Muscle Menaces: What Causes Muscle Weakness?
Economy will shrink sometimes. There is one investment that we can control, to a large extent, and one that we can’t afford to neglect! How you manage your muscles now might affect your future more than you realize. Because muscle strength is directly associated with functionality and independence, shrinking skeletal muscle mass can lead to declining health. Age-related loss of muscle is closely related to loss of bone tissue. And decreased muscle mass and function can significantly contribute both to disabilities and several major chronic diseases. Obviously, muscles are for more than display! Their health is fundamentally connected to our well-being. Ready for a strategy that reduces muscle loss and increases the enjoyment of your life? Stay tuned!
Microscopic-size blood vessels or capillaries supply each muscle with oxygen and nutrients, and physically link the muscles with the cardiovascular system. Each muscle cell may be connected to as many as eight capillaries, depending on fiber-type, size, and physical training. One square-inch cross-section of muscle can contain between 125,000 to 250,000 capillaries! However, this number is not static. Endurance exercise, for example, can stimulate the growth of more capillaries. It also can improve the delivery and removal functions of this fantastic network of vessels. The total number of capillaries per muscle in endurance-trained athletes is about 40 percent higher than in untrained persons!
The Nerve Connection to Muscle Health
By sending signals from the brain to the muscles, motor neurons initiate movements. A motor unit is composed of a motor neuron and all the muscle fibers (cells) that it innervates. Unfortunately, the number of spinal cord motor neurons and functional motor units decline with age—up to 50 percent loss after age 60. Through age-associated neuropathy, diabetes, alcoholism, B-12 deficiency, or inflammation, muscle cells shrink and motor neurons die. Slow-twitch fibers replace fast-twitch fibers. As a result, muscle movement tends to become slower and less precise.1
The Hormones and Muscle Connection
Hormone status also affects muscle function. For the healthiest muscles, we want to physiologically improve growth-hormone production and insulin sensitivity, while reducing stress hormones.
Deep sleep, regular exercise, short fasting, and a vegetarian diet including arginine from nuts and legumes in particular, improve growth hormone synthesis. In contrast, obesity and a high-fat diet decrease its production. Fortunately, many of the same factors that improve growth-hormone synthesis also improve insulin sensitivity. This means that more amino acids enter the muscle cells for growth and repair.
Excessive amounts of the hormone, cortisol, however inhibit protein synthesis in the body, including muscle cells, so that there is less repair and regeneration. Prolonged stress, visceral fat, sleep deprivation, and a high protein diet all increase cortisol levels. Other hormones, like testosterone, thyroid hormones, and parathyroid hormone, also influence the health of our skeletal muscles.
Up in Smoke
Smoking causes muscle fiber atrophy. Unfortunately, it also acutely and adversely affects small blood vessels by decreasing the production of nitric oxide, a molecule that helps them to dilate. Less dilation results in a deceased supply of oxygen to muscle cells. This is seen in research demonstrating that exercise-induced vasodilation is lower in smokers during physical activity compared to non-smokers. Even in healthy young adults, exposure to tobacco smoke impairs the ability of the arteries to dilate.2
The carbon monoxide in cigarettes also contributes to a decreased delivery of oxygen to muscle fibers. In addition, to displacing hemoglobin in the blood, which normally carries oxygen throughout the body for each cell’s use, the carbon monoxide and other substances in cigarette smoke actually inhibit energy- generating enzymes in the mitochondria of the muscles.3 Consequently there is less oxygen for ATP synthesis.
Not surprising, then, that smokers also experience greater muscle fatigue than do non-smokers. The practice inhibits protein synthesis and growth in skeletal muscles.4 Research has shown that the biological markers for muscle formation were 40 percent less in smokers than non-smokers!5 No wonder this detrimental habit erodes muscular endurance.
Alcohol’s Detrimental Effects
The development of alcohol-induced muscle disease from chronic consumption of liquor affects both cardiac and skeletal muscle and consequently leads to morbidity and mortality in heavy drinkers. Chronic alcoholic, skeletal muscle myopathy (disease of muscles) is characterized by a selective atrophy of fast-twitch fibers so that up to 20 percent of the entire skeletal musculature is lost. Alcohol consumption, like smoking compromises the cellular proteins. The dynamic balance of proteins in striated muscle is dependent upon rates of protein synthesis and protein degradation. Alcohol consumption depresses protein synthesis in skeletal muscles. 6,7 So if you want to keep strong healthy muscles, abstain from intoxicating beverages.
Muscle weakness is a possible symptom of many diseases and should be evaluated carefully. Contributing causes of muscle weakness include infectious, neurological, endocrinal, inflammatory, rheumatological, genetic, metabolic, and electrolyte- or drug-induced (such as from statins) conditions. Mental depression can also reduce muscle strength, as measured by a person’s handgrip.
