What type of muscle contraction happens through a range of motion but maintains a constant resistance?

The correct choice describes an isotonic contraction, which occurs when a muscle changes length while producing force against a constant load. During an isotonic contraction, the muscle shortens (concentric contraction) or lengthens (eccentric contraction) through a full range of motion while able to maintain a consistent level of resistance. This type of contraction is commonly seen in exercises like bicep curls or squats, where the weight remains constant throughout the movement, allowing for dynamic action and muscle strengthening.

In contrast, isometric contractions involve muscle tension without any change in muscle length, meaning the muscle does not shorten or lengthen while maintaining force. Isokinetic contractions are characterized by a consistent speed of movement throughout the range of motion, usually measured with specialized equipment, and eccentric contractions specifically refer to the muscle lengthening while under tension. Hence, isotonic is the most appropriate term to describe muscle contractions that provide a constant load through a complete motion.