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) b ody mass) or placebo (P, sodium chloride 0.045 g . kg(-1) body mass), at local barometric pressure (N, P-B approximately 740 mmHg, 98.7 kPa) or hypobaric hypoxia (HH, P-B = 463 mmHg, 61.7 kPa). At 2 h after ing estion of the solution, the subjects performed prolonged isometric kne e-extension at 35% of the maximal voluntary contraction (MVC) measured either in N or HH. Results showed that ingestion of C led to an impro vement in muscle endurance (P < 0.01). However, this increase in endur ance time for knee extensor muscles was only significant in N(+22%, P < 0.05, compared to +15%, NS, at N and HH, respectively). Following in gestion of sodium citrate, pre-exercise bicarbonate concentrations and pH levels were significantly higher than those measured after P inges tion. A significant treatment effect was observed for blood lactate co ncentrations 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 contr action at 35% MVC. The mean power frequency (MPF) significantly decrea sed in time under both N-P and N-C conditions. In HH, no significant d ecrease in MPF was observed with time. The results suggest that C inge stion was an ergogenic aid enhancing endurance during a sustained isom etric contraction. In addition, it is suggested that fatigue during pr olonged isometric contraction in HH was not directly related to factor s determining the EMG signs of fatigue.