Progression of Sprint Interval Training Set Performance and Physiological Responses during a Six-Week Training Period

The aim of this study was to examine the progression and the effect of sprint interval training (SIT) on swimmers’ performance and physiological responses during and after a 6-week period. Eight swimmers (age: 16.7 ± 4.2 years) performed maximum efforts for (a) 200 and 400 m front crawl for the determination of critical speed (CS), (b) four 50 m repetitions (4 × 50 m) and a 100 m test before (Pre) and after (Post) the 6-week training period. SIT was applied three times per week including two sets of 4 × 50 m sprints starting every 2 min. Pre and Post swimming time (T), blood lactate (BL), heart rate (HR), and rate of perceived exertion (RPE) were evaluated. CS increased by 4.4 ± 5.2% (p = 0.01) after 6 weeks. The Pre vs. Post values of T in 4 × 50 and 100 m and BL were unchanged (T: d = 0.05, 0.09, p = 0.14, 0.47, respectively; BL: d = 0.12, p = 0.42), while HR was decreased (d = 0.24, p = 0.04). The progression of T in 4 × 50 m training sprints was unchanged (p = 0.25) while BL increased in weeks 3 (9.4 ± 5.9%) and 5 (13.9 ± 7.8%) compared to week 1 (p = 0.01). SIT improved the swimmers’ aerobic endurance. The lactate response progressively increased despite similar SIT performance during the 6-week period.