Abstract
OBJECTIVE: To determine whether the common practice of estimating energy cost of walking (CW) using only aerobic energy (oxygen consumption, O (2) ) while excluding anaerobic energy (excess carbon dioxide production, CO (2) ) introduces systematic and/or random error into the CW change estimates in individuals with chronic stroke. DESIGN SETTING AND PARTICIPANTS: The HIT-Stroke Trial randomized 55 individuals with walking limitations in chronic stroke to moderate or high intensity walking training. INTERVENTION: Both groups performed walking exercise 3 times per week for 12 weeks. MAIN OUTCOME: Treadmill graded exercise testing with metabolic data collection was performed after 0, 4, 8, and 12 weeks of walking training. Mean CW changes (averaged across 4, 8 and 12 weeks) were estimated using only O (2) (CW (O2) ) versus using both O (2) and CO (2) (CW (O2+CO2) ). CW changes were calculated during the final 3 minutes of each exercise test (i.e. peak-speed ) and during equivalent speeds of the last 3 minutes of the shortest exercise test (i.e, matched-speed ). Linear mixed-effects models and bootstrapping were used to compare CW change estimates and their standard errors (SE) between CW (O2) and CW (O2+CO2) . RESULTS: At peak-speed , CW (O2) showed similar changes to CW (O2+CO2) (difference: -0.04 J/kg/m, 95% CI: -0.09, 0.03), and had the same relative SE (coefficient of variation difference: 0.0% [-0.9, 0.7]). At matched-speeds , CW (O2) underestimated improvements by 18.2% (0.08 J/kg/m, 95% CI: 0.04, 0.15) compared to CW (O2+CO2) , and had higher relative SE (+10.3% [5.7, 13.5]). CONCLUSION: Disregarding anaerobic contributions (excess CO (2) ) during CW calculation may result in underestimation of training-related improvement and reduce measurement precision when estimating CW changes at matched-speeds .