What is the difference between concentric and eccentric muscle contractions?

Concentric and eccentric muscle contractions have distinct characteristics and roles in movement and strength training. Concentric contractions occur when a muscle shortens while generating tension; this typically happens when a muscle contracts to lift a weight or overcome resistance. For example, during a bicep curl, as you lift the weight towards your shoulder, the bicep muscle is performing a concentric contraction.

On the other hand, eccentric contractions involve the muscle lengthening while still under tension. This often occurs when a muscle is controlling the descent of a weight or resisting being stretched. Using the bicep curl example again, when you lower the weight back down, your bicep muscle lengthens even though it is still engaged to control the motion.

Understanding this distinction is crucial for designing effective training programs, as both contraction types contribute differently to muscle strength, endurance, and injury prevention.