Using 23 elite male athletes (8 cyclists, 7 kayakists, and 8 swimmers), the contribution of the anaerobic energy system to the time to exhaustion (t_lim) at the minimal exercise intensity (speed or power) at which maximal oxygen uptake (VO_2max) occurs (I_VO2max) was assessed by analysing the relationship between the t_lim and the accumulated oxygen deficit (AOD). After 10-min warming up at 60% of VO_2max, the exercise intensity was increased so that each subject reached his I_VO2max in 30 s and then continued at that level until he was exhausted. Pre-tests included a continuous incremental test with 2 min steps for determining the I_VO2max and a series of 5-min submaximal intensities to collect the data that would allow the estimation of the energy expenditure at I_VO2max. The AOD for the t_lim exercise was calculated as the difference between the above estimation and the accumulated oxygen uptake. The mean percentage value of energy expenditure covered by anaerobic metabolism was 15.2 [(SD 6)%, range 8.9-24.1] with significant differences between swimmers and kayakists (16.8% vs 11.5%, P ≤ 0.05) and cyclists and kayakists (16.4% vs 11.5%, P ≤ 0.05). Absolute AOD values ranged from 26.4 ml. kg^-1 to 83.6 ml. kg^-1 with a mean value of 45.9 (SD 18) ml. kg^-1. Considering all the subjects, the t_lim was found to have a positive and significant correlation with AOD (r = 0.62, P < 0.05), and a negative and significant correlation with VO_2max (r = -0.46, P < 0.05). The data would suggest that the contribution of anaerobic processes during exercise performed at I_VO2max should not be ignored when t_lim is used as a supplementary parameter to evaluate specific adaptation of athletes.