Effects of training on free fatty acid metabolism during exercise

Although utilization of free fatty acids (FFA) during exercise has been shown to be more extensive in athletes than untrained subjects, the effects of training per se are incompletely understood. 6 healthy, physically active subjects were studied at rest, during exercise at two levels of power output (400 and 800 Kpm/min) each maintained for 20 mins., and in recovery, before and after a six week period of training. Maximum oxygen uptake increased in all subjects. For a given level of O2 uptake consistent reductions in heart rate, respiratory exchange ratio and ventilation were found. Cardiac output was unchanged. Blood lactate levels were lower in 4 subjects and unchanged in 2. Changes in blood glycerol with exercise were unchanged, indicating that free fatty acid (FFA) mobilization from adipose tissue was probably unaffected. Blood FFA levels also were not changed consistently; FFA uptake from blood did not appear to be influenced by training. In individuals, changes in FFA levels were related to changes in blood glycerol levels but not to changes in blood lactate levels. The consistent reduction in respiratory exchange ratio, although possibly due in part to lower levels of lactic acid production, may be an indication that training led to an increased utilization of stored fat in muscle during exercise.