Sarcopenia and Age-Related Muscle Loss
The ability to lead an active lifestyle throughout the aging process is a significant determinant of an individual’s quality of life. When someone is young, they may not think twice before hopping up from the floor or going on a run. However, with age, activities that were once easy to do can become much more challenging. Daily tasks such as completing household chores, going to the grocery store, or standing up from a low chair may become increasingly difficult.
Progressive muscle loss can occur with age and result in decreased strength. This decrease in strength leads to reduced functional mobility, places an individual at an increased risk for falls, and contributes to overall fragility with aging. By understanding the risk factors and underlying mechanisms of muscle loss, strategies for management and prevention can be applied early to improve health outcomes and quality of life with age.
What Is Sarcopenia?
Sarcopenia is generally considered age-related muscle loss, resulting in decreased muscle strength, quality, and quantity. Sarcopenia can occur at any age. However, it is more prevalent in the aging population, ranging from 5% to 50%, depending on an individual’s gender, age, and contributing medical co-morbidities. The severity of sarcopenia is considered probable when muscle strength is low. However, a formal diagnosis requires an individual to have decreased muscle strength combined with either low quality or low quantity of muscle. Sarcopenia is deemed severe when the levels of muscle strength and quality are so low that physical performance is affected.
Functional Mobility And Strength Testing
Healthcare providers may perform several tests to evaluate muscle strength and functional mobility to assess muscle performance. Examples of mobility testing include a five-time sit-to-stand chair rise test, a timed up-and-go test (TUG), a Short Performance Battery Protocol (SPPB), or an assessment of gait speed. Strength can be directly tested by isometrically testing a specific muscle or assessing grip strength. Diminished grip strength has been correlated with decreased lower extremity strength. Diagnostic imaging can also be performed, including dual-energy X-ray (DXA), cross-sectional lumbar CT (computed tomography), or an MRI (magnetic resonance imaging).
Risk Factors
Risk factors for developing age-related muscle loss are associated with a sedentary lifestyle and medical co-morbidities. Living a sedentary lifestyle can contribute to disuse atrophy of the muscles. This results when the muscles are not challenged on a regular basis and become smaller as a result. Excessive alcohol consumption and poor nutritional intake increase the risk of developing sarcopenia.
Medical conditions such as CHF (congestive heart failure), COPD (chronic obstructive pulmonary disease), chronic kidney disease, rheumatoid arthritis, and cancer are also considered risk factors for developing sarcopenia. Chronic inflammatory conditions contribute to anabolic resistance, which affects the body’s ability to stimulate muscle growth. The development of insulin resistance impedes muscle growth. Additionally, hormonal changes that occur with age, such as a reduction in testosterone levels, can affect the ability to gain muscle mass and strength.
Nutrition
A decline in nutritional intake with age can lead to malnutrition. This can be due to a combination of decreased food consumption or malabsorption issues. Adequate protein intake is essential for the formation of lean muscle mass. Spacing meals out and evenly allocating protein throughout each meal may help with absorption and building lean muscle mass.
Protein quality and amino acid distribution are essential factors in the protein’s ability to have an anabolic or stimulating effect on muscle growth. Leucine is a branch-chain amino acid that aids in muscle protein synthesis. Leucine is in lower concentrations for plant-based proteins. Additionally, B-hydroxy-B-methylbutyrate (HMB), which is an active leucine metabolite, has been shown to increase muscle protein synthesis.
Vitamin D is essential for maintaining skeletal health, and low vitamin D levels have been associated with reduced muscle mass. Vitamin D supplementation can have a positive influence on muscle strength and mass. Additionally, Omega-3 fatty acids in fatty fish can also help build muscle and reduce inflammation.
Creatine Monohydrate is present in food and can also be synthesized in the body. Creatine is primarily stored in skeletal muscle and is important for muscle contraction. However, levels of creatine in the body are reduced in older individuals. Supplementation with creatine can assist with improving muscle mass.
Changes In Muscle Composition
With age, body composition is often redistributed with decreased muscle mass and increased fat distribution that results from a more sedentary lifestyle. It has been suggested that potential causes of sarcopenia can start with the transition from an active lifestyle to a more sedentary one from the ages of 20 years to 40 years. This change in activity may contribute to a decline in cardiovascular VO2 max and reduced ability to perform high-intensity burst activities such as sprinting.
Muscles contain a combination of type I (slow twitch) and type II (fast twitch) fibers. Slow twitch fibers are responsible for sustained low-intensity activities, such as walking. Fast twitch muscle fibers are responsible for generating high-intensity movements required for sprinting. Changes in muscle fiber recruitment can occur with age, resulting in a reduction of type II muscle fibers. This change in muscle composition and the ability of muscle to generate high-intensity force continue to decline as lifestyles become increasingly sedentary in the later decades of life.
Exercise And Strength Training
Resistance training is the cornerstone of building and maintaining lean muscle mass. Muscle strengthening can occur with both concentric and eccentric loading of the tissue. Concentric loading occurs when a muscle is shortening, and eccentric loading occurs when a muscle is lengthening. Eccentric strength training effectively strengthens muscles with less energy output and may be more suitable for older individuals. Activities such as descending stairs or lowering phase of a bicep curl from a fully flexed position are examples of eccentric movements.
Another form of exercise is high-intensity interval training (HIIT). This type of training alternates between bursts of high-intensity followed by short periods of low-intensity activities and has been shown to positively affect sarcopenia. However, high-intensity training may not be suitable for some older individuals with certain medical co-morbidities.
Aerobic exercise has been shown to benefit cardiovascular health, help increase adenosine triphosphate (ATP) production, and improve overall metabolic function. The incorporation of aerobic exercise on a regular basis can help increase overall activity levels and reduce the effects of a sedentary lifestyle.
Conclusion
The onset of age-related muscle loss has been associated with a sedentary lifestyle, poor nutritional intake, chronic inflammatory conditions, and medical co-morbidities. Risk factors for the development of sarcopenia can be reduced with a healthy and active lifestyle. Through the implementation of muscle-preserving strategies combined with a focus on mobility and strength training, a high level of function and quality of life can be maintained throughout one’s later years.
References
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