Obesity Affects Submaximal Oxygen Uptake-Heart Rate Relationship and Exercise Economy Differently in Pre- and Post-pubescent Boys and Girls

Abstract

The purpose of this study was to develop regression equations for estimating the intensity of the exercise work rate (relative peak oxygen uptake-heart rate [%VO₂-HR]) and the metabolic energy expenditure (MEE) for exercise prescription and rehabilitation medicine that are specific to children. This study took into account that the specific data in terms of obesity, sex, and pubertal status are currently unavailable. Our hypothesis was that obesity would affect the submaximal exercise the oxygen uptake (VO₂), heart rate (HR), and metabolic energy expenditure (MEE), and exercise economy (ExEco). In this retrospective study, the regression analysis was performed on 126 children, matching groups for Tanner pubertal status (prepubertal: 1.8±0.7; postpubertal: 4.1±0.7), BMI-for-age percentile (lean: 50±26; obese: 96±4), and sex (girls: 48%; boys: 52%). Percent peakVO₂ was regressed against HR, MEE against work rate (watt), and exercise economy (ExEco, mLO₂·kg lean body mass^-1·min^-1) against work rate. Additionally, stepwise linear regression was used to identify predictors for exercise peak work rate. Prepubertal and postpubertal boys exercise at lower work rates than obese (%peakVO2-HR slope; P=0.01). The reverse was true in girls, lean prepubertal work at lower compared lean postpubertal (%peakVO2-HR slope; P=0.03). Boys expend more calories during exercise compared to girls (MEE-slope; P=0.01), with no effect of puberty or obesity. Obese prepubertal children have poor ExEco compared to lean prepubertal children (ExEco-work rate slopes; P<0.01) but not in postpubertal children. Strong correlations (r=0.92-0.94) for %peakVO₂-HR and MEE regressions for boys and girls accounted for 85-92% variation. Height, lean leg, and leg fat mass accounted for 83% of the variance for predicting peak work rate. Obesity, sex, and puberty affect exercise characteristics in children and should be considered for an individualized approach to exercise prescription in children.

Keywords: Pediatrics; exercise economy; heart rate; metabolic energy expenditure; oxygen uptake.

Figure 1

The relationship between percent peak VO₂ and percent peak HR in lean/obese and younger/older boys (A) and girls (B).

Figure 2

Comparison of adult regressions (27) to regressions for boys (A) and girls (B). Regression equations were as follows: lean younger boys: %VO₂ = 1.546 × %HR – 57.76; lean older boys: %VO₂ = 1.563 × %HR – 59.1; obese younger boys: %VO₂ = 1.623 × %HR – 63.05; obese older boys: %VO₂ = 1.406 × %HR – 45.43; lean younger girls: %VO₂ = 1.501 × %HR – 55.91; lean older girls: %VO₂ = 1.388 × %HR – 45.06; obese younger girls: %VO₂ = 1.527 × %HR – 56.85; obese older girls: %VO₂ = 1.577 × %HR – 61.66.

Figure 3

Metabolic energy expenditure (MEE) for lean/obese and younger/older boys (A) and girls (B). Regression equations were as follows: lean younger boys: MEE = 3.385 × W + 79.4; lean older boys: MEE = 3.956 × W + 80.17; obese younger boys: MEE = 3.768 × W + 113.9; obese older boys: MEE = 4.049 × W + 156.2; lean younger girls: MEE = 3.886 × W + 75.44; lean older girls: MEE = 3.687 × W + 73.94; MEE = 3.687 × W + 73.94; obese younger girls: MEE = 3.771 × W + 89.07; obese older girls: MEE = 3.561 × W + 136.2.

Figure 4

Exercise economy in lean/obese and younger/older boys (A) and girls (B).