OBJECTIVE: To investigate the in vivo effect of exercise training at high and low intensity on beta-adrenergic stimulated fat metabolism in obese men at rest. METHOD: Twenty-three obese, healthy subjects were randomly divided in a low-intensity exercise training program (40% VO2max, n = 7), a high-intensity exercise training program (70% VO2max; n = 8), or a non-exercising control group (n = 8). The exercise training program lasted for 12 weeks with a training frequency of 3 times per week. Before and after the intervention body composition and maximal aerobic capacity were measured as well as fat metabolism at rest and during beta-adrenergic stimulation by isoprenaline. For comparison, six lean subjects served as a control group. They participated in a low-intensity exercise training program and underwent the same measurements as the obese subjects. RESULTS: Relative fat oxidation decreased significantly during infusion of an increasing dose of isoprenaline in the obese low-intensity and high-intensity exercise training groups as well as in the lean group (p < 0.01). Exercise training failed to influence the effect of beta-adrenergic stimulation on relative fat oxidation in obese men at both intensities and in lean men. In addition, beta-adrenergic-mediated lipolysis did not seem to be different after low intensity exercise training in lean and obese men. Lipolysis might be increased after high-intensity exercise training in obese men. CONCLUSION: Low- and high-intensity exercise training in obese men failed to affect beta-adrenergic mediated relative fat oxidation in vivo. Beta-adrenergic-mediated lipolysis might be increased in obese men after HI exercise training only. The effect of low-intensity exercise training on beta-adrenergic-mediated fat metabolism was similar in lean and obese men.

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