SUBSTRATE UTILIZATION DURING PROLONGED EXERCISE IN OBESE WOMEN DIFFERING IN BODY-FAT DISTRIBUTION

The present investigation compared the pattern of substrate utilizatio n during prolonged walking in obese women with upper (UB) and lower (L B) body fat patterns and the effect of beta-adrenergic receptor blocka de on that response. Twenty healthy, premenopausal, obese volunteers ( % fat greater than or equal to 30%) were characterized by waist-to-hip (WHR) circumference ratios into two distinct groups (UB: WHR greater than or equal to 0.85, LB: WHR less than or equal to 0.75). The groups (n = 10 each) were similar for BMI, age, % fat, and maximal aerobic p ower (VO(2)max). Subjects participated in two 60-min walk bouts at 55- 60% VO(2)max. The trials (placebo (C) and 80mg propranolol (PR)) were performed in random order, 110min after ingestion, with 2-4 days betwe en tests. Open-circuit spirometry was employed to calculate the VO2, V CO2 and respiratory exchange ratio (RER) at 10 min intervals. A signif icant (P < 0.0001) decline in RER with time was evident in both trials . However, no group differences existed in RER Values during either th e C trial (RER range = 0.81-0.88) or the PR trial (RER range = 0.86-0. 98). The PR trial induced a 23% reduction in the amount of calories ut ilized as fat compared to C in both WHR groups. Both groups of women s howed equal capabilities for performing prolonged exercise with typica l and appropriate metabolic shift in fuel mobilization from carbohydra te to fat. Despite the well-defined differences in metabolic activity of adipose cells shown in vitro, this study indicates that women with significantly different regions of adipose tissue stores have similar physiological potentials for substrate use during exercise.