OBJECTIVE—To compare the pattern of pelvic girdle muscle activation in normal subjects and hemiparetic patients while stepping and maintaining standing balance. DESIGN—Group comparison. METHOD—Seventeen patients who had regained the ability to walk after a single hemiparetic stroke were studied together with 16 normal controls. Median interval between stroke and testing was 17 months. Amplitude and onset latency of surface EMG activity in hip abductors and adductors were recorded in response to sideways pushes in either direction while standing. Similar recordings were made in the same subjects during gait initiation and a single stride. RESULTS—In the standing balance task, normal subjects resisted a sideways push to the left with the left gluteus medius (74 ms) and with the right adductor (111 ms), and vice versa. In hemiparetic patients, the amplitude of activity was reduced in the hemiparetic muscles, the onset latencies of which were delayed (gluteus medius 96 ms, adductor 144 ms). Contralateral, non-paretic, adductor activity was increased after a push towards the hemiparetic side of patients with stroke and the latency was normal (110 ms). During self initiatedsideways weight shifts at gait initiation, hemiplegic muscle activationwas impaired. By contrast, the pattern and peak amplitude of hip muscleactivation in stepping was normal in both hemiparetic andnon-hemiparetic muscles of the subjects with stroke. CONCLUSIONS—Inambulant patients with stroke, a normal pattern of activation ofhemiparetic muscles is seen in stepping whereas the response of thesemuscles to a perturbation while standing remains grossly impaired andis compensated by increased activity of the contralateral muscles. Thissuggests that hemiparetic patients should be able to step beforeregaining standing balance.
