The Interplay Between Walking Speed, Economy, and Stability After Stroke

Background and Purpose: Energy minimization is thought to underlie the naturally selected, preferred walking speed; however, people post-stroke walk slower than their most economical speed, presumably to optimize other objectives, such as stability. The purpose of this study was to examine the interplay between walking speed, economy, and stability. Methods: Seven individuals with chronic hemiparesis walked on a treadmill at 1 of 3 randomized speeds: slow, preferred, and fast. Concurrent measurements of speed-induced changes in walking economy (ie, the energy needed to move 1 kg of bodyweight 1 ml O-2/kg/m) and stability were made. Stability was quantified as the regularity and divergence of the mediolateral motion of the pelvic center of mass (pCoM) during walking, as well as pCoM motion relative to the base of support. Results: Slower walking speeds were more stable (ie, pCoM motion was 10% +/- 5% more regular and 26% +/- 16% less divergent) but 12% +/- 5% less economical. Conversely, faster walking speeds were 9% +/- 8% more economical, but also less stable (ie, pCoM motion was 17% +/- 5% more irregular). Individuals with slower walking speeds had an enhanced energetic benefit when walking faster (r(s) = 0.96, P < 0.001). Individuals with greater neuromotor impairment had an enhanced stability benefit when walking slower (r(s) = 0.86, P = 0.01). Discussion and Conclusions: People post-stroke appear to prefer walking speeds that are faster than their most stable speed but slower than their most economical speed. The preferred walking speed after stroke appears to balance stability and economy. To encourage faster and more economical walking, deficits in the stable control of the mediolateral motion of the pCoM may need to be addressed.