It’s a fact of life – you start to lose muscle mass after the age of 30 – at a rate of about a third of a pound per year. You also lose muscle strength, and the ability of your muscles to generate force diminishes even faster after the age of 50. What’s happening at the level of the muscle to bring about these changes? In general, muscle aging is characterized by three major types of transformation, none of which are healthy. The good news is these changes can be greatly reduced by physical activity.
Unfortunately, no part of your body is immune to the effects of time – and that includes your muscles. Your muscles age along with the rest of your body. If you were to slice a muscle lengthwise and look inside, a 70-year-old muscle from a sedentary person would like quite different from that of a 20-year-old muscle. Plus, if you were to look under a microscope, you’d see changes in the way the muscle cells or fibers look as well. Here are three of the age-related changes that muscles undergo:
The Ratio of Slow-Twitch to Fast-Twitch Fibers Changes
You have two main types of muscle fibers – fast-twitch and slow-twitch fibers. Fast-twitch fibers are those best adapted for generating strength and power and they do it well. The downside is these “fast” fibers “poop out” quickly. To give your muscles more flexibility and adaptability, you also have slow-twitch fibers. Muscles of the slow-twitch variety are built for endurance. While they can’t generate much strength or power, they CAN contract for long periods of time without fatiguing. You use mostly fast-twitch fibers when you sprint, do a kettlebell swing, lift heavy weights, or jump while slow-twitch fibers are called into play when you walk or jog long distances or perform resistance exercises using light weights and high reps.
What does this have to do with aging muscles? Research shows you lose a higher ratio of fast-twitch muscle fibers relative to slow-twitch as you age. This means your strength and power capabilities decline more than your endurance skills as the years pass – and, yes, that matters. Those fast-twitch muscles are important! Did you know you use fast-twitch muscle fibers every time you get up from a chair? No wonder older people who don’t exercise have difficulty getting around after a certain age. They don’t have enough fast-twitch fibers to propel them out of their seat!
Now you know why strength and power training are so important – they help you preserve fast-twitch muscle fibers.
Muscle Cells Lose Mitochondria
Another change that happens to muscles with age takes place at the cellular level. Inside muscle cells are tiny powerhouse organelles called mitochondria. These organelles spend most of their time making ATP, the energy currency that muscles use to contract. When muscles are young, they have lots of mitochondria that are efficient at doing their job, but aging leads to a reduction in the total number of these hardworking organelles and how the ones you’re left with function. Aging mitochondria become less efficient at making energy. That’s one reason older people lack energy and stamina.
Why mitochondria “die off” as we age isn’t clear, although one theory is they’re damaged by exposure to free radicals. The best way to preserve mitochondria as you age is to eat a healthy diet with lots of fruits and vegetables to reduce free radical damage and do aerobic exercise, including HIIT training. In response to aerobic exercise, muscles make new mitochondria through a process called mitochondrial biogenesis.
Your Muscles Become Fattier
Remember how we said an older person’s muscles look different when you slice them open? That’s because a 70-year old muscle has a higher proportion of fat relative to a 20 or 30-year-old muscle. If the 70-year old in question is sedentary, they can accumulate quite a bit of fat inside their muscles. You can actually see how fat and muscle look in a region like the thigh with an MRI scan. The muscle looks dark grey while the fat looks white. The problem with having muscles that contain more fat is it reduces muscle strength AND makes the muscle more insulin resistant. As you may know, insulin resistance becomes more common with age and the fact that muscles become fatter and flabbier is a contributing factor.
Exercise is your staunchest ally when it comes to keeping your muscles from turning to fat. If you compared a thigh muscle MRI of a 70-year-old sedentary person to a 70-year- old triathlete, you’d see the majority of what’s inside the triathlete’s thigh is muscle tissue, similar to what someone in their 30s would have. In contrast, the thigh of a sedentary 70-year-old is up to 50% fat. That’s why exercise, including resistance training, is so important.
The Bottom Line
It may not be possible to have the same strength and muscle size you had at age 20 when you’re 70, but research shows that much of the muscle strength and size you lose as you age is preventable through physical activity, especially resistance training. When you look at the fat and muscle composition of a 70-year-old triathlete’s thigh, it’s not much different from that of a 30 something-year-old. Plus, older people who have already lost strength and muscle size can reverse some of that loss through training.
Other things you can do, beyond exercise, to preserve lean body mass is to:
. Maintain a normal vitamin D level. Many people have a sub-optimal one.
. Add more protein to your diet. Research suggests you need more after the age of 60.
. Add more long-chain omega-3s to your diet. Research suggests they reduce age-related muscle loss.
By far the most important thing you can do to maintain as much muscle strength and size as possible is to do a combination of aerobic and resistance training. Bonus: You’re also preserving bone density as well. It’s a winning situation.
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