTE
EFFECT OF 8-WEEK HIGH-INTENSITY STRETCHING
TRAINING ON BICEPS FEMORIS ARCHITECTURE
SANDRO R. FREITAS AND PEDRO MIL-HOMENS
University of Lisbon, Faculty of Human Kinetics, CIPER, Lisbon, Portugal
ABSTRACT
Freitas, SR and Mil-Homens, P. Effect of 8-week high-intensity
stretching training on biceps femoris architecture. JStrength
Cond Res 29(6): 1737–1740, 2015—Previous studies have
reported no changes on muscle architecture (MA) after static
stretching interventions; however, authors have argued that
stretching duration and intensity may not have been sufficient.
A high-intensity stretching intervention targeting the knee flexors
with an 8-week duration was conducted to observe the effects
on biceps femoris long head (BF) architecture. Participants
(n= 5) performed an average of 3.1 assisted-stretching sessions
per week, whereas a control group (n= 5) did not perform
stretching. The knee extension passive maximal range of motion
(ROM), and BF fascicle length (FL), fascicle angle, and muscle
thickness were assessed before and after the intervention. A
significant increase was observed for FL (+12.3 mm, p= 0.04)
and maximal ROM (+14.28,p= 0.04) for the stretching group
after the intervention. No significant changes were observed for
the control group in any parameter. An 8-week high-intensity
stretching program was observed to efficiently increase the BF
FL, as well as the knee extension maximal ROM. Stretching inten-
sity and duration may play an important role on MA adaptation.
KEY WORDS fascicle angle, fascicle length, flexibility, range of
motion, ultrasonography
INTRODUCTION
Muscle architecture (MA) is an important factor
in functional task performance (6,8), because it
relates to muscle force-length and force-
velocity properties (13). Previous studies have
observed that MA parameters can be changed in consequence
of strength training (1); however, previous studies have found
no changes on MA in consequence of static stretching
(4,5,10). For instance, Nakamura et al. (10) performed a 4-
week static stretching to the plantarflexors (self-stretching;
volume: 2 360 seconds daily; intensity: “largest stretch that
participants were willing to tolerate”) and found no changes in
fascicle length (FL), fascicle angle (FA), or muscle thickness
(MT). Lima et al. (5) also found no differences in the MA
parameters after an 8-week static stretching program (assisted
stretching; volume: 3 330 seconds with 30-second rest
between repetitions, 3 times a week; intensity: “within the
physiological limit and preceding the pain threshold”). Lima
et al. (5) suggested that the lack of change in MA could be
due to the low intensity and duration of the static stretching
intervention, since adaptations on MA after static stretching
has been observed in studies with animal models (12,15). In
addition, there is evidence of a greater maximal range of
motion (ROM) increase when performing static stretching
with higher stretching intensity (14), duration (7), repetitions
(2), and stretching session frequency (6). Thus, a change on
MA parameters after a static stretching may depend on the
stretching intensity; however, this has never been tested.
Recently, it was demonstrated that a stretching with no
rest interval between the repetitions induces a greater ROM
increase during the stretching compared with a conventional
rest interval protocol (3). The purpose of this pilot study was
to determine whether 8 weeks of high-intensity static
stretching by using a nonrest interval protocol would change
the MA architecture.
METHODS
Experimental Approach to the Problem
A randomized controlled trial was conducted to determine
the effects of a knee flexor stretching (Figure 1A) interven-
tion on the biceps femoris long head (BF) architecture and
passive knee extension maximal ROM (Figure 1B).
Subjects
Ten healthy university students [mean 6SD:allmen;
physically active; age = 21.2 60.8 years; body mass =
72.7 611.6 kg; height = 175.9 64.9 cm (age range from 18
to 23)] volunteered to this study. During the study, participants
performed normal daily living activities but were not involved
in specific exercise program (i.e., strength or stretching). The
local University Ethics Council approved this study (#1/2013),
and informed consent was obtained from all participants.
Procedures
Participants were allocated in 2 groups: a control (CG, n=5)
and a high-intensity stretching training (SG, n= 5). The CG
Address correspondence to Sandro R. Freitas, sfreitas@fmh.ulisboa.pt.