Chronic disease is another condition that can adversely affect the musculoskeletal system. Both chronic pulmonary obstruction (COPD) and congestive heart failure contribute significantly to muscle weakness. In diabetes mellitus, chronic heart failure, COPD, renal and liver failure, trauma, sepsis, and senescence, the chemistry of the body shifts, causing an increase of the catabolic hormones, cortisol, epinephrine, and norepinephrine that break down tissues. This altered body chemistry also increases the level of pro-inflammatory chemicals that damage the skeletal muscles. Consequently, proteins in the skeletal and heart muscles are broken down. Bottom line? All of the above-mentioned conditions produce predominantly catabolic molecules, eventually resulting in significant muscular wasting and metabolic impairment.
Damage from Diabetes
We’ve touched on diabetes, but its effects on the muscles deserve a closer look. Both chemical measurement and actual biopsy of diabetic individuals reveal significant problems. The loss of fast muscle fibers result in an increased risk both for muscle fatigue and for falling. Structural and functional changes in the muscle cells’ powerhouses or mitochondria are present, even in active young individuals who have type 1 diabetes.8
The efficiency of the mitochondria in skeletal muscles declines, leading to impaired fat-burning ability. This holds true even for nondiabetic obese individuals. Diabetes also decreases skeletal muscle contractility, induces atrophy, and reduces the ability of the muscles cells to regenerate.
Fortunately, regular aerobic and resistance-type exercise, especially when combined with a healthful diet, can increase the number and efficiency of mitochondria in diabetic individuals and thus ameliorate some detrimental effects of this prevalent metabolic disease.
Insult by Injury
Common causes of muscle injury include:
- Excess muscle tension
- Lack of flexibility
- Improper warm-up
- Improper spine alignment: when the spine is not in proper alignment, the muscles, ligaments, and joints between vertebrae are placed under extra stress
- Muscle imbalance: the muscles that flex often become stronger than those that extend
Sarcopenia is the age-related loss of skeletal muscle mass, strength, and function and affects more than 20% of the aging population. This condition is both a process and a consequence. Beginning in the fourth decade of life, adults lose three to five percent of muscle mass per decade, a rate of decline that increases to one to two percent per year after age fifty. In sarcopenia there is both a decrease in the number of fibers and an atrophy of remaining muscle fibers.9 It also increases the likelihood of oxidation. Oxidative damage to the DNA, proteins, and lipids in the skeletal muscle occurs when more free radicals are being generated than the muscle has antioxidant capacity to rectify. Sarcopenia negatively affects gait and the activity of daily light.
Inflammatory processes can be involved in sarcopenia as well. Aging is associated with significant increases in inflammatory agents that cause an undesirable reduction in blood flow to the skeletal muscles. This disrupted circulation can damage the innermost lining of blood vessels in the muscles.
Mitochondrial dysfunction also contributes to sarcopenia. Atrophy, oxidation, inflammation, and mitochondrial dysfunction, these can trigger consequent apoptosis (cell suicide) of muscle cells. Again, regular exercise is one of the best ways to improve the efficiency of mitochondria. Keeping your blood glucose well within the normal range helps the powerhouses in the muscles.
Healthful Lifestyle Can Combat Sarcopenia
Animal studies suggest that an eight-percent reduction in caloric intake may protect from sarcopenia.10 Recent epidemiological studies show that low-serum or plasma carotenoids in community-dwelling older adults are independently associated with low skeletal-muscle strength and the development of walking disability.11 A tasty solution? Bring on those carotenoid-rich carrots, yams, and collards! Vitamin D hormone (calcitriol), the “sunshine vitamin,” can also slow sarcopenia by stimulating bone turnover and protecting osteoblasts (cells involved with bone formation) from dying by apoptosis. Calcitriol also helps preserve the function of fast muscle fibers. These two contributions of calcitriol aid in preserving muscle strength and reducing falls.12 Please note elderly people do not get sufficient vitamin D from sun exposure!
Protein and Sarcopenia
Some authorities propose an intake of 1.0-1.2 g/kg of body weight per day of protein as optimal for skeletal muscle and bone health in elderly people without severely impaired renal function. But there is a caveat here. These same researchers also found that excess intake of acid-producing nutrients (meat and cereal grains) in combination with low intake of alkalizing fruits and vegetables may have negative effects on musculoskeletal health and recommend that modifying the diet to include more fruits and vegetables is likely to benefit both bones and muscles.13 Emerging evidence also suggests that vitamin B12 and/or folic acid play a role in improving muscle function and strength.14 Vitamin B-12 is necessary for protein synthesis and healthy nerves both of which are essential to muscle health.
