Cardiac responses to exercise in competitive child cyclists

Purpose: Cardiovascular responses to exercise in highly trained child endur ance athletes have not been well-defined. This study compared hemodynamic r esponses with progressive cycle exercise in seven competitive child cyclist s (mean age 11.9 yr) compared with 39 age-matched untrained boys. Methods: Doppler echocardiography and gas exchange variables were utilized to assess cardiovascular changes during submaximal and maximal exercise. Results: Me an (V) over dotO(2max) was 60.0 (+/-6.0) and 47.0 (+/-5.8) mL.kg(-1).min(-1 ) in the cyclists and nonathletes, respectively. At rest and maximal exerci se, the cyclists demonstrated greater stroke index than the untrained subje cts (resting mean 59 (+/-6) vs 44 (+/-9) mL.m(-2); maximal mean 76 (+/-6) v s 60 (+/-11) mL.m(-2)), but the ratio of maximal:rest stroke index was simi lar in both groups (1.31 for cyclists, 1.41 for nonathletes). Both groups s howed a plateau in stroke volume beyond low-intensity work levels. No signi ficant difference was observed in maximal arteriovenous oxygen difference. Conclusions: These findings indicate that 1) maximal stroke volume is the c ritical determinant of the high (V) over dotO(2max) in child cyclists and 2 ) factors that influence resting stroke volume are important in defining (V ) over dotO(2max) differences between child endurance athletes and untraine d boys.