Muscle atrophy, the loss of muscle tissue, can emerge after a period of inactivity.

Age-related muscle loss, called sarcopenia, is a natural part of getting older. But after an injury, illness, or any prolonged period of inactivity, muscle loss can occur faster, leading to muscle atrophy. The consequences are greater weakness, poor balance, and even frailty.

“People older than age 65 are especially vulnerable to muscle atrophy,” says Jodi Klein, a physical therapist with Harvard-affiliated Brigham and Women’s Hospital. “It can take longer for the body to recover from dramatic muscle loss, but with the right strategy, older adults can protect themselves from muscle atrophy and rebound easier if it occurs, no matter what their age.”

Signs of weakness

Muscle atrophy can occur from a disease that primarily affects the muscles, such as polymyositis (an autoimmune inflammatory disease). Diseases that rob the muscles of energy, like cancer and malnutrition, are other causes.

But muscle loss most often is due to physiologic atrophy, which happens when people don’t use their muscles enough for an extended period. Besides an injury or surgery, physiologic atrophy can occur because of osteoarthritis, which makes staying active difficult, or a sedentary lifestyle.