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The thermogenic responses of ten lean and ten moderately obese women to food, exercise, and food plus exercise were measured using open circuit respirometry for five minutes every half hour for four hours under six conditions: during five minutes of bicycle exercise at a workload of 300 kpm/min with and without eating a 910 kcal mixed meal; cycling at a workload just below the anaerobic threshold with and without food; and at rest with and without food. Over the four-hour period, the thermic effect of food at rest was similar for the lean and obese groups: 50 kcal and 47 kcal, respectively. Eating before exercise increased the exercise metabolic rate by 11% for the lean women and by 4% for the obese women (P less than 0.005). Exercise potentiated the thermic effect of food for the lean women but nor for the obese women: the thermic effect of food was 2.54 times greater during exercise than at rest for the lean group, but only 1.01 times greater for the obese women (P less than 0.005). This reduced response to the combined stimulus of food plus exercise may constitute a subtle metabolic factor associated with obesity.

To clarify further the independent relationships of body composition parameters to energy expenditure, resting metabolic rate (RMR) and postprandial thermogenesis were studied in four groups who were matched for absolute fat mass (study 1) and relative fatness (study 2). In study 1, five lean [group A, 15.4 +/- 0.6% (+/- SE) body fat] and five obese men (group B, 25.0 +/- 0.9% fat) were matched on body fat mass (13.0 +/- 0.9 vs. 14.4 +/- 0.8 kg, respectively). Fat-free mass (FFM) and total weight were greater for group A than B. RMR was measured for 3 h in the fasted state and after a 720-kcal mixed meal. RMR was greater for group A than B (1.38 +/- 0.08 vs. 1.14 +/- 0.04 kcal/min, P less than 0.05). The thermic effect of food, calculated as 3 h postprandial minus fasting RMR, was greater for group A than B (65 +/- 6 vs. 23 +/- 9 kcal/3 h; P less than 0.05). In study 2, two groups (n = 6 men/group) were matched for percent body fat (33 +/- 1% fat for both) but differed in lean, fat, and total weights: 50.8 +/- 3.1 kg FFM for the lighter (group C) vs. 68.0 +/- 2.8 kg FFM for the heavier (group D) group, P less than 0.05. RMR was lower for group C than D (1.17 +/- 0.06 vs. 1.33 +/- 0.04 kcal/min, P less than 0.05), but the thermic effect of food was not significantly different (31 +/- 3 vs. 20 +/- 6 kcal/3 h).(ABSTRACT TRUNCATED AT 250 WORDS)

This study 1) further validated the relationship between total body electrical conductivity (TOBEC) and densitometrically determined lean body mass (LBMd) and 2) compared with existing body composition techniques (densitometry, total body water, total body potassium, and anthropometry) two new electrical methods for the estimation of LBM: TOBEC, a uniform current induction method, and bioelectrical impedance analysis (BIA), a localized current injection method. In a sample of 75 male and female subjects ranging from 4.9 to 54.9% body fat the correlation between LBMd and LBM predicted from TOBEC by use of a previously developed regression equation was extremely strong (r = 0.962), thus confirming the validity of the TOBEC method. LBM predicted from BIA by use of prediction equations provided with the instrument also correlated with LBMd (r = 0.912) but overestimated LBM compared with LBMd in obese subjects. However, no such systematic error was apparent when new prediction equations derived from this heterogeneous sample of subjects were applied. Thus the TOBEC and BIA methods, which are based on the differing electrical properties of lean tissue and fat and which are convenient, rapid, and safe, correlate well with more cumbersome human body composition techniques.

Changes in blood (BV), red cell (RCV), and plasma (PV) volumes were computed from hemoglobin and hematocrit values during submaximal treadmill exercise at 5 work intensities (30, 45, 60, 75, and 90% VO2 max) in 5 male subjects. RCV remained constant under all conditions. Changes in BV (hemoconcentration) could, therefore, be accounted for entirely by decreases in PV at all work levels. PV was a linear function of work intensity from rest through 60% VO2 max. However, a "break" occurred at that point in the data. Modeling of this break was accomplished by the use of one model (the "Fold" catastrophe) taken from the generalized catastrophe therory. However, several limitations to the acceptance of the model are presented, including the need to demonstrate a hysteresis in PV occurring at about 65% VO2 max.