title: The slow component of oxygen uptake during intense, sub-maximal exercise in man is associated with additional fibre recruitment.
abstract: Single muscle fibre metabolites and pulmonary oxygen uptake (VO2) were measured during moderate and intense, sub-maximal exercise to test the hypothesis that additional fibre recruitment is associated with the slow component of VO2. Seven healthy, male subjects performed 20 min moderate (MOD, approximately 50% of VO(2,max)) and intense (INT, approximately 80% VO(2,max)) cycling at 70 rpm. Glycogen content decreased significantly in type I and IIa fibres during INT, but only in type I fibres during MOD. During INT, creatine phosphate (CP) content decreased significantly both in types I and II fibres in the first 3 min (DeltaCP: 16.0+/-2.7 and 16.8+/-4.7 mmol kg(-1) d.w., respectively) and in the next 3 min (DeltaCP: 16.2+/-4.9 and 25.7+/-6.7 mmol kg(-1) d.w., respectively) with no further change from 6-20 min. CP content was below the pre-exercise level (mean-1 SD) in 11, 37, 70 and 74% of the type I fibres after 0, 3, 6 and 20 min of INT, respectively, and in 13, 45, 83 and 74% of the type II fibres. During INT, VO2 increased significantly by 6+/-1 and 4+/-1% in the periods 3-6 and 6-20 min, respectively (Delta VO(2,(6-3 min)): 0.14+/-0.02 l min(-1)), whereas VO2 was unchanged from 3 to 20 min of MOD. Exponential fitting revealed a slow component of VO2 during INT that appeared after approximately 2.6 min and amounted to 0.24 l min(-1). The present study demonstrates that additional type I and II fibres are recruited with time during intense sub-maximal exercise in temporal association with a significant slow component of VO2.
authors.affiliation: Institute of Exercise and Sport Sciences, Department of Human Physiology, August Krogh Institute, University of Copenhagen, Universitetsparken 13, 2100 Copenhagen Ø, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Krustrup
authors.forename: Karin
authors.initials: K
authors.lastname: Söderlund
authors.forename: Magni
authors.initials: M
authors.lastname: Mohr
authors.forename: Jens
authors.initials: J
authors.lastname: Bangsbo
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D006801:Humans; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology*
chemical_list: D010100:Oxygen