Development of Ventilatory Responses to Exercise in Normal White Children (Results)

Development of Ventilatory Responses to Exercise in Normal White Children (Results)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.

The pattern of change for absolute variables is similar at both submaximal and maximal exercise intensities: a linear increase in Ve, curvilinear rise in Vt, and progressive decline in fR. The average rise in Ve and Vt per year was 8.8 (1.9) and 0.20 (0.10) L, respectively. Maximal Ve increased with age (A) according to the following equation:

VEmax= — 11.1 + 8.46A.

When Ve and Vt were expressed relative to body mass, similar patterns at submaximal and maximal exercise with time were again observed. Submaximal Vt per kilogram did not change significantly over the 5 years, with an average value in the combined gender group of 21.8 (2.2) mL/kg. As a consequence, the decline in submaximal fR from 45 to 36 breaths/min resulted in a progressive fall in Ve per kilogram.

At maximal exercise, Vt per kilogram was stable over the 5 years with a mean value of 29.8 (1.5) mL/kg. Breathing rate declined from 64 to 57 breaths/min. A trend for VEmax per kilogram to decrease was observed, but the change did not reach statistical significance (p>0.05). However, a gender difference was apparent in this trend, as a steady decline in VEmax per kilogram across the years was observed in female subjects, while values remained stable in male subjects (Fig 4). Average combined VEmax per kilogram was 1.83 (0.04) L/kg. Allometrie analysis indicated that absolute VEmax changed relative to body mass (M) and height (H) over the 5 years by

VEmax=0.38M

VEmax=03.6H2

The rise with age in absolute Ve at both maximal and submaximal exercise lagged behind increases in total body metabolic rate. Ve/Vo2 fell progressively during the study period in both sexes, except for stable maximal values in the girls (Fig 5). At each year, the value of Ve/Vo2 was significantly greater in the female subjects, the only statistically significant gender-related variable observed in this study.

Table 1—Weight and Height Changes With Age: Mean (SD) Values

Year
]1 2 3 4 5
Weight, kg
Boys 37.1 (6.1) 42.3 (7.4) 47.3 (9.2) 54.3 (12.6) 57.5(14.2)
Girls 35.4 (11.1) 40.2(14.0) 43.5(14.7) 49.8 (16.7) 57.3 (18.8)
Height, cm
Boys 142 148 154 161 168
Girls 140 145 151 159 165

Table 2—Submaximal Physiologic Variables With Age: Mean (SD) Values

Year
1 2 3 4 i5
Ve, L/min
Boys 34.2 (5.0) 36.0 (5.5) 39.7 (9.2) 39.8 (9.6) 40.8 (10.6)
Girls 34.9(10.0) 36.6(12.5) 40.2(17.6) 40.2(14.0) 43.4(16.2)
Ve, L/kg/min
Boys 0.93(0.11) 0.86 (0.13) 0.84(0.11) 0.74 (0.08) 0.71 (0.08)
Girls 1.00(0.13) 0.92 (0.09) 0.91 (0.12) 0.81 (0.06) 0.75 (0.06)
Vt, L
Boys 0.84 (0.10) 0.89(0.10) 1.00 (0.09) 1.08(0.14) 1.25 (0.17)
Girls 0.76(0.18) 0.85 (0.23) 0.90 (0.22) 1.04 (0.32) 1.19 (0.39)
Vt, L/kg
Boys 0.023 (0.002) 0.021 (0.002) 0.021 (0.003) 0.020 (0.001) 0.022 (0.002)
Girls 0.028 (0.003) 0.021 (0.002) 0.021 (0.002) 0.021 (0.003) 0.021 (0.002)
fR, b/min
Boys 43 42 41 38 34 
Girls 47 44 43 39 38 
Ve/Vo2
Boys 31.45 (5.10) 28.61 (3.11) 28.27 (2.75) 27.74 (2.88) 26.34 (2.66)
Girls 32.28 (2.80) 30.90 (2.47) 30.66 (3.85) 30.18(1.89) 29.05 (2.34)

Table 3—Maximal Physiologic Variables With Age: Mean Values (SD)

Year
i1 2 3 4 i5
Ve, L/min
Boys 65.9 (8.0) 78.2 (9.3) 85.5 (12.3) 94.4 (13.1) 105.1 (16.3)
Girls 64.1 (11.9) 71.0(14.1) 76.3 (19.8) 83.1 (18.0) 95.3 (22.7)
Ve, IVkg/min
Boys 1.82 (0.35) 1.89 (0.27) 1.85 (0.31) 1.79 (0.27) 1.86 (0.31)
Girls 1.90 (0.32) 1.88 (0.43) 1.82 (0.34) 1.74 (0.28) 1.71 (0.38)
Vt, L
Boys 1.07 (0.11) 1.27 (0.13) 1.37 (0.17) 1.55 (0.17) 1.95 (0.38)
Girls 1.07 (0.25) 1.17(0.33) 1.27 (0.33) 1.41 (0.38) 1.75 (0.53)
Vt, L/kg
Boys 0.029 (0.002) 0.030 (0.003) 0.029 (0.002) 0.029 (0.004) 0.034 (0.004)
Girls 0.030 (0.002) 0.029 (0.002) 0.029 (0.004) 0.028 (0.003) 0.031 (0.004)
fR, b/min
Boys 65 62 63 61 57 
Girls 63 63 61 60 57 
Ve/Vo2
Boys 37.15 (3.54) 35.29(1.72) 34.44 (2.32) 35.90 (2.76) 34.05 (2.58)
Girls 39.64 (2.26) 39.22 (3.35) 37.98 (2.30) 39.50 (2.04) 39.37 (3.88)

figure-1

Figure 1. Changes in maximal and submaximal Ve with age.

figure-2

 

Figure 2. Changes in maximal and submaximal Vt with age.

figure-3

 

Figure 3. Changes in maximal and submaximal fR with age.

figure-4

 

Figure 4. Changes in maximal Ve per kilogram in boys and girls with age.

figure-5

 

Figure 5. Changes in Ve/Vo2 at maximal and submaximal exercise in boys and girls according to age.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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