Weight training involves creating muscle damage and inflammation. The muscles react by repairing the damage and triggering muscle hypertrophy, which reduces stress in the future. However, excessive damage and inflammation prevent training gains and can lead to long term metabolic problems and disease. A Brazilian study showed decreases in makers of inflammation and muscle damage in rats subjected to chronic low levels of exercise and caffeine. When weight training, balance stress and recovery to achieve the greatest gains. Taking caffeine before workout might help protect muscles against excessive damage and inflammation and help promote training gains.
Caffeine’s main effect on the body is to increase alertness and arousal, which can make workouts seem not so bad. It also may help the muscles burn more fat. Here’s the theory: Muscles use glycogen, a stored version of glucose, for energy, and when glycogen stores run out, muscles get weaker and less efficient, leading to exhaustion. But muscles can also burn fat, and when they do, muscles don’t tire as easily. Caffeine can shift muscles to burn fat more quickly, which can preserve glycogen stores and give muscles more time before they wear out. This leads to a longer and less painful workout. Some researchers also believe that caffeine may work directly on muscle by improving its efficiency in generating power.
But caffeine may take some time to work. The benefits are more obvious in longer bouts of endurance exercise rather than short-term kinds of exercise, since muscles turn to glycogen first. It’s not yet conclusive how long you have to exercise for caffeine to trigger the shift to fat-burning, but most studies have tested caffeine’s effect on muscles after about two hours. Caffeine’s energizing effects start to peak about an hour after ingestion and can last from three to six hours.