Systematic analysis of adaptations in aerobic capacity and submaximal energy metabolism provides a unique insight into determinants of human aerobic performance

Abstract

It has not been established which physiological processes contribute to endurance training-related changes (Δ) in aerobic performance. For example, the relationship between intramuscular metabolic responses at the intensity used during training and improved human functional capacity has not been examined in a longitudinal study. In the present study we hypothesized that improvements in aerobic capacity (V̇O 2max) and metabolic control would combine equally to explain enhanced aerobic performance. Twenty-four sedentary males (24 ± 2 yr; 1.81 ± 0.08 m; 76.6 ± 11.3 kg) undertook supervised cycling training (45 min at 70% of pretraining V̇O 2max) 4 times/wk for 6 wk. Performance was determined using a 15-min cycling time trial, and muscle biopsies were taken before and after a 10-min cycle at 70% of pretraining V̇O 2max to quantify substrate metabolism. Substantial interindividual variability in training-induced adaptations was observed for most parameters, yet "low responders" for ΔV̇O 2max were not consistently low responders for other variables. While V̇O 2max and time trial performance were related at baseline (r 2 = 0.80, P < 0.001), the change in V̇O 2max was completely unrelated to the change in aerobic performance. The maximal parameters ΔV̇E max and ΔVeq max (ΔV̇E/V̇O 2max) accounted for 64% of the variance in ΔV̇O 2max (P < 0.001), whereas Δperformance was related to changes in the submaximal parameters Veq submax (r 2 = 0.33; P < 0.01), muscle Δlactate (r 2 = 0.32; P < 0.01), and Δacetyl-carnitine (r 2 = 0.29; P < 0.05). This study demonstrates that improvements in high-intensity aerobic performance in humans are not related to altered maximal oxygen transport capacity. Altered muscle metabolism may provide the link between training stimulus and improved performance, but metabolic parameters do not change in a manner that relates to aerobic capacity changes.