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There is still considerable debate and some confusion as to the most appropriate method of scaling or normalizing maximum oxygen uptake ( _ V O 2max ) for differences in body mass (m) in both adults and children. Previous studies on adult populations have demonstrated that although the traditional ratio standard _ V O 2max (ml kg )1 min )1 ) fails to render _ V O 2max independent of body mass, the ratio standard is still the best predictor of running performance. However, no such evidence exists in children. Hence, the purpose of the present study was to investigate whether the ratio standard is still the most appropriate method of normalising _ V O 2max to predict 1-mile run speed in a group of 12-year-old children (n=36). Using a power function model and log-linear regression, the best predictor of 1-mile run speed was given by: speed (m s . With both the _ V O 2max and body mass exponents being close to unity but with opposite signs, the model suggest the best predictor of 1-mile run speed is almost exactly the traditional ratio standard recorded in the units (ml kg )1 min )1 ). Clearly, reporting the traditional ratio standard _ V O 2max , recorded in the units (ml kg )1 min )1), still has an important place in publishing the results of studies investigating cardiovascular fitness of both children and adults.

Maximal oxygen uptake (VO2max) in females, expressed as ml x kg(-1) x min(-1), declines steadily during the first three decades of life. The contribution of diminished cardiovascular function to this apparent fall in aerobic fitness is unknown. Cardiac responses to maximal cycle exercise were compared in 24 premenarcheal females (mean age 11.7 years) and 17 young adult women (mean age 27.4 years) using Doppler echocardiography. Mean VO2max was 40 ml x kg(-1) x min(-1) and 34.7 ml x kg(-1) x min(-1) in the girls and women, respectively (p < 0.05). When VO2max was expressed relative to allometrically-derived mass(0.52), however, no significant difference was observed in aerobic fitness between the two groups. Similar allometric analyses revealed no significant differences in average maximal cardiac output (10.50 vs 10.07 L x min(-1) BSA(-1.11) for girls and women, respectively) nor maximal stroke volume (53 vs 56 ml BSA(-1.13) respectively). These findings suggest that 1) allometric scaling is important in eliminating the effects of body size on VO2max, 2) body dimension differences can account for variations in VO2 in young females, and 3) cardiac functional reserve is similar in premenarcheal girls and young adult women.

Background: Endurance run tests are administered in schools to assess cardiovascular fitness, defined in the laboratory as maximum oxygen consumption. Objective: To examine the validity of this concept, assessing the influences of body fat and maximum values of oxygen consumption per unit time, stroke volume, heart rate, and arteriovenous oxygen difference on 1-mile (1.6km) run time in healthy sixth-grade boys. Study Design: Subjects were 36 boys with a mean (SD) age of 12.2 (0.5) years. The relationship was examined between body fat content (estimated by skinfold measurements) and maximum oxygen consumption per kilogram and cardiac variables (during maximum cycle testing) with 1-mile run velocity. Results: Body fat content and maximum oxygen consumption per kilogram (independent of body fat) accounted for 31% and 28% of the variance in run velocity, respectively. Stroke volume was the only component of maximum oxygen consumption that related to run performance. Conclusions: These findings suggest that cardiovascular fitness and body fat content contribute equally to 1-mile run time in healthy boys and together account for only 60% of the variance in performance on this endurance fitness test. Consequently, 1-mile run performance in children may not serve as a strong indicator of cardiovascular fitness.

Previous studies have suggested that submaximal energy expenditure relative to body mass during weight-bearing exercise may be greater in boys compared to girls. This two-part study examined a) gender-related five-year longitudinal changes in submaximal walking economy and b) gross, net, and delta muscle work efficiency during submaximal cycle exercise in a cross-sectional analysis of boys and girls. In the longitudinal study, the influence of pre-exercise metabolic expenditure, stride frequency, and substrate utilization (by RER) on changes in economy were examined. During the five years, mean VO2 per kg during submaximal treadmill walking (measured at 8% slope, 3.25 mph) decreased 16% in girls and 13% in boys (p > 0.05 for gender). Likewise, no significant gender differences were observed in decline of stride frequency over time. RER values were similar between sexes except in the final two years when girls had significantly greater values than the boys. No gender-related differences were observed in any measure of muscle work efficiency. This study failed to reveal significant gender differences in utilization of energy during submaximal exercise in children.

Previous studies have indicated the importance of allometric scaling of VO2max for body size. However, no information is available on adjusting maximal cardiac output (Qmax) and stroke volume (SVmax) for body dimensions. The allometric exponent b was determined for the equation Y = aXb (where Y is the physiological outcome and X is the anthropometric variable) for VO2max, Qmax, and SVmax relative to mass, height, and body surface area (BSA) in 24 premenarcheal girls (mean age 12.2 years) during cycle testing. Values for b were 1.08 and 1.05 for BSA relative to Qmax and SVmax, approximating that of 1.0 using the traditional ratio standard (cardiac index and stroke index). Exponents of body mass relative to VO2max, Qmax, and SVmax (0.55, 0.55, and 0.59, respectively) eliminated the effects of body size, but the ratio standard (M1.0) did not. In this group of subjects, use of the ratio standard BSA was an appropriate means of adjusting maximal values of Q and SV for body size.

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Little is known regarding the physiological determinants of maximal oxygen uptake (VO2max) in children. A group of 39 healthy sixth-grade boys (mean age, 12.2 years) underwent maximal cycle testing with determination of cardiovascular factors using Doppler echocardiography as well as standard gas exchange variables. Maximal stroke index was related to VO2max/kg (r=0.52, p < .05), but no relationship was observed between VO2max/kg and either maximal heart rate or calculated maximal arteriovenous oxygen difference. Values of maximal stroke index were closely related to those at rest (r = 0.67). These findings suggest that factors influencing resting stroke volume are primarily responsible for inter-individual differences in VO2max per kg in healthy, non-athletically-trained boys.