Relevance of sprint interval and repeated sprint training protocols to the physiological and kinematic demands of 25 and 50-m swimming: A randomized experimental case study

Purpose To compare the physiological and kinematic responses of sprint interval training (SIT) and repeated sprint training (RST) with the demands of maximal 25- and 50-m freestyle swimming in a national-level sprint swimmer. Methods A 19-year-old male national-level freestyle specialist completed maximal 25 and 50 m freestyle time trials, a SIT protocol (2 × 4 × 25 m, 40 s recovery), and a RST protocol (2 × 8 × 12.5 m, 20 s recovery) on separate testing days. Blood lactate ([La − ]) concentration, blood glucose (BG), maximal lactate concentration rate (VLa max ), swimming speed (SS), stroke number (SN), stroke length (SL), stroke rate (SR), and stroke index (SI) were assessed to determine the physiological and biomechanical relevance of each training protocol. Results [La − ] reached 10.7 mmol·L −1 after the 50 m trial, compared with 11.8 and 13.4 mmol·L −1 following the SIT and RST protocols, respectively. BG demonstrated a similar pattern, with the highest values observed after completion of the RST protocol. Also, the RST protocol better maintained stroke mechanics across repetitions, whereas the SIT protocol elicited greater changes in stroke rate. Conclusions Both SIT and RST reproduced the high anaerobic demands of 50 m freestyle swimming. However, the proposed RST protocol induced the greatest glycolytic response while maintaining swimming velocity and race-specific stroke characteristics, suggesting that short repeated maximal efforts may provide a more event-specific stimulus for sprint swimmers.