Aging and muscle loss are natural and inevitable processes responsible for a decrease in the strength, speed, and endurance of human beings.
Older people have a slower or even erratic gait, which makes them at risk of falling. Their bones might be more brittle, so they are likely to experience fractures. In some cases, muscle loss can be a deciding factor in choosing to be in an assisted-living facility, so help and guidance are available anytime.
But why are older adults prone to muscle loss? Several factors contribute to this degradation:
1. Oxidative Stress
Muscle tissue loss is a common side effect of many chronic diseases, and it can be challenging to treat. Some studies suggest that oxidized proteins from muscle cells react with specific antibodies, triggering immune reactions. These can lead to inflammatory processes and further muscle loss.
But how does oxidative stress occur, and what is its link to aging? Oxidative stress happens when free radicals outnumber antioxidants. Free radicals are molecules with one or more unpaired electrons.
Although they are by-products of normal metabolic processes, they are also unstable.
These molecules will attempt to steal electrons found in other cells, damaging them in the process. Antioxidants can slow down the production of these free radicals by inhibiting oxidation.
Aging, though, can mean the accumulation of these free radicals and higher oxidative stress. When a person lacks antioxidants for a long time, their advanced age only makes them more susceptible to chronic diseases.
2. Mitochondrial Dysfunction
Muscles are a very metabolically active tissue. One way to see this is by examining the muscle fibers under a microscope. Nearly every fiber contains mitochondria, the tiny organelles that produce cellular energy.
Researchers who study mitochondrial function in aging muscles have noted an age-related decline in mitochondrial density but not in specific enzymatic activity. They speculate that decreased “quality” rather than the number of mitochondria accounts for increased fatigability (or susceptibility to fatigue).
Mitochondrial dysfunction can explain why many older adults experience fatigue. However, the lack of energy to do anything can also increase the risk of muscle loss since they are likely to spend more time not exercising and instead sit for long periods.
3. Chronic Inflammation
Inflammation is important to initiate repair in the body. When inflammation occurs, chemicals are released that call other cells to the area of injury (neutrophils, macrophages, etc.).
Some of these cells will become phagocytes and engulf some dead tissue and debris, which are then degraded by lysosomes into soluble proteins and lipids. This process aims to clean up the cell before it dies, so the cells do not release dangerous substances as they decompose.
The problem is that sometimes the body produces a lot of inflammatory cells for various reasons, including high oxidative stress. It will create more cytokines and chemokines, stimulating even more neutrophils and macrophages into this area (TNF-α, IL-6). Some of these inflammatory cytokines induce muscle cells to take up the protein TNF-α, which then kills these cells through apoptosis.
To make matters worse, when a muscle is injured, it releases myokines such as IL-6 and TNF-α. Myokines are molecular signals that precede inflammation (similarly to cytokines) and stimulate many cells, including adipocytes and endothelial cells, to produce more inflammatory cytokines.
This is known as a positive feedback loop. This process creates even more inflammation in tissues surrounding the muscle injuries and contributes to waste.
Older adults are prone to diabetes for two reasons: increased risk of insulin resistance and poorer function of the pancreas, which produces insulin, the hormone that delivers glucose to cells for energy.
The mitochondria of the cells need glucose to produce cellular energy. When the supply seems low due to the lower sensitivity of these cells to insulin, the person is then likely to experience feelings of fatigue.
Diabetes can also contribute to muscle loss in two ways:
- A high glucose concentration in the blood causes glycation of proteins and lipids, which can damage tissues, muscles included.
- Insulin deficiency or insulin resistance associated with diabetes can cause catabolism of the muscle tissue (muscle wasting) by breaking it down into amino acids and converting it to sugar for energy.
Effects of Muscle Loss
When someone loses muscles, they can become weaker and more prone to injury. Further, muscles regulate the metabolic activity of cells and maintain body temperature through vasodilation (dilation of blood vessels). Loss of muscle mass hinders these functions, which can lead to various health problems.
Additionally, a person’s physical appearance changes drastically with the loss of muscle tissues. Muscle is the main tissue involved in metabolism as well as maintaining optimum weight for healthy living. When you lose your muscles, you lose not only their function but also their shape.
This leads to rapidly changing body shapes that we term “sarcopenia.” Sarcopenia causes loss of muscular tone, strength, and endurance. As a result, it makes movement difficult and strenuous—something that is not easily noticeable at first.
Muscle loss occurs very slowly over a long period. It becomes especially significant after age 50. This is when the rate of muscle loss exceeds the rate of development by around 2 percent each year, ultimately leading to thinning bones and frailty.
Older adults, therefore, who might already have problems with gait, posture, grip, endurance, and strength can benefit from professional healthcare support to reduce their risks of injury.