The effects of six sprint interval training sessions on muscle oxygenation and swimming performance in untrained swimmers

The current study examined the changes in muscle oxygenation values and swimming performance after six sessions of sprint interval training during a three-week period in untrained swimmers. Twelve swimmers of both genders (age: 23.5 ± 5.6yrs) executed the twice-weekly experimental training protocol (EXP, <i>n</i> = 12), consisting of a 4 × 50 m front-crawl swimming (repeated sprint training-RST) with maximal intensity, and 2 min of passive recovery in between, after a short in-water warm-up. The control group (CON, <i>n</i> = 9) performed a continuous swimming set (200 m) at 120 b pm^-1, with the same weekly frequency. Performance times in two maximum swim trials (400 m: T400 and 50 m: T50), muscle oxygenation of the deltoid muscle (SmO₂) immediately after T400 and T50, 1-min heart rate recovery (HRR1) after T400, T50, and swim strokes during both swim trials (S/T400, S/T50) were assessed. For the EXP group, T400 improved by 2.4 (<i>p</i> = 0.011). In contrast, T50 presented no significant improvement (1%, <i>p</i> > 0.05). SmO₂ decreased at T400 (5.5%, <i>p</i> = 0.017) and increased at T50 (3.7%, <i>p</i> = 0.030). HRR1 improved after T400 (7.9%, <i>p</i> = 0.002), T50 (4.6%, <i>p</i> = 0.005) and RST (9.6%, <i>p</i> = 0.002). S/T400 and S/T50 remained relatively unchanged (<i>p</i> > 0.05). The CON group presented no significant changes in any of the variables examined. In conclusion, six sprint interval training sessions can improve aerobic capacity over a 3-week training period, as indicated by the enhanced T400 performance and the reduced HRR1 values, in previously trained swimmers. Finally, the sensitivity of the near-infrared spectroscopy method to detect short-term training-induced changes is highlighted.