Purpose: Rotation of the body about its longitudinal axis or "body roll" in front crawl swimming may reduce injury risk, enhance propulsion, and reduce drag. An upper limb amputation may hinder body roll and diminish the benefits associated with this movement. This study examined the external fluid torques (buoyant and hydrodynamic) acting on unilateral upper limb amputee swimmers and their influence on whole-body roll, shoulder roll, and hip roll during front crawl. Methods: Ten Para swimmers with unilateral at-elbow amputation completed front crawl trials at sprinting speed. Three-dimensional motion analysis provided shoulder roll and hip roll angle-time histories. Swimmer`s center of mass (CM), center of buoyancy (CB), and whole-body angular momentum (H) were determined relative to the body roll axis. Whole-body roll was calculated by dividing H by the moment of inertia at each time and integrating over the cycle. Buoyant torque was obtained from the cross product of the CM-CB position vector and the buoyant force vector. Net external torque was computed as the time derivative of H, and hydrodynamic torque was then found by subtracting buoyant torque from net external torque. Results: Shoulder roll amplitude, maximum buoyant torque, and buoyant torque-impulse were greater (P < 0.01) during recovery (over-water phase) of the nonimpaired limb than during recovery of the impaired limb. No significant bilateral differences were found for whole-body roll, hip roll, or trunk-twist amplitudes. Mean contributions of buoyant torque and hydrodynamic torque to whole-body roll over the full upper limb cycle were 48% and 52%, respectively. Conclusions: Swimmers with unilateral forearm amputation experience an asymmetric buoyant torque, requiring them to sacrifice propulsive force to counterbalance the torque asymmetry and maintain symmetric whole-body roll.
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