FATNESS IN RELATION TO SUBSTRATE OXIDATION DURING EXERCISE

The aim of this study was to test the hypothesis that differences in f uel utilisation during exercise, determined by muscle fibre-type profi le, are an aetiological factor for obesity as proposed by Wade et al. (Lancet 1990, 335, 805-8). An investigation was carried out of relatio nships between body fatness (assessed by skinfolds, densitometry and d ual X-ray absorptiometry) and fuel utilisation represented by the resp iratory exchange ratio (RER, assessed by indirect calorimetry) during three cycle ergometer exercises. Exercise 1 was an exact replication o f the Wade protocol (fixed 100 Watt load and unstandardised with respe ct to antecedent diet and activity). Exercises 2 (fasted) and 3 (fed) were highly standardised and adjusted to represent the same relative w orkload for each subject (45% VO2max). The subjects were 37 randomly-s elected untrained men. None of the exercises yielded significant corre lations between fatness and RER. The results refute the initial hypoth esis linking substrate oxidation and body fatness. Inspection of the b ody composition data for Wade's subjects reveals that they were abnorm ally lean. This suggests that their findings may have been confounded by coincident correlations between fitness and fatness, and may not re present a true causal relationship.