Meeting Abstract
Intrinsic muscle properties such as force-velocity and length-tension effects are often used in musculoskelatal modelling and are important when considering muscle function in vivo. Several research studies have examined how muscle length affects the influx of calcium into the muscle during isotonic twitches but no one has examined how length affects the kinetics of the twitch in terms of timing and force development. My research examines the effects of length on the kinetics of force development in skeletal muscle across the length-tension curve. We measured the force of single twitches in isolated muscle preparations from the silver lamprey (Ichthyomyzon unicuspis) to quantify the length-tension curve, starting at the ascending limb, proceeding through past optimal length, and onto the descending limb. From each of the twitches, the force produced by the muscle and the timing of various points relative to the stimulus was measured. During muscle contraction and relaxation we measured the time that the muscle reached 50%, 90%, and 100% maximal force and then relaxed to 50% and 90% relaxation. From these data the average rate of force development and decay were calculated at different times within the twitch. In addition, the instantaneous rate of force development and relaxation were examined to see the effects of length throughout the twitch. Our results suggest that the rate of force development during contraction is constant up to 50% of maximal force, but the rate of force development from 50% to maximal force increases as the length increases. Our results suggest that the twitch response of skeletal muscle depends on length and other considerations may have to be considered when determining the effect of length on force production.
