Meeting Abstract
Despite being a critical daily activity for many mammals, how species transition from supine to standing postures is not clear. Only human sit-to-stand (STS) movement has been studied extensively: the movement has been shown to be a demanding task, presumably due to the unique musculoskeletal demands associated with the motion. However, how demanding this movement is for other tetrapods is unclear. For example, cursorial-limbed animals such as the greyhound have adaptations for running, which uses small joint ranges of motion when the limb is loaded most. In contrast, the STS movement constitutes a postural change that requires large joint angle excursions and muscle force generation occurs over a wide range of limb configurations, including those with poor mechanical advantage. We aimed to determine whether, like in humans, STS transitions in cursorial mammals are highly demanding. We combined a musculoskeletal model of a greyhound hindlimb with experimental data to generate computer simulations of the STS movement and quantify muscle activity and fibre length changes. Simulations revealed that Mm. biceps femoris, gastrocnemius, and extensor digitorum longus activity remained high throughout the first half of the motion when joint angles deviated most from “normal” locomotor angles. Hip adductor muscle activity was also high; hence, greyhounds may compensate for limitations in sagittal plane muscle capacity by recruiting non-sagittal hip muscles. Although limb forces are less than those experienced in running during STS, substantial forces from the limb muscles are still required due to unfavourable mechanical advantage – these demands are further amplified by muscle fibres operating at suboptimal lengths over much of the motion.
