What coincides with - but does not necessarily cause- the muscle fatigue and burning pain in the muscles that accompanies intense physical exercise?

The build-up of lactic acid in muscles are the reason for fatigue and pain.

Some are the reason of muscle fatigue and cramps are Altered neuromuscular control, Dehydration, Electrolyte depletion, Doing a new activity, change in climate.

Having had "charley horse" cramps since I was quite young I have looked for answers to this question for years. I found out that there are two things that are believed to cause muscle cramps. Low...

the build up lactic acid and positive hydrogen ions

Normally the main cause of muscle pain is strain or fatigue, hope this helps you :)