The Mathematics of Refeed Days: Targeted Ketogenic Dieting (TKD) & Glycogen Dynamics
When carbohydrate timing aids high-intensity glycolytic performance without causing metabolic relapse.
Nutritional ketosis is an exceptional metabolic state for endurance athletics, Zone 2 aerobic base building, and sustained mental focus. However, competitive powerlifters, CrossFit athletes, and sprinters often encounter a mechanical ceiling when repeated anaerobic efforts demand rapid glycolytic flux.
1. Aerobic Fat Oxidation vs. Anaerobic Glycolysis above 85% VO2 Max
During sub-maximal exercise (below 70% VO2 max), mitochondrial beta-oxidation breaks down fatty acids and circulating ketone bodies with near-infinite endurance. But when power output exceeds 85% VO2 max, ATP production via oxidative phosphorylation is too slow.
The cell requires substrate-level phosphorylation via glycolysis, which relies entirely on intramyocellular glycogen. Without adequate glycogen, high-intensity anaerobic power output drops by 10% to 18%.
2. The Targeted Ketogenic Diet (TKD) Dextrose Protocol
Rather than engaging in unscientific weekend 'carb binges' that wipe out fat adaptation, advanced athletes utilize Targeted Ketogenic Dieting (TKD). The protocol consists of consuming 15g to 30g of pure, rapid-acting dextrose or glucose polymers exactly 30 to 45 minutes prior to a high-intensity training bout.
Dextrose stimulates insulin just enough to translocate GLUT-4 glucose transporters to muscle cell membranes. Crucially, because the muscles immediately oxidize the glucose during training, it never saturates hepatic glycogen stores. Post-workout blood ketone readings typically return to baseline (>0.5 mmol/L) within two hours.
3. Why Fructose Is Strictly Prohibited on TKD
A fatal error in carbohydrate timing is consuming sucrose, high-fructose corn syrup, or fruit smoothies pre-workout. Fructose cannot be directly oxidized by skeletal muscle tissue; it is preferentially metabolized by the liver via fructokinase.
Hepatic fructose metabolism replenishes liver glycogen first, shutting down hepatic ketogenesis and knocking the athlete completely out of nutritional ketosis for 48 to 72 hours. Only pure glucose or dextrose satisfies the muscle without poisoning the liver's ketone engine.
If you perform explosive anaerobic athletics, use 15g–30g of pre-workout dextrose via TKD. Avoid fructose entirely to keep liver glycogen depleted and ketosis intact.
Align your macros with heavy training demands.
Repast calibrates exact workout-day macro allocations so high-intensity athletes can train hard without compromising ketosis.
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