Daily variability in exercise ventilation.

The purpose of this study was to quantify daily variability in ventilation (VE) during submaximal exercise and establish the number of testing sessions required to produce stable exercise ventilation measures. Following 60 min of treadmill accommodation, four male (M) and four female (F) distance runners completed 5 weeks of daily treadmill testing at the same time of day while engaged in a normal routine of training and racing. During each test session, subjects completed three 6-min level treadmill runs at either 3.13, 3.57, and 4.02 m.sec-1 for F or 3.57, 4.02, and 4.47 m.sec-1 for M. Measures of VE were obtained during the last 2 min of each 6-min run. Results indicated that the mean coefficient of variation (CV) for VE across speeds was 4.33%. Reliability analyses examining all possible combinations of testing days over the 5-week period revealed that 97% of the variation in mean VE was accounted for in either 2 consecutive or non-consecutive days, while 98% of the variation in mean VE was accounted for in 5 consecutive days. These data suggest that when treadmill exposure and circadian variation are controlled, intraindividual differences in exercise VE are relatively small in male and female subjects following an unrestricted program of training and competitive racing. Additionally, acceptably stable VE values in this cohort can be derived by averaging duplicate measures obtained from consecutive or non-consecutive testing sessions.