Length change of human gastrocnemius aponeurosis and tendon during passive joint motion

The extent of elongation and slackness of aponeurosis and tendon, and muscle fiber length of human medial gastrocnemius muscle are determined in vivo using ultrasonography. The ankle joint is passively moved at 50/s within the joint range of -36 to 7degrees (0degrees = neutral anatomic position; positive values for dorsiflexion) by a dynamometer while the length change of the aponeurosis and tendon is determined using ultrasonography (n = 8 men), Strain is calculated as the length change relative to the reference length of aponeurosis and tendon when the passive joint moment is 0. Elongation (positive strain Accepted after revision: February 10, 2002 values) of aponeurosis and tendon at 7degrees are 2.1 +/- 1.1 and 2.4 +/- 1.0%, respectively. The extent of slackness (negative strain values) of aponeurosis and tendon at -36degrees are -1.8 +/- 1.1 and -3.5 +/- 1.6%, respectively, and there is a significant difference between them (p < 0.05). This may be related to the existence of muscle fibers that attach to the aponeurosis over its whole length and do not allow it to fold. The results indicate that the length change of aponeurosis and tendon of medial gastrocnemius muscle occurs over the range of ankle joint positions even during passive joint motions. Copyright (C) 2002 S. Karger AG, Basel.