Mechanical energy production and energetic interactions between the thrower and the hammer in hammer throwing

Although hammer throw kinematics have been extensively described, the energetic mechanisms underlying the thrower-hammer coupling remain unclear. This study quantified mechanical energy exchanges within the global system, and examined how production is distributed across the phases of the throw. Hammer trajectory was reconstructed in 3D using video analysis and fused with full-body inertial motion capture. Following spatiotemporal synchronization, an anthropometric model was used to compute hammer and thrower kinetic energy, and system gravitational potential energy, allowing determination of total mechanical energy. Hammer and thrower kinetic energy varied in phase opposition (p < 0.001), indicating internal energy exchange within the coupled system. Periods of hammer kinetic energy decrease were associated with simultaneous increases in thrower kinetic energy and system gravitational potential energy (both p < 0.001). Then, this energy was transferred back to the hammer, accounting for its subsequent re-acceleration. Furthermore, total mechanical energy production was not uniformly distributed across phases, but was significantly higher during double support (p < 0.001). Production was concentrated in the first half of double support, while the second half contribution decreased across turns. These findings indicate that reductions in hammer velocity reflect internal storage of mechanical energy rather than dissipation. From a methodological perspective, the results illustrate the potential of inertial sensor-based modelling for energetic analysis of complex human-implement interactions in ecological settings. From a practical standpoint, emphasis should be placed on maximizing total mechanical energy production during the first half of double support, rather than attempting to minimize fluctuations in hammer velocity.