Researchers are standing behind new data on how people’s posteriors reflect changes linked to aging and diabetes.

Shrinkage or inflammation of the gluteus maximus muscles of the buttocks may reflect frailty, sitting time, fat deposition and diabetes risk, and these changes may occur differently among men and women, the British team said.

“Unlike past studies that mainly looked at muscle size or fat, we used 3D shape mapping to pinpoint exactly where the muscle changes, giving a much more detailed picture,” noted study coauthor Marjola Thanaj, a senior research fellow at the University of Westminster’s Research Centre for Optimal Health in London.  

Her team will present their findings next week in Chicago at the annual meeting of the Radiological Society of North America (RSNA).

In the study, Thanaj and colleagues examined more than 61,000 MRI scans collected as part of the ongoing UK Biobank database. They also had detailed information on the Biobank participants’ physical measurements, medical histories and lifestyles. 

Overall, this allowed the team to assess 86 different variables and track associations with changes in buttock muscle shape over time.

Speaking in a RSNA news release, Thanaj reported that "people with higher fitness, as measured by vigorous physical activity and hand grip strength, had a greater gluteus maximus shape, while aging, frailty and long sitting times were linked to muscle thinning.”

Men designated as being frail showed a greater thinning of the gluteus maximus compared to frail women, the study found.

And when it came to people diagnosed with Type 2 diabetes, the glutes of males showed a pronounced thinning, whereas women showed enlarged muscle mass in their glutes, perhaps due to the infiltration of fat within tissues.

All of this suggests that the shape of the buttocks, rather than size, is more closely tied to underlying metabolic changes in the body, the study authors said. 

Sex differences in buttock shape also suggest that disease could impact the biological responses of men and women differently, Thanaj said. That could be especially true when it comes to Type 2 diabetes. 

As one of the largest muscles in the human body, the gluteus maximus may play a crucial role in metabolic health, noted study lead author Louise Thomas, professor of metabolic imaging at the university. 

Because these findings were presented at a medical meeting, they should be considered preliminary until published in a peer-reviewed journal.