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.

What Are Eccentric and Concentric Contractions? Eccentric contractions occur when a muscle lengthens under load, such as lowering a dumbbell during a biceps curl. Concentric contractions happen when ...

"Hearst Magazines and Yahoo may earn commission or revenue on some items through these links." If you tend to breeze through the "easy" part of an exercise—like lowering into a squat or letting your ...