LOWER ACTIVITY OF OXIDATIVE KEY ENZYMES AND SMALLER FIBER AREAS IN SKELETAL-MUSCLE OF POSTOBESE WOMEN

Muscle fiber morphology and activities of four key enzymes, as well as energy metabolism, were determined in nine normal-weight postobese wo men and nine matched control subjects. No differences in fiber type co mposition, but a smaller mean fiber area and area of fiber types I and IIb, were found in postobese compared with control subjects (P < 0.05 ). The activities of beta-hydroxyacyl-CoA dehydrogenase (HADH) and cit rate synthase (CS) were 20% lower in postobese than in control subject s (P < 0.05). However, the activities of lactate dehydrogenase and lip oprotein lipase were not significantly different between postobese and control subjects. Basal metabolic rate and respiratory exchange ratio were also similar, but maximal oxygen uptake ((V) over dot o(2max)) t ended to be lower in postobese than in control subjects (P = 0.06). Wh en adjustments were made for differences in (V) over dot o(2max), HADH and CS were not different between postobese and control subjects. In conclusion, these data suggest that smaller fiber areas and lower enzy me activities, i.e., markers of aerobic capacity of skeletal muscle, b ut not fiber composition, may be factors predisposing to obesity.