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

Vollaard NB, Constantin-Teodosiu D, Fredriksson K, Rooyackers O, Jansson E, Greenhaff PL, Timmons JA, Sundberg CJ. Systematic analysis of adaptations in aerobic capacity and submaximal energy metabolism provides a unique insight into determinants of human aerobic performance. J Appl Physiol 106: 1479-1486, 2009. First published February 5, 2009; doi:10.1152/japplphysiol.91453.2008.-It has not been established which physiological processes contribute to endurance training-related changes (Delta) 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) over dotO(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 (V) over dotO(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) over dotO(2max) to quantify substrate metabolism. Substantial interindividual variability in training-induced adaptations was observed for most parameters, yet "low responders" for Delta(V) over dotO(2max) were not consistently low responders for other variables. While (V) over dotO(2max) and time trial performance were related at baseline (r(2) = 0.80, P < 0.001), the change in (V) over dotO(2max) was completely unrelated to the change in aerobic performance. The maximal parameters Delta(V) over dotE(max) and Delta Veq(max) (Delta(V) over dotE/(V) over dotO(2max)) accounted for 64% of the variance in Delta(V) over dotO(2max) (P < 0.001), whereas Delta performance was related to changes in the submaximal parameters Veq(submax) (r(2) = 0.33; P < 0.01), muscle Delta lactate (r(2) = 0.32; P < 0.01), and Delta acetyl-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.