Background While Nordic hamstring exercise(NHE)training has been shown to reduce hamstring strains,the muscle-specific adaptations to NHE across the 4 hamstrings remain unclear.This study investigates architectural an...Background While Nordic hamstring exercise(NHE)training has been shown to reduce hamstring strains,the muscle-specific adaptations to NHE across the 4 hamstrings remain unclear.This study investigates architectural and microstructural adaptations of the biceps femoris short head(BFsh),biceps femoris long head(BFlh),semitendinosus(ST),and semimembranosus(SM)in response to an NHE intervention.Methods Eleven subjects completed 9 weeks of supervised NHE training followed by 3 weeks of detraining.Magnetic resonance imaging was performed at pre-training,post-training,and detraining to assess architectural(volume,fiber tract length,and fiber tract angle)and microstructural(axial(AD),mean(MD),radial(RD)diffusivities,and fractional anisotropy(FA))parameters of the 4 hamstrings.Results NHE training induced significant but non-uniform hamstring muscle hypertrophy(BFsh:22%,BFlh:9%,ST:26%,SM:6%)and fiber tract length increase(BFsh:11%,BFlh:7%,ST:18%,SM:10%).AD(5%),MD(4%),and RD(5%)showed significant increases,but fiber tract angle and FA remained unchanged.After detraining,only ST showed a significant reduction(8%)in volume,which remained higher than the pre-training value.While fiber tract lengths returned to baseline,AD,MD,and RD remained higher than pre-training levels for all hamstrings.Conclusion The 9-week NHE training substantially increased hamstring muscle volume with greater hypertrophy in ST and BFsh.Hypertrophy was accompanied by increases in fiber tract lengths and cross-sections(increased RD).After 3 weeks of detraining,fiber tract length gains across all hamstrings declined,emphasizing the importance of sustained training to maintain all the protective adaptations.展开更多
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
基金financial support from the general electric (GE) healthcareAustralian Research Council Discovery Project (DP200101476)+5 种基金in parts by National Institutes of Health (NIH) grants (R01 AR077604, R01 EB002524, R01 AR079431, P41 EB02706)Stanford Graduate FellowshipThe University of Queensland Graduate ScholarshipNational Health and Medical Research Council of Australia Fellowship (#1194937)Wu Tsai Human Performance Alliance at Stanford Universitythe Joe and Clara Tsai Foundation
文摘Background While Nordic hamstring exercise(NHE)training has been shown to reduce hamstring strains,the muscle-specific adaptations to NHE across the 4 hamstrings remain unclear.This study investigates architectural and microstructural adaptations of the biceps femoris short head(BFsh),biceps femoris long head(BFlh),semitendinosus(ST),and semimembranosus(SM)in response to an NHE intervention.Methods Eleven subjects completed 9 weeks of supervised NHE training followed by 3 weeks of detraining.Magnetic resonance imaging was performed at pre-training,post-training,and detraining to assess architectural(volume,fiber tract length,and fiber tract angle)and microstructural(axial(AD),mean(MD),radial(RD)diffusivities,and fractional anisotropy(FA))parameters of the 4 hamstrings.Results NHE training induced significant but non-uniform hamstring muscle hypertrophy(BFsh:22%,BFlh:9%,ST:26%,SM:6%)and fiber tract length increase(BFsh:11%,BFlh:7%,ST:18%,SM:10%).AD(5%),MD(4%),and RD(5%)showed significant increases,but fiber tract angle and FA remained unchanged.After detraining,only ST showed a significant reduction(8%)in volume,which remained higher than the pre-training value.While fiber tract lengths returned to baseline,AD,MD,and RD remained higher than pre-training levels for all hamstrings.Conclusion The 9-week NHE training substantially increased hamstring muscle volume with greater hypertrophy in ST and BFsh.Hypertrophy was accompanied by increases in fiber tract lengths and cross-sections(increased RD).After 3 weeks of detraining,fiber tract length gains across all hamstrings declined,emphasizing the importance of sustained training to maintain all the protective adaptations.
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.
