From the time you are born to around the time you turn 30, your muscles grow larger and stronger. But at some point in your 30s, you start to lose muscle mass and function. The cause is age-related sarcopenia or sarcopenia with aging.

Physically inactive people can lose as much as 3% to 5% of their muscle mass each decade after age 30. Even if you are active, you’ll still have some muscle loss.

There’s no test or specific level of muscle mass that will diagnose sarcopenia. Any loss of muscle matters because it lessens strength and mobility.

Sarcopenia typically happens faster around age 75. But it may also speed up as early as 65 or as late as 80. It’s a factor in frailty and the likelihood of falls and fractures in older adults.