title: Progressive effect of endurance training on metabolic adaptations in working skeletal muscle.
abstract: We investigated the hypothesis that a program of prolonged endurance training, previously shown to decrease metabolic perturbations to acute exercise within 5 days of training, would result in greater metabolic adaptations after a longer training duration. Seven healthy male volunteers [O2 consumption = 3.52 +/- 0.20 (SE) l/min] engaged in a training program consisting of 2 h of cycle exercise at 59% of pretraining peak O2 consumption (VO2peak) 5-6 times/wk. Responses to a 90-min submaximal exercise challenge were assessed pretraining (PRE) and after 5 and 31 days of training. On the basis of biopsies obtained from the vastus lateralis muscle, it was found that, after 5 days of training, muscle lactate concentration, phosphocreatine (PCr) hydrolysis, and glycogen depletion were reduced vs. PRE (all P < 0.01). Further training (26 days) showed that, at 31 days, the reduction in PCr and the accumulation of muscle lactate was even less than at 5 days (P < 0.01). Muscle oxidative potential, estimated from the maximal activity of succinate dehydrogenase, was increased only after 31 days of training (+41%; P < 0.01). In addition, VO2peak was only increased (10%) by 31 days (P < 0.05). The results show that a period of short-term training results in many characteristic training adaptations but that these adaptations occurred before increases in mitochondrial potential. However, a further period of training resulted in further adaptations in muscle metabolism and muscle phosphorylation potential, which were linked to the increase in muscle mitochondrial capacity.
authors.affiliation: Department of Kinesiology, University of Waterloo, Ontario, Canada.
authors.forename: S M
authors.initials: SM
authors.lastname: Phillips
authors.forename: H J
authors.initials: HJ
authors.lastname: Green
authors.forename: M A
authors.initials: MA
authors.lastname: Tarnopolsky
authors.forename: G J
authors.initials: GJ
authors.lastname: Heigenhauser
authors.forename: S M
authors.initials: SM
authors.lastname: Grant
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D019343:Citric Acid / Q000378:metabolism; D004734:Energy Metabolism; D005947:Glucose / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010806:Physical Education and Training; D010807:Physical Endurance; D019289:Pyruvic Acid / Q000378:metabolism; D014280:Triglycerides / Q000378:metabolism
chemical_list: D010710:Phosphates; D014280:Triglycerides; D019343:Citric Acid; D019344:Lactic Acid; D019298:Glucose-6-Phosphate; D019289:Pyruvic Acid; D006003:Glycogen; D005947:Glucose