Comparative analysis of two fibreglass fin models in nonlinear underwater displacement among elite rugby players: A crossover study

Underwater rugby is a contact sport played in deep pools, where fins are essential for effective locomotion. This study compared the effects of two fibreglass fin models, Rocket and Waterway, on nonlinear underwater displacement times in elite players. A crossover study was conducted with 61 elite adult athletes (31 females and 30 males), all with at least 2 years of experience using fibreglass fins. Participants completed the Change of Direction Submerged (CDS) test with both fin types, with a 1-week interval between sessions. Each condition was tested twice per session to reduce intraday variability. Measurement reliability was assessed using the Intraclass Correlation Coefficient (ICC) and the Coefficient of Variation (CV). Among males, mean completion times were 6.89 ± 0.45 s (Rocket) and 6.86 ± 0.58 s (Waterway). Among females, times were 7.55 ± 0.73 s (Rocket) and 7.73 ± 0.74 s (Waterway), reflecting a small performance advantage for Rocket fins. Reliability was moderate in both sexes (ICC = 0.523 in males; ICC = 0.636 in females). CV analysis showed greater variability in females: 9.70% (Rocket) and 9.56% (Waterway), versus 6.56% (Rocket) and 8.47% (Waterway) in males. While performance differences were not statistically significant, Rocket fins showed a trend towards better consistency and slightly faster times, particularly in female athletes. These results highlight the potential of fin design to influence performance and support evidence-based selection of equipment in underwater sports. Further research is needed to explore underlying biomechanical and physiological mechanisms.