Effects of exercise intensity and duration on lipid metabolism in trained men

Introduction

Achten et al.[1] were one of several research groups to show that fat oxidation is lower at a low intensity compared to a moderate intensity and is lower again at a high exercise intensity. However the exercise duration of those researches were fairly short(3min.-30min). The purpose of this study was to identify the point(% Vo2 max) of maximal rate of fat oxidation and the changes in lipid metabolism during 2-hour treadmill exercise at intensities of 30, 50 and 70 %Vo2 max.

Μethods

The subjects were 9 healthy, trained men ( aged 19-23 years) who exercised regularly 4- 5 days a week. The exercise session was held after the subjects ingested the same lunch( a bowl of rice with meat and vegetables cooked in the Chinese style with salad; about 950 kcal) and rested for 2 hours and 30 minutes. Subjects completed 2-hour exercise protocols, requiring them to exercise at three different workloads, 30,50 and 70 %Vo2 max. Fat and CHO oxidation and energy expenditure were calculated using stoichiometric equations[2]. Also, plasma substrates , adorenalin and noradorenaline were examined at 60 min. and 120 min. after the beginning of the exercise. One way analysis of variance with repeated measures was used to test for differences across the three submaximal exercise intensities for each metabolic variable. Post hoc tests were used to detect differences between means.

Results

The rate of fat oxidation , measured every 30 minutes during the exercise, increased with duration at all intensities, but the increases between 90 and 120 minutes were particularly notable. In addition , the fat oxidation during 2-hour exercise at 70 %Vo2 max was significantly greater than 30 and 50 %V02 max (p<0.05) and significantly increased between 90 and 120 minutes at all three intensities (P<0.05). Glycerol and glucagon increased with enhancement of exercise intensity, but the glucose level decreased characteristically. Also, the concentrations of adorenaline and noradorenaline at 70 %Vo2 max were almost twice greater as compared with 30 and 50 %Vo2 max. The value of all parameters increased rapidly during the latter 60 minutes, and the increases were the largest at 70 %Vo2 max.

Discussion/Conclusions

It was suggested that the fat oxidation was most enhanced at 70 %Vo2 max. Also, it was observed that lipid metabolism was accelerated further when exercise was longer than 90 minutes at all intensities. The finding that a relatively heavy exercise intensity elicits maximal fat oxidation in nine trained men has application in exercise prescription, as it refutes the belief that low -intensity exercise is best for fat loss.

References

[1] Achten.J .et al.(2002). Med. Sci. Sports Exerc.,, 34, 92-97.
[2] Frayn KN. (1997). J Appl physiol., 55, 628-634