Table 7 Summary of study hydrodynamics data
Reference | Trials | Hydrodynamic mechanism |
|---|---|---|
Atkison et al. [10] | 3 × 15 m max UUS from a push start in prone body position 2D kinematic analysis | Peaks in horizontal velocity occurred at the same time as, or immediately following peaks in vertical toe velocity. Furthermore, there was a greater increase in horizontal velocity for the down kick (1.67 m s−1, r = 0.983*) than the up kick (1.62 m s−1, r = 0.993*), corresponding to faster peak vertical toe velocities during the down kick phase (DK = − 2.38 m s−1, UK = 1.99 m s−1). The authors interpreted these findings to suggest an association between magnitude of peak vertical toe velocity and vortex magnitude, and timing of peak vertical toe velocity and timing of vortex shedding, based on the idea that efficient swimmers create a large static vortex at the end of the down kick and a small vortex at the end of the up kick |
Elipot et al. [14] | 3 × 15 m max UUS from a grab start in prone body position 2D kinematic analysis | By increasing kick amplitude, swimmers create a bigger wake of counter-rotation vortices that contribute to the leg propulsive forces. However, when kick amplitude is increased, the swimmer’s form drag will also increase |
Hochstein et al. [44] | 20 m max UUS trial from a standing start in the prone body position 2D Particle Image Velocimetry (PIV) | Resulting vortex rings after the up and down kick merge into longitudinal vortex strings in the swimmer’s wake Increased vortex generation indicates increased drag |
Miwa et al. [46] | 5 × steady UUS in a swimming flume (1.0 m s−1) 2D flow analysis | The results confirm the existence of a pair of vortices and jet flow in the wake of undulatory kicking motion. After the upward motion, some pairs of small vortices and the jet flow were also confirmed; however most were from the down kick The swimmer created the vortex ring for propulsion |
Shimojo et al. [48] | 41 × 15 s steady UUS in a swimming flume in prone body position (0.8 m s−1) (12–20 UWK cycles) | During the downward kick, the lower limbs moved downwards with internal rotations and ankle plantar flexion, and the pressure difference between the dorsal and ventral side produced a fluid force The pressure difference produced a leading edge vortex that travelled from the ventral to dorsal side of the feet through the toes. After a clockwise rotating vortex generated by the leading edge, the vortex was shed from the foot, inducing downstream flow. The shedding of vortices from the feet expanded and created a cluster The swimmer externally rotated his lower limbs at the end of the downward kick, and the toes of the feet approached and then separated each other. This action generated a strong cluster of vortices and jet flow in the wake resulting in thrust The cluster of shed vortices and jet flow were released from the feet after the downward kick, and moved towards to the ventral side of the swimmer During the upward kick, upstream flow was created with small vortex structure |