Caffeine is ergogenic, enhancing physical performance and stamina, by eliminating fatigue.
It drives the adrenal glands to produce stress hormones like adrenaline and cortisol. The induced adrenaline rush can cause the affected persons to experience muscle tension, rapid heart beat, fast pulse, and quick breathing.
Glycogen is the main fuel muscles use for energy production. Working out naturally depletes muscle glycogen, which in turn leads way to muscle fatigue. Caffeine is thought to slow down this glycogen depletion process and thus increasing endurance.
With Glycogen depletion, the body is forced to look for another energy source – fat, which requires more oxygen. Low oxygen triggers Lactic Acid production, making the muscles more acidic which can cause a burning sensation.
A study done at the University of Illinois in 2009 reported that 300 mg of caffeine reducing muscle burning, which is commonly associated with Lactic Acid build-up, during intense exercise.