title: VO2 kinetics and performance in soccer players after intense training and inactivity.
abstract: OBJECTIVE
  The study's purpose was to examine the effects of a short-term period with intensified training or training cessation of trained soccer players on VO(2) kinetics at 75% maximal aerobic speed, oxidative enzymes, and performance in repeated high-intensity exercise.
  
  
  METHODS
  After the last match of the season, 18 elite soccer players were, for a 2-wk period, assigned to a high-intensity training group (n = 7) performing 10 training sessions mainly consisting of aerobic high-intensity training (8 × 2 min) and speed endurance training (10-12 × 30-s sprints) or a training cessation group (n = 11) that refrained from training.
  
  
  RESULTS
  For the training cessation group, VO(2) kinetics became slower (P < 0.05) with a larger time constant (τ = 21.5 ± 2.9 vs 23.8 ± 3.2 s (mean ± SD, before vs after)) and a larger mean response time (time delay + τ = 45.0 ± 1.8 vs 46.8 ± 2.2 s). The amount of muscle pyruvate dehydrogenase (17%, P < 0.01) and maximal activity of citrate synthase (12%) and 3-hydroxyacyl-CoA (18%, P < 0.05) were lowered. In addition, the fraction of slow twitch fibers (56% ± 18% vs 47% ± 15%, P < 0.05), Yo-Yo intermittent recovery level 2 test (845 ± 160 vs 654 ± 99 m), and the repeated sprint performance (33.41 ± 0.96 vs 34.11 ± 0.92 s, P < 0.01) were reduced. For the high-intensity training group, running economy was improved (P < 0.05), and the amount of pyruvate dehydrogenase (17%) and repeated sprint performance (33.44 ± 1.17 vs 32.81 ± 1.01 s) were enhanced (P < 0.05).
  
  
  CONCLUSIONS
  Inactivity slows VO(2) kinetics in association with a reduction of muscle oxidative capacity and repeated high-intensity running performance. In addition, intensified training of already well-trained athletes can improve mechanical efficiency and repeated sprint performance.
authors.affiliation: Copenhagen Muscle Research Centre, Department of Exercise and Sport Sciences, Section of Human Physiology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Christensen
authors.forename: Peter
authors.initials: P
authors.lastname: Krustrup
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Gunnarsson
authors.forename: Kristian
authors.initials: K
authors.lastname: Kiilerich
authors.forename: Lars
authors.initials: L
authors.lastname: Nybo
authors.forename: Jens
authors.initials: J
authors.lastname: Bangsbo
mesh_terms: D000328:Adult; D056352:Athletes; D054874:Athletic Performance / Q000502:physiology*; D002950:Citrate (si)-Synthase / Q000032:analysis; D006801:Humans; D008297:Male; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism / Q000502:physiology; D010101:Oxygen Consumption / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology; D011768:Pyruvate Dehydrogenase Complex / Q000032:analysis; D012420:Running / Q000502:physiology; D012916:Soccer / Q000502:physiology*; D055815:Young Adult
chemical_list: D011768:Pyruvate Dehydrogenase Complex; D002950:Citrate (si)-Synthase