As important as nutrition is on the development of sarcopenia, exercise is even more important! Sufficient protein intake has the potential to slow the loss of muscle mass, but is not as influential in maintaining strength and function. Physical activity (and in particular resistance training) when performed at higher intensities, is beneficial for muscle strength and functioning.15
Skeletal muscle shrinks when it is not used and this atrophy is accompanied by marked decreases of collagen formation. Collagen is the primary protein found in tendons and bones. Exercise not only stimulates protein synthesis in the muscles, but also in tendons. Regular exercise increases strength, endurance, and the number of mitochondria in skeletal muscles. It also improves flexibility as well as enzyme efficiency in muscle, including those involved in glucose metabolism. A cross-sectional study has found that exercising consistently in middle age is a protective factor against sarcopenia and effective in maintaining muscle strength and physical performance.16 For more benefits of exercise on muscles, see https://wildwoodhealth.com/blog/dont-forget-your-muscle-health/. Stretching, aerobic, and resistant exercises should be included.
Health Nerves Can Promote Muscle Health!
By the age of 75, individuals typically have around 30 — 50% fewer nerves controlling their legs. Unfortunately this leaves parts of their muscles disconnected from the nervous system. Without proper nerve connection, muscles are unable to function, become useless, and waste away.17
However, healthy muscles have a form of protection, in that surviving nerves can send out new branches to rescue some, but not all, of the detached muscle fibers. This protective mechanism is most successful in older adults with large, healthy muscles. When the internal protective mechanism is not successful and nerves are unable to send out new branches, it can result in extensive muscle loss as seen in sarcopenia. Diabetes, persistent alcohol consumption, B-12 deficiency, vitamin D deficiency, and elevated blood fats (triglycerides) attack the nerves. So get your lab work, control your blood glucose, and take supplements if you have a deficiency.
In most cases, a healthful lifestyle can substantially reduce one’s risk for muscle weakness. In a future article we will more natural remedies for muscle weakness and disease.
© 2018 – 2020, Wildwood Sanitarium. All rights reserved.
Disclaimer: The information in this article is educational and general in nature. Neither Wildwood Lifestyle Center, its entities, nor author intend this article as a substitute for medical diagnosis, counsel, or treatment by a qualified health professional.
- Zaccher, R.J., Health-related implications and management of sarcopenia. JAAPA, 19(10):24-29, 2006.
- Celermajer, D.S., et al, Impaired Endothelium-Dependent Arterial Dilation in Healthy Young Adults. NEJM, 334:150-55, 1996
- Morse, C.I., et al., Carbon monoxide inhalation reduces skeletal muscle fatigue resistance, Acta Physiol (Oxf), 192(3): 397-401, 2008.
- Peterson, A.M., et al., Smoking impairs muscle protein synthesis and increases the expression of myostatin and MAFbx in muscle, Am J Physiol Endocrinol Metab 293(3):E843-8, Jul 3, 2007.
- Ravin, Jorge, Researchers find that smoking wastes muscle away. www.associatedcontent.com , Jul 10, 2007.
- Vary, T.C., Assessing effects of alcohol consumption on protein synthesis in striated muscles. Methods Mol Biol, 447: 343-55, 2008.
- Preedy, V.R., et al., Alcoholic muscle disease: Features and mechanisms. J Pathology, 173(4): 309-315, 1994.
- McMaster University. “Active young adults with Type 1 diabetes have muscle complications: Changes in muscles could impair ability to manage blood sugar.” ScienceDaily, 18 April 2018. www.sciencedaily.com/releases/2018/04/180418092042.htm.
- Dirks, A.J., et al., Tumor necrosis factor alpha signaling in skeletal muscle: effects of age and caloric restriction. J Nutr Biochem, 17(8):501-8, 2006.
- Shaap, L.A., et al., Inflammatory markers and loss of muscle mass (sarcopenia) and strength. Am J Med,119(6):526.e9-17, 2006.
- Marzetti E., et al., Modulation of age-induced apoptotic signaling and cellular remodeling by exercise and calorie restriction in skeletal muscles, Free Radic Biol Med, 44(2):160-8, 2008.
- Semba, R.D., et al., Carotenoids as protection against sarcopenia in older adults. Ach Biochem Biophys, 458(2):141-5, 2007.
- Montero-Odasso, M., et al., Vitamin D in the aging musculoskeletal system: and authentic strength preserving hormone, Mol Aspects Med, 26(3): 203-19, 2005.
- Mithal A. Impact of nutrition on muscle mass, strength, and performance in older adults. Osteoporosis International, 2012; DOI: 10.1007/s00198-012-2236-y.
- International Osteoporosis Foundation. “Which nutritional factors help preserve muscle mass, strength and performance in seniors?.” ScienceDaily, 18 January 2013. www.sciencedaily.com/releases/2013/01/130118111714.htm.
- International Osteoporosis Foundation. “Regular exercise in middle age protects against muscle weakness later in life.” Science Daily, 14 December 2013. www.sciencedaily.com/releases/2013/12/131214144848.htm.
- The Physiological Society. “Can we turn back time? Muscles’ own protective systems could help reduce frailty.” ScienceDaily. 12 March 2018. www.sciencedaily.com/releases/2018/03/180312085120.htm.