Cardiovascular responses to submaximal treadmill running in 11 to 13 year olds

The influence of age, sex, maturity, body size and body fatness on cardiac output (Q) and stroke volume (SV) during treadmill running at 2.22 m x s(-1) was examined longitudinally. Mass, stature, triceps and subscapular skinfold thickness, and oxygen uptake (VO2) were recorded and Q was estimated using the CO2 rebreathing technique on each of three annual measurement occasions. Maturity was assessed using the indices for pubic hair described by Tanner. At the onset, subjects were 11.3 (0.4) y of age and data were available from a total of 274 Q determinations with equal numbers from boys and girls. Age-, sex- and maturity-associated changes in Q and SV adjusted for differences in body size and fatness were examined using multilevel regression modelling within an allometric framework. Changes in Q in both sexes were essentially in direct proportion to body surface area but, even with anthropometric variables controlled for, girls demonstrated a lower SV than boys, which was compensated for by a higher heart rate (HR) at each observation.

At a given level of submaximal exercise over the age range 11-13 y Q is directly related to body size in both sexes. With body size and fatness controlled for, boys have greater SVs than girls when exercising at the same absolute VO2, Q and treadmill running speed. Age and maturation do not exert independent effects on either Q or SV.