Maximal aerobic capacity of 66 ten year old ice hockey players was measured on a treadmill twice over a 4 to 5 month period. This time approximated mid (T1) to post (T2) competitive season. The results of these VO2 max tests were grouped according to the presence or absence of a plateau in the oxygen uptake (less than 2.1 ml/kg-min) during the last work loads before fatigue. The mean values for T1 and T2 were not significantly different for any of the measurements made; the reproducibility was considered to be high. The reliability of the measures varied with the presence or absence of a plateau at maximum, for example; VO2 max, plateau r = 0.74, no plateau r = 0.27; heart rate, plateau r = 0.92, no plateau r = 0.40. The differences between the mean values for the "double plateau" group when compared to the "no plateau" group were not significant for VO2 max, HR or VE. The differences were significant for the post-exercise blood lactate and respiratory exchange values at T2 only; the "double plateau" group reached higher values in each case (R = 1.00 vs 0.92; blood lactate 6.5 vs 5.4 mM/1).