Cardiac responses to maximal upright cycle exercise in healthy boys and men.

Previous investigations have indicated that children demonstrate a lower cardiac output at a given oxygen uptake during exercise compared with adults. This study compared cardiac responses with maximal upright cycle exercise in 15 boys (mean age 10.9 yr) and 16 men (mean age 30.7 yr) to determine whether this observation reflects differences in size or age-related influences on myocardial function. Stroke volume, aortic peak velocity, and systolic ejection time were measured to peak exercise in all subjects using Doppler ultrasound techniques. No significant differences were observed in resting, submaximal, or peak mean values for these variables relative to body size between the boys and men. Average values for peak stroke index, cardiac index, and peak aortic velocity were 59 (+/-11) mL.m-2, 11.33 (+/-2.32) L.min-1.m-2, and 152 (+/-30) cm.s-1, respectively, for the boys. Respective values for the men were 61 (+/-14) mL.m-2, 11.08 (+/-2.52) L.min-1.m-2, and 144 (+/-24) cm.s-1 (P > 0.05). This study failed to demonstrate evidence of impaired cardiac responses to maximal exercise in prepubertal boys compared with that in adult males.