It’s common for people to lose muscle after surgery. Such degradation can result in longer recovery periods and increased risk of injury or death. But people often experience different degrees of muscle loss — even after undergoing the exact same procedure.

Understanding this variation may help to identify high-risk patients, develop therapies to prevent muscle degradation, and expedite recovery.

New research from the National Heart and Lung Institute at the Imperial College in London suggests two factors may be key: levels of the stress hormone cortisol, which causes muscle breakdown; and the health of your mitochondria prior to surgery. 

To evaluate these factors, the researchers used ultrasound imaging to scan the rectus femoris — a larger muscle in the thigh — of 20 male patients before and after aortic valve surgery. In addition, blood samples were collected to search for both compounds excreted by dysfunctional mitochondria and stress hormones such as cortisone and cortisol.

When the body is under stress, cortisone converts to cortisol, which signals for muscles to be broken down for emergency fuel. This cortisol is then converted back to inactive cortisone through the enzyme 11‐βHSD2. Researchers found that the ratio of cortisol relative to the amount of cortisone was higher in patients who experienced more muscle loss. This indicates that 11‐βHSD2 may be less active in these patients.

Mitochondria are small subunits of animal and plant cells in charge of producing energy and maintaining electron balance. When these subunits are damaged, as in diseases such as diabetes, cancer, or other diseases, they take up less fuel from the blood and produce more compounds associated with inflammation. In surgery patients who lost more muscle, researchers detected less mitochondrial fuel uptake and more inflammatory markers.

This research indicates that genetic factors that influence cortisol inactivation and mitochondrial damage due to pre-existing conditions like diabetes may make a person more likely to lose muscle after surgery.