The Differential Effects of Fast Walking Speed on Muscle Coactivation in the Paretic and Non-Paretic Extremities Post-Stroke

Background: Clinical practice guidelines for walking recovery post-stroke recommend high aerobic intensity training, which usually involves walking at fast speeds. However, the acute effect of fast speeds on the neuromuscular control of walking is unclear. Objectives: (1) Assess the criterion validity of the Dynamic Motor Control Index (WalkDMC) as a measure of coactivation post-stroke. (2) Assess acute speed-dependent coactivation post-stroke. (3) Assess how clinical characteristics shape the speed-dependent coactivation response. (4) Assess the relationship between heart rate and coactivation post-stroke. We hypothesized that WalkDMC is correlated with function and impairment measures. We also hypothesize that coactivation measured via the WalkDMC increases for speeds above or below self-selected speeds (SSS). Methods: 32 chronic stroke survivors and 17 age and sex-matched controls walked at SSS, fast, and slow speeds. EMGs were measured bilaterally on 7 lower extremity muscles. We used non-negative matrix factorization to calculate WalkDMC. We used regression to assess the relationship between WalkDMC, speed, heart rate, and clinical outcomes. Results: WalkDMC was correlated with clinical outcomes, supporting its criterion validity. We observed a quadratic relationship between speed and coactivation: for the paretic extremity, the predicted speed that would lead to the lowest coactivation was ~120% higher than SSS. Slow speeds consistently increased coactivation in controls and participants post-stroke. Coactivation in the paretic extremity was significantly predicted by speed, balance, and impairment. Conclusions: Our results suggest that increased speeds lead to differential improvements in coactivation in the paretic and non-paretic extremities. These results may inform speed prescriptions for HIT interventions.