Biological variation in variables associated with exercise training.

To be able to identify a training induced change in a certain variable, it is necessary to know the background variation. In this study the coefficient of variation (total, between-subjects, within-subjects), the relative sources of variance (between-subjects and within-subjects), and the critical difference (within-subjects) were estimated in four categories of variables (performance and physiological variables, metabolic and hormonal variables, immunological variables, and mood state variables) in 15 moderately trained male runners measured on three different occasions over a period of 7 weeks. In the performance and physiological variables, 78.9 % of the variance was due to variation between subjects and they had the lowest critical difference (11.9 %). In contrast, the metabolic and hormonal variables had the highest critical difference (59.9 %) and 53.4 % of the variance was due to variations within subjects. The immunological and psychological variables had about two thirds of the variance arising from variation between subjects. However, the critical difference for the immunological variables was high (47.4 %), while it was relatively low for the psychological variables (26.8 %). The low critical difference and variation within subjects of the psychological and in particular the performance and physiological variables indicate that they may be beneficial as primary markers of training induced changes.