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.
Hausswirth
C
C
Département de Physiologie Systémique, Centre d'Etudes et de Recherches de Médecine Aérospatiale, Brétigny sur Orge, France.
Bigard
A X
AX
Lepers
R
R
Berthelot
M
M
Guezennec
C Y
CY
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