by LAUREN J. YOUNG
Here’s why older adults naturally lose muscle mass over time and how regular physical activity and resistance training can help
Almost everyone shrinks with old age. Many older adults have more difficulty gaining muscle than they did in their childhood and teenage years. And when it comes to maintaining that muscle, the phrase “use it or lose it” holds weight, says Michelle Gray, a physiologist and professor of exercise at the University of Arkansas.
“I work primarily with older adults who are trying to either build and/or maintain muscle throughout their life span, and really how that happens is you use it or lose it,” Gray says.
But she adds that not all hope is lost. “It really is the neurology, as well as the muscular system and the interactions between the two, that changes,” she says. “There’s a fair amount of evidence that says all of those things are still there and [that] we can retrain them.”
Several factors contribute to involuntary age-related muscle loss. The exact age people start to see muscle mass decline varies, Gray says, but many begin to see noticeable changes in their 30s. Studies suggest that muscle mass decreases by about 3 to 8 percent per decade after age 30 and at higher rates after age 60. Losing that strength may not only be frustrating in keeping up with daily activities but can also have significant health consequences.
“If you look at who’s shrinking, and how much they’re shrinking, it predicts really important stuff, like how long you’re going to live, how vulnerable you are to getting sick and having to be in the hospital, how likely you are to develop problems taking care of yourself,” says Stephanie Studenski, a geriatrician and professor emeritus at the University of Pittsburgh.
Changes in Muscle Tissue and Cells
Muscle is a dynamic tissue, Studenski explains. “Your whole life, there’s turnover. We’re growing new muscle and breaking down old muscle all the time,” she says.
There are three main types of muscle tissue: smooth muscle lines the gut wall and organs, except the heart; cardiac muscle is striated and covers the heart; and skeletal muscle, which can be found in the arms and legs, is also striated. Skeletal muscle is often the kind that’s assessed for sarcopenia, a type of muscular atrophy in which age-related loss of muscle and strength is accelerated. Sarcopenia was classified as a disease in 2016. Muscle tissue is made up of long, slim fibers, each one containing a single muscle cell. The cells produce specific proteins—actin and myosin—that cause muscles to contract and relax like rubber bands at different speeds. But as we age, there is a decline in the overall number of muscle cells—along with mitochondria, which are essential for producing and storing energy in muscle. Mutations build up over time in the cells, sometimes causing the production of defunct proteins, which makes those rubber bands overstretched or less snappy, Studenski says.
Faulty muscle proteins and mitochondria, along with some other changes with age, have been linked to the impairment of the connection between muscles and the nervous system, called the neuromuscular junction. This junction between motor nerves and muscle tissue is where brain signals are transmitted for muscle contraction and movement. Issues in communication between nerves and muscles can create weakness and a decline in muscle mass.
Changes in hormone levels are also linked to age-related muscle loss. The gradual decrease in testosterone we experience as we age, for example, can lead to a decrease in the production of muscle proteins. Poor diet and malnutrition also influence muscle loss—generally, appetite and food intake tend to decrease with age.
Scientific American for more