EFFECT OF ENDURANCE TRAINING ON PLASMA-FREE FATTY-ACID TURNOVER AND OXIDATION DURING EXERCISE

Plasma free fatty acid (FFA) levels tend to be lower and the plasma li polytic hormone response to prolonged exercise of the same intensity i s blunted after endurance exercise training. To determine whether trai ning elicits a corresponding decrease in plasma FFA turnover and metab olism during prolonged exercise, we measured plasma [1-C-13]palmitate kinetics and oxidation and respiratory gas exchange in 13 subjects dur ing the latter portion of a 90- to 120-min bout of cycle ergometer wor k performed before and after 12 wk of alternate-day cycling and runnin g. Training increased total fat oxidation during prolonged exercise by 41% (P < 0.005). However, for the final 30-60 min of the cycle ergome ter protocol, the rate of (CO2)-C-13 production from [1-C-13]palmitate oxidation was 27% lower (P < 0.05), the rate of palmitate turnover wa s 33% less (P < 0.05), and plasma FFA and glycerol concentrations were 32 and 20% lower (P < 0.05), respectively, than in the untrained stat e. Thus endurance exercise training results in decreased plasma FFA tu rnover and oxidation during a 90- to 120-min bout of submaximal exerci se because of a slower rate of FFA release from adipose tissue.