As people lose physical reserve, they may progress from robust to prefrail and, eventually, frail. Researchers often assess frailty using five physical signs: unintentional weight loss, exhaustion, low physical activity, slow walking pace, and weak grip strength. One or two signs indicate prefrailty; three or more indicate frailty.
These changes are not limited to old age. A 2018 study in The Lancet Public Health, involving nearly half a million UK Biobank participants aged 37 to 73, found that both frailty and prefrailty were present in middle age.
A 2024 study of adults in Malaysia found that, among participants younger than 60, 67.9 percent were classified as prefrail and 10.4 percent as frail. However, researchers used a broader measure of health problems and limitations than the five physical signs assessed in the UK study.
Several biological changes can help explain this decline. The body gradually loses motor neurons, and muscles become less responsive to the signals that stimulate growth. Changes in mitochondria, which produce energy for cells, and rising levels of low-grade inflammation may also play a role. In women, hormonal changes during menopause can accelerate muscle and bone loss, Favero said.
“None of these is frailty, but they shrink the buffer or reserve that protects you later, when an illness, injury, or hospital stay hits,” he says.