When lactate build up in a runners muscles it causes a burning sensation. what causes the burning?

The burning sensation in a runner's muscles during intense exercise is primarily caused by the accumulation of lactate, which is a byproduct of anaerobic metabolism. When energy demands exceed the oxygen supply, the body shifts to anaerobic pathways, leading to increased lactate production. Additionally, the accumulation of hydrogen ions (H+) that accompany lactate can lower the pH in muscles, contributing to the sensation of muscle fatigue and discomfort.