The purpose of this study was to examine blood lactate (BLa) levels and ratings of perceived exertion (RPE) in nine boys (10.5 ± 0.7 yr) and nine men (25.3 ± 2.0 yr) during exercise relative to ventilatory threshold (VT). VT and VO2max were determined during a graded exercise test on a cycle ergometer. On three additional days each subject exercised for 10 min at either 80, 100, or 120% of the VO2 at VT. Capillary BLa levels and RPE were assessed at minutes 5 and 10 of each trial.VO2max averaged 47.7 ± 5.4 and 50.2 ± 6.2 mL·g·-1min-1 in the boys and men, respectively(P > 0.05). VT expressed as %VO2max was 67.2 ± 3.5% in the boys and 67.3 ± 4.9% in the men (P > 0.05). BLa levels ranged from 2.0 ± 0.7 to 4.7 ± 0.9 mmol·L-1 in the boys and from 2.6 ± 0.5 to 8.2 ± 2.1 mmol·L-1 in the men across the three intensities. Corresponding RPE values ranged from 11.2 ± 1.8 to 16.2 ± 2.2 in the boys and from 10.2 ± 1.2 to 15.8 ± 1.7 in the men. A group× time × intensity interaction (P < 0.05) indicated that BLa in the men increased more so across time and intensity. There were no significant group difference or interactions involving RPE during exercise. Setting exercise intensity relative to VT did not abolish child-adult differences with respect to submaximal BLa levels. Despite maintaining lower BLa levels, RPE values were similar between boys and men.
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