TRIGLYCERIDE FATTY-ACID CYCLING IS INCREASED AFTER EXERCISE

After exercise, there is a prolonged increase in O2 consumption termed the excess postexercise O2 consumption (EPOC). In this study, we have assessed the relative contribution of the triglyceride/fatty acid ( TG FA) substrate cycle to EPOC. Six healthy, young men exercised for 2 hours at 51% of maximal O2 uptake. The total energy expenditure and the rate of FA oxidation were estimated from measurements of O2 uptake, respiratory exchange ratio, and urinary nitrogen excretion while the subjects rested in bed for 3.5 hours postexercise. During the last part of the recovery period, the rate of FA mobilization was determined by infusion of glycerol. The rate of TG FA cycling was calculated from the difference between the rate of FA mobilization and oxidation. An identical control study without exercise was also performed. The total EPOC during the recovery period was 7.82 ± 1.51 L O2 (a 15% ± 3% increase above the control O2 consumption). The rate of FA oxidation increased from 252 ± 36 μmol/min (control) to 360 ± 27 μmol/min (3 hours postexercise). The rate of FA mobilization increased from 666 ± 108 μmol/min (control) to 1833 ± 456 μmol/min (3 hours postexercise). TG FA cycling was found to increase from 414 ± 90 μmol FA/min (control) to 1473 ± 435 μmol FA/min (3 hours postexercise). The energy cost of these rates of TG FA cycling was found to be 0.09 ± 0.02 kJ/min (control) and 0.31 ± 0.09 kJ/min (3 hours postexercise). It is concluded that the energy cost of the increased TG FA cycling rate may account for as much as half of the delayed component of EPOC. © 1990.