Isotonic exercise typically involves which characteristic?

• A. Shortening and lengthening the muscle through a complete ROM with constant external load
• B. Muscle contracts without changing length
• C. Resistance that changes to keep speed constant
• D. Requires oxygen for endurance

Answer: (A)

Isotonic contraction involves shortening and lengthening the muscle through a full range of motion while the external load stays constant. This dynamic movement means the muscle actively changes length as you lift and lower a fixed resistance, such as a dumbbell during a bicep curl. This is different from isometric actions, where the muscle contracts without changing length; from isokinetic actions, where a device adjusts resistance to keep movement speed constant; and from endurance activities, which emphasize sustained oxygen use over time. The key idea is moving through the complete range with a constant load.