In female rats that were trained for endurance, their liver cells used more lactate to make glucose when stimulated, and this extra fuel use completely explains why they made more glucose—meaning the key change was how much lactate got into the cells, not how fast the cells processed it.

Female rats that did treadmill training for 10 weeks made more glucose in their liver cells, even when resting and without hormones, compared to rats that didn’t train.

After 10 weeks of endurance training, female rat liver cells become more sensitive to a stress hormone called norepinephrine, meaning they start producing more sugar with much smaller amounts of the hormone compared to untrained rats.

Liver cells from female rats that were trained for endurance produce way more sugar when triggered by a stress hormone, compared to liver cells from untrained rats — showing their bodies are better tuned to respond under stress.

In rat liver cells, a type of fat called palmitate boosts sugar production just as much as a stress hormone does, and adding both together doesn’t do more — suggesting they work through the same switch in the cell.