29(6)/1737–1740
Journal of Strength and Conditioning Research
Ó2015 National Strength and Conditioning Association
VOLUME 29 | NUMBER 6 | JUNE 2015 | 1737
Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.
were not involved in any type of stretching program during
the intervention period. The SG performed a stretching at
a ROM that corresponded to the highest tolerable torque
before the onset of pain for 450 seconds (Figure 1C). To
assure that the maximum passive torque was obtained, the
ROM was increased every 90 seconds to a new maximal
ROM, and thus not resting between repetitions (3). When
participants reported that they could not stretch further,
the knee was held statically until the end of the 450 seconds.
We previously observed that this type of protocol achieves
a greater ROM and passive peak torque during the
stretching than a conventional rest interval protocol, and
consequently a higher intensity (3). The SG group was mon-
itored for maximal ROM (Lafayette Gollehon Extendable,
Model 01135, IN, USA) every training session at the begin-
ning and during the stretching session. Experienced exercise
professionals assisted the stretching maneuvers (Figure 1A).
Participants were asked to participate in 5 sessions per week.
Both groups were assessed for BF architecture parameters
before and after the training period by an experienced
researcher (Figure 1B), using a 6-cm 10-MHz linear probe
(EUB-7500; Hitachi Medical Corporation, Chiyoda-ku,
Tokyo, Japan). A blinded researcher digitized the sonograms
(1.47v; ImageJ software, Bethesda, MD, NIH, USA). A classic
linear extrapolation method was used to calculate the BF archi-
tecture parameters (11). The FL was calculated using the equa-
tion: FL = L+(h/sina), where Lis the observable FL from the
midmuscle aponeurosis to the most visible end point, h is the
distance between the superficial aponeurosis and the fascicle
visible distal end point, and bis the angle between the fascicle
(drawn linearly) and the superficial aponeurosis (Figure 1B).
Statistical Analyses
Data were analyzed using the SPSS software (Version 20.0,
IBM Corp., Armonk, NY). Interday assessment reliability was
previously confirmed for FL (Intraclass correlation coeficient
(ICC) = 0.79 [0.55–0.91]), FA (ICC = 0.80 [0.56–0.91]), and
MT (ICC = 0.94 [0.86–0.98]) in a previously study with 20
participants (data not published); and the minimal detectable
difference determined was 8.4 mm, 1.58, and 1.6 mm for FL,
FA, and MT, respectively. Wilcoxon tests were used to deter-
mine pre- to post-effects on FL, FA, MT, and maximal ROM.
Figure 1. A) Training setup for stretching the knee flexors and to assess knee extension ROM. B) Typical sonogram of biceps femoris long head for 1
participant with the digitalization procedure to calculate the FL. C) Typical example for a participant passive knee extension torque-ROM response to a nonrest
interval stretching protocol assessed using an isokinetic setup detailed elsewhere (3); in this case, the participant tolerated the increase in ROM 3 times. ROM =
range of motion; FL = fascicle length.
Stretching and Muscle Architecture
1738
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Cohen’s dcoefficient was calculated to determine the magni-
tude of the MA and ROM changes. Statistical significance was
set to p#0.05. Data are presented as mean 6SD.
RESULTS
The SG participants performed a total of 25.0 66.4 training
sessions (i.e., 3.1 60.8 sessions per week). The knee extension
maximal ROM before, during, and after the stretching program
are shown in Figure 2A. The BF architecture parameters before
and after the stretching program are shown in Figure 2B.
