Meeting Abstract
Pregnancy is a metabolically demanding condition in mammals that directly affects individual fitness. Most pregnant animals must remain active to avoid predators and secure increased food demands. However, during pregnancy hormonal effects alter the morphology and material properties of muscle-tendon units that are key during locomotion. The effect of these changes is not at all well understood despite its significance to mammalian evolution and public health. Using the rat as an animal model, I measured morphological and mechanical properties of the gastrocnemius muscle that have been shown to be significant contributors to muscle-tendon function. I found that both the longitudinal Young’s modulus of connective tissues such as the aponeurosis and muscle mass relative to total body mass both decreased by a factor of 1.3. A computational model of muscle-tendon interactions is used to explore the effect of these changes on cyclical muscle contractions that simulate walking on flat, incline and decline surfaces and compare these with three-dimensional high-speed video data of animals walking under these conditions to examine the effects of pregnancy at multiple levels of organization. Preliminary results suggest that the total force produced by a muscle-tendon unit of a pregnant animal during optimally activated work loops drops by 46% compared to contractions in a non-pregnant animal. This drop is entirely due to the change in maximum magnitude and dissipation profile of the passive force, while the maximum active force produced by both the pregnant and non-pregnant muscles remains unchanged. These results suggest that pregnancy-induced morphological and mechanical changes may limit the capacity of muscles to utilize elastic energy storage and may change where muscles operate on the force-length curve in vivo.
