Starting at age 40, muscle mass begins to decline. It accelerates by 50. Bone mass or density loss in women after menopause is common and our bones begin to lose calcium and other minerals. The rate of muscle loss is faster than the muscle we gain. Our bodies don't work as efficiently as they used to, which leads to a slower metabolism and fat accumulation. Muscle weakening or atrophy sets in. The reasons for atrophy are many. I will share four of them with you: age, sedentary lifestyle, medications and disease.
Age Related Changes in Muscle
Muscles lose their size and strength as we get older, which contributes to fatigue, weakness and less tolerance to exercise. This is due in part because the number of muscle fibers start to reduce in size and numbers. Muscle tissue is also replaced more slowly. As the nervous system changes, muscles become less toned and the ability to contract them gets more difficult. Bone structure changes result in a loss of bone tissue, calcium and other minerals making this another contributing factor. Joints lose their lubrication (synovial fluid) becoming stiffer and less flexible.
You've heard the saying, "use it or lose it". Inactivity causes our joint cartilage to shrink and stiffen, reducing joint mobility. A sedentary lifestyle causes muscles to lose their mitochondria. The main function of the mitochondria is to produce energy for various parts of the body. It burns fat or sugar for energy. If the body does not need energy, fat gets stored. This fat increases the number of fat cells in the body making it harder to lose weight. Being sedentary increases the body's capacity for fat storage, which results in a greater chance for developing high levels of LDL or bad cholesterol. A common thought is that this inactivity causes transdifferentiation (a conversion of one differentiated cell type into another) resulting in the muscle cells changing to fat cells. The body gets signals that it no longer needs those muscle cells.
There are a few medications prescribed for specific conditions that cause muscle weakness. One of those medications is systemic corticosteroids, often prescribed for people with asthma or inflammatory conditions such as rheumatoid arthritis or lupus. Statins are used for preventing and treating atherosclerosis that causes chest pain, heart attacks, strokes, cholesterol and diabetes - muscle pain is one of the side effects.
The beneficial effects of strength training include replacing muscle, reducing fat, increasing metabolic rate, relieving or decreasing low back and arthritic pain, lowering blood pressure, minimizing osteoporosis, enhancing glucose utilization, mitigating depression and improving blood lipid levels.