MECHANICALLY INDUCED STUMBLING DURING HUMAN TREADMILL WALKING

A new method to study the reactions to unexpected mechanical perturbat ions during human walking on a treadmill is presented. Perturbations c onsisted of an obstruction of the forward swinging foot during the ear ly swing phase. These were caused by obstacles which were dropped on t he treadmill in front of the subject. The timing of the perturbation w as controlled by an electromagnet which released the obstacle at a pre programmed delay after left or right heel strike. This kind of perturb ation evoked stumbling reactions. The electromyographic (EMG) response s during these stumbling reactions had mean latencies of 76 ms in both the ipsilateral biceps femoris and rectus femoris when perturbations were applied in early swing. During the perturbed swing, increased fle xion in the knee occurred to lift the foot over the obstacle. Both the EMG and kinesiologic responses were reproducible when perturbations w ere presented in the same part of the swing phase of different step cy cles.