Kawakami Y, Kubo, K., Kanehisa H, Fukunaga T

Eur. J. Appl. Physiol., 87: 381-387, 2002.

The influence of muscle series elasticity on the relationship between torque and joint angle during dynamic contractions was studied. The torque-angle relationship during the maximal isokinetic knee extension was determined for six male subjects (25 - 45 yr) at 0.52, 1.05, 1.57, 2.09, 2.62, 3.49 rad/s. The knee joint angle at which peak torque was observed showed a systematic shift to more extended positions, i.e., the quadriceps muscle-tendon unit length became shorter, as the velocity increased (from 1.01 +- 0.12 [0.52 rad/s] to 0.75 +- 0.14 rad [3.49 rad/s], mean +- SD). The corresponding difference in muscle-tendon unit length between 0.52 and 3.49 rad/s, estimated from the peak torque angle shift and moment arm length change of the quadriceps muscles, was 9 +- 4 mm. The relationship between estimated changes in muscle-tendon unit length and muscle force of the vastus lateralis and intermedius (VLI) over the seven velocities (including isometric contraction) coincided with the load-elongation properties of the series elastic component of VLI, determined separately in vivo by ultrasonography when the same subjects performed a ramp isometric knee extension. The results suggest that the torque-angle relationship is affected by the interaction between contractile and elastic components, and that peak torque angle shift is attributable to the elongation of tendinous tissues as a function of force applied to them.