A whole-body characterization of individual strategies, gender differences and common styles in overarm throwing

Overarm throwing is a fundamental human skill. Since paleolithic hunter-gatherer societies, the ability of throwing played a key role in brain and body co-evolution. For decades, throwing skill acquisition has been the subject of developmental and gender studies. However, due to its complex multi-joint nature, whole-body throwing has found little space in quantitative studies of motor behavior. Here we examine how overarm throwing varies within and between individuals in a sample of untrained adults. To quantitatively compare whole-body kinematics across throwing actions, we introduced a new combination of spatiotemporal principal component, linear discrimination and clustering analyses. We found that the identity and gender of a thrower can be robustly inferred by the kinematics of a single throw, reflecting the characteristic features in individual throwing strategies and providing a quantitative ground for the well-known differences between males and females in throwing behavior. We also identified four main classes of throwing strategies, stable within individuals, and resembling the main stages of throwing proficiency acquisition during motor development. These results support earlier proposals linking inter-individual and gender differences in throwing, with skill acquisition interrupted at different stages of the typical developmental trajectory of throwing motor behavior.