title: Potassium kinetics in human muscle interstitium during repeated intense exercise in relation to fatigue.
abstract: Accumulation of K+ in skeletal muscle interstitium during intense exercise has been suggested to cause fatigue in humans. The present study examined interstitial K+ kinetics and fatigue during repeated, intense, exhaustive exercise in human skeletal muscle. Ten subjects performed three repeated, intense (61.6+/-4.1 W; mean+/-SEM), one-legged knee extension exercise bouts (EX1, EX2 and EX3) to exhaustion separated by 10-min recovery periods. Interstitial [K+] ([K+]interst) in the vastus lateralis muscle were determined using microdialysis. Time-to-fatigue decreased progressively (P<0.05) during the protocol (5.1+/-0.4, 4.2+/-0.3 and 3.2+/-0.2 min for EX1, EX2 and EX3 respectively). Prior to these bouts, [K+]interst was 4.1+/-0.2, 4.8+/-0.2 and 5.2+/-0.2 mM, respectively. During the initial 1.5 min of exercise the accumulation rate of interstitial K+ was 85% greater (P<0.05) in EX1 than in EX3. At exhaustion [K+]interst was 11.4+/-0.8 mM in EX1, which was not different from that in EX2 (10.4+/-0.8 mM), but higher (P<0.05) than in EX3 (9.1+/-0.3 mM). The study demonstrated that the rate of accumulation of K+ in the muscle interstitium declines during intense repetitive exercise. Furthermore, whilst [K+]interst at exhaustion reached levels high enough to impair performance, the concentration decreased with repeated exercise, suggesting that accumulation of interstitial K+ per se does not cause fatigue when intense exercise is repeated.
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: Magni
authors.initials: M
authors.lastname: Mohr
authors.forename: Nikolai
authors.initials: N
authors.lastname: Nordsborg
authors.forename: Jens Jung
authors.initials: JJ
authors.lastname: Nielsen
authors.forename: Lasse Danneman
authors.initials: LD
authors.lastname: Pedersen
authors.forename: Christian
authors.initials: C
authors.lastname: Fischer
authors.forename: Peter
authors.initials: P
authors.lastname: Krustrup
authors.forename: Jens
authors.initials: J
authors.lastname: Bangsbo
mesh_terms: D000328:Adult; D015308:Anaerobic Threshold / Q000502:physiology*; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000378:metabolism; D007866:Leg / Q000502:physiology; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010807:Physical Endurance / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D012508:Sarcolemma / Q000378:metabolism
chemical_list: D019344:Lactic Acid; D006003:Glycogen; D011188:Potassium