It has not been established which physiological processes contribute to endurance training-related changes (?) 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 (V?O2max) 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 V?O 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 V?O2max to quantify substrate metabolism. Substantial interindividual variability in training-induced adaptations was observed for most parameters, yet "low responders" for ?V?O2max were not consistently low responders for other variables. While V?O2max and time trial performance were related at baseline (r2 = 0.80, P < 0.001), the change in V?O 2max was completely unrelated to the change in aerobic performance. The maximal parameters ?V?Emax and ?Veqmax (?V?E/V?O2max) accounted for 64% of the variance in ?V?O2max (P < 0.001), whereas ?performance was related to changes in the submaximal parameters Veqsubmax (r 2 = 0.33; P < 0.01), muscle ?lactate (r2 = 0.32; P < 0.01), and ?acetyl-carnitine (r2 = 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. Copyright © 2009 the American Physiological Society.
- Low responder
- Maximal oxygen uptake capacity