Antagonist muscle architecture and aponeurosis/tendon strain of biceps femoris long head during maximal isometric efforts.

INTRODUCTION: Examination of the mechanical behavior of the hamstrings when acting as antagonists provides information about loading of this muscle group and its role for joint stability during forceful quadriceps contractions. The aim of this study was to quantify biceps femoris long head fascicle length (FL), angle of pennation (PA) and distal tendon/aponeurosis strain during maximum voluntary contraction efforts of the knee extensors using real-time ultrasound.

METHODS: Fourteen participants performed passive joint movements and maximum voluntary knee extension and flexion efforts of the knee flexors at 0°, 45° and 90° of knee flexion. An ultrasound probe was used to visualize FL, PA and tendon/aponeurosis strain from the distal part of the muscle.

RESULTS: Two-way analysis of variance designs indicated that: (a) antagonist BFlh tendon/aponeurosis strain increased significantly up to 2.77 ± 1.25% relative to rest (p < 0.05). The FL increased non-significantly (2.86 ± 6.81%) while the PA was unaltered during isometric MVC efforts of the knee extensors (p > 0.05) (b) FL, PA and tendon/aponeurosis strain of the BFlh when acting as antagonist were not significantly affected by knee joint angular position (p > 0.05).

CONCLUSIONS: Antagonist hamstring function takes the form of a lengthened tendon/aponeurosis, no fascicle shortening and submaximal neural activation. Future research could examine whether exercise interventions that aim to alter tendon/aponeurosis mechanical properties of the hamstrings when acting as antagonists are beneficial for injury prevention and rehabilitation.