Álvarez, JCB, D'ottavio, S, Vera, JG, and Castagna, C. Aerobic fitness in futsal players of different competitive level. J Strength Cond Res 23(7): 2163-2166, 2009-Recently the use of small-sided games (mainly 5 vs. 5) proved to be a valid training method to improve aerobic fitness in soccer. Thus, it could be hypothesized that professional futsal (soccer 5-a-side indoor version) players may possess a well-developed aerobic fitness as a consequence of training and game participation. The aim of this study was to examine maximal oxygen uptake (JOURNAL/jscr/04.02/00124278-200910000-00037/ENTITY_OV0312/v/2017-07-20T235407Z/r/image-pngO2max), ventilatory threshold (VT), and running economy (RE, JOURNAL/jscr/04.02/00124278-200910000-00037/ENTITY_OV0312/v/2017-07-20T235407Z/r/image-pngO2 at 8 km·h−1) of futsal players of different competitive levels to determine whether aerobic fitness is a discriminative variable for futsal success. Subjects were 24 male futsal players from a professional top-ranked second division team (PT, n = 11) and a semi-professional top-ranked third division team (ST, n = 13). Aerobic fitness was assessed with a running protocol performed on a motor-driven treadmill. Professional team and ST players' JOURNAL/jscr/04.02/00124278-200910000-00037/ENTITY_OV0312/v/2017-07-20T235407Z/r/image-pngO2max were 62.9 ± 5.3 and 55.2 ± 5.7 mL·kg−1·min−1, respectively (p < 0.05). RE was 34.1 ± 2.7 and 32.4 ± 2.7 mL·kg−1·min−1 for PT and ST, respectively (p >0.05). PT and ST attained VT at 70.5 ± 2.7 and 71.3 ± 5.2% of JOURNAL/jscr/04.02/00124278-200910000-00037/ENTITY_OV0312/v/2017-07-20T235407Z/r/image-pngO2max, respectively (p > 0.05). Results showed that JOURNAL/jscr/04.02/00124278-200910000-00037/ENTITY_OV0312/v/2017-07-20T235407Z/r/image-pngO2max may be considered a competitive-level dependent physical variable in futsal. VO2max values of or above 60 mL·kg−1·min−1 are advisable to play futsal at the professional level.