Within- and between-day stability of treadmill walking VO2 in children with hemiplegic cerebral palsy

Within- and between-day stability in locomotor energy use was quantified in 13 children with hemiplegic cerebral palsy (CP). During testing, subjects were familiarized with the laboratory environment (Session 1), performed three 5 min level treadmill walks (Trials 1-3) at 0.67 m*s−1 (Session 2), and completed a single 5 min walk (Trial 4) at 0.67 m* s−1 (Session 3). In Sessions 2 and 3, heart rate (HR) was assessed and expired air was collected and analyzed to determine VO2. Data analyses revealed no significant difference (P>0.05) in either net VO2 (ml kg−1*min−1) or EEIHR (b*m−1) across the three trials performed in Session 2 and between average measures of net VO2 and EEIHR quantified in Session 2 and those obtained in Session 3. Mean within-day coefficient of variation (CV) values for net VO2 and EEIHR were 8.6%±8.5% and 13.9%±7.8%, respectively. Analysis of between-day variability and energy expenditure revealed a between-day CV value of 13.1% for net VO2 and 24.0% for EEIHR. In addition, significant inverse relationships between Gross Motor Function Measure (GMFM) scores and within- (r=−0.61) and between-day (r=−0.58) CV values for net VO2 were detected. Viewed in concert, these data suggest that fairly stable within- and between-day measures of locomotor energy expenditure during level treadmill walking can be achieved in subjects with hemiplegic CP if testing is preceded by a short period of treadmill accommodation. However, children with greater motor dysfunction may require an extended period of treadmill accommodation to reduce trial-to-trial variability in walking energy use.