Meeting Abstract
Skeletal muscles not only accelerate our bodies during movement, they also play a crucial role in deceleration. During decelerating tasks, such as landing and braking, muscles are stretched while actively producing force in order to dissipate mechanical energy. One negative consequence of energy dissipation is that active lengthening can cause muscle damage. While we know a lot about the implication of different architectures and fiber-type compositions for force production, it is unclear how these muscle parameters affect the likelihood of damage. We used the natural variation in muscle fiber type and architecture in rat muscles to investigate the link between muscle parameters and injury. Soleus is a slow, paralleled fiber muscle (20% fast fibers, 4° pennation) while plantaris is a fast, pennate fiber muscle (95% fast fibers, 16° pennation). We used an in situ muscle preparation where a servomotor measured the force, velocity and length of the entire MTU. Eccentric stretches applied to the muscles were made relative to P0. After an eccentric contraction, the extent of the muscle injury was estimated by the amount of force decline and a leftward shift in the muscle’s force-length curve. We observed that the pennate muscle could withstand an eccentric contraction up to 200% P0 while the parallel muscle experienced complete failure at 150% P0. This is consistent with studies that propose that architectural gear ratio of pennate muscles provide protection from stretch-induced damage and studies showing an increase in pennation angle with eccentric training. These results suggest that variation in muscle architecture may serve to predict a muscle’s propensity for damage during energy dissipating tasks.
