What acid do tired muscles contain?

Answer 1

Tired muscles contain lactic acid. Therefore, we must do more exercises... and not overwork ourselves.
The acid accumulated in the muscle, as a result of the metabolic activitites, is called lactic acid. Usually this lactic acid is broken down, in the presence of oxygen, so we don't get cramps. However, if there is a shortage of oxygen, then this acid accumulates and doesn't break down, causing cramps.
During exercise muscles in the body create lactic acid (also called lactates). Lactic acid is created in the muscles through the breakdown of glucose and can be used a source of glucose.
lactic acid
lactic acid. it is then passed through the blood and to the lungs to be released as air!
Lactic Acids
lactic acid

Answer 2

Hydrochloric acid