Improved hemiparetic muscle activation in treadmill versus overground walking

Treadmill training is a promising tool for retraining gait after stroke. The treadmill induces an immediate shift toward symmetry and longer paretic stance times due to altered muscle activation (active) or the motorized belt (passive). The authors investigated vastus lateralis and medial hamstrings activation differences between treadmill and overground walking in participants with stroke. Methods. Vastus lateralis and medial hamstrings surface electromyography was recorded during velocity-matched overground and treadmill walking in 19 chronically hemiparetic subjects. Variables from ensemble averages of electromyography included burst onset and offset times (% cycle), duration (% cycle), integrated amplitude (m V (.) % cycle), and onset relative to foot strike (% cycle). Conditions were compared using paired t-tests (alpha = 0.05). Results. Paretic vastus lateralis onset occurred earlier in the treadmill condition (overground: 47.1%, treadmill: 41.9%, P = 0.01). For nonparetic vastus lateralis in the treadmill condition, onset occurred later (overground: 85.2%, treadmill: 87.6%, P = 0.09), offset occurred earlier (overground: 54.7%, treadmill: 47.8%, P = 0.03), duration was shorter (overground: 69.1%, treadmill: 61.2%, P = 0.01), and integrated amplitude was lower (overground: 14.1, treadmill: 10.6, P = 0.05). Within limbs, paretic vastus lateralis onset occurred earlier relative to paretic foot strike. Nonparetic vastus lateralis onset occurred later relative to nonparetic foot strike. Conclusions. Treadmill walking induces immediate changes in vastus lateralis, but not medial hamstrings, activation patterns. These alterations (earlier paretic vastus lateralis onset and later nonparetic vastus lateralis onset) during treadmill versus overground walking parallel the increased symmetry in gait patterning.