The oxygen uptake efficiency slope reflects exercise-training induced changes in VO2max in obese children

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.