Effects of Prescribed Sub-Maximal Paces on Underwater Undulatory Swimming Techniques

Underwater undulatory swimming (UUS) is a technique used in competitive swimming and its performance is usually associated with faster race times. Previous research mainly focused on maximal-effort UUS. It remains unclear how swimmers adjust their UUS technique to race-specific sub-maximal paces. This study investigated how swimmers naturally modified their UUS technique when tasked to swim at maximum effort, at a 100 m pace, and at a 200 m pace. Nine competitive male swimmers (World Aquatics points: 778±137) undertook multiple UUS trials at each prescribed pace in prone orientation. Kinematic data were captured using six underwater motion capture cameras, and nine key kinematic variables were calculated. The metrics were then analysed using repeated-measures ANOVA and correlation analyses. Results showed that kick frequency, toe delay, kick amplitude, and hip extension at peak toe vertical position were strongly affected by the pace. Moreover, toe delay appeared to be a good indicator of coordination and was strongly associated with changes in amplitude and frequency. Correlation analyses revealed the participants employed different coordination changes to achieve similar decreases in swimming velocity at the slower prescribed paces. These findings improve the knowledge of sub-maximal race-relevant UUS techniques while highlighting the importance of further investigating such paces.