DISCUSSION
The main finding of this pilot study was that the BF
architecture and the knee extension maximal ROM were
changed in vivo in consequence of an 8-week high-intensity
stretching program. FL increased 13.6% and the FA
decreased 15.1% (p= 0.13) in the SG. Previous studies have
reported changes of up to
+33% for FL and +20% for
FA as a consequence of resis-
tance training (1). However,
this is the first study showing
changes in consequence of
a stretching intervention. The
previous studies have reported
no significant changes in MA
after a stretching program
(4,5,10). However, studies in
animal models suggest that
static stretching can change
MA (12,15). We think that this
might be due to the duration
and intensity of the stretching
intervention. Participants have
stretched for 450 seconds in
each session and had a fre-
quency of 3.1 60.8 sessions
per week (;1406 seconds of
stretching for week). This
duration is much higher than
those used in previous studies
(5,6,10). We also used a method
that led to greater maximal
ROM and torque during the
stretching, and this may have
been higher than in previous
studies.
Another observation was the
magnitude of ROM increase
after the intervention. The total
knee extension maximal ROM
increase was 14.3 610.78
(+11.2 69.5%) at the end of
the program. This is much
higher compared with the re-
sults of previous studies examining the knee extension flex-
ibility (5,6). This was also probably due to the intensity and
duration of the stretching (6,7,9,13,14). In this study, the
ROM was increased every 90 seconds during the 450-
second stretching maneuver until the maximal ROM, until
the participant report that he could not stretch further without
felling pain, and stretching was superior to 300 seconds (7).
A major study limitation was the small sample size in both
groups. However, it must be noted that the change in both
FL and FA was higher than the minimal detectable change
using ultrasonography to assess BF MA (i.e., 8.4 mm and
1.58, for FL and FA, respectively). A future study should be
conducted with a higher sample size and should assess other
mechanical variables (e.g., joint passive torque-angle).
In conclusion, a high-intensity stretching program of
8 weeks was observed to efficiently increase the FL and
decrease the FA of the BF, as well to increase the knee
Figure 2. A) Maximal ROM before (pre), during (gray), and after (week 8) the stretching program. B) BF
architecture parameters before (pre) and after (post) the stretching program. *Statistical difference at p#0.05.
ROM = range of motion; BF = biceps femoris long head.
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extension maximal ROM. These findings are important to
those who seek MA changes through physical training. A
larger sample size is wanted in a future study to confirm
these results.
PRACTICAL APPLICATIONS
Muscle architecture is recognized as an important physical
performance variable. In this study, we observed a BF
architecture change in consequence of knee flexors static
stretching intervention. Approximately, 3 stretching sessions
per week, for 8-week duration, with a high stretching
intensity (i.e., by using a nonrest interval protocol) and
a duration of 450 seconds (i.e., considerable superior to
conventional practice) was seen to increase the FL and
passive knee extension maximal ROM, without affecting the
MT. It is possible that stretching intensity and duration are
a key variable to induce changes in MA.
ACKNOWLEDGMENTS
The authors acknowledge the support of the Portuguese
Scientific Foundation, and the kind contribution of Joa
˜o
Marmeleira for their co-operation in data digitalization,
and all the participants for their effort. All the authors
declare that they have no conflicts of interest regarding this
article.
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Stretching and Muscle Architecture
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... While no acute change in peak torque could be found, in accordance with previous literature (Freitas et al. 2018;Freitas and Mil-Homens 2015;Konrad and Tilp 2014), there was a moderate effect size for chronic PPT enhancements measured in end ROM (ES: 0.55, p = 0.005). These results support previous beliefs of the delayed occurrence in stretch sensation. ...
... Stiffness adaptations, as well as PPT, are often described as the underlying physiologic parameters of flexibility enhancements (Freitas et al. 2015(Freitas et al. , 2018Konrad and Tilp 2014). However, even though contributing to flexibility, both seem to be of a more phenomenological nature. ...
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... Similar to stretching, there is an ongoing discussion regarding the underlying mechanisms of foam rolling. While chronic stretch-induced ROM enhancements were attributed to a combination of structural adaptations (muscle and/or tendon properties) [25,93,94] and neuronal changes such as changes in the stretching pain threshold [21][22][23]95], foam rolling studies generally agree in attributing ROM increases to enhanced pain tolerance rather than stiffness changes [96,97]. Non-significant effects were discussed to be attributable to the low-volume interventions of the studies [12,16]. ...
