title: 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 (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 (Vo(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 Vo(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 Vo(2max) to quantify substrate metabolism. Substantial interindividual variability in training-induced adaptations was observed for most parameters, yet "low responders" for DeltaVo(2max) were not consistently low responders for other variables. While Vo(2max) and time trial performance were related at baseline (r(2) = 0.80, P < 0.001), the change in Vo(2max) was completely unrelated to the change in aerobic performance. The maximal parameters DeltaVe(max) and DeltaVeq(max) (DeltaVe/Vo(2max)) accounted for 64% of the variance in DeltaVo(2max) (P < 0.001), whereas Deltaperformance was related to changes in the submaximal parameters Veq(submax) (r(2) = 0.33; P < 0.01), muscle Deltalactate (r(2) = 0.32; P < 0.01), and Deltaacetyl-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.
authors.affiliation: The Wenner-Gren Institute, Arrhenius Laboratories, Stockholm Univ., Sweden.
authors.forename: Niels B J
authors.initials: NB
authors.lastname: Vollaard
authors.forename: Dimitru
authors.initials: D
authors.lastname: Constantin-Teodosiu
authors.forename: Katarina
authors.initials: K
authors.lastname: Fredriksson
authors.forename: Olav
authors.initials: O
authors.lastname: Rooyackers
authors.forename: Eva
authors.initials: E
authors.lastname: Jansson
authors.forename: Paul L
authors.initials: PL
authors.lastname: Greenhaff
authors.forename: James A
authors.initials: JA
authors.lastname: Timmons
authors.forename: Carl Johan
authors.initials: CJ
authors.lastname: Sundberg
mesh_terms: D000108:Acetylcarnitine / Q000032:analysis / Q000378:metabolism; D000222:Adaptation, Physiological / Q000502:physiology*; D000251:Adenosine Triphosphatases / Q000032:analysis / Q000378:metabolism; D000328:Adult; D001706:Biopsy; D002950:Citrate (si)-Synthase / Q000032:analysis / Q000378:metabolism; D042967:Electron Transport Complex I / Q000032:analysis / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000032:analysis / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D019344:Lactic Acid / Q000032:analysis / Q000378:metabolism; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D016133:Polymerase Chain Reaction; D052097:Quadriceps Muscle / Q000737:chemistry / Q000378:metabolism; D055815:Young Adult
chemical_list: D019344:Lactic Acid; D000108:Acetylcarnitine; D003576:Electron Transport Complex IV; D002950:Citrate (si)-Synthase; D000251:Adenosine Triphosphatases; D042967:Electron Transport Complex I