Background: The underwater phase after the start and turns are relevant sections of a swimming race. During this phase, underwater undulatory swimming (UUS) is performed to generate propulsion and maintain speed. Expanding the UUS diagnostics to include a load-velocity-profile (LVP) could provide further information about individual performance. Until now, LVP have not yet been applied to UUS. Aim: The aim of this work is to develop LVP for UUS in youth swimmers and to examine the relationship with the 15 m UUS performance. Methods: A cross-sectional analysis was conducted involving young athletes from the national swimming association's squad system (n = 24 (10 females, 14 males); age: 16.5 ± 1.1 y). The swimmers performed UUS against three different loads and without additional load. The loads were applied using the electronic resistance device "1080 Sprint". The theoretical maximal velocity (V0), maximal absolute and relative load (L0, rel. L0) and the slope of the regression line were analysed from the LVP. Stroke cycle frequency was analysed from the raw data. Results: The individual load-velocity relationships showed a linear fit with an average R2 of 0.98 (0.88-1.00). The following average LVP parameters were obtained for the pooled sample: V0: 1.44 ± 0.21 m/s, L0: 10.12 ± 4.58 kg, rel. L0: 0.14 ± 0.05 kg/kg BW. The 15 m UUS performance was 7.82 ± 0.73 s. There were significant (p < .05) sex differences for these parameters. In the pooled sample, 15 m UUS performance showed significant negative correlations with V0 (-0.91; p < .001) and L0 (-0.74; p < .001). The correlations between 15 m UUS performance and LVP parameters were higher in male swimmers (V0: -0.88; p < .001; L0: -0.53; p = .05) than in female swimmers (V0: -0.22; p = .54; L0: -0.09; p = .81). Conclusion: The initial results indicate that LVP can be applied to UUS and may provide relevant information of the UUS performance of youth swimmers. The high significant correlation between V0 and 15 m UUS performance in the pooled sample suggests that theoretical maximal velocity is closely related to UUS performance in a pooled sample. However, because sex differences were observed for all LVP parameters, future analyses should consider sex-specific interpretation of LVP outcomes.
© Copyright 2026 XVth International Symposium on Biomechanics and Medicine in Swimming Proceedings. All rights reserved.