Introduction and methodology
In freestyle, butterfly, and backstroke events, after the start and turns swimmers glide and then propel themselves forward using the underwater undulatory swimming (UUS). Except for the dive, the highest velocities are reached during the UUS, making this technique one of the most influential variables on race performance (Mason & Cossor, 2000).
https://www.youtube.com/watch?v=AOl_QFJqwRU&t=11s
The UUS is a leg-dominated technique (Higgs, Pease, & Sanders, 2017), in which the arms are outstretched and held together over the head, adopting a streamlined body position, while performing body undulations (Arellano, Pardillo, & Gavilán, 2002). Each kick cycle comprises a complete downward (downbeat) and upward (upbeat) movement of the lower limbs. The fact that swimmers travel underwater results in the potential for higher swimming velocity than in the surface swimming, since as depth increases the wave drag, which represents 50-60% of the total passive drag force, decreases noticeably (Vennell, Pease, & Wilson, 2006).
Despite the variety of kinematic parameters used to assess UUS and glide performance, the effects of training on UUS and gliding kinematics in age-group swimmers were scarce. Therefore, the study aimed to evaluate the performance and kinematics changes after a period of training in young swimmers (Ruiz-Navarro et al., 2021). Seventeen age-group swimmers (ten boys: 11.6 ± 0.2 years; seven girls: 10.6 ± 0.4 years) were evaluated at two points in time: 1) after two familiarization sessions with the testing procedures (PRE); 2) after seven weeks of UUS and glide training (POST)
The training comprised three 30 min sessions per week conducted during swimmers’ regular training sessions. Exercises were divided into five groups: ‘body awareness’, ‘gliding’, ‘gliding + propulsion’, ‘propulsion’, and ‘speed’. The difficulty in each content progressed over the whole training period. The exercises performed for each content were shown in supplementary file 2.
Understanding the effects of training on underwater undulatory swimming performance and kinematicshttps://t.co/ZAuQu90BwT #SportsBiomechNew by @Ruiz_NavarroPhD, @MartaCanoAdamuz, @AndersenScience, @Cuenca_Fernandz, López-Contreras, @ScienceJos & @R_Arellano_C pic.twitter.com/qZhVeesZRx
— Sports Biomechanics (@sportsbiomechj) March 15, 2021
The assessment was conducted in a 12.50 m long x 5.94 m wide x 1.20 m depth swimming pool using an electronic timing system (ALGE-TIMING, TP1890C Anschlagplatte, Lustenau, Austria) and a speedometer cable (linear transducer, Heidenhain, D83301, Traunreut, Germany) attached to the swimmer’s hip via a belt. After a standardized warm-up, two 10 m maximal UUS efforts and two maximal underwater gliding efforts from an in-water push-start were evaluated. From the best UUS effort, six kicks were analyzed (excluding the first two kick to avoid the effect from the push (Arellano et al., 2002)):
- Time to cover 10 m (Ttime) (s).
- Average underwater velocity (Uavg) (m/s).
- Average underwater peak velocity (Upeak) (m/s).
- Average underwater minimum velocity (Umin) (m/s).
- Kick frequency (Hz).
And the best underwater gliding trial:
- Average gliding velocity (Gavg) (m/s).
- Push-off velocity (m/s).
- Time taken to slow down to 2 m/s (T2) (s).
- Time taken to slow down to 1 m/s (T1) (s).
- Time taken to slow down to 0.15 m/s (T0.15) (s).
Results and discussion
Despite anthropometric changes were obtained after the eight weeks, these changes were not correlated with the performance enhancement, yet the combined effect of the change in height, weight, and arm span might have influenced the outcome. The rest of the kinematic variables were highly correlated with performance in either PRE and POST measurements.
After the seven weeks of training, the Ttime decreased by almost 8% during the UUS trials. Despite swimmers enhanced the velocity reached during the downbeat, the changes in performance were mostly produced by a better execution of the upbeat (Ruiz-Navarro et al., 2021). This result was of great interest since the successful execution of the upbeat can be challenging and differentiates the fastest swimmers from the rest (Atkison, Dickey, Dragunas, & Nolte, 2014). Moreover, the performance enhancement might have been due to changes in propulsive and resistive forces. However, as the authors did not measure hydrodynamic forces, this fact was not clarified.
