Restricting carbohydrate during recovery from prolonged exercise does not effect intramuscular triglyceride resynthesis

INTRODUCTION: Intramuscular triglycerides are an important substrate during prolonged moderate-intensity exercise, and therefore post-exercise IMTG resynthesis is an important part of recovery. Nutritional guidelines advise the consumption of carbohydrate following prolonged exercise in order to support glycogen resynthesis, but a high CHO diet impairs IMTG resynthesis. More recent evidence suggests that actually restricting CHO in the post-exercise period may maximise the adaptive response to exercise, but how this strategy effects post-exercise IMTG resynthesis has not been investigated. To address this, this study aimed to examine IMTG resynthesis when acutely restricting CHO in the post-exercise period following prolonged exercise. METHODS: 14 male elite triathletes <27 ± 1y, 66.5 ± 1.3 mL.kg-1.min-1> were recruited as part of a previous study . Muscle samples were collected pre, post, 4h post and 24h post 4h of glycogen depleting cycling exercise. In the 4h period immediately following exercise 7 participants consumed a high CHO diet while the other 7 consumed only water. For the remaining recovery period <20h> all participants received the same CHO-enriched diet. Muscle samples were analysed using confocal immunofluorescence microscopy to determine muscle fibre type and subcellular-specific IMTG content and LD morphology. RESULTS: Exercise reduced IMTG content by 53% in type I muscle fibres , and specifically in the central region of the fibre , which was driven by a 47% decrease in LD number . In recovery, IMTG content in type I fibres increased from post-exercise to 24h post in the water condition only . Specifically, IMTG content increased in the central region , with a trend for increases in LD number from post to post 24hr <58%, P=0.084>. However, no significant differences in IMTG content were observed between groups by 24h post . CONCLUSION: IMTG utilisation during exercise was evident in the central region of type I fibres only, and a corresponding increase in IMTG content was only apparent in the water condition. Although IMTG resynthesis was significantly greater when restricting CHO immediately post-exercise, IMTG content was similar between groups at 24h post-exercise. Together, these results suggest that IMTG resynthesis following prolonged exercise is unaffected when acutely restricting CHO in the post-exercise period. Future studies will investigate the role of lipid droplet proteins in mediating this response.