... Nevertheless, although serial sarcomere accumulation was not measured directly in humans, there are some indications such as increased ROM [3,9,[98][99][100][101][102], reduced pain threshold [21][22][23]95], changes in the optimal force production angle or strength increases in long muscle lengths [184][185][186] as well as changes in fascicle lengths [187] after performing long-term stretching programmes. These adaptations, however, were not exclusively related to stretching exercises, but also to resistance training. ...
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... The increase in stiffness seen after chronic stretching may have also resulted in other muscle architectural changes in the proximal and middle regions, such as changes in fascicle angle and length effects or changes in collagen content, type, or organization, which were not assessed in this study. Therefore, future research is needed in these areas [33,34]. ...
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Full-text available
  • Sep 2024
Background The chronic effect of static stretching (SS) on muscle hypertrophy is still unclear. This study aimed to examine the chronic effects of SS exercises on skeletal muscle hypertrophy in healthy individuals. Methods A systematic literature search was conducted in the PubMed, Web of Science, Cochrane Library, and SPORTDiscus databases up to July 2023. Included studies examined chronic effects of SS exercise compared to an active/passive control group or the contralateral leg (i.e., utilizing between- or within-study designs, respectively) and assessed at least one outcome of skeletal muscle hypertrophy in healthy individuals with no age restriction. Results Twenty-five studies met the inclusion criteria. Overall, findings indicated an unclear effect of chronic SS exercises on skeletal muscle hypertrophy with a trivial point estimate (standardised mean difference [SMD] = 0.118 [95% prediction interval [95% PI] = − 0.233 to 0.469; p = 0.017]) and low heterogeneity (I² = 24%). Subgroup analyses revealed that trained individuals (β = 0.424; 95% PI = 0.095 to 0.753) displayed larger effects compared to recreationally trained (β = 0.115; 95% PI = − 0.195 to 0.425) and sedentary individuals (β = − 0.081; 95% PI = − 0.399 to 0.236). Subanalysis suggested the potential for greater skeletal muscle hypertrophy in samples with higher percentages of females (β = 0.003, [95% confidence interval [95% CI] = − 0.000 to 0.005]). However, the practical significance of this finding is questionable. Furthermore, a greater variety of stretching exercises elicited larger increases in muscle hypertrophy (β = 0.069, [95% CI = 0.041 to 0.097]). Longer durations of single stretching exercises (β = 0.006, [95% CI = 0.002 to 0.010]), time under stretching per session (β = 0.006, [95% CI = 0.003 to 0.009]), per week (β = 0.001, [95% CI = 0.000 to 0.001]) and in total (β = 0.008, [95% CI = 0.003 to 0.013]) induced larger muscle hypertrophy. Regarding joint range of motion, there was a clear positive effect with a moderate point estimate (β = 0.698; 95% PI = 0.147 to 1.249; p < 0.001) and moderate heterogeneity (I² = 43%). Moreover, findings indicated no significant association between the gains in joint range of motion and the increase in muscle hypertrophy (β = 0.036, [95% CI = − 0.123 to 0.196]; p = 0.638). Conclusions This study revealed an overall unclear chronic effect of SS on skeletal muscle hypertrophy, although interpretation across the range of PI suggests a potential modest beneficial effect. Subgroup analysis indicated larger stretching-induced muscle gains in trained individuals, a more varied selection of SS exercises, longer mean duration of single stretching exercise, increased time under SS per session, week, and in total, and possibly in samples with a higher proportion of females. From a practical perspective, it appears that SS exercises may not be highly effective in promoting skeletal muscle hypertrophy unless a higher duration of training is utilized. PROSPERO registration number: CRD42022331762.
