Ultrasonographic determination of tendon compliance in human biceps brachii muscle

This study aimed to estimate in vivo the compliance of tendon structure in human biceps brachii (BB) muscle for eight healthy male subjects. Elongation of the tendon of BB during isometric elbow-flexion was directly measured by ultrasonography. Muscle force of BB(F-BB) was calculated from the elbow flexion torque and moment arm of elbow-flexor. When the FBB increased to 80%MVC (maximum voluntary contraction), the tendinous tissue of BB was elongated 10.24 +/- 2.52 mm, horizontally. The relationship between tendon length and FBB was curvilinear and consisted of an initial region characterized by a large increase in tendon length with increasing FBB under 50% MVC, immediately followed by a linear region. The compliance of tendinous tissues, estimated from the slope of the linear region, was 0.010 +/- 0.005 mm/N, and did not show a significant correlation with MVC and muscle volume of the elbow flexors, estimated from muscle thickness. The compliance value observed here was lower than those of the medial gastrocnemius muscle and the tibialis anterior muscle, reported previously using the same ultrasonic method as the present study. This may be related to the functional differences among limb muscles in various human movements.