Isometric contractions are best described as:

• A. The muscle shortens during contraction.
• B. The muscle lengthens during contraction.
• C. The muscle tension increases without a change in length.
• D. The muscle produces no tension.

Answer: (C)

Isometric contractions occur when a muscle is activated to produce force but the joint angle stays fixed, so the muscle length does not change. This is exactly described by increasing tension without a change in length. Think of holding a still position, like a plank or pressing against an immovable object—the muscle fibers are firing and generating force, but there’s no movement at the joint.

In contrast, shortens under load describes concentric contraction (lifting or moving a load upward), lengthens under tension describes eccentric contraction (lowering a load with control), and producing no tension would mean the muscle isn’t actively contracting.