Acute Carbohydrate Restriction During Recovery From Prolonged Exercise Enhances Intramuscular Triglyceride Resynthesis

Abstract

Intramuscular triglyceride (IMTG) is an important substrate during moderate-intensity exercise, but providing a high carbohydrate (CHO) diet following exercise impairs IMTG resynthesis. Restricting CHO intake in the post-exercise period may augment the adaptive response to exercise, but whether this strategy enhances IMTG resynthesis is not known. Furthermore, because the lipid droplet (LD)-associated perilipin (PLIN) proteins promote IMTG storage, their distribution and interaction with LD may determine their role in post-exercise IMTG resynthesis. PURPOSE: To determine the effect of acutely restricting CHO during recovery from prolonged exercise on IMTG resynthesis and PLIN protein dynamics. METHODS: 14 male triathletes (27±1 y, 66.5±1.3 ml.kg-1.min-1) completed 4 h of cycling at ~56% VO2max. In the initial 4 h period following exercise 7 participants consumed a high CHO diet whereas 7 participants consumed only water. For the remaining recovery period (20 h) all participants received the same CHO-rich diet. Muscle samples collected pre and post-exercise, and 4 and 24 h post-exercise were analysed using confocal immunofluorescence microscopy to determine muscle fibre type-specific IMTG content and PLIN localisation to LDs. RESULTS: Exercise reduced IMTG content in type I fibres (-53%, P<0.05), with LD both associated and not associated with PLIN2, PLIN3, and PLIN5 being used. During recovery, IMTG content tended to increase in type I fibres after 4 h in the water condition only (+63%, P=0.076), and at 24 h IMTG content was similar to pre-exercise levels (P=0.987). Despite no change in PLIN protein content, the number of LD with PLIN2 or PLIN3 associated tended to increase during recovery in type I fibres only (P=0.08), and to a similar extent between conditions, whereas the number of LD with PLIN5 associated only increased in the CHO condition (P=0.002). CONCLUSION: Acute restriction of CHO during recovery from prolonged exercise has a tendency to initially enhance IMTG resynthesis, although a CHO-rich diet does not impair overall IMTG resynthesis 24 h later. A redistribution of PLIN proteins appears to support post-exercise IMTG resynthesis, but the predominant PLIN isoform supporting post-exercise IMTG storage may be dependent on post-exercise CHO availability.