Intramuscular triayclglycerol (IMTG) utilization, glycogen resynthesis and pyruvate dehydrogenase activation (PDHa) were examined during an 18 h recovery period after glycogen depleting exercise.
Eight endurance-trained males completed an exhaustive bout of exercise (∼90 min) on a cycle ergometer followed by ingestion of carbohydrate (CHO)-rich meals (64–70% of energy from carbohydrate) at 1, 4 and 7 h of recovery. Duplicate muscle biopsies were obtained at exhaustion, 3, 6 and 18 h of recovery.
Despite the large intake of CHO during recovery (491 ± g or 6.8 ± 0.3 g·kg−1), respiratory exchange ratio values of 0.77 to 0.84 indicated a greater reliance on fat as an oxidative fuel. However, there was no net IMTG utilization during recovery. IMTG content at exhaustion was 23.5 ± 3.5 mmol·kg−1 dry wt, and remained constant at 24.6 ± 2.6, 25.7 ± 2.8 and 28.4 ± 3.0 mmol·kg−1 dry wt after 3, 6 and 18 h of recovery. Muscle glycogen increased significantly from 37 ± mmol·kg−1 dry wt at exhaustion to 424 ± mmol·kg−1 dry wt by the end of recovery. PDHa was reduced at 6 and 18 h when compared to exhaustion, but did not change during the recovery period. Acetyl-CoA, acetylcarnitine and pyruvate contents declined significantly after 3 h of recovery compared to exhaustion, and thereafter remained unchanged.
IMTG has a negligible contribution to the enhanced fat oxidation during recovery from exhaustive exercise. It appears that when glucose and insulin are elevated following high CHO meals during recovery, glycogen resynthesis is of high metabolic priority. Plasma fatty acids and very low density lipoprotein triacylglycerols, as well as intramuscular acetylcarnitine stores are likely to be important fuel sources during the first few hours of recovery. Supported by NSERC Grant and Canadian Institutes of Health Research