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Effects of Chronic Static Stretching on Maximal Strength and Muscle Hypertrophy: A Systematic Review and Meta-Analysis with Meta-Regression
Article
Full-text available
  • Apr 2024
Background Increases in maximal strength and muscle volume represent central aims of training interventions. Recent research suggested that the chronic application of stretch may be effective in inducing hypertrophy. The present systematic review therefore aimed to syntheisize the evidence on changes of strength and muscle volume following chronic static stretching. Methods Three data bases were sceened to conduct a systematic review with meta-analysis. Studies using randomized, controlled trials with longitudinal (≥ 2 weeks) design, investigating strength and muscle volume following static stretching in humans, were included. Study quality was rated by two examiners using the PEDro scale. Results A total of 42 studies with 1318 cumulative participants were identified. Meta-analyses using robust variance estimation showed small stretch-mediated maximal strength increases (d = 0.30 p < 0.001) with stretching duration and intervention time as significant moderators. Including all studies, stretching induced small magnitude, but significant hypertrophy effects (d = 0.20). Longer stretching durations and intervention periods as well as higher training frequencies revealed small (d = 0.26–0.28), but significant effects (p < 0.001–0.005), while lower dosage did not reach the level of significance (p = 0.13–0.39). Conclusions While of minor effectiveness, chronic static stretching represents a possible alternative to resistance training when aiming to improve strength and increase muscle size. As a dose-response relationship may exist, higher stretch durations and frequencies as well as long program durations should be further elaborated.
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Acute and Chronic Effects of Static Stretching on Neuromuscular Properties: A Meta-Analytical Review
Article
Full-text available
  • Nov 2023
The aim of this review was to provide an overview of the recent findings on the acute and chronic effects of static stretching on joint behaviors and neuromuscular responses and to discuss the overall effects of acute and chronic static stretching on selected outcomes via meta-analyses, using a total of 50 recent studies. The results of our meta-analyses demonstrated that acute static stretching results in increased range of motion (ROM), decreased passive resistive torque (PRT), increased maximum tolerable PRT (PRTmax), decreased maximum voluntary isometric torque, decreased muscle–tendon unit stiffness, decreased muscle stiffness, decreased tendon stiffness, and decreased shear elastic modulus. Moreover, the chronic effects of static stretching included increased ROM, increased PRTmax, decreased muscle stiffness, and decreased shear elastic modulus (or shear wave speed). These results suggest that static stretching interventions have the potential to increase ROM and reduce the mechanical properties of muscle–tendon tissue, but they may not change corticospinal excitability and spinal reflex excitability or muscle architecture parameters.
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Are Rest Intervals Between Stretching Repetitions Effective to Acutely Increase Range of Motion?
Article
Full-text available
  • Jul 2014
Static stretching with rest between repetitions is often performed to acutely increase joint flexibility. PURPOSE: To test 1) the effects of the lack of resting between stretching repetitions, and 2) the minimal number of stretching repetitions required to change the maximal range of motion (ROM), maximal tolerated joint passive torque (MPT), and submaximal passive torque at a given angle (PT). METHODS: Five static stretching repetitions with a 30-s rest interval (RI) and non-rest interval (NRI) stretching protocols were compared. Participants (n=47) were encouraged to perform the maximal ROM without pain in all the repetitions. Each repetition lasted 90 s. Maximal ROM, MPT, PT, and muscle activity were compared between protocols for the same number of stretching repetitions. RESULTS: The NRI produced a higher increase in maximal ROM and MPT during and after stretching (P<0.05). PT decreased in both protocols, although the NRI tended to have a lower decrement across different submaximal angles (0.05<P<0.08) in the initial range of the torque-angle curve. Significantly changes in maximal ROM (P<0.01) and PT (P<0.01) were obtained at the 3rd and 2nd repetition of RI, respectively. The RI did not significantly increase the MPT (P=0.12) after stretching, only the NRI did (P<0.01). CONCLUSIONS: Lack of rest between repetitions more efficiently increased the maximal ROM and capacity to tolerate passive torque during and after stretching. The use of 30-s rest between repetitions potentiates the decrease in passive torque. Rest intervals should not be used if the aim is to acutely increase the maximal ROM and peak passive torque.
