Effects of active recovery between series on performance during an intermittent exercise model in young endurance athletes

The purpose of our study was to compare time to exhaustion (t_lim) and time spent at a high level of oxygen uptake (V̇O₂) during two high-intensity short intermittent exercises (30 s-30 s) realized with or without series. Eleven young endurance-trained athletes [16.6 (0.4) years] took part in three field tests until exhaustion: (1) a maximal graded test to measure their maximal aerobic velocity (MAV) and maximal oxygen uptake (V̇O_2max); (2) and (3) two randomized intermittent exercises (30 s at 110% of MAV alternated with 30 s at 50% of MAV): one alternating repetitions non-stop (IE) and another including 4 min recovery every six repetitions (IEs). The mean t_lim measured during IEs was significantly longer than IE [respectively 960.0 (102.0) s vs 621.8 (56.2) s]. The time spent at V̇O_2max(t_V̇O2max) and the time spent above 90% of V̇O_2max(t_90%V̇O2max) did not differ significantly according to the type of exercise: with or without series [respectively t_V̇O2max was 158.2 (59.7) s vs 178.0 (56.5) s and t_90%V̇O2max was 290.4 (84.3) s vs 345.0 (61.6) s] but when expressed as a relative value, t_90%V̇O2max during IEs was significantly lower than during IE [respectively 36.4 (10.4)% t_lim vs 58.3 (8.7)% t_lim]. Despite a significant decrease (P<0.005) of time to achieve 90% of V̇O_2max at the start of each series during IEs [respectively 165.0 (43.1) s for the first series and 82.5 (15.8) s for the second series (n=6)] the time spent under 90% of V̇O_2max limited the t_90%V̇O2max during each series. In conclusion, our results showed that intermittent exercise with series does not permit an increase in the time spent at a high level of V̇O₂; however, the athletes performed more repetitions of short intense exercise.