Purpose: Given percentages of VO2max are widely used for training and study purposes although they might not result in homogeneous metabolic strain. Therefore, the homogeneity of metabolic responses to prolonged exercise at fixed percentages of VO2max should be investigated. Procedures: Twenty-one healthy male subjects (29±5 years, 77±8kg, VO2max: 59.9±11.8mlmin-1kg-1) performed two incremental tests to exhaustion on a cycle ergometer to determine VO2max. Subsequently, two 60min tests at 60 and 75% VO2max were conducted in randomised order. VO2 was kept constant by adjusting the work rate. Blood lactate (La) responses as primary outcome variable to quantify metabolic strain were assessed. Findings: Mean La was 2.1±1.1mmoll-1 (min-max: 0.7-5.6mmoll-1) during the 60% VO2max test and 4.6±1.9 mmol l-1 (min-max: 2.2-8.0 mmol l-1) during the 75% VO2max test. The coefficients of variation of La amounted for 52.4 and 41.3% during the 60 and 75% VO2max test, respectively. La responses did not differ significantly between three subgroups of the subjects (N =7 with VO2max<55mlmin-1kg-1, N=7 with VO2max 55-65mlmin-1kg-1, and N=7 with VO2max>65 mlmin-1kg-1; P>=0.08). Conclusion: Altogether, prolonged exercise at given percentages of VO2max leads to inhomogeneous metabolic strain as indicated by the large variability of La responses. This holds true even in subgroups of similar aerobic capacity. Thus, intensity prescription for endurance training and study purposes should not be solely based upon percentages of VO2max when a comparable metabolic strain is intended.
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