PURPOSE:Poor cardiorespiratory fitness is associated with increased all cause morbidity and mortality. In children with obesity, maximum oxygen uptake (V̇O2max) may not be achieved due to reduced motivation and peripheral fatigue. We aimed to identify a valid submaximal surrogate for V̇O2max in children with obesity.METHOD:Ninety-two children with obesity (7-16 years) completed a maximal exercise treadmill test and entered a three-month exercise and/or nutrition intervention after which the exercise test was repeated (n = 63). Participants were required to reach V̇O2max to be included in this analysis (n = 32 at baseline and n = 13 at both time-points). The oxygen uptake efficiency slope (OUES) was determined as the slope of the line when V̇O2 (L/min) was plotted against log V̇E. Associations between the maximal OUES, submaximal OUES (at 3, 4, 5 and 6 min of the exercise test) and V̇O2max were calculated.RESULTS:In the cross-sectional analysis, V̇O2max (L/min) was strongly correlated with 5-min OUES independent of Tanner puberty stage and sex (R2 = .80, p < .001). Longitudinal changes in V̇O2max were closely reflected by changes in 5-min OUES independent of change in percent body fat (R2 = .63, p < .05).CONCLUSION:The 5-min OUES is a viable alternative to V̇O2max when assessing children with obesity.

An improvement in cardiorespiratory fitness (CRF) following an exercise intervention is a primary indicator of training efficacy. In obese children, maximal oxygen uptake (VO2max) may not be achieved during an exercise test due to reduced motivation or peripheral fatigue. Identifying a valid surrogate for VO2max, obtained with a submaximal exercise effort, would therefore be advantageous in this population. PURPOSE: To determine whether exercise-training induced changes in VO2max are associated with changes in a submaximal six-minute oxygen uptake efficiency slope (6minOUES) protocol in obese children. METHODS: Sixty-three obese children (BMI>95th percentile for age & sex) completed a maximal exercise treadmill test with ventilatory expired gas analysis before and after a three-month exercise intervention. Participants who satisfied oxygen uptake plateau criteria and achieved a peak respiratory exchange ratio (RER) ≥1.05 were classified as reaching VO2max. Thirteen participants (age 13.0±2.0; Tanner puberty stage 3 (2.5-4.5), female 69%) reached VO2max prior to and following the intervention and were included in this analysis. The OUES was determined as the slope of the line when VO2 (ml/min) was plotted against logVE. Maximal OUES (OUESmax) was calculated from start to end of the test while 6minOUES was calculated from start of the test to the 6-minute marker. Body fat percentage was quantified using dual x-ray absorptiometry or air displacement plethysmography. VO2max, OUESmax and 6minOUES were normalised to body weight and change scores were calculated. RESULTS: There was an increase in VO2max of 2.85±5.48 ml/kg/min following a three-month exercise intervention. This was closely reflected by a mean increase in OUESmax (3.45±7.60) and 6minOUES (3.62±8.49). The increase in VO2max was strongly correlated with an increase in OUESmax (r2 = 0.81, p<0.05) and an increase in 6minOUES (r2 = 0.77, p<0.05) independent of sex and change in percent body fat. The increase in 6minOUES was strongly correlated with the increase in OUESmax (r2 = 0.91, p<0.05). CONCLUSION: The 6minOUES treadmill protocol is a valid submaximal measure of exercise-training induced CRF changes in obese children. This may be valuable when VO2max is not achieved in exercise testing designed to determine training-induced improvements.

Poor cardiorespiratory fitness (CRF) is associated with increased all cause morbidity and mortality. CRF assessment in obese youth provides valuable information on present and future health status as well as assessing efficacy of an exercise intervention. Maximal oxygen uptake (VO2max) is often difficult to achieve in a sedentary paediatric population due to a lack of motivation and peripheral fatigue, resulting in submaximal test results. Due to the tight linear relationship throughout exercise, the oxygen uptake efficiency slope (OUES) holds possible utility as a predictor of VO2max. PURPOSE: To determine whether a submaximal six-minute OUES (6minOUES) protocol accurately predicts maximal oxygen uptake (VO2max) in obese children. METHODS: Eighty-nine obese children (BMI>95th percentile for age and sex) completed a maximal graded exercise treadmill test with ventilatory expired gas analysis. Participants who satisfied oxygen uptake plateau criteria and achieved a peak respiratory exchange ratio (RER) ≥1.05 were classified as reaching VO2max and were included in this analysis. The OUES was determined as the slope of the line when VO2 (ml/min) was plotted against logVE. Maximal OUES (OUESmax) was calculated from start to end of the test while 6-minute OUES (6minOUES) was calculated from start of the test to the 6-minute time-point. A multivariate linear regression was used to determine the relationship between VO2max, 6minOUES, and OUESmax, as well as to derive a prediction equation for VO2max. RESULTS: Thirty-two obese children (age 12.4±1.9; Tanner puberty stage 3 (2-4), female 59%) achieved a VO2max of 31.2±5.5 ml/kg/min. Participants attained an OUESmax of 2.82±0.89 and a 6minOUES of 2.77±1.01. VO2max (L/min) was strongly correlated with OUESmax in L/min (r2 = 0.93, p<0.001) and 6minOUES in L/min (r2 = 0.83, p<0.001) independent of Tanner stage and sex. Furthermore, 6minOUES was strongly correlated with OUESmax (r2 = 0.91, p<0.001). The VO2max prediction equation derived from this cohort is as follows: VO2max= 0.651*6minOUES + 0.026*Tanner Stage + 0.565 (r = 0.90, standard error of the estimate = 0.34). CONCLUSIONS: The 6minOUES treadmill protocol may be used to predict VO2max in obese children when oxygen uptake plateau criteria and peak RER indicate submaximal exercise performance.