Background Eccentric training,such as Nordic hamstring exercise(NHE)training,is commonly used as a preventive measure for hamstring strains.Eccentric training is believed to induce lengthening of muscle fascicles and ...Background Eccentric training,such as Nordic hamstring exercise(NHE)training,is commonly used as a preventive measure for hamstring strains.Eccentric training is believed to induce lengthening of muscle fascicles and to be associated with the addition of sarcomeres in series within muscle fibers.However,the difficulty in measuring sarcomere adaptation in human muscles has severely limited information about the precise mechanisms of adaptation.This study addressed this limitation by measuring the multiscale hamstring muscle adaptations in response to 9 weeks of NHE training and 3 weeks of detraining.Methods Twelve participants completed 9 weeks of supervised NHE training,followed by a 3-week detraining period.We assessed biceps femoris long-head(BFlh)muscle fascicle length,sarcomere length,and serial sarcomere number in the central and distal regions of the muscle.Additionally,we measured muscle volume and eccentric strength at baseline,post-training,and post-detraining.Results NHE training over 9 weeks induced significant architectural and strength adaptations in the BFlh muscle.Fascicle length increased by 19%in the central muscle region and 33%in the distal muscle region.NHE also induced increases in serial sarcomere number(25%in the central region and 49%in the distal region).BFlh muscle volume increased by 8%,and knee flexion strength increased by 40%with training.Following 3 weeks of detraining,fascicle length decreased by 12%in the central region and 16%in the distal region along with reductions in serial sarcomere number.Conclusion Nine weeks of NHE training produced substantial,region-specific increases in BFlh muscle fascicle length,muscle volume,and force generation.The direct measurement of sarcomere lengths revealed that the increased fascicle length was accompanied by the addition of sarcomeres in series within the muscle fascicles.展开更多
Purpose The present study aimed to test if a long-term passive stretching training causes adaptations of the medial gastroc-nemius architecture and the Achilles tendon (AT) tangent modulus.Methods A total of 20 males ...Purpose The present study aimed to test if a long-term passive stretching training causes adaptations of the medial gastroc-nemius architecture and the Achilles tendon (AT) tangent modulus.Methods A total of 20 males took part in the study.The stretching group (n =12),performed stretching exercises for the plantar flexors for 10 weeks,4-5 times a week,which comprised two static positions sustained twice each during 30 s.Results For the stretching group,maximum dorsiflexion angle,peak passive torque,and muscle-tendon unit maximum length significantly increased after training.No other differences were found related to muscle architecture and AT tangent modulus.Conclusion Joint amplitude gain after a long-term stretching of the triceps surae was not accompanied by structural or mechanical changes of the medial gastrocnemius and AT tendon,and seems to reflect an increasing stretch tolerance level.展开更多
Background Serial sarcomere number(SSN)critically influences muscle function and is hypothesized to protect against injury.While most evidence for SSN addition comes from non-human animal studies,eccentric exercise is...Background Serial sarcomere number(SSN)critically influences muscle function and is hypothesized to protect against injury.While most evidence for SSN addition comes from non-human animal studies,eccentric exercise is often proposed as a key stimulus due to its association with increased fascicle length in humans.However,the most efficient exercise stimuli and the effectiveness of eccentric training in increasing SSN remain unclear.The objective of this study was to provide a detailed historical overview of research exploring the mechanical factors regulating muscle/fiber length and its relationship with function,and to explore more recent evidence that eccentric muscle contractions might be an important stimulus for SSN regulation using a meta-analytic approach.Methods An extensive literature search with snowballing was conducted to build the historical review.A systematic review with random-effect meta analyses was performed to compare proposed types of fiber-lengthening exercises to control conditions.Results The historical review demonstrated that the application of forces at long fiber lengths,but not specifically the use of greater excursions,plays an important role in increasing SSN.Animal data showed changes in SSN exceeding 20%over several weeks with varied forms of activities.Nonetheless,the meta-analysis revealed a lack of effect of eccentric resistance training in animal models(Δ=1%;Cohen’s d=0.19(95%confidence interval:–0.29 to 0.67),p=0.449).Conclusion High active or passive muscle forces applied at long fiber lengths appear to be the key stimuli triggering sarcomerogenesis.Eccentric exercise does not seem to be a key promoter of SSN.Too few studies exist to draw conclusions as to the effect of eccentric exercise on SSN in humans.Understanding the mechanical triggers and physiological mechanisms involved in serial sarcomere addition could help in the development of exercise(and other)interventions to optimize muscle function and reduce injury risk.展开更多
