INTRAMUSCULAR TRIGLYCERIDE REPLETION FOLLOWING PROLONGED ENDURANCE EXERCISE

Abstract

Intramuscular triglyceride (IMTG) stores form an important substrate source during endurance exercise in trained athletes, with an estimated contribution of up to 25% of total energy expenditure. PURPOSE To investigate the role of fat content in the diet on IMTG repletion following prolonged endurance exercise. METHODS Nine endurance-trained athletes (VO2max: 68±2 ml/kg/min) were provided with standardized meals for 3 days after which they performed a 3 h exercise trial at a 55% Wmax workload. Before, immediately after exercise and after 24 and 48 h of post-exercise recovery, Magnetic Resonance Spectroscopy was performed to quantitate IMTG content in the M. vastus lateralis. In addition, after 48 h of recovery, a muscle biopsy was taken to determine IMTG content using quantitative fluorescence microscopy. The entire procedure was performed twice in random order, in which post-exercise diet composition was altered. In one trial, a normal, medium-fat containing diet was provided (MF trial: 39 En% fat, 49 En% carbohydrates, 14 En% protein), in the other a typical (carbohydrate-rich) athletes' diet, low in fat (LF trial: 24 En% fat, 62 En% carbohydrates, 14 En% protein). RESULTS Following the exercise trials, IMTG content had decreased by 21.4±3.1%. During the recovery period, IMTG content significantly increased in the MF trial only, reaching pre-exercise levels after 48 h. In the LF trial, IMTG content was not significantly increased during the 2 day recovery period. In line with these findings, quantitative fluorescence microscopy showed significantly higher IMTG content in type I muscle fibers in the MF compared to the LF trial (2.1±0.2 and 1.4±0.2% area lipid staining, respectively). CONCLUSION A carbohydrate-rich, low-fat diet, as normally used by endurance athletes, limits post-exercise IMTG repletion. IMTG content is not repleted within 48 h of post-exercise recovery when using such a diet.