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Researchers from University of Tsukuba investigated the propulsion mechanism by visualizing water flow around a swimmer during underwater dolphin-kick swimming in a water channel via particle image velocimetry. Their findings revealed that swimmers can utilize water flow and vortexes more effectively as their speed increases.

Tsukuba, Japan—The swimming motion imparts momentum to water, a fluid, thereby generating a propulsive force. Thus, we can understand the propulsion mechanism by examining the water flow generated by a swimmer's motion. However, observing colorless, transparent water with the naked eye or a camera is challenging. To address this issue, researchers employed particle image velocimetry, a technique utilized in fluid dynamics, to visualize water-flow patterns. They investigated how water flow changes as swimmers change their speed while executing the dolphin-kick swimming technique. This investigation was conducted in an experimental circulating-water channel (a pool with flowing water).

The results revealed that the water-flow velocity increased with increasing swimming speed during the underwater dolphin-kick lower-limb action, generating a strong vortex during the kicking action. This phenomenon possibly contributes to the increased propulsive force. Additionally, recycling of the flow generated during the downward-kick phase was observed during the transition to the upward-kick phase, with the effect becoming more pronounced as the swimming speed increased. This study marks the first observation of water-flow changes during dolphin-kick swimming at varying speeds.

This study is expected to advance research on water flow, a critical topic in swimming research. It offers scientific evidence for instructors to adopt kick-swimming techniques.

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This work was supported by Japan Science and Technology Agency, Grant Number 22 K19725.

Original Paper

Title of original paper:

Impact of variations in swimming velocity on wake flow dynamics in human underwater undulatory swimming

Journal:

Journal of Biomechanics

DOI:

10.1016/j.jbiomech.2024.112020

Correspondence

Assistant Professor TSUNOKAWA Takaaki
Institute of Health and Sport Sciences, University of Tsukuba / Advanced Research Initiative for Human High Performance (ARIHHP)

Assistant Professor SHIMOJO Hirofumi
Department of Health and Sports, Niigata University of Health and Welfare

Related Link

Institute of Health and Sport Sciences

Advanced Research Initiative for Human High Performance (ARIHHP)