Effect of physical training on thermogenic responses to cold and ephedrine in obesity

The metabolic response to two tests: ephedrine and cooling in water at 15 degrees, was measured in eight obese and 13 normal weight persons matched for age and body height. The increase in heat production caused by ephedrine was significantly lower in the obese subjects than in the normal weight subjects. Also a 0.3 degree C degree fall in tympanic temperature during cold exposure induced a significantly smaller increase in energy expenditure and a reduced plasma noradrenaline response in the obese subjects. Six obese and six normal weight persons performed aerobic bicycle training for five weeks, and the tests were repeated. Bicycle ergometer training for one hour per day (heart rate 140-160 bpm) for five weeks increased the maximal oxygen uptake by 13% and 12% (P < 0.05) in the obese and the normal weight subjects, respectively. After training, the responses of the obese to ephedrine tended to increase, whereas no significant improvement in their cold-induced thermogenesis was found. The study shows that obese subjects have a decreased thermogenic response to sympathomimetic stimulation and to cold exposure, which was only slightly improved by endurance training.