Meeting Abstract
Muscle shape changes in pennate muscles affect the force and speed of contraction because they influence the gear ratio through which muscle fibers transmit force and speed to the whole muscle. It has been hypothesized that aponeuroses, the sheet-like tendinous structures that rest on the surface of muscle in close association with fibers, influence muscle gear ratio via their effect on muscle shape change. Specifically, aponeuroses may restrict width-wise bulging during low-force contractions, forcing muscle fibers to rotate to steeper angles of pennation during shortening. We used an in situ preparation of the turkey lateral gastrocnemius (LG) muscle to test the hypothesis that disrupting an aponeurosis’ ability to transmit transverse forces impedes its ability to resist width changes, leading to an increase in muscle width and decreased gearing during isotonic muscle contractions. Measurement of muscle length and muscle fiber length for a series of contractions at different force levels allowed us to examine how gearing varied with force before and after incising the aponeurosis. Consistent with previous work, we found that gearing decreased with increasing contractile force in the intact muscle. This relationship between gearing and force was maintained even after longitudinal incisions reduced the aponeurosis’ ability to transmit transverse forces. Furthermore, incising the aponeurosis did not cause a decrease in gearing during low force contractions. These results suggest that other muscle components such as the intramuscular connective tissue play an important role in modulating dynamic gearing.
