Which contraction type occurs when there is tension without shortening because the load cannot be moved?

Which contraction type occurs when there is tension without shortening because the load cannot be moved?

• A. Isometric contractions
• B. Isotonic contractions
• C. Incomplete tetanus
• D. Fused tetanus

Answer: (A)

Isometric contractions occur when the muscle develops tension but does not shorten because the load cannot be moved. The muscle fibers generate force through cross-bridge cycling, but the sarcomeres don’t change length since the external resistance matches or exceeds the muscle’s force, so there is no movement of the joint. This is why you can hold a heavy object steady without any visible shortening of the muscle. In contrast, when the load can be moved, the muscle shortens while producing force—that’s an isotonic contraction, which includes concentric (shortening) and eccentric (lengthening) actions. The other terms describe patterns of electrical stimulation, not whether the muscle changes length, so they don’t describe a situation where tension exists without shortening.

Isometric contractions occur when the muscle develops tension but does not shorten because the load cannot be moved. The muscle fibers generate force through cross-bridge cycling, but the sarcomeres don’t change length since the external resistance matches or exceeds the muscle’s force, so there is no movement of the joint. This is why you can hold a heavy object steady without any visible shortening of the muscle.

In contrast, when the load can be moved, the muscle shortens while producing force—that’s an isotonic contraction, which includes concentric (shortening) and eccentric (lengthening) actions. The other terms describe patterns of electrical stimulation, not whether the muscle changes length, so they don’t describe a situation where tension exists without shortening.