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Increased range of motion after static stretching is not due to changes in muscle and tendon structures
Article
Full-text available
  • May 2014
Background: It is known that static stretching is an appropriate means of increasing the range of motion, but information in the literature about the mechanical adaptation of the muscle-tendon unit is scarce. Therefore, the purpose of this study was to investigate the influence of a six-week static stretching training program on the structural and functional parameters of the human gastrocnemius medialis muscle and the Achilles tendon. Methods: A total of 49 volunteers were randomly assigned into static stretching and control groups. Before and following the stretching intervention, we determined the maximum dorsiflexion range of motion with the corresponding fascicle length and pennation angle. Passive resistive torque and maximum voluntary contraction were measured with a dynamometer. Muscle-tendon junction displacement allowed us to determine the length changes in tendon and muscle, and hence to calculate stiffness. Fascicle length, pennation angle, and muscle tendon junction displacement were measured with ultrasound. Findings: Mean range of motion increased significantly from 30.9 (5.3) to 36.3 (6.1) in the intervention group, but other functional (passive resistive torque, maximum voluntary contraction) and structural (fascicle length, pennation angle, muscle stiffness, tendon stiffness) parameters were unaltered. Interpretation: The increased range of motion could not be explained by the structural changes in the muscle-tendon unit, and was likely due to increased stretch tolerance possibly due to adaptations of nociceptive nerve endings.
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Structural adaptations of rat lateral gastrocnemius muscle-tendon complex to a chronic stretching program and their quantification based on ultrasound biomicroscopy and optical microscopic images
Article
Full-text available
  • Nov 2013
A chronic regimen of flexibility training can increase range of motion, with the increase mechanisms believed to be a change in the muscle material properties or in the neural components associated with this type of training. This study followed chronic structural adaptations of lateral gastrocnemius muscle of rats submitted to stretching training (3 times a week during 8weeks), based on muscle architecture measurements including pennation angle, muscle thickness and tendon length obtained from ultrasound biomicroscopic images, in vivo. Fiber length and sarcomere number per 100μm were determined in 3 fibers of each muscle (ex vivo and in vitro, respectively), using conventional optical microscopy. Stretching training resulted in a significant pennation angle reduction of the stretched leg after 12 sessions (25%, P=0.002 to 0.024). Muscle thickness and tendon length presented no significant changes. Fiber length presented a significant increase for the stretched leg (8.5%, P=0.00006), with the simultaneous increase in sarcomere length (5%, P=0.041) since the stretched muscles presented less sarcomeres per 100μm. A stretching protocol with characteristics similar to those applied in humans was sufficient to modify muscle architecture of rats with absence of a sarcomerogenesis process. The results indicate that structural adaptations take place in skeletal muscle tissue submitted to moderate-intensity stretching training.
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Training intensity and duration in flexibility
Article
  • Jan 1996
The effect of static stretching intensity and duration on the flexibility of the hamstrings was investigated in 24 healthy male (mean age 32.2 years) and 24 healthy female (mean age 31.2 years) participated. Subjects were given a maximal-effort sit-and-reach test with each leg on Day 1. Subjects were then randomly assigned an intensity (60%, 85%, or 100% of baseline test value) and duration (10 seconds or 30-seconds) at which to train. Training took place on Days 2-7. Subjects were retested on Day 8. ANOVA and Newman-Keuls post hoc tests revealed that a duration of 30 seconds produced significantly greater flexibility than 10 seconds. The 85% and 100% intensities resulted in significantly greater flexibility than 60%. There were no significant differences between the 85% and 100% intensities. There were no gender differences in improvement. These results suggest that the higher duration (30 seconds) and intensity (85% and 100%) of stretching produce greater improvement in flexibility.
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Acute Effects of Static Stretching on Muscle Hardness of the Medial Gastrocnemius Muscle Belly in Humans: An Ultrasonic Shear-Wave Elastography Study
Article
  • Jun 2014
  • ULTRASOUND MED BIOL
This study investigated the acute effects of static stretching (SS) on shear elastic modulus as an index of muscle hardness and muscle stiffness and the relationship between change in shear elastic modulus and change in muscle stiffness after SS. The patients were 17 healthy young males. Muscle stiffness was measured during passive ankle dorsiflexion using a dynamometer and ultrasonography before (pre) and immediately after (post) 2 min of SS. In addition, shear elastic modulus was measured by a new ultrasound technique called ultrasonic shear wave elastography. The post-SS values for muscle stiffness and shear elastic modulus were significantly lower than the pre-SS values. In addition, Spearman's rank correlation coefficient indicated a significant correlation between rate of change in shear elastic modulus and rate of change in muscle stiffness. These results suggest that SS is an effective method for decreasing shear elastic modulus as well as muscle stiffness and that shear elastic modulus measurement using the shear wave elastography technique is useful in determining the effects of SS.