基金supported by the Australian Research Council Discovery Project(DP200101476)in part by National Institute of Health grants(R01 AR077604,RO1 EB002524,RO1 AR079431,and P41 EB02706)+1 种基金Stanford Graduate Fellowship,The University of Queensland Graduate Scholarship,National Health and Medical Research Council of Australia Fellowship(#1194937)by Wu Tsai Human Performance Alliance at Stanford University and the Joe and Clara Tsai Foundation。
文摘Background Eccentric training,such as Nordic hamstring exercise(NHE)training,is commonly used as a preventive measure for hamstring strains.Eccentric training is believed to induce lengthening of muscle fascicles and to be associated with the addition of sarcomeres in series within muscle fibers.However,the difficulty in measuring sarcomere adaptation in human muscles has severely limited information about the precise mechanisms of adaptation.This study addressed this limitation by measuring the multiscale hamstring muscle adaptations in response to 9 weeks of NHE training and 3 weeks of detraining.Methods Twelve participants completed 9 weeks of supervised NHE training,followed by a 3-week detraining period.We assessed biceps femoris long-head(BFlh)muscle fascicle length,sarcomere length,and serial sarcomere number in the central and distal regions of the muscle.Additionally,we measured muscle volume and eccentric strength at baseline,post-training,and post-detraining.Results NHE training over 9 weeks induced significant architectural and strength adaptations in the BFlh muscle.Fascicle length increased by 19%in the central muscle region and 33%in the distal muscle region.NHE also induced increases in serial sarcomere number(25%in the central region and 49%in the distal region).BFlh muscle volume increased by 8%,and knee flexion strength increased by 40%with training.Following 3 weeks of detraining,fascicle length decreased by 12%in the central region and 16%in the distal region along with reductions in serial sarcomere number.Conclusion Nine weeks of NHE training produced substantial,region-specific increases in BFlh muscle fascicle length,muscle volume,and force generation.The direct measurement of sarcomere lengths revealed that the increased fascicle length was accompanied by the addition of sarcomeres in series within the muscle fascicles.
基金financial support of FAPERJ(Rio de Janeiro State Research Funding Agency)CAPES(Brazilian National Research Funding Agency)+2 种基金CNPq(National Counsel of Technological and Scientific Development)FINEP(Funding Authority for Studies and Projects)the facility support of the Biomechanics Laboratory of Physical Education School of the Army.
文摘Purpose The present study aimed to test if a long-term passive stretching training causes adaptations of the medial gastroc-nemius architecture and the Achilles tendon (AT) tangent modulus.Methods A total of 20 males took part in the study.The stretching group (n =12),performed stretching exercises for the plantar flexors for 10 weeks,4-5 times a week,which comprised two static positions sustained twice each during 30 s.Results For the stretching group,maximum dorsiflexion angle,peak passive torque,and muscle-tendon unit maximum length significantly increased after training.No other differences were found related to muscle architecture and AT tangent modulus.Conclusion Joint amplitude gain after a long-term stretching of the triceps surae was not accompanied by structural or mechanical changes of the medial gastrocnemius and AT tendon,and seems to reflect an increasing stretch tolerance level.
文摘Background Serial sarcomere number(SSN)critically influences muscle function and is hypothesized to protect against injury.While most evidence for SSN addition comes from non-human animal studies,eccentric exercise is often proposed as a key stimulus due to its association with increased fascicle length in humans.However,the most efficient exercise stimuli and the effectiveness of eccentric training in increasing SSN remain unclear.The objective of this study was to provide a detailed historical overview of research exploring the mechanical factors regulating muscle/fiber length and its relationship with function,and to explore more recent evidence that eccentric muscle contractions might be an important stimulus for SSN regulation using a meta-analytic approach.Methods An extensive literature search with snowballing was conducted to build the historical review.A systematic review with random-effect meta analyses was performed to compare proposed types of fiber-lengthening exercises to control conditions.Results The historical review demonstrated that the application of forces at long fiber lengths,but not specifically the use of greater excursions,plays an important role in increasing SSN.Animal data showed changes in SSN exceeding 20%over several weeks with varied forms of activities.Nonetheless,the meta-analysis revealed a lack of effect of eccentric resistance training in animal models(Δ=1%;Cohen’s d=0.19(95%confidence interval:–0.29 to 0.67),p=0.449).Conclusion High active or passive muscle forces applied at long fiber lengths appear to be the key stimuli triggering sarcomerogenesis.Eccentric exercise does not seem to be a key promoter of SSN.Too few studies exist to draw conclusions as to the effect of eccentric exercise on SSN in humans.Understanding the mechanical triggers and physiological mechanisms involved in serial sarcomere addition could help in the development of exercise(and other)interventions to optimize muscle function and reduce injury risk.
