title: Chronic intermittent hypoxia and incremental cycling exercise independently depress muscle in vitro maximal Na+-K+-ATPase activity in well-trained athletes.
abstract: Athletes commonly attempt to enhance performance by training in normoxia but sleeping in hypoxia [live high and train low (LHTL)]. However, chronic hypoxia reduces muscle Na(+)-K(+)-ATPase content, whereas fatiguing contractions reduce Na(+)-K(+)-ATPase activity, which each may impair performance. We examined whether LHTL and intense exercise would decrease muscle Na(+)-K(+)-ATPase activity and whether these effects would be additive and sufficient to impair performance or plasma K(+) regulation. Thirteen subjects were randomly assigned to two fitness-matched groups, LHTL (n = 6) or control (Con, n = 7). LHTL slept at simulated moderate altitude (3,000 m, inspired O(2) fraction = 15.48%) for 23 nights and lived and trained by day under normoxic conditions in Canberra (altitude approximately 600 m). Con lived, trained, and slept in normoxia. A standardized incremental exercise test was conducted before and after LHTL. A vastus lateralis muscle biopsy was taken at rest and after exercise, before and after LHTL or Con, and analyzed for maximal Na(+)-K(+)-ATPase activity [K(+)-stimulated 3-O-methylfluorescein phosphatase (3-O-MFPase)] and Na(+)-K(+)-ATPase content ([(3)H]ouabain binding sites). 3-O-MFPase activity was decreased by -2.9 +/- 2.6% in LHTL (P < 0.05) and was depressed immediately after exercise (P < 0.05) similarly in Con and LHTL (-13.0 +/- 3.2 and -11.8 +/- 1.5%, respectively). Plasma K(+) concentration during exercise was unchanged by LHTL; [(3)H]ouabain binding was unchanged with LHTL or exercise. Peak oxygen consumption was reduced in LHTL (P < 0.05) but not in Con, whereas exercise work was unchanged in either group. Thus LHTL had a minor effect on, and incremental exercise reduced, Na(+)-K(+)-ATPase activity. However, the small LHTL-induced depression of 3-O-MFPase activity was insufficient to adversely affect either K(+) regulation or total work performed.
authors.affiliation: School of Human Movement, Recreation and Performance (FO22) Victoria University of Technology, P.O. Box 14428, MCMC, Melbourne, Victoria 8001, Australia.
authors.forename: R J
authors.initials: RJ
authors.lastname: Aughey
authors.forename: C J
authors.initials: CJ
authors.lastname: Gore
authors.forename: A G
authors.initials: AG
authors.lastname: Hahn
authors.forename: A P
authors.initials: AP
authors.lastname: Garnham
authors.forename: S A
authors.initials: SA
authors.lastname: Clark
authors.forename: A C
authors.initials: AC
authors.lastname: Petersen
authors.forename: A D
authors.initials: AD
authors.lastname: Roberts
authors.forename: M J
authors.initials: MJ
authors.lastname: McKenna
mesh_terms: D000328:Adult; D000531:Altitude; D001642:Bicycling; D002908:Chronic Disease; D004789:Enzyme Activation; D015444:Exercise; D005786:Gene Expression Regulation; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology*; D010807:Physical Endurance; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013177:Sports; D013997:Time Factors
chemical_list: D000254:Sodium-Potassium-Exchanging ATPase