Medbø Responds to Bangsbo's Paper

Abstract

I have several comments to Bangsbo's paper. My main points are organised so that they appear in the same order as the issues addressed in Bangsbo's paper. 1. The anaerobic capacity is exhausted when the muscle lactate concentration reaches a maximum value, which for humans may be around 30 mmol . kg-' wet muscle mass. When the muscle glycogen concentration is normal before exercise, exhaustion is reached long before the glycogen stores are emptied. The energy sources are therefore not exhausted during high-intensi ty exercise. 2. There is no mathematical coupling in Figure 2 in M e d b ~ and Tabata ( 1993; Figure 2 in Bangsbo's paper). By expressing both entities as rates, the range of values is enlarged, thus allowing the study of the relationship between the two entities. If the exercise economy is reduced at high intensities or at the onset of exercise, thus requiring a disproportionately large rate of energy release, the points should be far below and to the right of the line of identity. This is not the case, and the analysis in this figure therefore suggests that the accumulated O2 deficit is an adequate measure of the anaerobic energy release during high-intensity bicycling. One reason for deviations from the line is differences between subjects (Medba et al., 1996). Linear regression within each group as proposed by Bangsbo is misleading. First, ordinary linear regression assumes that the x-value is determined without error and assigns all variability to the y-value. The error of determination is larger for the muscle metabolites (x) than for the O2 deficit (y) , and ordinary linear