Adaptation of the walking pattern to uphill walking in normal and spinal-cord injured subjects

Lower-limb movements and muscle-activity patterns were assessed from seven normal and seven ambulatory subjects with incomplete spinal-cord injury (SC I) during level and uphill treadmill walking (5, 10 and 15 degrees). Increa sing the treadmill grade from 0 degrees to 15 degrees induced an increasing ly flexed posture of the hip, knee and ankle during initial contact in all normal subjects, resulting in a larger excursion throughout stance. This ad aptation process actually began in mid-swing with a graded increase in hip flexion and ankle dorsiflexion as well as a gradual decrease in knee extens ion. In SCI subjects, a similar trend was found at the hip joint for both s wing and stance phases, whereas the knee angle showed very limited changes and the ankle angle showed large variations with grade throughout the walki ng cycle. A distinct coordination pattern between the hip and knee was obse rved in normal subjects, but not in SCI subjects during level walking. The same coordination pattern was preserved in all normal subjects and in five of seven SCI subjects during uphill walking. The duration of electromyograp hic (EMG) activity of thigh muscles was progressively increased during uphi ll walking, whereas no significant changes occurred in leg muscles. In SCI subjects, EMG durations of both thigh and leg muscles, which were already a ctive throughout stance during level walking, were not significantly affect ed by uphill walking. The peak amplitude of EMG activity of the vastus late ralis, medial hamstrings, soleus, medial gastrocnemius and tibialis anterio r was progressively increased during uphill walking in normal subjects. In SCI subjects, the peak amplitude of EMG activity of the medial hamstrings w as adapted in a similar fashion, whereas the vastus lateralis, soleus and m edial gastrocnemius showed very limited adaptation during uphill walking. W e conclude that SCI subjects can adapt to uphill treadmill walking within c ertain limits, but they use different strategies to adapt to the changing l ocomotor demands.