Day-to-day variation in oxygen consumption and energy expenditure during submaximal treadmill walking in female adolescents

The day-to-day variation in oxygen consumption (V˙O ₂) and energy expenditure (EE) during horizontal treadmill walking was measured using indirect calorimetry in 20 female adolescents (mean age 17·3 years). Two different walking speeds were used: 5 km h^?1 and an individually convenient speed of 3·0 km h^?1 (mean). The two sets of measurements were performed on 2 consecutive days, and great care was taken to minimize possible disturbing factors. The mean V˙O ₂ was 919 ml min^?1 at 5 km h^?1 and 622 ml min^?1 at the individual speed, and the mean values of EE were 4·5 kcal min^?1 and 3·1 kcal min^?1 respectively. The individual day-to-day variation in V˙O ₂ (at 5 km h^?1) was between ?11·7% and +12·6% of the mean V˙O ₂. The coefficient of variation (CV) was 6·4% when values were calculated in ml min^?1 kg^?1. The energy expenditure varied somewhat less between the 2 days (CV = 5·7%). The corresponding value for EE when walking at the individual speed was 7·2%, and the mean day-to day variation in V˙O ₂ was 7·5% (CV). The rate of perceived exertion according to Borg's scale was lower on day 2 (11·9) compared with day 1 (13·0) when walking at 5 km h^?1. There was no difference in heart rate between the 2 days. It is concluded that EE varies somewhat less than V˙O ₂ on successive days, probably because of an interchangeable relationship between breathing gases, depending on which substrate is used for combustion. When using V˙O ₂ and EE for evaluation of physical capacity, the day-to-day variation in the measurements must be taken into consideration.