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Assessment of Muscle Architecture of the Biceps Femoris and Vastus Lateralis by Ultrasound After a Chronic Stretching Program
Article
  • Jan 2014
To evaluate the chronic effects of a static stretching program on the muscle architecture of biceps femoris (BF) and vastus lateralis (VL) muscles in ultrasound (US) images. Randomized controlled longitudinal trial. Biomechanics Laboratory of Physical Education School of the Army, Rio de Janeiro, Brazil. The study included 24 healthy and physically active male volunteers (19.05 ± 1.40 years, 1.73 ± 0.07 m, and 73.15 ± 8.33 kg), randomly allocated to 1 of 2 groups: stretching group (SG, n = 12) and control group (n = 12). The SG was submitted to 3 sets of 30 seconds of static stretching 3 times a week during 8 weeks. Ultrasound equipment (7.5 MHz) was used for the evaluation of BF and VL muscle architecture variables (pennation angle, fiber length, muscle thickness, and fascicle displacement) before and after training. Knee range of motion (ROM) and isometric flexion and extension torque (TQ) were also measured. There were no significant changes in muscle architecture, TQ, and maximum knee flexion angle (P > 0.05). However, maximum knee extension angle (MEA) increased significantly in the SG (pretraining: 159.37 ± 7.27 degrees and posttraining: 168.9 ± 3.7 degrees; P < 0.05). Volume or intensity (or both) of the stretching protocol was insufficient to cause structural changes in the VL and BF muscles. The increase in MEA could not be explained by muscle architecture changes. To describe changes in the VL and BF muscle tendon unit using US after a long-term stretching program to identify which structures are responsible for ROM increase.
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Predictors of High-Intensity Running Capacity in Collegiate Women During a Soccer Game
Article
  • Dec 2013
  • J STRENGTH COND RES
The purpose of this investigation was to determine which physiological assessments best predicted high intensity running performance during a women's collegiate soccer game. A secondary purpose was to examine the relationships among physiological performance measures including muscle architecture on soccer performance (distance covered, HIR, and sprints during the game) during a competitive collegiate women's soccer game. Ten National Collegiate Athletic Association (NCAA) Division I women soccer players performed physiological assessments within a two-week period prior to a competitive regulation soccer game performed during the spring season. Testing consisted of height, body mass, ultrasound measurement of dominant (DOMleg) and non-dominant leg (NDOMleg) vastus lateralis for muscle thickness (MT) and pennation angle (PA), VO2max, running economy, and Wingate anaerobic test (WAnT) for peak power (PP), mean power (MP), and fatigue rate (FR). During the game, distance run, high intensity running (HIR), and sprints were measured via a 10-Hz GPS system. Stepwise regression revealed that VO2max, dominant leg thickness, and dominant leg pennation angle were the strongest predictors of HIR distance during the game (R=0.989, SEE=115.5m, p=0.001). VO2max was significantly correlated with total distance run (r=0.831; p=0.003), HIR (r=0.755; p=0.012), WAnTPP (r=-0.737; p=0.015), WAnTPP[BULLET OPERATOR]kg (r=-0.706; p=0.022), and WAnTFR (r=-0.713; p=0.021). DOMlegMT was significantly correlated with WAnTFR (r=0.893; p=0.001). DOMlegPA was significantly correlated with WAnTFR (r=0.740; p=0.023). The NDOMlegPA was significantly correlated to peak running velocity (r=0.781; p=0.013) and WAnTMP[BULLET OPERATOR]kg (r=0.801; p=0.01). Results of this study indicate that VO2max and muscle architecture are important characteristics of NCAA Division I women soccer players and may predict HIR distance during a competitive contest.
