In which contraction type does muscle tension remain the same while the muscle achieves movement?

Isotonic contractions are characterized by a consistent muscle tension while the muscle changes length to produce movement. This means that during an isotonic contraction, the muscle is able to shorten (in a concentric contraction) or lengthen (in an eccentric contraction) while the force generated remains adequate to lift a weight or overcome resistance. In terms of practical application, when you perform a bicep curl, the bicep muscle shortens as you lift the weight, demonstrating a concentric isotonic contraction. Conversely, when lowering the weight, the bicep lengthens but still maintains tension, which is an eccentric isotonic contraction.

This understanding distinguishes isotonic contractions from other types such as isometric contractions, where muscle tension is generated without any change in muscle length, meaning no movement occurs. Similarly, isokinetic contractions involve muscle shortening or lengthening at a constant speed, but this is not the primary focus in the context of the question concerning muscle tension during movement.