RESUMO
AIM: The aim of this paper was to investigate the acute effects of two different initial heart rates intensities when testing the repeated sprint ability (RSA) performances in young soccer players. METHODS: Since there are many kinds of pre-match warm-ups, we chose to take as an absolute indicator of internal load the heart rate reached at the end of two different warm-up protocols (60 vs. 90% HRmax) and to compare the respective RSA performances. The RSA tests were performed on fifteen male soccer players (age: 17.9±1.5 years) with two sets of ten shuttle-sprints (15+15 m) with a 1:3 exercise to rest ratio, in different days (randomized order) with different HR% (60 & 90% HRmax). In order to compare the different sprint performances a Fatigue Index (FI%) was computed, while the blood lactate concentrations (BLa-) were measured before and after testing, to compare metabolic demand. RESULTS: Significant differences among trials within each sets (P<0.01) were found. Differences between sets were also found, especially comparing the last five trials for each set (Factorial ANOVA; P<0.01), effect size values confirming the relevance of these differences. Although the BLa- after warm-up was higher (36%) between 90% vs. 60% HRmax, after the RSA test the differences were considerably low (7%). CONCLUSION: Based on physiological information's this methodological approach (testing with initial 90%HRmax) reflects more realistically the metabolic background in which a soccer player operates during a real match. This background may be partially reproduced by warming up protocols that, by duration and metabolic commitment, can reproduce conveniently the physiological conditions encountered in a real game (e.g. HRmax≈85-95%; BLa->4 mmol/L(-1)).