The relationship between relative aerobic load, energy cost, and speed of walking in individuals post-stroke

Background Individuals post-stroke walk slower than their able-bodied peers, which limits participation. This might be attributed to neurological impairments, but could also be caused by a mismatch between aerobic capacity and aerobic load of walking. Research question What is the potential impact of aerobic capacity and aerobic load of walking on walking ability post-stroke? Methods In a cross-sectional study, forty individuals post-stroke (more impaired N=21; preferred walking speed (PWS)<0.8m/s, less impaired N=19), and 15 able-bodied individuals performed five, 5-minute treadmill walking trials at 70%, 85%, 100%, 115% and 130% of PWS. Energy expenditure (mlO 2 /kg/min) and energy cost (mlO 2 /kg/m) were derived from oxygen uptake . Relative load was defined as energy expenditure divided by peak aerobic capacity and by at ventilatory threshold . Relative load and energy cost at PWS were compared between groups with one-way ANOVA’s. The effect of speed on these parameters was modeled with GEE. Results Both more and less impaired individuals post-stroke showed lower PWS than able-bodied controls (0.44[0.19-0.76] and 1.04[0.81-1.43] vs 1.36[0.89-1.53] m/s) and higher relative load at PWS (50.2±14.4 and 51.7±16.8 vs peak and 101.9±20.5 and 97.0±27.3 vs ). No differences in relative load were found between stroke groups. Energy cost at PWS of more impaired (0.30[.19-1.03] mlO 2 /kg/m) was higher than less-impaired (0.19[0.10-0.24] mlO 2 /kg/m) and able-bodied (0.15[0.13-0.18] mlO 2 /kg/m). For post-stroke individuals, increasing walking speed above PWS decreased energy cost, but resulted in a relative load above endurance threshold. Significance Individuals post-stroke seem to reduce walking speed to prevent unsustainably high relative aerobic loads at the expense of reduced economy. When aiming to improve walking ability in individuals post-stroke, it is important to consider training aerobic capacity.