Background: The Edmonton Obesity Staging System-pediatrics (EOSS-p) is based on the EOSS for adults, which has shown better predictive value for mortality than BMI. To our knowledge, no study has examined the EOSS-p in relation to health and wellbeing outcomes in a pediatric sample with obesity. The purpose of this study was to compare the associations of EOSS-p and BMI percentile with quality of life (QOL), cardiorespiratory fitness (CRF), muscular strength, and adherence to an exercise intervention in adolescents with obesity. 
Methods: Participants were enrolled in the Healthy Eating Aerobics Resistance Training in Youth trial (N= 299). QOL, CRF (peak oxygen uptake, VO2peak) and muscular strength were assessed by the Pediatric QOL Inventory (PedsQL), indirect calorimetry during a maximal treadmill test, and 8-RM bench and leg press tests respectively. QOL, CRF, and muscular strength were assessed at baseline and 6-months after the intervention. Adherence was determined as a percentage of attended exercise sessions. Participants were staged from 0 to 3 (absent to severe health risk) according to EOSS-p. The association of EOSS-p and BMI percentile with outcomes were assessed using general linear models adjusting for age and sex. 
Results: Baseline QOL decreased with increasing EOSS-p stages (p<0.001). QOL was 75.7 +/- 11.4 in stage 0/1, 69.1 +/- 13.1 in stage 2, and 55.4 +/- 13.0 in stage 3. Stage 3 showed smaller improvements with 6-month CRF than stage 0/1 and 2 (p=0.001, B=-3.882 mlO2/kg/min). BMI percentile was associated with baseline VO2peak (p<0.001, B=-1.044 mlO2/kg/min), bench press (p=0.029, B=0.832 kg) and leg press (p=0.003, B=3.992 kg). Similar associations were observed between BMI percentile and 6-month outcomes. 
Conclusion: As EOSS-p stages increase, QOL decreases.  EOSS-p stage 3 had lower 6-month CRF, which suggests stage 3 may require a longer, more intensive or different intervention to achieve similar CRF improvements. BMI percentile showed contradicting health associations with cardiorespiratory fitness and muscular strength.