Do physical fitness measures influence internal training load responses in high-level futsal players?

Background: The aim of the present study was to verify whether aerobic fitness and ability to perform repeated high-intensity efforts influence the internal training load (ITL), which consists of the actual stress imposed in the athletes' organisms, in professional futsal players. Methods: Twelve high-level futsal players (age: 26.3 +/- 4.9 years, body mass: 73.5 +/- 7.5 kg) participated in the study. The investigated athletes took part in a 5-week pre-season period. The ITL was quantified by means of the session-Rating of Perceived Exertion method. The athletes performed the Yo-yo Intermittent Recovery Test level 2 (YYIR2) in order to assess the ability to perform repeated high-intensity actions, and the multistage shuttle-run test (MSRT) in order to evaluate aerobic fitness, before (T-0) and after (T-1) the pre-season period. Maximal oxygen uptake (VO2max.), oxygen uptake at Respiratory compensation point (VO2-RCP) and maximal aerobic speed (MAS) obtained in MSRT were retained for analyses. Results: The results from Pearson's correlation test showed significant and a very large correlation between ITL and YYIR2 performance (r=-0.75). Moreover, a significant and large correlation between ITL and VO2max. (r=-0.62), ITL and MAS (r=-0.67), and ITL and VO2-RCP (r=-0.58) were also observed. Conclusion: It can be concluded that aerobic fitness and ability to perform repeated high-intensity actions may influence ITL responses in professional futsal players.