Place · Level 3 · Movement
Glycogen supercompensation
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In one pass Glycogen supercompensation sounds like a race-week menu. Educational content, not medical advice — consult a clinician.
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Chapter 1
Only the leg that worked
只有做过功的那条腿
Glycogen supercompensation sounds like a race-week menu. What actually happens is more local: a muscle that has just been emptied will pack glucose into glycogen past its usual fill line.
In 1966 Bergström and Hultman had people ride one leg to exhaustion, rest the other, then eat carbohydrate on both sides. Glycogen overshot baseline only in the leg that had worked. Their own conclusion is hard: the enhancing factor sits inside those muscle cells, not in a circulating whole-body hormone.
This island is not how to eat before a race. It is which enzyme stays on after this tissue has been emptied.
In 1966 Bergström and Hultman had people ride one leg to exhaustion, rest the other, then eat carbohydrate on both sides. Glycogen overshot baseline only in the leg that had worked. Their own conclusion is hard: the enhancing factor sits inside those muscle cells, not in a circulating whole-body hormone.
This island is not how to eat before a race. It is which enzyme stays on after this tissue has been emptied.
Mechanism · why the other leg is the ruler
Same person, same meal, same hormones in the blood — and the two legs come apart. The only thing that can make that difference is what that leg just did.In the emptied fibre the glycogen particle shrinks, the brake on synthesis eases, and the next glucose that arrives is built past the line this muscle usually stops at. The rested leg was not emptied; synthase keeps the everyday fill line, and the same carbohydrate stops near baseline.
The n is small. The weight of this step is not the statistic. It is the contralateral design: it takes a whole-body menu out of the explanation. The molecular work later asks which enzyme inside the cell was left in the on position.
Chapter 2
Synthase is not the door
合酶不是那扇门
The carbs island on this site already covered a door: GLUT4 is pushed to the muscle membrane by contraction and by insulin, and only then does glucose get in. The door matters. It explains whether sugar can enter the cell. It does not explain why, once inside, it is stacked past the everyday fill line.
The enzyme that hangs glucose onto the glycogen particle is glycogen synthase. It has two switches: the more phosphate groups it wears, the duller it is; glucose-6-phosphate inside the cell can wake it without that phosphate being taken off. Jensen 2012 writes the hours after exercise as two things stacked: the cell is more insulin-sensitive, so the door opens wider; and synthase itself is more active, so incoming sugar is built into glycogen first.
Supercompensation is the second thing still running. It is not another name for the first.
The enzyme that hangs glucose onto the glycogen particle is glycogen synthase. It has two switches: the more phosphate groups it wears, the duller it is; glucose-6-phosphate inside the cell can wake it without that phosphate being taken off. Jensen 2012 writes the hours after exercise as two things stacked: the cell is more insulin-sensitive, so the door opens wider; and synthase itself is more active, so incoming sugar is built into glycogen first.
Supercompensation is the second thing still running. It is not another name for the first.
Mechanism · the phosphate brake and the G6P wake-up
Glycogen synthase hangs UDP-glucose onto the particle's α-1,4 chain. Phosphorylation dulls it toward its substrate — a brake. Insulin and contraction have phosphatases take those phosphates off, and the brake eases.The other road does not touch the phosphates: once glucose is in, hexokinase hangs a phosphate on it and it becomes glucose-6-phosphate (G6P). When G6P rises, synthase can be allosterically woken even while still phosphorylated, and phosphorylase on the breakdown side is held down — so unpacking and building do not both run at full speed.
So GLUT4 sending sugar in only gives G6P a chance to rise. What decides whether the fill line is crossed is how long synthase stays on along that line.
Chapter 3
AMPK leaves synthase on
AMPK 把合酶留在开着
Once the door has done its job, synthase should turn itself off as glycogen fills back in — more glycogen feedback-inhibits synthesis. Hingst 2018 emptied one human leg, then fed carbohydrate, and saw glycogen synthase and AMP-activated protein kinase: The cell's 'low fuel' sensor — switches on when energy is low to make energy and pause building. still on after glycogen had returned to the pre-exercise line. That is the feedback brake held off for a stretch.
