Sarcopenia refers to age-related reduction in muscular strength and mass. By age 70, skeletal muscle mass decreases by approximately 40 percent and strength decreases by approximately 30 percent compared to performance at age 20, according to a 1993 study published in "Exercise and Sport Sciences Reviews." The varied mechanisms of action that trigger the dramatic reduction in muscular strength work together to create weakened, reduced muscle mass, though current research suggests that the most significant factors in the decline of muscular strength are neuromuscular in nature.
Sarcopenia is a substantial decrease in both the quantity and quality of muscle mass. Decreases in muscular strength are caused by a reduction in the number of muscle fibers, a reduction in the ability of existing muscle fibers to contract efficiently, and a decrease in the types of physiological processes that trigger and facilitate muscular movement. Despite ongoing research regarding the causes and consequences of sarcopenia, experts do not agree on the primary mechanism of action that causes the marked loss of muscle strength associated with advanced age. Instead, researchers agree that several processes that happen simultaneously contribute to age-related loss of muscular strength.
Several changes in the way muscles are built and maintained in your body affect muscular strength. A 2005 research review published in the "American Journal of Clinical Nutrition" reports that the protein synthesis processes that build new muscle and support existing muscle tissue slow down due to aging. As a result, muscles burn more energy than they are able to synthesize into new muscle tissue, resulting in a loss of both muscular mass and strength. Muscular strength is also thought to be reduced due to decreased action of the neurotransmitters that trigger muscle contraction, the driving mechanism behind muscular force.
Muscular growth and the protein synthesis that supports growth are triggered by the presence of naturally occurring growth hormones like testosterone and dihydrotestosterone. During the aging process, production of these human growth factors significantly decreases, reducing the rate at which muscles are able to synthesize proteins and support new muscle growth. Insulin is another natural growth factor that promotes the health of existing muscle tissue. As people age, they develop a resistance to growth factors like insulin that inhibit muscle growth and synthesis.
The physiological factors that cause a decrease in muscular strength are exacerbated by lifestyle changes that accompany aging. An increase in age is most often accompanied by a decrease in physical activity or an increase in the likelihood that an individual is experiencing a sedentary lifestyle. As physical activity decreases, muscle fibers reduce in density and strength. As individuals feel their strength and endurance decreasing, they become even less likely to engage in physical activity, and the cycle of muscle loss continues. Though studies suggest a moderate increase in muscle mass as a result of increased physical activity, researchers note that even incredibly active older adults experience muscle loss through aging.