Liver vs Skeletal Stores
In humans the majority of glycogen is stored in skeletal muscles (∼500 g) and the liver (∼100 g). Glycogen is accumulated in the liver primarily during the postprandial period and in the skeletal muscle predominantly after exercise. Muscle glycogen decreases by ~30% after roughly 72 hours of fasting at rest.
As a point of reference for skeletal muscle glycogen usage in working musculature: using 80% of 1 rep max weight to failure of bicep curls for consecutive sets, glycogen levels are depleted ~12.5% after the first set and by ~25% of original storage by the third set.1 This suggests that skeletal muscle glycogen stores are actively depleted during resistance exercise, but it appears that there is a relative state of diminishing returns with regards to how much glycogen is depleted.
Even when performing high volume training (16 total sets of 160 reps of a single muscle group), muscle glycogen stores were only depleted ~33%.2 Standard eating patterns will easily replenish this before a training bout the following day. Therefore muscle glycogen stores are unlikely to become a limiting factor in resistance training.
The reduced glycogen stores in skeletal muscles after exercise allow carbohydrates to be stored as muscle glycogen and prevents glucose from being channeled to de novo lipid synthesis, which over time can cause ectopic fat accumulation and insulin resistance. The reduction of skeletal muscle glycogen after exercise allows a healthy storage of carbohydrates after meals and prevents development of type 2 diabetes.
- DOI: 10.1139/h99-017
- DOI: 10.1007/s00421-005-0118-0