Author(s): SEKINE, K., MURATA, E.1, SATO, M.2, Institution: MEIJI UNIVERSITY, Country: JAPAN, Abstract-ID: 898

INTRODUCTION:
Whole-body coordinated movements such as tennis strokes rely on effective temporal sequencing of segmental contributions, often described as the kinetic chain, in which forces generated against the ground are transmitted through the trunk, chest, wrist, and ultimately to the racket. Previous biomechanical studies have primarily investigated this sequencing using optical motion capture or high-speed video systems with multiple markers, which require specialized equipment and controlled laboratory environments. Consequently, assessment of temporal movement structure in practical sports settings has often depended on qualitative observation. Although wearable IMUs provide a simple alternative, it remains unclear how impact-centered temporal sequencing of multiple body segments can be extracted from a single IMU.
METHODS:
Acceleration data were collected during hand-fed tennis forehand strokes using a single inertial measurement unit (IMU) attached to the dominant wrist. All trials were temporally aligned to the racket–ball impact, identified from the acceleration signal and defined as time zero.
The acceleration waveform was decomposed into multiple frequency bands, and envelope waveforms were extracted for each band. These envelopes were analyzed as time-varying components corresponding to the trunk, chest, wrist, and racket.
The timing of each component relative to impact was examined to characterize the temporal structure of segmental contributions. Temporal patterns were compared between a skilled player and a recreational player to examine differences in movement organization.

RESULTS:
Decomposition of the acceleration signal revealed differences in the timing of segment-related activities before impact. Envelope waveforms corresponding to the trunk, chest, wrist, and racket exhibited activity peaks at distinct time points in the pre-impact phase.
In the skilled player, trunk- and chest-related components tended to appear earlier, followed by wrist- and racket-related components closer to impact. In contrast, in the recreational player, segment-related activities were more concentrated around impact, showing less temporal separation.
These results indicate that impact-centered temporal analysis using a single IMU can capture differences in pre-impact movement organization associated with skill level.
CONCLUSION:
This study demonstrated that impact-centered temporal analysis based on a single wrist-worn IMU can reveal differences in the temporal organization of segmental contributions before impact. This approach provides a practical framework for examining movement sequencing in real-world sports settings without complex measurement systems.