Development of Ventilatory Responses to Exercise in Normal White Children (Discussion End)
However, others have described stable values for VEmax per kilogram across the childhood years. In the study of Robinson,2 the 6- and 15-year-olds demonstrated a mean value of 1.59 and 1.60 L/kg/ min, respectively. Morse et al could find no relationship of maximal Ve per kilogram to age in boys whose ages ranged from 10 to 17 years. The longitudinal data from Rutenfranz et al describe a linear relation of VEmax to stature in female subjects until a height of 160 cm was reached. Above this height, values decreased. In male subjects, the relationship between height and maximal ventilation remained linear throughout the study. As with submaximal exercise, Rutenfranz et al were unable to demonstrate a fall in Ve/Vo2 at maximal effort as their subjects aged. This is a contradiction to findings in the present study as well as those of Astrand and Andersen et al which indicate a decline in maximal Ve/Vo2 with increasing age in children. canadian neighbor pharmacy
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Unlike other links in the oxygen delivery chain, such as cardiac output and muscle aerobic activity, the components of ventilation (Ve, Vt, and fR) are easily measured during exercise testing. Thus, barring technical error, reported data such as that provided in this study can be presumed to provide an accurate assessment of developmental changes in ventilatory function during exercise. In addition, longitudinal observations can be expected to provide a clearer picture of such changes compared with cross-sectional investigations. The findings in this study indicate that at a given level of treadmill work, Ve increases as the child ages. This rise in not, however, simply related to increase in body size. Vt increases in proportion to body mass as the child grows, but the frequency of breathing at a given submaximal work load progressively declines. As a result, submaximal Ve rises slower with age than would be expected for body mass. 
Changes in weight and height for boys and girls over the 5 years are presented in Table 1. Although the boys were heavier and taller at all ages, no significant gender differences were observed. Mean values (SD) for maximal oxygen uptake (Vo2max) at the initial testing session were 48.9 (7.2) and 47.7 (6.4) mL/kg/min for the boys and girls, respectively. These are consistent with previously reported average values of aerobic fitness for the childhood population. All exercise tests conformed to criteria for maximal effort. Tables 2 and 3 list physiologic variables for male and female subjects at submaximal and maximal exercise. No significant differences were observed by gender over time for Ve, Vt, and fR, and combined longitudinal data for these variables are presented in Figures 1-3.
Twenty children (11 boys, nine girls) volunteered for annual treadmill testing over 5 years for assessment of submaximal and maximal measurements of respiratory exchange variables. Data from one girl who moved away were not available for the final testing session. The subjects were generally physically active. Seventeen were participants on community sports teams, but none was engaged in regular endurance training. With the exception of one child, all were white, and all subjects were in good health, taking no medications that would affect exercise testing results. Data from these subjects were included in a previous report of walking economy in children. 
Cross-sectional studies have indicated that the pattern of ventilatory responses to exercise evolves during the course of childhood. This 5-year study was designed to provide a longitudinal assessment of minute ventilation (Ve), tidal volume (Vt), and breathing frequency (fR) in 20 children (11 girls, nine boys) between the ages of 9 and 13 years. Subjects performed maximal and identical submaximal steady-state treadmill walking tests annually. No significant gender differences were observed in any of the three variables. At submaximal exercise, Vt per kilogram remained stable, with a progressive fall in fR. As a result, submaximal Ve per kilogram declined with age. A similar pattern was observed at maximal exercise, but the decrease in Ve per kilogram was not statistically significant. Ventilatory equivalent for oxygen (Ve/Vo2) fell with age at submaximal exercise but declined only in the boys with maximal testing. Ve/Vo2 at maximal and submaximal exercise was greater in the girls at all ages. These findings support previous data derived from cross-sectional studies.