Human locomotion must be flexible in order to meet varied environmental demands. Alterations to the gait pattern occur on different time scales, ranging from fast, reactive adjustments to slower, more persistent adaptations. A recent study in humans demonstrated that the cerebellum plays a key role in slower walking adaptations in interlimb coordination during split-belt treadmill walking, but not fast reactive changes. It is not known whether cerebral structures are also important in these processes, though some studies of cats have suggested that they are not. We used a split-belt treadmill walking task to test whether cerebral damage from stroke impairs either type of flexibility. Thirteen individuals who had sustained a single stroke more than 6 months prior to the study (four females) and 13 age- and gender-matched healthy control subjects were recruited to participate in the study. Results showed that stroke involving cerebral structures did not impair either reactive or adaptive abilities and did not disrupt storage of new interlimb relationships (i.e. after-effects). This suggests that cerebellar interactions with brainstem, rather than cerebral structures, comprise the critical circuit for this type of interlimb control. Furthermore, the after-effects from a 15-min adaptation session could temporarily induce symmetry in subjects who demonstrated baseline asymmetry of spatiotemporal gait parameters. In order to re-establish symmetric walking, the choice of which leg is on the fast belt during split-belt walking must be based on the subject's initial asymmetry. These findings demonstrate that cerebral stroke survivors are indeed able to adapt interlimb coordination. This raises the possibility that asymmetric walking patterns post-stroke could be remediated utilizing the split-belt treadmill as a long-term rehabilitation strategy.

Background and Purpose-Physical inactivity propagates disability after stroke through physical deconditioning and learned nonuse. We investigated whether treadmill aerobic training (T-AEX) is more effective than conventional rehabilitation to improve ambulatory function and cardiovascular fitness in patients with chronic stroke. Methods-Sixty-one adults with chronic hemiparetic gait after ischemic stroke (Ͼ6 months) were randomized to 6 months (3ϫ/week) progressive T-AEX or a reference rehabilitation program of stretching plus low-intensity walking (R-CONTROL). Peak exercise capacity (VO 2 peak), O 2 consumption during submaximal effort walking (economy of gait), timed walks, Walking Impairment Questionnaire (WIQ), and Rivermead Mobility Index (RMI) were measured before and after 3 and 6 months of training. Results-Twenty-five patients completed T-AEX and 20 completed R-CONTROL. Only T-AEX increased cardiovascular fitness (17% versus 3%, ␦% T-AEX versus R-CONTROL, PϽ0.005). Group-by-time analyses revealed T-AEXimproved ambulatory performance on 6-minute walks (30% versus 11%, PϽ0.02) and mobility function indexed by WIQ distance scores (56% versus 12%, PϽ0.05). In the T-AEX group, increasing training velocity predicted improved VO 2 peak (rϭ0.43, PϽ0.05), but not walking function. In contrast, increasing training session duration predicted improved 6-minute walk (rϭ0.41, PϽ0.05), but not fitness gains. Conclusions-T-AEX