The UUS performance can be improved by increasing the kick frequency (Arellano et al., 2002). Nevertheless, in the present study, the performance was enhanced without evidencing changes in kick frequency, which suggested that swimmers might have improved their ability to use the same kick frequency.
The initial push-off velocity and hydrodynamic drag are the two factors that determines underwater gliding performance (Lyttle, Blanksby, Elliot, & Lloyd, 1998). In the present study, while the push-off velocity did not increase, T2, T1, and T0.15 were significantly improved. This fact indicated that swimmers reduced the Hydrodynamic drag, likely by holding a more streamlined body position. Although T2 is similar to the swimming velocity achieved in sprint racing, T1 might be more suitable for age-group, as young swimmers are not able to reach 2 m/s. Moreover, while swimmers never slow down to 0.15 m/s, the T0.15 provides an understanding of a swimmer’s ability to maintain their body position and whether core stability should be enhanced (Willardson, 2007).
Applications for coaches
Understanding the effects of training that lead to performance enhancement is crucial. Coaches should not just focus on whether performance improved or not, but also on what are the factors that led to that enhancement. The current study provides a detailed assessment of UUS and underwater gliding kinematics that aid to better understand the changes produced by a training period. The variables were easily collected and without big processing time, which makes them appropriate for periodic evaluation.
Original version of the study
Ruiz-Navarro, J. J., Cano-Adamuz, M., Andersen, J. T., Cuenca-Fernández, F., López-Contreras, G., Vanrenterghem, J., & Arellano, R. (2021). Understanding the effects of training on underwater undulatory swimming performance and kinematics. Sports Biomechanics, 1-16. https://doi.org/10.1080/14763141.2021.1891276
Acknowledgments
This study was supported by grants awarded by the Ministry of Science, Innovation, and Universities (Spanish Agency of Research) and the European Regional Development Fund (ERDF); PGC2018-102116-B-I00 ‘SWIM II: Specific Water Innovative Measurements: Applied to the performance improvement’ and the Spanish Ministry of Education, Culture and Sport: FPU17/02761 grant.
References
Arellano, R., Pardillo, S., & Gavilán, A. (2002). Underwater Undulatory Swimming: Kinematic Characteristics, Vortex Generation and Application During the Start, Turn and Swimming Strokes. In Proceedings of the XXth International Symposium on Biomechanics in Sports (pp. 29–41). Caceres, Spain.
Atkison, R. R., Dickey, J. P., Dragunas, A., & Nolte, V. (2014). Importance of sagittal kick symmetry for underwater dolphin kick performance. Human Movement Science, 33(1), 298–311.
Higgs, A. J., Pease, D. L., & Sanders, R. H. (2017). Relationships between kinematics and undulatory underwater swimming performance. Journal of Sports Sciences, 35(10), 995–1003. https://doi.org/10.1080/02640414.2016.1208836
Lyttle, A. D., Blanksby, B. A., Elliot, B. C., & Lloyd, D. G. (1998). The effect of depth and velocity on drag during the streamlined glide. Journal of Swimming Research, 13, 15–22.
Mason, B., & Cossor, J. (2000). What can we learn from competition analysis at the 1999 pan pacific swimming championship? In XVIII Symposium on Biomechanics in Sports: Applied Program: Application of Biomechanical Study in Swimming. (pp. 75–82). Hong Kong.
Ruiz-Navarro, J. J., Cano-Adamuz, M., Andersen, J. T., Cuenca-Fernández, F., López-Contreras, G., Vanrenterghem, J., & Arellano, R. (2021). Understanding the effects of training on underwater undulatory swimming performance and kinematics. Sports Biomechanics, 00(00), 1–16. https://doi.org/10.1080/14763141.2021.1891276
Vennell, R., Pease, D., & Wilson, B. (2006). Wave drag on human swimmers. Journal of Biomechanics, 39(4), 664–671. https://doi.org/10.1016/j.jbiomech.2005.01.023
Willardson, J. M. (2007). Core stability training: applications to sports conditioning programs. Journal of Strength and Conditioning Research, 21(3), 979–985. https://doi.org/10.1080/16070658.1983.11689315
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