Which contraction type involves muscle shortening with weight?

The correct answer is concentric contraction. This type of muscle contraction occurs when a muscle generates force while shortening in length, typically against an external load or weight. During concentric contractions, the muscle fibers contract and shorten, which allows movements such as lifting an object or pushing against resistance. For example, during a bicep curl, as you lift the weight towards your shoulder, your biceps are undergoing a concentric contraction to generate the necessary force to lift the weight.

In contrast, eccentric contraction involves the muscle lengthening while under tension, usually as it controls the descent of a weight after a lift. Isometric contraction refers to muscle activation without any change in muscle length or joint angle, meaning that while the muscle is engaged, it is neither shortening nor lengthening. Lastly, isotonic contraction is a more general term that encompasses both concentric and eccentric contractions, referring to movements where muscle length changes while producing force. Thus, for muscle shortening specifically with weight, concentric contraction is the most accurate choice.