During which of the following muscle contractions does a muscle lengthen as it contracts?

Question

BlackTom AI · Accepted Answer

Eccentric contraction occurs when an active muscle produces force while being lengthened by an external load.

Relevant concepts: muscle contraction types are classified by whether the muscle changes length and whether external force does work on the muscle. Concentric contraction — muscle shortens while producing force; isometric (static) — muscle produces force with no change in length; eccentric — muscle produces force while lengthening, often controlling or decelerating movement and absorbing energy.

Step-by-step reasoning:
1. Consider muscle force (Fm) versus external load force (Fe). If Fm > Fe, the muscle overcomes the load and shortens (concentric). If Fm = Fe, length stays constant (isometric/static). If Fm < Fe while the muscle remains active, the external force overcomes the muscle and the muscle lengthens while still generating force (eccentric).
2. Example numeric illustration: suppose Fm = 50 N and Fe = 70 N. Because Fe > Fm, the muscle cannot shorten; it lengthens under the larger external load while still producing 50 N of tension — this is eccentric action.
3. Functional example: lowering a dumbbell in a biceps curl — the biceps is active but lengthens as it controls the downward movement (eccentric). Negative work is done on the muscle, and eccentric contractions commonly cause more muscle damage and delayed-onset muscle soreness.

Why the correct answer is correct: eccentric explicitly describes an active lengthening contraction. The muscle is contracting (actively generating force) yet increasing in length because external torque/load exceeds muscle torque, matching the definition.

Why other options are incorrect:
- Static: implies no movement; not lengthening. Often used synonymously with isometric.
- Isometric: muscle generates force without changing length — not lengthening.
- Concentric: muscle shortens as it contracts — opposite of lengthening.

Conclusion: the correct answer is eccentric, which matches the provided answer.

During which of the following muscle contractions does a muscle lengthen as it contracts?Single choice

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