Meeting Abstract
The musculoskeletal system is dynamic, adapting to changes in biomechanical loading through the process of functional adaptation. Hard, mechanically resistant diets increase the strains experienced by the feeding complex, inducing growth and remodeling. Here we test the hypothesis that the consumption of hard diets by growing individuals results in larger adult chewing muscles with an increase in type II muscle fibers. Male Sprague-Dawley rats were raised from weaning to adulthood in four treatment groups (n=5/group). Two groups were raised on stable diets of either “hard” pellets or “soft” meal. Two variable diet groups were weaned onto a hard/soft diet then switched to the opposite diet at the experimental midpoint. Fixed in-situ cranial muscles were diceCT scanned and semi-manually segmented in 3D Slicer. Isolated masseter muscles were processed for ICH with anti-myosin heavy chain (MHC) antibody, and ImageJ was used to collect type I and II fiber counts and areas. Results indicate that animals raised on variable diets, regardless of the timing of these diets, tend to have larger chewing muscles as adults. This is particularly pronounced in the superficial masseter and temporalis muscles. These results suggest that intra-individual variability in muscle use, as well as the timing and intensity of that use, is important for maximizing muscle growth. Additionally, in rats raised on harder diets, a greater percentage of the masseter is composed of type II muscle fibers due to an increase in type II fiber area and a decrease in type I fiber number. The trade-off between fiber number and area may indicate a need for increased force production generated during feeding on a hard diet. Future studies are needed to investigate ontogenetic changes in masticatory muscle plasticity.
