Day-to-day variation in oxygen consumption at submaximal loads during ergometer cycling by adolescents.

The day-to-day variation in oxygen consumption (VO2) during ergometer cycling by 20 healthy adolescents, 10 females and 10 males, was measured using indirect calorimetry. The two sets of measurements were performed on two consecutive days. Great care was taken to minimize possible disturbing factors. Cycling started at 50 and 100 W for female and male adolescents, respectively. The load was increased at a rate of 5 W 30 s(-1). In order to reach steady state, the load was kept constant for 3.5 min twice during the cycling session, at 100 and 130 W for the females and at 130 and 160 W for the males. Cycling continued until exhaustion. The maximal loads were 196 W (mean) and 271 W (mean) for females and males, respectively. At the maximal loads the day-to-day variation (+/-2 SD) in oxygen consumption (VO2) was +/-330 ml min(-1) for females and 390 ml min(-1) for males. At the submaximal loads the day-to-day variation in heart rate (HR) was 9.3 beats min(-1) (+/-2 SD) (coefficient of variation, CV=3.4% at 130 W) for both sexes. The day-to-day variation in oxygen consumption (VO2) was +/-199 ml min(-1) (+/-2 SD) at the different submaximal loads and did not differ between female and male adolescents (CV=5.7% at 130 W). This natural day-to-day variation must be taken into consideration when using a submaximal ergometer cycling test for the evaluation of physical capacity in the two sexes.