Repeated measurement of the gas exchange threshold: relative size of measurement and biological variabilities.

If an individual's gas exchange threshold (GET) is measured on several separate occasions, without a change in aerobic fitness, a random variability will be observed. However, it is not known how much of this variability is biologically determined and how much results from variability in the calibration and measurement processes. The statistical re-sampling technique of Bootstrapping was used to estimate the variability of the GET on a single occasion. This analysis provides the first estimate of the combined contribution of breath-by-breath measurement and calibration processes (6%), to the total between-occasion random variability, leaving biological variability to account for the remainder of the imprecision in the measurement of the GET.