Presentation Information
[P2-34]Timing Control of Upper Body Movements in Playground Swing Pumping: The Role of External Forces
*Chiaki Hirata1, Shun'ichi Kitahara1 (1. Jumonji University (Japan))
Keywords:
phase shift,external forces,coupled oscillator system,playground swing
Playground swing pumping represents a coupled oscillator system consisting of the swing apparatus and the human swinger. Dynamic simulations using equations of motion reveal that for seated pumping, swing amplification requires synchronization between the swing's resonant frequency and the swinger's upper body movements. Furthermore, a progressive phase shift between the swing and upper body motion is essential for effective pumping. Specifically, when swing amplitude is small, maximum backward lean of the upper body should occur when the swing moves forward and the swing is at the vertical. As swing amplitude increases, the timing of maximum backward lean must shift earlier toward the swing's back extreme.
Motion capture analysis of 10 untrained participants pumping an in-lab playground swing showed that while one swing cycle lasted approximately 2.5 seconds, the phase shift advanced about 30 milliseconds per cycle. This precise phase control was consistent across all participants, suggesting it occurs without conscious intention.
Our hypothesis proposes that external forces—including inertial, fictitious, and centrifugal forces—acting on the swinger's upper body drive this phase shift. To test this hypothesis, we constructed a virtual reality swing environment consisting of a head-mounted display connected to a personal computer and a stationary bar stool with poles mimicking swing chains. The VR swing responds to upper body movements synchronized with swing motion, but critically, no external forces act on the swinger's body since the seat remains fixed to the ground.
Ten participants successfully pumped both VR swing. Importantly, during VR swing pumping, the phase relationship between the seat and upper body remained constant throughout the pumping process, contrasting with the progressive phase shift observed in physical swing pumping.
These findings demonstrate that external forces are crucial for the automatic phase shift that enables effective swing pumping. This research advances our understanding of how environmental constraints shape motor coordination in coupled oscillatory systems.
Motion capture analysis of 10 untrained participants pumping an in-lab playground swing showed that while one swing cycle lasted approximately 2.5 seconds, the phase shift advanced about 30 milliseconds per cycle. This precise phase control was consistent across all participants, suggesting it occurs without conscious intention.
Our hypothesis proposes that external forces—including inertial, fictitious, and centrifugal forces—acting on the swinger's upper body drive this phase shift. To test this hypothesis, we constructed a virtual reality swing environment consisting of a head-mounted display connected to a personal computer and a stationary bar stool with poles mimicking swing chains. The VR swing responds to upper body movements synchronized with swing motion, but critically, no external forces act on the swinger's body since the seat remains fixed to the ground.
Ten participants successfully pumped both VR swing. Importantly, during VR swing pumping, the phase relationship between the seat and upper body remained constant throughout the pumping process, contrasting with the progressive phase shift observed in physical swing pumping.
These findings demonstrate that external forces are crucial for the automatic phase shift that enables effective swing pumping. This research advances our understanding of how environmental constraints shape motor coordination in coupled oscillatory systems.