Final answer:
An eccentric contraction is where a muscle lengthens while contracting against a load that is greater than the force it can produce. This differs from isometric and concentric contractions where the muscle tension remains constant but the muscle either does not change length or shortens, respectively.
Step-by-step explanation:
A muscle contraction against a resistance that is greater than the force and causes muscle lengthening is known as an eccentric contraction. In these contractions, the muscle lengthens even though it is contracting because the load is moving in the opposite direction of the contraction and exceeds the tension the muscle is generating. This is in contrast to other types of muscle contractions, such as isometric contractions, where muscle length remains the same because the tension cannot move the load, and concentric contractions, where the muscle shortens as it contracts to move a load.
An example of an eccentric contraction is when the biceps brachii muscle controls the lowering of a hand weight. During this movement, the amount of cross-bridges between actin and myosin within the sarcomeres is decreasing; consequently, the muscle lengthens while still maintaining tension to ensure a slow and controlled lowering of the weight.
Understanding these differences is important for various applications in exercise routines and rehabilitation, emphasizing the specificity of training regimes to target different muscle actions and outcomes.