The role of postural control in the association between aerobic capacity and walking capacity in chronic stroke: A cross-sectional analysis

BACKGROUND: Reports on the association between aerobic capacity and walking capacity in people after stroke show disparate results. AIM: The aim of this study was to determine: 1) if the predictive validity of peak oxygen uptake (VO_2peak) for walking capacity post stroke is different from that of maximal oxygen uptake (VO_2max), and 2) if postural control, hemiplegic lower extremity muscle strength, age and gender distort the association between aerobic capacity and walking capacity. DESIGN: Cross-sectional study. SETTING: General community in Utrecht, The Netherlands. POPULATION: Community-dwelling people more than three months after stroke. METHODS: Measurement of aerobic capacity were performed with cardiopulmonary exercise testing (CPET) and differentiated between the achievement of VO_2peak or VO_2max. Measurement of walking capacity with the 6-Minute Walk Test (6MWT), postural control with the Performance-Oriented Mobility Assessment (POMA) and hemiplegic lower extremity muscle strength with the Motricity Index (MI-LE). RESULTS: Fifty-one out of 62 eligible participants, aged 64.7±12.5 years were included. Analysis of covariance (ANCOVA) showed a non-significant difference between the predictive validities of VO_2max (N.=22, β=0.56; 95% CI: 0.12-0.97) and VO_2peak (N.=29, β=0.72; 95% CI: 0.38-0.92). Multiple regression analysis of the pooled sample showed a significant decrease in the β value of VO_2peak (21.6%) for the 6MWT when adding the POMA as a covariate in the association model. VO_2peak remained significantly related to 6MWT after correcting for the POMA (β=0.56, 95% CI: 0.39-0.75). CONCLUSIONS: The results suggest similar predictive validity of aerobic capacity for walking capacity in participants achieving VO_2max compared to those only achieving VO_2peak. Postural control confounds the association between aerobic capacity and walking capacity. Aerobic capacity remains a valid predictor of walking capacity. CLINICAL REHABILITATION IMPACT: Aerobic capacity is an important factor associated with walking capacity after stroke. However, to understand this relationship, postural control needs to be measured. Both aerobic capacity and postural control may need to be addressed during interventions aiming to improve walking capacity after stroke.