Some athletes choose to take performance enhancing drugs to improve their endurance and performance.

Hmmm... The accumulation of acetylcholine would cause continuous stimulation of the muscles, glands, and central nervous system. A common substance that mimics ACh is nicotine. I know that once nicotine enters the body and makes its way to the brain through the blood stream, one of the main areas that it can attach itself to is the receptor sites for acetylcholine. Acetylcholine is a neurotransmitter responsible for a variety of bodily operations including breathing, heart rate, muscle movement and cognition. Nicotine increases the activity of these receptor sites which is why many smokers feel an increase of energy or an increase in ability to concentrate directly after smoking a cigarette.

Haha this is a bio question accidentally put physics!

Thanks for your help