Abstract

Muscle fatigue is defined as the loss in force of power production in response to a muscle contraction and, during exercise, this results in the inability to sustain exercise at a given intensity. Although exercise-induced muscle fatigue is a complex and multifactorial phenomenon, it is accepted that hydrogen cation (H⁺) accumulation in skeletal muscle during intense exercise, which causes a reduction in the intramuscular pH, disrupts muscle energetics and muscle contraction and is a major cause of peripheral fatigue. The resultant increase in H⁺ within the skeletal muscle can negatively affect performance, particularly in those high-intensity events lasting between 1–10 minutes. The body has several intracellular and extracellular buffering systems that maintain pH homeostasis, although these may be exceeded during exercise. Nutritional interventions that might increase intracellular or extracellular buffering capacity could delay H⁺ accumulation and ultimately fatigue. Beta-alanine, sodium bicarbonate, sodium citrate and calcium, and sodium lactate are all buffering supplements with the capacity to increase intracellular or extracellular buffering capacity. Each of these supplements has been shown to improve exercise capacity and performance on numerous occasions, although several factors may modify their efficacy. The most promising of these are chronic supplementation with beta-alanine (to increase intramuscular buffering via an increase in muscle carnosine content) and acute supplementation with sodium bicarbonate (to increase extracellular buffering via an increase in circulating bicarbonate), which have been shown to be particularly effective for high-intensity exercise lasting 1–10 minutes in duration.