Stiffness and passive peak force changes at the ankle joint: the effect of different joint angular velocities

Objective. To compare peak force and stiffness at the ankle joint in response to repetitive dorsiflexion at two joint angular velocities (5 and 25 deg s(-1)). Design. Pre- post-repeated measures design. Background. Stretching affects the biomechanical properties of tissues. In many instances, stretching is performed in a cyclic manner. An important factor that might influence the effects of stretching is the speed at which the tissues are lengthened. Methods. Eighteen healthy subjects participated. A dynamometer repeatedly moved the ankle joint from 0 deg of dorsiflexion to 80% of maximum dorsiflexion over a 2 min period. Two joint angular velocities were examined: 5 and 25 deg s(-1). Force and angle data were recorded simultaneously. Electromyographic activity from plantar and dorsiflexor muscles was monitored. The variables of interest were peak passive force and average stiffness at the first and last repetition of motion. Results. Peak force was significantly higher (P < 0.05) at 25 deg s(-1) for the first repetition. At both joint angular velocities, peak passive force decreased significantly over the 2 min of motion. The decreases were 13% and 21% at 5 and 25 deg s(-1) respectively. Peak passive force was not significantly different (P > 0.05) across velocities at 2 min. Stiffness was greater at 25 deg s(-1) initially (P < 0.05), however, it decreased significantly across time. The magnitude of the decrease was 20% and 31% at 5 and 25 deg s(-1) respectively. After 2 min of motion, there was no significant difference (P > 0.05) in stiffness across the joint angular velocities examined. Conclusion(s). The findings showed that while significant differences existed in stiffness and peak force across angular velocities at the start of the stretching motion, the differences decreased considerably with repeated motion, and were relatively similar within 2 min.