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 ((V)over dotO(2)) 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 ((V)over dotO(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 (V)over dotO(2max)(t((V)over dotO2max)) and the time spent above 90% of (V)over dotO(2max)(t(90%(V)over dotO2max)) did not differ significantly according to the type of exercise: with or without series [respectively t((V)over dotO2max) was 158.2 (59.7) s vs 178.0 (56.5) s and t(90%(V)over dotO2max) was 290.4 (84.3) s vs 345.0 (61.6) s] but when expressed as a relative value, t(90%(V)over dotO2max) 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 (V)over dotO(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 (V)over dotO(2max) limited the t(90%(V)over dotO2max) 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 (V)over dotO(2); however, the athletes performed more repetitions of short intense exercise.