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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.

Cardiovascular responses to exercise in trained endurance child athletes have been largely unexplored. Doppler echocardiography was utilized to compare cardiac variables during progressive upright cycle exercise to exhaustion in trained male prepubertal distance runners (n = 8) and untrained control boys (n = 14). Athletes demonstrated a greater maximal stroke index and cardiac index. Stroke volume rose progressively with increasing workloads in the runners but remained stable beyond low intensities in the non-athletes. No significant differences in stroke volume were observed between the two groups at rest. This contrasts with the greater resting stroke volumes typically seen in adult endurance athletes compared to non-athletes. Likewise, values for maximal stroke index were less in the child runners than those typically seen in trained adults. This study demonstrated that the stroke volume response to exercise differs in boy runners compared to non-athletes. The findings also suggest quantitative differences in such responses between prepubertal and young adult athletes.

ABSTRACT.Background. Animal studies and investigations of adult endurance athletes indicate a transient depression of myocardial function after prolonged highintensity exercise.Purpose. To determine whether a similar decrease is observed in child distance runners after a 4-km competitive road race.Methods. Anthropometric measures, resting M-mode echocardiograms, maximal cycle exercise tests with estimation of cardiac output, and electrocardiograms were performed before a 4-km road race in nine run-trained boys (mean age, 12.2 years). Weight and resting echocardiogram and electrocardiogram were assessed immediately after the race. The entire test battery was repeated 24 hours later.Results. Small but significant decreases in mean body weight and left ventricular end-diastolic dimension were observed immediately after the race, but there were no changes in shortening fraction. These findings are consistent with the effects of dehydration. Measurements returned to prerace values by 24 hours of recovery. Peak work capacity, maximal stroke volume, and maximal cardiac output were similar on prerace and 24-hourpostrace testing. No electrocardiographic abnormalities were observed.Conclusions. No adverse cardiac effects were observed from a competitive 4-km road race in male child distance runners. Pediatrics 1997;100(3). URL: http:// www.pediatrics.org/cgi/content/full/100/3/e2; echocardiography, children, exercise.ABBREVIATIONS. LVSF, left ventricular shortening fraction; VTI, velocity time integral; LVED, left ventricular end diastolic dimension; bpm, beats per minute.T he emergence of the elite-level child athlete has raised concern regarding possible adverse physiologic and psychologic effects of intense sports training and competition during the growing years.1 Little scientific data are available, however, to evaluate the reality of these potential risks. Consequently, creating appropriate guidelines for safe participation by children in competitive sports remains difficult.Evidence does exist that high-intensity sports may impose significant acute stress on the cardiovascular system. Echocardiographic evidence of myocardial dysfunction immediately after competition in prolonged distance running events has been demonstrated in adult endurance athletes.2,3 This depressed contractility, manifested as a decrease in left ventricular shortening fraction (LVSF), typically resolves within 24 hours after a race. Findings of left ventricular dysfunction after sustained running have also been corroborated in the laboratory setting.4 Animal studies support the concept that transient myocardial fatigue after sustained high-intensity exercise may be expressed as depressed contractility, possibly related to alterations in calcium transport capacity of the sarcoplasmic reticulum. 5,6 This study was performed to determine whether cardiac functional alterations are evident after shorter distance competitions in trained child runners. Resting electrocardiograms and two-dimensional echocardiograms were performed before and immediate...