They then took both machines apart in mice: delete muscle AMPK, or give synthase a form that cannot hear G6P, and supercompensation fails. So this step is not 'eat more carbohydrate and more will be stored'. Depletion lengthens the synthase-and-AMPK window, and only then is the same mouthful of carbohydrate built past the line.
They then took both machines apart in mice: delete muscle AMPK, or give synthase a form that cannot hear G6P, and supercompensation fails. So this step is not 'eat more carbohydrate and more will be stored'. Depletion lengthens the synthase-and-AMPK window, and only then is the same mouthful of carbohydrate built past the line.
Mechanism · feedback should have stopped at baseline
At rest the glycogen particle is itself a signal: a high fill line pushes synthase down and glucose uptake down, so the cell does not build onto the particle without limit. For supercompensation to happen, something has to keep holding that feedback after the fill line is already normal.Hingst narrows the candidates to two: AMP-activated protein kinase: The cell's 'low fuel' sensor — switches on when energy is low to make energy and pause building. (the cell's battery meter) and synthase itself. In the human one-legged data both stay active after glycogen is back on the line; in the mouse, taking either out makes the overshoot disappear. The hypothesis in the paper: they offset glycogen's tight feedback on synthesis and uptake.
Keep an edge on the reading: this is the molecular ledger after one depleting bout, not a carbohydrate menu you can run every day.
References · 4
- Bergström, J., & Hultman, E. (1966). Muscle glycogen synthesis after exercise: an enhancing factor localized to the muscle cells in man. Nature, 210(5033), 309-310. One-legged exhaustive exercise then carbohydrate feeding: glycogen overshoot is confined to the exercised leg. The authors' own conclusion is that the enhancing factor is inside those muscle cells, not a circulating whole-body hormone. n is tiny; the load-bearing fact is the contralateral localisation, later replicated. 10.1038/210309a0
- Jensen, T. E., & Richter, E. A. (2012). Regulation of glucose and glycogen metabolism during and after exercise. The Journal of Physiology, 590(5), 1069-1076. Symposium review: contraction raises glucose transport (GLUT4), glycogen phosphorylase and glycogen synthase are both regulated by covalent and allosteric signals, and glucose-6-phosphate allosterically activates synthase while inhibiting phosphorylase. Post-exercise insulin sensitisation of glucose transport plus synthase activation can produce an overshoot of intramuscular glycogen (supercompensation). Narrative, not a systematic review. 10.1113/jphysiol.2011.224972
- Hingst, J. R., Bruhn, L., Hansen, M. B., Rosschou, M. F., Birk, J. B., Fentz, J., Foretz, M., Viollet, B., Sakamoto, K., Færgeman, N. J., Havelund, J. F., Parker, B. L., James, D. E., Kiens, B., Richter, E. A., Jensen, J., & Wojtaszewski, J. F. P. (2018). Exercise-induced molecular mechanisms promoting glycogen supercompensation in human skeletal muscle. Molecular Metabolism, 16, 24-34. One-legged glycogen-depleting exercise in humans plus transgenic mouse follow-ups. Glycogen synthase and AMPK stay activated beyond the point where muscle glycogen has returned to the pre-exercise line; the authors' hypothesis is that this offsets the usual feedback inhibition of synthesis and glucose uptake by glycogen. Inducible muscle AMPK deletion, and a glycogen synthase that cannot be allosterically activated by glucose-6-phosphate, both abolish supercompensation. Conclusion in the paper: AMPK and glycogen synthase are both key regulators of supercompensation after a single depleting bout. 10.1016/j.molmet.2018.07.001
- Sherman, W. M., Costill, D. L., Fink, W. J., & Miller, J. M. (1981). Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. International Journal of Sports Medicine, 2(2), 114-118. Three 6-day regimens in trained runners: classic low-then-high carbohydrate, mixed-then-high, and mixed throughout. Muscle glycogen on day 7 reached 207, 203, and 159 mmol glucosyl units/kg wet tissue. The 20.9 km performance run was not faster after the two high-glycogen regimens. The paper's own three conclusions: glycogen can be raised with a moderate exercise-diet regimen; starting glycogen changes how much is used; carbohydrate loading did not help this 20.9 km run. 10.1055/s-2008-1034594