High- and low-ankle flexibility and motor task performance.

The effect of widely differing but normal passive ankle flexibility on function was investigated by using able-bodied males selected from the upper and lower tails of a group normally distributed for passive dorsiflexion (DF) flexibility. Ankle, knee and hip kinematics, and kinetics were quantified during stair descent, walking and standing up. The effect of DF flexibility was apparent during stair descent, but not in standing up or walking. Mean peak DF in stance phase of stair descent was 11.5 degrees lower for 'inflexible' compared with 'flexible' subjects, but the net moment about the ankle at peak DF and the timing of peak DF were comparable between groups.