What characterizes eccentric muscle contraction?

Eccentric muscle contraction is characterized by the muscle lengthening while it is still under tension. This often occurs when the muscle is acting against a load that exceeds its force production capability, such as when lowering a weight. During eccentric contractions, the muscle fibers are actively engaged and generating force, but they are also being elongated; this is a crucial aspect of various movements and is particularly important in activities like running or weightlifting when controlling the descent of weights or stabilizing the body.

The other options describe different types of muscle contractions. When a muscle shortens during contraction, that is referred to as concentric contraction. The scenario where no movement occurs corresponds to isometric contraction, which involves tension in the muscle without any change in length. Isometric contraction is different from eccentric and concentric as it does not involve lengthening or shortening of the muscle at all. Therefore, option B clearly defines the nature of eccentric contractions, highlighting the characteristic of lengthening under tension.