The document discusses the effect of interval training on muscle fatigue. Interval training involves periods of high intensity exercise alternated with recovery periods. It improves cardiovascular fitness and performance but can also increase muscle fatigue. Exercise at high intensities increases ATP utilization and lactate production, restricting metabolic processes. This causes increased muscle fatigue. Recovery periods allow restoration of metabolic concentrations to reduce fatigue. The document explores how interval training impacts muscle fatigue through its intense periods and recovery intervals.