title: Prior heavy exercise eliminates VO2 slow component and reduces efficiency during submaximal exercise in humans.
abstract: We investigated the hypothesis that the pulmonary oxygen uptake (VO2) slow component is related to a progressive increase in muscle lactate concentration and that prior heavy exercise (PHE) with pronounced acidosis alters VO2 kinetics and reduces work efficiency. Subjects (n= 9) cycled at 75% of the peak VO2 (VO2peak) for 10 min before (CON) and after (AC) PHE. VO2 was measured continuously (breath-by-breath) and muscle biopsies were obtained prior to and after 3 and 10 min of exercise. Muscle lactate concentration was stable between 3 and 10 min of exercise but was 2- to 3-fold higher during AC (P < 0.05 versus CON). Acetylcarnitine (ACn) concentration was 6-fold higher prior to AC and remained higher during exercise. Phosphocreatine (PCr) concentration was similar prior to exercise but the decrease was 2-fold greater during AC than during CON. The time constant for the initial VO2 kinetics (phase II) was similar but the asymptote was 14% higher during AC. The slow increase in VO2 between 3 and 10 min of exercise during CON (+7.9 +/- 0.2%) was not correlated with muscle or blood lactate levels. PHE eliminated the slow increase in VO2 and reduced gross exercise efficiency during AC. It is concluded that the VO2 slow component cannot be explained by a progressive acidosis because both muscle and blood lactate levels remained stable during CON. We suggest that both the VO2 slow component during CON and the reduced gross efficiency during AC are related to impaired contractility of the working fibres and the necessity to recruit additional motor units. Despite a pronounced stockpiling of ACn during AC, initial VO2 kinetics were not affected by PHE and PCr concentration decreased to a lower plateau. The discrepancy with previous studies, where initial oxidative ATP generation appears to be limited by acetyl group availability, might relate to remaining fatiguing effects of PHE.
authors.affiliation: Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark. ksahlin@health.sdu.dk
authors.forename: K
authors.initials: K
authors.lastname: Sahlin
authors.forename: J B
authors.initials: JB
authors.lastname: Sørensen
authors.forename: L B
authors.initials: LB
authors.lastname: Gladden
authors.forename: H B
authors.initials: HB
authors.lastname: Rossiter
authors.forename: P K
authors.initials: PK
authors.lastname: Pedersen
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D015308:Anaerobic Threshold / Q000502:physiology*; D004735:Energy Transfer / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D019344:Lactic Acid / Q000097:blood*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*
chemical_list: D019344:Lactic Acid; D010100:Oxygen
references.citation: Muscle Nerve. 2000 Jul;23(7):1095-104
references.pmid: 10883005
references.citation: J Biol Chem. 1955 Nov;217(1):383-93
references.pmid: 13271402
references.citation: J Physiol Pharmacol. 2001 Jun;52(2):167-84
references.pmid: 11453098
references.citation: Exerc Sport Sci Rev. 2001 Jul;29(3):129-33
references.pmid: 11474961
references.citation: Exerc Sport Sci Rev. 2001 Jul;29(3):134-8
references.pmid: 11474962
references.citation: J Physiol. 2001 Nov 15;537(Pt 1):291-303
references.pmid: 11711581
references.citation: J Physiol. 2002 Feb 1;538(Pt 3):931-9
references.pmid: 11826176
references.citation: Med Sci Sports Exerc. 2002 Apr;34(4):655-61
references.pmid: 11932575
references.citation: J Appl Physiol (1985). 2002 Jul;93(1):167-74
references.pmid: 12070201
references.citation: Eur J Appl Physiol. 2002 Aug;87(4-5):424-32
references.pmid: 12172883
references.citation: J Appl Physiol (1985). 2003 Feb;94(2):533-41
references.pmid: 12391053
references.citation: J Physiol. 2003 May 15;549(Pt 1):255-69
references.pmid: 12651917
references.citation: J Appl Physiol (1985). 2003 Sep;95(3):1105-15
references.pmid: 12754181
references.citation: Eur J Appl Physiol. 2004 Mar;91(2-3):238-45
references.pmid: 14566567
references.citation: Pflugers Arch. 2004 Mar;447(6):855-66
references.pmid: 14758477
references.citation: Med Sci Sports Exerc. 2004 Jun;36(6):973-82
references.pmid: 15179167
references.citation: J Physiol. 2004 Aug 1;558(Pt 3):985-92
references.pmid: 15169844
references.citation: J Appl Physiol (1985). 2004 Oct;97(4):1227-36
references.pmid: 15145915
references.citation: Scand J Rehabil Med. 1970;2(2):92-8
references.pmid: 5523831
references.citation: J Appl Physiol. 1972 Apr;32(4):516-22
references.pmid: 5026501
references.citation: Scand J Clin Lab Invest. 1974 Apr;33(2):109-20
references.pmid: 4852173
references.citation: Pflugers Arch. 1976 Dec 28;367(2):143-9
references.pmid: 13343
references.citation: J Appl Physiol Respir Environ Exerc Physiol. 1982 Jun;52(6):1506-13
references.pmid: 6809716
references.citation: Fed Proc. 1986 Dec;45(13):2942-7
references.pmid: 3536593
references.citation: J Appl Physiol (1985). 1987 Jul;63(1):440-2
references.pmid: 3624147
references.citation: J Appl Physiol (1985). 1991 Oct;71(4):1245-60
references.pmid: 1757346
references.citation: J Appl Physiol (1985). 1992 May;72(5):1818-25
references.pmid: 1601791
references.citation: Med Sci Sports Exerc. 1992 Jul;24(7):782-8
references.pmid: 1501563
references.citation: Med Sci Sports Exerc. 1994 Jan;26(1):37-43
references.pmid: 8133736
references.citation: J Appl Physiol (1985). 1994 Feb;76(2):787-92
references.pmid: 8175590
references.citation: Med Sci Sports Exerc. 1994 Nov;26(11):1319-26
references.pmid: 7741865
references.citation: J Clin Invest. 1996 Feb 1;97(3):879-83
references.pmid: 8609248
references.citation: J Appl Physiol (1985). 1996 Jan;80(1):99-107
references.pmid: 8847338
references.citation: J Physiol. 1996 Dec 15;497 ( Pt 3):781-94
references.pmid: 9003563
references.citation: Am J Physiol. 1998 Feb;274(2 Pt 1):E377-80
references.pmid: 9486171
references.citation: Am J Physiol Endocrinol Metab. 2001 Jun;280(6):E956-64
references.pmid: 11350777