Muscle Manual Practice Test 2025 - Free Practice Questions and Study Guide for Muscle Anatomy

Isotonic contraction refers to a type of muscle contraction where the muscle length changes while maintaining a relatively constant tension throughout the movement. This means that during an isotonic contraction, a muscle is able to shorten (concentric contraction) or lengthen (eccentric contraction) as it works against a load. This type of contraction is essential for movements where the force and movement direction need to be controlled, such as lifting a weight or performing a squat.

In isotonic contractions, the muscle fibers contract and slide past each other, allowing for the dynamic movement that characterizes many physical activities. This contrasts with other forms of muscle contraction, such as isometric contractions, where the muscle generates tension without a change in length, thus not producing any movement.

The other choices do not accurately describe isotonic contraction. The first choice describes isometric contractions, the second highlights the production of heat which can occur in any type of contraction but isn't specific to isotonic contraction, and the fourth option refers to high resistance which is not a defining characteristic of isotonic contractions. Therefore, option C accurately captures the essence of isotonic contractions as it includes the critical aspect of changes in muscle length under tension.