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Growth-related changes in oxygen uptake and heart rate during progressive exercise in children
Insights
This study found that the relationship between oxygen uptake (VO2) and heart rate (HR) in children during exercise is constant when normalized to body weight. This indicates optimized oxygen delivery to muscles, with boys showing a slightly higher ratio than girls.
Area of Science:
- Pediatric Exercise Physiology
- Cardiorespiratory Fitness
Background:
- Children's aerobic responses to exercise are regulated for optimized oxygen delivery to muscles.
- The relationship between oxygen uptake (VO2) and heart rate (HR) is hypothesized to be a key regulated response.
Purpose of the Study:
- To investigate if the relationship between VO2 and HR during progressive exercise changes with body size in children.
- To determine if normalizing VO2/HR to body weight reveals a constant relationship, reflecting muscle mass correlation.
Main Methods:
- Cross-sectional study of 107 children (50 girls, 57 boys, ages 6-17).
- Progressive exercise test on a cycle ergometer with a ramp forcing function.
- Breath-by-breath gas exchange for VO2 and beat-by-beat HR measurement; linear regression analysis.
Main Results:
- The slope (M) of the VO2 = M X HR - B equation increased significantly with body weight in both sexes.
- When normalized to body weight (M/kg), there was no systematic change with increasing weight or age (mean 0.33 ± 0.10 ml/min/kg).
- Boys exhibited a significantly higher normalized value (0.37 ± 0.10) than girls (0.29 ± 0.08).
Conclusions:
- The VO2/HR relationship, normalized to body weight, is constant in children during growth.
- This supports the hypothesis of regulated oxygen delivery to muscle, independent of absolute size.
- Sex differences in normalized VO2/HR suggest potential variations in muscle efficiency or oxygen utilization between boys and girls.
Abstract:
Although body size and muscle mass increase considerably during growth in children, certain aerobic responses to exercise appear to be regulated so that the delivery of oxygen to muscle is maintained at optimized levels. We proposed that the relationship between oxygen uptake, (VO2) and heart rate (HR) was one of the regulated responses. We further hypothesized that the increase in VO2 per increase in HR during progressive exercise would differ in subjects of different size, but when normalized to body weight would be constant since changes in muscle mass are highly correlated to changes in body mass. To test this, we performed a cross-sectional study of 107 normal children, 50 girls and 57 boys ranging in age from 6 to 17 years. The protocol consisted of a continuously increasing work rate on a cycle ergometer, to the limit of the child's tolerance (ramp forcing function). Gas exchange was measured breath-by-breath for the determination of VO2, and heart rate was measured beat-by-beat. We used linear regression techniques to determine M, the slope, and B, the y intercept of the equation: VO2 = M X HR - B. In both boys and girls, M increased significantly with body weight, but when normalized for body weight (M/kg), there was no systematic change with increasing weight or age, the mean value being 0.33 +/- 0.10 ml/min/kg (SD). The mean value for the boys was 0.37 +/- 0.10 which was significantly greater than that of the girls (0.29 +/- 0.08, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)