Cortisol and Muscle growth

When cortisol becomes chronically elevated it can severely hurt muscle growth via several mechanisms:

1. It directly increases muscle breakdown. The amount of muscle you build depends on the difference between protein breakdown (catabolism) and protein synthesis (anabolism). If you increase protein breakdown (which cortisol does) it becomes a lot harder to be in a significantly positive balance.
2. It decreases nutrient uptake by the muscles. This makes it harder to shuttle amino acids to the muscle to build new tissue and restore muscle glycogen stores.