Investigating a non-invasive method for determining muscle fiber composition

Abstract

This study aims to explore a new method for analysis of muscle fiber type, using data collected from weightlifts on a leg press. A dynamic muscle model is developed, which utilizes the Descherevskii kinetic theory in combination with a muscle "matrix" model to predict net muscle contraction forces and velocities as a function of fiber type. These relationships are integrated into a dynamic model for lifting a weight, allowing for the derivation of joint trajectories in time, from the molecular properties of muscle. The model-predicted velocity trajectories for the lift are compared with curves obtained experimentally from weightlifting trials. Longer lifts with slower peak velocities indicate higher ratios of slow-twitch fibers, and shorter lifts with greater peak velocities indicate higher ratios of fast-twitch fibers. This idea is supported by both the model results and in experimental trends. With further refinement of experimental protocols, the leg press test has the potential to be a powerful training tool for athletes-both to compare their muscle makeup with other athletes, and to track their own progress over the course of their training.