The main function of citric acid is the reduction of physical fatigue (35). The reason for this is due to citric acid being a major component of the tricarboxylic acid (TCA) cycle. TCA cycle is the process of converting carbohydrates, fats and proteins into carbon dioxide and water (36). By increasing citric acid it activates the TCA cycle and in turn speeds up ATP production thus replenishing energy.
35 – Sugino, T., Aoyagi, S., Shirai, T., Kajimoto, Y., & Kajimoto, O. (2007). Effects of citric acid and L-carnitine on physical fatigue. Journal of clinical biochemistry and nutrition, 41(3), 224.
36 – Baldwin, J. E., & Krebs, H. (1981). The evolution of metabolic cycles.