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Acute Effects of Different Stretching Durations on Passive Torque, Mobility, and Isometric Muscle Force
Article
  • Mar 2013
  • J STRENGTH COND RES
Static stretching is widely applied in various disciplines. However, the acute effects of different durations of stretching are unclear. Therefore, the present study was designed to investigate the acute effects of different stretching durations on muscle function and flexibility, and provide insight into the optimal duration of static stretching. This randomized crossover trial included 24 healthy students (17 men and 7 women) who stretched their right hamstrings for durations of 20, 60, 180, and 300 s in a random order. The following outcomes were assessed using an isokinetic dynamometer as markers of lower limb function and flexibility: static passive torque (SPT), dynamic passive torque (DPT), stiffness, straight leg raise (SLR), and isometric muscle force. SPT was significantly decreased after all stretching durations (p < 0.05). SPT was significantly lower after 60, 180, and 300 s of stretching compared with after 20-s stretching, and stiffness decreased significantly after 180- and 300-s stretching (p < 0.05). In addition, DPT and stiffness were significantly lower after 300 s than after 20-s stretching (p < 0.05), and SLR increased significantly after all stretching durations (p < 0.05). SLR was higher after 180- and 300-s stretching than after 20-s stretching and higher after 300-s stretching than after 60-s stretching (p < 0.05). Isometric muscle force significantly decreased after all stretching durations (p < 0.05). Therefore, increased duration of stretching is associated with a decrease in SPT but an increase in SLR. Over 180 s of stretching was required to decrease DPT and stiffness, but isometric muscle force decreased regardless of stretching duration. In conclusion, these results indicate that longer durations of stretching are needed to provide better flexibility.
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Relationship Between Muscle Architecture and Joint Performance During Concentric Contractions in Humans
Article
  • Aug 2012
The purpose of this study was to examine the relationship between muscle architecture of the triceps brachii (TB) and joint performance during concentric elbow extensions. Twenty-two men performed maximal isometric and concentric elbow extensions against various loads. Joint torque and angular velocity during concentric contractions were measured, and joint power was calculated. Muscle length, cross-sectional areas and volume of TB were measured from magnetic resonance images. Pennation angle (PA) of TB at rest was determined by ultrasonography. The PA was significantly correlated with the maximal isometric torque (r = 0.471), but not to the torque normalized by muscle volume (r = 0.312). A significant correlation was found between PA and the angular velocity at 0 kg load (r = 0.563), even when the angular velocity was normalized by the muscle length (r = 0.536). The PA was significantly correlated with the maximal joint power (r = 0.519), but not with the power normalized by muscle volume (r = 0.393). These results suggest that PA has a positive influence on the muscle shortening velocity during an unloaded movement, but does not have a significant influence on the maximum power generation in untrained men.
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Effects of a 4-week static stretch training program on passive stiffness of human gastrocnemius muscle-tendon unit in vivo
Article
  • Nov 2011
  • EUR J APPL PHYSIOL
Static stretch is commonly used to prevent contracture and to improve joint mobility. However, it is unclear whether the components of the muscle-tendon unit are affected by a static stretch training program. This study investigated the effect of a four-week static stretch training program on the viscoelastic properties of the muscle-tendon unit and muscle. The subjects comprised 18 male participants (mean age 21.4 ± 1.7 years). The range of motion (ROM), passive torque, myotendinous junction (MTJ) displacement and, muscle fascicle length of the gastrocnemius muscle were assessed using both ultrasonography and a dynamometer while the ankle was passively dorsiflexed. After the initial test, the participants were assigned either to a group that stretched for 4 weeks (N = 9) or to a control group (N = 9). The tests were repeated after the static stretch training program. The ROM and MTJ displacement significantly increased, and the passive torque at 30° significantly decreased, in the stretching group after the study period. However, there was no significant increase in muscle fascicle length. These results suggest that a 4-week static stretch training program changes the flexibility of the overall MTU without causing concomitant changes in muscle fascicle length.
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