Tsukuba, Japan—The underwater dolphin kick is a swimming technique in which propulsion is generated solely through the undulatory motion of the lower limbs, increasing swimmers' speed by moving the body in a wavelike pattern similar to fish or marine mammals. However, because the human body is not naturally adapted to such undulatory movements, swimmers must master advanced motor skills to improve performance in this technique.
This study analyzed time-series data of joint movements during underwater dolphin kick to examine differences in swimmer performance levels. Using conducting kinematic synergy analysis, the researchers identified two primary coordination patterns in this technique—the coordinated motion of the shank and foot, and hip flexion and extension centered on thigh movement. Together, these two synergies accounted for over 99% of the movement across all performance levels. Importantly, faster swimmers performed greater shoulder extension during the downward kick and displayed increased lower trunk movement during the upward kick. This arm-trunk-thigh coordination helps swimmers maintain a horizontal upper body and reduce water resistance throughout the kicking cycle.
This research is the first to identify the coordination patterns in underwater dolphin kick using kinematic synergy analysis. Its findings offer valuable insights into the refinement of underwater dolphin kick drills and the effective design of land-based training programs. Future studies are expected to apply similar analyses to other swimming techniques that involve more complex movements.
Title of original paper:
Joint kinematics and inter-segmental coordination during underwater undulatory swimming: Comparing swimmers of different performance levels
Journal:
Journal of Biomechanics
DOI:
10.1016/j.jbiomech.2025.113085
Assistant Professor YAMAKAWA, Keisuke
Institute of Health and Sport Sciences, University of Tsukuba
Institute of Health and Sport Sciences
Journal of Biomechanics
10.1016/j.jbiomech.2025.113085
Joint kinematics and inter-segmental coordination during underwater undulatory swimming: Comparing swimmers of different performance levels
24-Nov-2025