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The exercise mobilization of stored body fat is impaired in extreme obesity but little is known if this is the response in moderate degrees of adiposity. To better under­stand lipolytic responses to prolonged submaximal exercise in moderately obese subjects a preliminary study was conducted to determine plasma free fatty acids and glycerol concentrations as well as respiratory exchange ratios during 90 min­utes of walking at about 35% of maximal oxygen consumption. Six moderately obese subjects and six subjects who were of average body fat as judged by norms for age and sex were compared. Body fat was determined by hydrostatic weighing procedures. Result of the trend analysis for exercise data revealed that plasma free fatty acids and glycerol levels increased significantly across time followed by a significant reduction in these levels during 60 minutes of recovery. There were no significant differences in absolute free fatty acid concentration or in changes from baseline values between the group with average body fat, mean percentage fat 21.8%, and the moderately obese group, mean percentage body fat 29.5%. Lipolysis and fat oxidation were not impaired by the moderate obesity and pro­longed moderate intensity walking enhanced fat metabolism for untrained, middle aged subjects who possessed a moderate degree of obesity.