Citrulline/malate promotes aerobic energy production in human exercising muscle

Br J Sports Med 2002;36:282–289
Background: Previous studies have shown an antiasthenic effect of citrulline/malate (CM) but the mechanism of action at the muscular level remains unknown.
Objective: To investigate the effects of CM supplementation on muscle energetics.

Methods: Eighteen men complaining of fatigue but with no documented disease were included in the study. A rest-exercise (finger flexions)-recovery protocol was performed twice before (D-7 and D0), three times during (D3, D8, D15), and once after (D22) 15 days of oral supplementation with 6 g/day CM. Metabolism of the flexor digitorum superficialis was analysed by 31P magnetic resonance spectroscopy at 4.7 T.

Results: Metabolic variables measured twice before CM ingestion showed no differences, indicating good reproducibility of measurements and no learning effect from repeating the exercise protocol. CM ingestion resulted in a significant reduction in the sensation of fatigue, a 34% increase in the rate of oxidative ATP production during exercise, and a 20% increase in the rate of phosphocreatine recovery after exercise, indicating a larger contribution of oxidative ATP synthesis to energy production. Considering subjects individually and variables characterising aerobic function, extrema were measured after either eight or 15 days of treatment, indicating chronological heterogeneity of treatment induced
changes. One way analysis of variance confirmed improved aerobic function, which may be the result
of an enhanced malate supply activating ATP production from the tricarboxylic acid cycle through anapldrotic

Conclusion: The changes in muscle metabolism produced by CM treatment indicate that CM may promote
aerobic energy production.