When lactate builds up in a runners muscles it a buring sensation. what causes this to occur?

The burning sensation in a runner's muscles when lactate builds up is primarily due to the accumulation of lactic acid, which is produced during anaerobic metabolism when the body needs energy quickly and oxygen supply is limited. As lactate levels increase, it can lower the pH in the muscle cells, leading to acidosis. This acidic environment can stimulate nerve endings, resulting in the characteristic burning feeling. Additionally, the buildup of lactate indicates that the muscles are working at high intensity, surpassing their aerobic capacity.