Kinematics of the compensatory step by the trailing leg following an unexpected forward slip while walking.

In this study, we described the joint angle changes of the trailing leg during the compensatory step used to recover balance following a forward slip while walking. Fifteen healthy young males walked on a walkway which incorporated a movable platform to simulate a forward slip while walking. In 12 out of the 15 subjects, the trailing leg was rapidly lowered during the swing phase and was placed on the ground behind the slipping foot following the onset of the slip. Time taken for the onset of the slip to the placing of the trailing foot was 0.28+/-0.03 s. The amount of hip flexion lessened after 52% of the normalized time, with 0% being the onset of the platform movement and 100% representing the placing of the trailing foot on the ground. The flexed knee began to extend at 72% of the normalized time, which continued until the foot was firmly placed. The plantarflexed ankle began to dorsiflex at 56% of the normalized time, the angle of which peaked at the moment the toe made contact with the walkway again-the end of the movement. These findings aided us in understanding the mechanism underlying the compensatory step to recover the loss of balance caused by a forward slip while walking.