- 大阪体育大学紀要 (ISSN:02891190)
- vol.35, pp.39-50, 2004-03-31
The exercise intensity at which lipid metabolism is enhanced most and changes in lipid metabolism with time were studied during 2-hours treadmill exercise at intensities of 30, 40, 50, 60, and 70% VO2max. The subjects were 6 healthy adult males (aged 20-28 years) who exercised regularly 2-5 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. Characteristics of lipid metabolism were examined on the basis of the plasma substrate and hormone levels, and metabolic responses. RER remained low at 30% and 40% VO2max from the beginning (0.91-0.93) to the end (0.87-0.88) of the exercise compared with the exercise intensity above 50% VO2max. The energy produced by combustion of fat, measured every 30 minutes during the exercise, increased with time at all exercise intensities, but the increases between 90 and 120 minutes were particularly notable (except at 30% VO2max). In addition, the energy derived from fat was the largest at 70% VO2max among the 5 exercise intensities 60 and 120 minutes after the beginning of the exercise with significant differences (p<0.05) compared with the other intensities. Concerning the blood substrate, glycerol mobilization and glucagon secretion increased, but the glucose level decreased characteristically, with increasing exercise were small in all parameters measured (glycerol, FFA, ketone bodies, glucose, glucagon) at all intensities, and no significant difference was observed among the intensities. However, the values of all parameters increased rapidly during the latter 60 minutes, and the increases were the largest at 70% VO2max. Also, noradrenaline was nearly doubled at 70% VO2max compared with the other intensities 60 and 120 minutes after the beginning of the exercise. From the above results, it was concluded that the energy produced by fat combustion was enhanced most at 70% VO2max. Also, it was shown to be accelerated further when exercise at 40% VO2max or above is continued for 90 minutes or longer.