One reason you probably weight train is to age-proof your body and to stay healthy and functional when you reach your retirement years. We begin to lose muscle tissue at around age 30 and the loss accelerates in women after menopause. In fact, by age 70, you will have lost as much as 25% of the muscle tissue you had as a young adult. That’s a substantial loss!
Unfortunately, loss of muscle tissue leads to functional declines as well and an increased risk of injuries and falls. Plus, muscle has an impact on metabolic health. As you lose muscle, your metabolism slows and you’re at higher risk of developing insulin resistance, as you have less muscle tissue to take up glucose from the bloodstream. It’s clear that we lose muscle tissue with age but the muscle we retain also changes. If you looked at a cross-section of a muscle and the microscopic muscle cells in a younger person and an older one, you’d see qualitative differences as well. Let’s look at some of the ways youthful muscle is different from older muscle.
Youthful Muscle Has Healthier Mitochondria
Mitochondria are the energy-producing portions of a muscle cell. These tiny organelles spend their existence churning out ATP, the energy currency of a cell that fuels muscle contraction. Youthful muscle has more mitochondria and the mitochondria in a younger person are healthier as well. Unfortunately, producing ATP is a high-risk occupation for mitochondria. Because they need oxygen to make ATP, they’re constantly bombarded with reactive oxygen species or free radicals.
Over time, constant exposure to free radicals damage muscle mitochondria. As the damage accrues, mitochondria become less efficient at making ATP and muscle function declines. Experts believe that damage to mitochondria is a strong contributor to metabolic aging and insulin resistance, a forerunner to type 2 diabetes. So, loss of and damage to mitochondria has far-reaching implications for overall health and wellness.
What can you do to boost the health of the mitochondria within each muscle cell? High-intensity interval training may be the ticket. A study sponsored by the NIH found that high-intensity interval training was linked with a 49% boost in mitochondrial capacity in younger people and a whopping 69% increase in older adults. Moderate-intensity aerobic exercise, too, has the capacity to enhance the activity of mitochondria and increase the number of mitochondria inside muscle cells. Exercise that boosts the heart rate and increases oxygen uptake gives a muscle cell greater ability to produce energy and that’s important for muscle health and overall health and well-being. Plus, eating a whole food, nutrient-rich diet with antioxidant-rich fruits and vegetables may help mitochondria better fight oxidative stress.
Youthful Muscle Become “Fattier”
We think of fat as accumulating around areas like our tummies and thighs, but muscle tissue accumulates fat with age too. Your muscles can use this fat as an energy source, but when too much of it builds up, it negatively affects muscle function. Studies show that higher levels of fat within muscles is linked with slower walking speed, problems getting up from a sitting position, and balance issues.
If you’re overweight or obese, you probably have more fat in your muscle than a lean individual. Healthy, youthful muscle has a fat content of around 1.5% whereas muscles from an obese individual could be as high as 5%. In an elderly person, intramuscular fat content could be as high as 11%. In fact, a study carried out by researchers at Tufts University showed that older people produce more of a fatty molecule called ceramide and it may be responsible for increased fat in the muscle due to aging.
Is there anything you can do about fatty muscle? Although we can’t control the aging process, we can reduce the accumulation of muscle tissue by not gaining weight as we grow older. Make sure you’re getting enough vitamin D too. A study of healthy, young women found that those with low levels of vitamin D had more fatty infiltration of the muscle.
The Ratio of Muscle Fiber Types Changes
Most people have a roughly equal quantity of fast-twitch and slow-twitch muscle fibers during youth. Fast-twitch fibers are those designed for short-term strength and power movements as they can generate lots of force but fatigue quickly. Slow-twitch fibers have substantial endurance but can’t generate lots of force or do it quickly. These fibers are better designed for endurance exercise. However, the ratio changes as we age. Studies show that we lose fast-twitch fibers at a faster rate than slow-twitch ones. In fact, as muscle fibers die, the circuitry is rerouted so that it turns into a slow-twitch fiber. That’s why you lose more strength and power as you age than you do endurance. Fit, older people can run marathons but are less proficient sprinters.
What can you do to slow the loss of fast-twitch fibers? Strength train and add power training to your routine. Heavy strength training and using lighter weights and making the movement explosive, both stimulate fast-twitch muscle fibers and help them “stay in the game.” The loss of power capabilities is critical since you need the power to propel yourself out of your seat as you grow older. Plus, studies show we lose power capabilities even faster than strength. In fact, we love power almost twice as quickly! It’s not enough to take a walk, the form of exercise many middle-aged and older people choose as their only form of physical activity. We need to work our muscles against resistance too.
The Bottom Line
You lose youthful muscle mass as you age and the muscle you retain is of poorer quality. However, you can preserve the health of your muscle tissue by strength and power training, watching your weight, eating a healthy diet, and getting enough vitamin D.
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