Meeting Abstract
External forces from our environment translate to transverse loads on our muscles. Studies in rats showed that transverse loads affect muscle force in the longitudinal direction, where increases in transverse load decreased maximum longitudinal force. Changes in muscle architecture during contraction may contribute to the observed force decrease. The aim of this study was to quantify changes in pennation angle, fascicle dimensions, and muscle thickness during contraction under external transverse load. Electrical stimuli were elicited to evoke maximal force twitches in the right calf muscles in man. Trials were conducted with transverse loads of 2, 4.5, and 10 kg. An ultrasound probe was placed on the medial gastrocnemius in line with the transverse load to quantify architectural muscle characteristics during muscle twitches. Ultrasound images were enhanced and quantified using manual digitization and image transformations. Transverse loading of the muscle resulted in a decrease in the initial muscle thickness and pennation angle, with higher loads causing greater decreases. During twitches the muscle belly and fascicles transiently increased in thickness and pennation angle. The increase in muscle thickness was reduced with greater transverse load, and the increases in pennation angle and fascicle thickness were also reduced. Maximum twitch force decreased with increased transverse loads. The 2, 4.5, and 10 kg of transverse load showed a 9, 13, and 16% decrease in longitudinal muscle force, respectively. Transverse load impacts muscle deformation and contraction dynamics. This study showed that increased transverse loads caused a decrease in ankle moment, muscle thickness, pennation angle, and deformation of the fascicles.
