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Introduction and methodology<\/strong><\/p>\n 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).<\/p>\n <\/p>\n https:\/\/www.youtube.com\/watch?v=AOl_QFJqwRU&t=11s<\/p>\n <\/p>\n 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, & Gavil\u00e1n, 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).<\/p>\n 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 \u00b1 0.2 years; seven girls: 10.6 \u00b1 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)<\/p>\n The training comprised three 30 min sessions per week conducted during swimmers\u2019 regular training sessions. Exercises were divided into five groups: \u2018body awareness\u2019, \u2018gliding\u2019, \u2018gliding + propulsion\u2019, \u2018propulsion\u2019, and \u2018speed\u2019. The difficulty in each content progressed over the whole training period. The exercises performed for each content were shown in supplementary file 2.<\/p>\n <\/p>\n Understanding the effects of training on underwater undulatory swimming performance and kinematicshttps:\/\/t.co\/ZAuQu90BwT<\/a> #SportsBiomechNew<\/a> by @Ruiz_NavarroPhD<\/a>, @MartaCanoAdamuz, @AndersenScience<\/a>, @Cuenca_Fernandz<\/a>, L\u00f3pez-Contreras, @ScienceJos<\/a> & @R_Arellano_C<\/a> pic.twitter.com\/qZhVeesZRx<\/a><\/p>\n — Sports Biomechanics (@sportsbiomechj) March 15, 2021<\/a><\/p><\/blockquote>\n\n