When most of us think about getting older, we think of declines in mental acuity and cognitive function, an increase in general aches and pains, and an increased risk of disease and illness – but we rarely think about our aging muscular system.
This is actually a little odd because your skeletal muscle tissue is incredibly important for managing day-to-day life.
While you probably know that healthy muscle tissue is integral to maintaining normal movement, it is important to realize that it also does much more than that. Healthy muscle tissue also:
- Stabilizes bones and joints, improving their ability to deal with external forces
- Assists in bone growth and the maintenance of normal bone health
- Promotes normal glucose metabolism and assists with metabolic health and
- Ensures normal amino acid metabolism
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But as you age, some of this changes – or at least, it becomes more difficult.
So, what is the effect of aging on the muscles?
Well, the aging of the muscular system results in a diseased state known as sarcopenia.
What is Sarcopenia and What Causes it?
Sarcopenia is the term used to describe the loss of skeletal muscle mass and muscular strength associated with aging. Loosely translated to poverty of flesh in Greek, sarcopenia is thought to be the driving force behind the declines in function and mobility that occur with normal aging.
What Causes Muscles to Deteriorate in Sarcopenia?
Sarcopenia appears to be the combined result of changes in lifestyle, nutrition, and hormones as you age.
Lifestyle, Aging, and Sarcopenia
From a lifestyle perspective, sarcopenia is thought to be driven by decreases in movement as you get older. Typically, when you age, you move less – plain and simple. Whether this is because of a reduction in physical labor, social sport, or general exercise, it doesn’t really matter because it all results in the same thing: inactivity.
And inactivity (at any age) results in muscle wastage.
In short, when it comes to your muscles, if you don’t use it, you lose it.
Diet, Aging, and Sarcopenia
Changes in diet during aging may also contribute to sarcopenia. For most people, there is a significant decline in food intake when they age. While the mechanisms behind this are not fully clear, is has been suggested to result from a combination of increased satiety (due to inactivity), declines in social interactions, and financial influences.
Whatever the mechanism, though, the result is the same. Their protein intake is so low that muscle development and repair becomes very difficult. So, muscle tissue starts to waste away.
Hormones, Aging, and Sarcopenia
As you get older, you see a significant decline in the body’s ability to produce key hormones responsible for muscle protein synthesis: testosterone, growth hormone (GH), insulin-like growth factor (IGF-1), and dehydroepiandrosterone (DHEA).
Each of these hormones is extremely anabolic (meaning that they strongly promote the development of new muscle tissue). Their reduced production, therefore, makes it much more difficult to retain healthy muscle mass. And when this is combined with inactivity and insufficient protein intake, you have a recipe for disaster.
Sarcopenia’s Effect on the Rest of the Body
Unfortunately, as your muscles become less and less healthy as sarcopenia progresses, they perform their functions in your body less and less well. This means that not only do you have more difficulty moving and lifting things, but you also see a drop in your muscles’ ability to carry out its roles in regulating your metabolism and bone health, as well.
Two of the most dreaded complications of sarcopenia on your bone health and metabolism are osteoporosis and diabetes, respectively.
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How is Muscle Aging Linked to Osteoporosis?
There are approximately 700 named skeletal muscles within the human body, each of which attaches to one (or in some cases, more) of the 206 bones that make up the human skeleton. When these muscles contract, they either act to create movement at a specific joint (a concentric muscle action), slow the movement at a specific joint (an eccentric muscle contraction), or secure a specific joint so that it doesn’t move at all (an isometric muscle contraction).
Muscle’s ability to push, pull and squeeze bones makes it a key player in distributing force throughout the body. This helps stabilizes bony structures and joint complexes during movements. By making sure external forces and movements are transferred safely to your bones, healthy muscle also helps protect bones from the wear-and-tear of daily life, shoring them up against osteoporosis
Additionally, controlled forces placed on bone by healthy muscle tissue also have the capacity to directly elicit beneficial bone growth. Regular and intense muscle contractions place mechanical stress on the bone, which activates special cells, called osteoblasts. When activated, osteoblasts start making new bone.
As you can imagine, when your muscle tissue develops sarcopenia, it cannot contract as hard as it once could. This decreases its ability to protect bone and joint structures from external loads, opening you up to bone damage, and decreases the how tightly the muscle can squeeze down on bones, removing the stimulus for your osteoblasts to make new bone.
Exaggerated bone damage and less new bone being made? That’s a dangerous combination for promoting the onset of osteoporosis.
How is Your Aging Muscular System Linked to Diabetes?
Glucose is the primary fuel source of the human body, and muscle tissue accounts for approximately 20% of all daily energy expenditure. To produce energy, muscles cells break down glucose to produce ATP (the energy currency of the body), which provides the body with the energy required to function.
To maintain this process, muscle tissue needs to be able to extract glucose from the blood – something that is mediated by the hormone insulin. Insulin is our key energy storage hormone. It is responsible for allowing the movement of glucose from the blood into the muscle tissue.
This process appears to happen quite easily when you have lots of healthy muscle that is highly receptive to insulin. Unfortunately, though, if you have too little healthy muscle, you can develop something called insulin resistance.
This essentially means that those individuals who have low muscle mass (from sarcopenia or another condition) are less receptive to the action of insulin, and can develop chronically elevated blood sugar levels as a result. This can create a vicious cycle: First, the body secretes more and more insulin into the blood to try and control the rising blood sugar levels. Then, the body develops a more and more severe resistance to insulin because there is so much in the blood.
This vicious cycle is a key mechanism behind the onset of type II diabetes. And it provides a clear link between sarcopenia and an increased risk of developing diabetes as you age.
Take Home Message
The aging process can be pretty rough on the muscular system. Aging causes some pretty serious declines in muscle health and function, eventually culminating in sarcopenia.
Unfortunately, sarcopenia has serious implications for not just your muscle health, but your bone and metabolic health as well; it can result in an increased risk of both osteoporosis and diabetes.
On a more positive note, while sarcopenia does occur in healthy and unhealthy adults alike, some of its drivers are very much lifestyle based, such as changes in diet and exercise. This suggests that by taking care of your muscular system (i.e. maintaining suitable exercise levels and ensuring adequate protein intake) you can limit some of the expected age-related declines in muscle health.