Eccentric contractions and stiffness.

<p>In a separate group of mice, EDL muscles were subjected to a mild eccentric contraction protocol. (A) is an example of an eccentric contraction, showing the change in force and length as the muscle is stretched by 15% of its optimal length L₀, then returned to resting length. 3 such eccentric contractions were performed for each muscle. (B) shows the force deficits following these eccentric contractions. Force deficits in aged mice were significantly higher than in adult mice. As an indicator of muscle stiffness, we also measured the percentage change in force for every 1% change in length during the stretch phase of the eccentric contraction. The results are shown in (C). The change in force was significantly higher in aged than in adult mice, indicative of greater stiffness in the muscles of aged mice.