title: Human muscle net K(+) release during exercise is unaffected by elevated anaerobic metabolism, but reduced after prolonged acclimatization to 4,100 m.
abstract: It was investigated whether skeletal muscle K(+) release is linked to the degree of anaerobic energy production. Six subjects performed an incremental bicycle exercise test in normoxic and hypoxic conditions prior to and after 2 and 8 wk of acclimatization to 4,100 m. The highest workload completed by all subjects in all trials was 260 W. With acute hypoxic exposure prior to acclimatization, venous plasma [K(+)] was lower (P < 0.05) in normoxia (4.9 +/- 0.1 mM) than hypoxia (5.2 +/- 0.2 mM) at 260 W, but similar at exhaustion, which occurred at 400 +/- 9 W and 307 +/- 7 W (P < 0.05), respectively. At the same absolute exercise intensity, leg net K(+) release was unaffected by hypoxic exposure independent of acclimatization. After 8 wk of acclimatization, no difference existed in venous plasma [K(+)] between the normoxic and hypoxic trial, either at submaximal intensities or at exhaustion (360 +/- 14 W vs. 313 +/- 8 W; P < 0.05). At the same absolute exercise intensity, leg net K(+) release was less (P < 0.001) than prior to acclimatization and reached negative values in both hypoxic and normoxic conditions after acclimatization. Moreover, the reduction in plasma volume during exercise relative to rest was less (P < 0.01) in normoxic than hypoxic conditions, irrespective of the degree of acclimatization (at 260 W prior to acclimatization: -4.9 +/- 0.8% in normoxia and -10.0 +/- 0.4% in hypoxia). It is concluded that leg net K(+) release is unrelated to anaerobic energy production and that acclimatization reduces leg net K(+) release during exercise.
authors.affiliation: Copenhagen Muscle Research Center, Rigshospitalet Section, Copenhagen Ø, Denmark. nnordsborg@ifi.ku.dk
authors.forename: Nikolai B
authors.initials: NB
authors.lastname: Nordsborg
authors.forename: José A L
authors.initials: JA
authors.lastname: Calbet
authors.forename: Mikael
authors.initials: M
authors.lastname: Sander
authors.forename: Gerrit
authors.initials: G
authors.lastname: van Hall
authors.forename: Carsten
authors.initials: C
authors.lastname: Juel
authors.forename: Bengt
authors.initials: B
authors.lastname: Saltin
authors.forename: Carsten
authors.initials: C
authors.lastname: Lundby
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D001810:Blood Volume; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005221:Fatigue / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D007866:Leg; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism; D010953:Plasma Volume; D012146:Rest