Muscle contraction is the tightening, shortening, or lengthening of muscles when you do some activity. It can happen when you hold or pick up something, or when you stretch or exercise with weights.

People can build muscle by using their muscles more, such as by lifting weights or working out. Eating enough calories and protein is also important. Skeletal muscle is one of the three major muscle ...

Introduction It has been shown that caffeine promotes vigilance, attention, mood and arousal 5. The potential mechanisms of caffeine’s action include its role as an adenosine receptor antagonist that ...