Muscle fat stores quickly increase after 1.5 days of fat supplements in athletes and are used during exercise based on their amount

Pre-exercise intramyocellular lipid (IMCL) concentrations were 55% higher after a high-fat diet compared to a low-fat diet.

• IMCL utilization during exercise was threefold greater with high fat compared to low fat.
• Higher IMCL levels were correlated with greater aerobic power and initial content.
• Glycogen levels and reductions during exercise were similar across diet conditions.
• Whole-body fat oxidation remained similar, but plasma fatty acid oxidation was lower during the first hour of exercise after the high-fat diet.
• Myocellular fuels accounted for 8% more of the total energy demands after the high-fat diet due to increased IMCL breakdown.

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