Assessment of cardiorespiratory exercise function in obese children and adolescents by body mass-independent parameters.

The parameters used to assess aerobic exercise function by gas exchange are usually adjusted for body mass and are expressed as millilitres per minute per kilogram. In the case of obese children this could lead to overcorrection with an underestimation of their exercise capacity. The purpose of the present study was to assess cardiorespiratory exercise function in obese subjects using body mass-independent parameters. As both carbon dioxide output (VCO2) and oxygen uptake (VO2) are usually corrected for body mass, the slope of VCO2 versus VO2 can be considered to be independent of body mass. This slope was calculated below the ventilatory threshold (S1) and above the ventilatory threshold (S3). Exercise tests were performed on a treadmill and respiratory gas exchange was measured breath-by-breath. A group of 29 obese children [mean age 11 (SD 2.5) years] were compared to 16 normal controls of the same age range [mean age 10.8 (SD 2.2); P > 0.05]. The patients were overweight by 36 (SD 17.9)% and had a body mass index of 25.0 (SD 3.8). The results showed that S3 in the obese subjects was significantly steeper compared to the normal controls [1.30 (SD 0.20) vs 1.10 (SD 0.20); P < 0.05]. The steepest values for S3 were found in the subjects with the highest degree of obesity. This method has some limitations, since in a large proportion of the patients (48%) no ventilatory threshold could be detected, which is prerequisite for calculation of these slopes. The latter was already suppressed at the onset of exercise in 21% of the sample or could not be detected because of breathing irregularity in 27%. It is suggested from this study that cardiorespiratory exercise function in obese children is reduced, especially when assessed by parameters of aerobic exercise which cancel the confounding effect of body mass.

Exercise therapy and hypocaloric diet in the treatment of obese children and adolescents.

Fourteen obese children and adolescents were treated with a combined therapy of low calorie diet and exercise and their progress compared to that of 11 obese children treated with diet only. Children treated with combination therapy were encouraged to perform aerobic exercises daily, for a period of time which was calculated to consume approximately 250 kcal per exercise session. After 4 months of therapy, a significantly (P less than 0.05) larger decrease of % overweight was observed in the group of children treated with diet and exercise (-25 +/- 13.5%) than in those treated with diet only (-15.8 +/- 10.5%). Treatment compliance was better in the group treated with diet and exercise than in the group which followed a low calorie diet only. We think that unsupervised exercise therapy can be successfully combined with a low calorie diet in the treatment of childhood obesity.

Cardiorespiratory function during exercise in obese children.

Fifteen obese children, aged 4 to 16 years and ranging in body weight from 27.3 to 95 kg (median 67.5) and percentage overweight from 22 to 127% (median 40), underwent graded exercise testing on a treadmill and were compared with healthy peers of comparable age. Cardiorespiratory performance capacity was assessed by determination of the ventilatory threshold. This was defined as the highest oxygen uptake at which the pulmonary ventilation stops to increase linearly with increasing exercise intensity. The ventilatory threshold, expressed as ml O2/min/kg, was significantly (p less than 0.05) lower than in normal children and averaged 70.6 +/- 13.5% of the normal mean value, matched for age. The habitual level of physical activity, assessed by a questionnaire, was 27% lower (p less than 0.01) in the obese children compared to healthy controls. As the ventilatory threshold was strikingly lower and also exceeded sooner in the majority of the obese children, compared with normal controls, it may be assumed that obese children avoid moderate or strenuous exercise, because of the higher degree of effort needed. This may contribute to the maintenance of overweight.