THE ROLE OF DEGREE OF OBESITY IN MAXIMAL PHYSIOLOGIC AND METABOLIC PARAMETERS IN OBESE YOUTH.

Abstract

242 Research indicates that obese children exhibit lower maximal oxygen uptake(VO2max) and heart rate (HRmax) values than non-obese children. However, it is unclear what impact the varied levels of obesity [defined as percentage of ideal body weight (%IBW)] i.e., severe (>200%IBW), moderate(150-199%IBW) and mild (121-150%IBW) will have on maximal physiologic and metabolic parameters during treadmill walking. We examined the impact of level of obesity on VO2max, HRmax, maximal ventilation (VEmax), maximal carbon dioxide (VCO2max) and respiratory exchange ratio (RER) in nonobese (<120%IBW) compared to severely, moderately and mildly obese children. Forty-seven subjects (M=15, F=32; 11.9±1.8 yrs.) were stratified into four groups by level of obesity. Subjects performed a graded treadmill test after 30 minutes (mn) of rest. Expired gases were collected with a Sensormedics MMC 2900C, HRmax with a Polar XL monitor as follows: 10 mn of unsupported standing; walking @ 0% grade for three 5-mn stages of 2.5, 3.0& 3.5 mph, respectively, then a 2% increase in grade every 2 mn @ 3.5 mph until fatigue. The results are: (mean±S.D).TableNo significant differences were noted in, VO2max L/min., VEmax and VCO2max. VO2max mL/kg/min. was significantly greater in nonobese& mild versus (vs.) moderate & severe obese subjects (p<0.0001). HRmax was significantly lower in severe obese subjects vs. all others(p<0.0045). RER was significantly lower in mild vs. severe & nonobese and also lower in moderate vs. non-obese subjects (p<0.035). We conclude that obesity levels >150%IBW negatively impact VO2max mL/kg/min. Severe obesity negatively impacts HRmax but positively impacts RER.