Blood glucose is regulated during exercise by negative feedback involving the pancreas, liver, skeletal muscles, and hormones. As working muscles increase glucose uptake, reduced insulin secretion and increased glucagon and adrenaline secretion stimulate the liver to release glucose into the blood.
The Homeostatic Mechanism
During exercise, skeletal muscles require more ATP, so their uptake and oxidation of glucose increase. Muscle contractions increase the movement of GLUT4 transport proteins to muscle-cell membranes, allowing glucose to enter cells even though the blood insulin concentration usually falls.
A decrease in blood glucose is detected by pancreatic alpha cells, which secrete glucagon. Glucagon acts mainly on the liver, stimulating glycogenolysis, the breakdown of liver glycogen into glucose, and gluconeogenesis, the production of glucose from non-carbohydrate substrates such as lactate, glycerol, and amino acids.
At the same time, reduced activity of pancreatic beta cells decreases insulin secretion. This limits glucose uptake by less-active tissues and reduces glucose storage, helping preserve glucose for working muscles and the brain. Adrenaline also increases during exercise and promotes liver glycogenolysis, particularly as exercise intensity rises.
| Exercise condition | Main regulatory response | Effect on blood glucose |
|---|---|---|
| Moderate exercise | Insulin decreases; glucagon increases | Liver glucose output matches muscle uptake |
| Prolonged exercise | Gluconeogenesis becomes increasingly important | Delays a fall in blood glucose |
| High-intensity exercise | Adrenaline strongly increases glycogenolysis | Blood glucose may temporarily rise |
| After exercise | Insulin sensitivity remains elevated | Glucose supports glycogen restoration |
A common misconception is that insulin must increase so muscles can absorb more glucose. During exercise, muscle contraction itself promotes GLUT4 translocation, while lower insulin helps prevent blood glucose from falling too rapidly.
Exam Technique
For an IB SEHS response on A.1.2 Maintaining homeostasis, identify the stimulus, receptor or control centre, hormonal effectors, and response. Link increased muscle glucose uptake to glucagon-driven liver glycogenolysis and gluconeogenesis, then state that this negative-feedback system maintains blood glucose within a narrow range.
