Sodium citrate ingestion and muscle performance in acute hypobaric hypoxia.
Eight subjects were studied on four occasions following ingestion of a 300-ml solution containing either sodium citrate (C, 0.4 g.kg-1 body mass) or placebo (P, sodium chloride 0.045 g.kg-1 body mass), at local barometric pressure (N, PB approximately 740 mmHg, 98.7 kPa) or hypobaric hypoxia (HH, PB = 463 mmHg, 61.7 kPa). At 2 h after ingestion of the solution, the subjects performed prolonged isometric knee-extension at 35% of the maximal voluntary contraction (MVC) measured either in N or HH. Results showed that ingestion of C led to an improvement in muscle endurance (P < 0.01). However, this increase in endurance time for knee extensor muscles was only significant in N (+22%, P < 0.05, compared to +15%, NS, at N and HH, respectively). Following ingestion of sodium citrate, pre-exercise bicarbonate concentrations and pH levels were significantly higher than those measured after P ingestion. A significant treatment effect was observed for blood lactate concentrations with values higher for C than for P after 4, 6 and 10 min of recovery (P < 0.05). Electromyographic signals (EMG) were obtained from the vastus lateralis muscle during the prolonged isometric contraction at 35% MVC. The mean power frequency (MPF) significantly decreased in time under both N-P and N-C conditions. In HH, no significant decrease in MPF was observed with time. The results suggest that C ingestion was an ergogenic aid enhancing endurance during a sustained isometric contraction. In addition, it is suggested that fatigue during prolonged isometric contraction in HH was not directly related to factors determining the EMG signs of fatigue.
Département de Physiologie Systémique, Centre d'Etudes et de Recherches de Médecine Aérospatiale, Brétigny sur Orge, France.
C
C
Hausswirth
A X
AX
Bigard
R
R
Lepers
M
M
Berthelot
C Y
CY
Guezennec
D000136:Acid-Base Equilibrium / Q000187:drug effects / Q000502:physiology; D000328:Adult; D000399:Air Pressure; D000471:Alkalosis / Q000139:chemically induced / Q000378:metabolism; D002951:Citrates / Q000494:pharmacology*; D019343:Citric Acid; D004576:Electromyography; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D018763:Muscle Fatigue / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000503:physiopathology*; D010807:Physical Endurance / Q000187:drug effects
D002951:Citrates; D019343:Citric Acid