Final answer:
Quick, powerful movements first involve an eccentric contraction where the muscle elongates under tension before engaging in a powerful concentric contraction.
Step-by-step explanation:
The type of contraction involved in quick, powerful movements, such as those found during reactive training, is typically an eccentric contraction. Eccentric contractions occur when the muscle elongates under tension, which is often the first action in reactive training exercises where muscles must quickly absorb impact and then produce force. The eccentric phase acts as a pre-stretch that enables a more forceful concentric contraction.
In the context of a bicep curl, an eccentric contraction occurs as the weight is lowered in a controlled manner. This movement requires the biceps to lengthen while still generating force. In the case of reactive training, such as a jump landing, the leg muscles would first undergo an eccentric contraction to absorb the force, shortly before a concentric contraction that facilitates the jump upwards.