Studies carried out with citrulline supplementation showed definite increase in exercise tolerance, reduced perception of fatigue, increased ATP(cell energy fuel) production and overall improvement is exercise performance. Below is a conclusion form British Journal of Sports Medicine.

Metabolic variables measured twice before Citrulline malate(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 anaplerotic reactions.

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