During an eccentric contraction, what occurs at the sarcomere?

• A. The neuron fires more rapidly to produce shortening
• B. Calcium release increases contraction speed
• C. Actin is pulled away from myosin, which results in lengthening of the muscle under tension.
• D. The sarcomere shortens as actin slides over myosin

Answer: (C)

During an eccentric contraction the muscle lengthens while generating force, so the sarcomere length increases even as cross-bridges are formed and resist the load. The statement that best fits this is that actin is pulled away from myosin, which results in lengthening of the muscle under tension. In eccentric action, external force pulls the filaments apart, and the cross-bridges still form and resist, but the net result is elongation rather than shortening. The other ideas describe neural firing driving shortening, calcium making contraction faster, or the sarcomere actually shortening, which correspond to different types of contraction (isometric/concentric) rather than eccentric lengthening.