The correct answer is hormonal glands
The answer to this question is lactic acid. The reason why sports psychologists would need to look for a buildup of this chemical is because it is the chemical that produces pain or "feeling the burn" in an exercise when someone pushes their limit. Also, after so long, a person with a lactic acid buildup needs to take a break because high levels of lactic acid is dangerous for the bloodstream.
All living things are made up in cells?
