The onset of muscle fatigue has hampered many athletes from achieving their maximum potential. The lactic acid buildup is a byproduct of anaerobic metabolism. Under normal activity levels, the body mostly relies on aerobic metabolism and hence lactate (another name for lactic acid) buildup is not a major concern.
However, with increased activity levels, specifically, when the metabolism switches from aerobic (oxidative) to anaerobic (glycolytic), as in power activities performed at high heart rates, lactate levels quickly build-up, which, if not cleared from muscles, cause fatigue and a burning sensation.
But how quickly lactic acid is cleared and how quickly a person feels this fatigue is also influenced by your genetics, especially the MCT1 gene. This article explains how individual differences affect the lactic acid clearance rate and muscle fatigue.