AUTHOR=Raiteri Brent J. , Beller Ronja , Hahn Daniel TITLE=Biceps Femoris Long Head Muscle Fascicles Actively Lengthen During the Nordic Hamstring Exercise JOURNAL=Frontiers in Sports and Active Living VOLUME=3 YEAR=2021 URL=https://www.frontiersin.org/journals/sports-and-active-living/articles/10.3389/fspor.2021.669813 DOI=10.3389/fspor.2021.669813 ISSN=2624-9367 ABSTRACT=
Current debate exists around whether a presumed eccentric exercise, the Nordic hamstring exercise (NHE), actually causes active hamstring muscle lengthening. This is because of the decoupling that can occur between the muscle fascicle and muscle-tendon unit (MTU) length changes in relatively compliant human lower-limb MTUs, which results in MTU lengthening not necessarily causing muscle fascicle lengthening. This missing knowledge complicates the interpretation of why the NHE is effective at reducing running-related hamstring muscle injury risk in athletes previously unfamiliar with performing this exercise. The purpose of the study was therefore to investigate if the most-commonly injured hamstring muscle, the biceps femoris long head (BF), exhibits active muscle lengthening (i.e. an eccentric muscle action) during the NHE up until peak force in Nordic novices. External reaction force at the ankle, knee flexion angle, and BF and semitendinosus muscle activities were recorded from the left leg of 14 participants during the NHE. Simultaneously, BF muscle architecture was imaged using B-mode ultrasound imaging, and muscle architecture changes were tracked using two different tracking algorithms. From ~85 to 100% of peak NHE force, both tracking algorithms detected that BF muscle fascicles (