What characterizes an isokinetic muscle contraction?

• A. Speed of movement is fixed and resistance varies with force exerted
• B. Muscle length shortens during contraction
• C. Movement speed is variable but resistance is constant
• D. Contraction occurs without energy expenditure

Answer: (A)

Isokinetic contractions are defined by keeping the movement speed constant throughout the motion, with the resisting load adjusted by equipment to match the muscle’s force output at every point in the range. The main idea is that the velocity is fixed, while the resistance varies to keep that speed steady. As the muscle’s ability to generate force changes with joint angle, the device automatically increases or decreases resistance to maintain the set speed, often using a dynamometer or similar apparatus. This is why you can have maximal force produced at all points in the range without the limb speeding up or slowing down.

Other descriptions don’t capture this key feature. If the muscle shortens during contraction, that can describe a concentric action under constant load, but it doesn’t imply a fixed movement speed. If speed is allowed to vary while resistance stays the same, that’s not isokinetic control. And contraction does use energy; saying it occurs without energy expenditure isn’t accurate for active muscular work.