Sarcopenia, Dynapenia, and the Impact of Advancing Age on Human Skeletal Muscle Size and Strength; a Quantitative Review

Abstract

Changing demographics make it ever more important to understand the modifiable risk factors for disability and loss of independence with advancing age. For more than two decades there has been increasing interest in the role of sarcopenia, the age-related loss of muscle or lean mass, in curtailing active and healthy aging. There is now evidence to suggest that lack of strength, or dynapenia, is a more constant factor in compromised wellbeing in old age and it is apparent that the decline in muscle mass and the decline in strength can take quite different trajectories. This demands recognition of the concept of muscle quality; that is the force generating per capacity per unit cross-sectional area (CSA). An understanding of the impact of aging on skeletal muscle will require attention to both the changes in muscle size and the changes in muscle quality. The aim of this review is to present current knowledge of the decline in human muscle mass and strength with advancing age and the associated risk to health and survival and to review the underlying changes in muscle characteristics and the etiology of sarcopenia. Cross-sectional studies comparing young (18–45 years) and old (>65 years) samples show dramatic variation based on the technique used and population studied. The median of values of rate of loss reported across studies is 0.47% per year in men and 0.37% per year in women. Longitudinal studies show that in people aged 75 years, muscle mass is lost at a rate of 0.64–0.70% per year in women and 0.80–00.98% per year in men. Strength is lost more rapidly. Longitudinal studies show that at age 75 years, strength is lost at a rate of 3–4% per year in men and 2.5–3% per year in women. Studies that assessed changes in mass and strength in the same sample report a loss of strength 2–5 times faster than loss of mass. Loss of strength is a more consistent risk for disability and death than is loss of muscle mass.

Age-related changes in motor unit firing pattern of vastus lateralis muscle during low-moderate contraction

“…Taking these observations together, neural factors or motor unit activation properties should be associated with the maximal muscle strength in the elderly and its decline with aging. Our results showing a correlation between motor unit firing characteristics and the maximal muscle strength in the elderly support this and suggest that a part of the inconsistency between decreases in muscle strength and muscle volume with aging (Mitchell et al 2012) can be explained by the attenuation of motor unit activation properties in the elderly.…”

“…The decrease in muscle strength with aging cannot be explained solely by a decrease in the muscle volume: age-related strength and muscle mass declines are 2.5~4.0 and 0.5~1.0 % per year, respectively, and age-related strength decline is 2~5 times greater than age-related muscle volume decline (Mitchell et al 2012). This suggests that in addition to morphological changes, other factors strongly contribute to the decline in muscle strength in the elderly.…”

Relationship between functional vision and balance and mobility performance in community-dwelling older adults

“…Decreasing physical activity may speed up sarcopenia and muscle strength especially after age of 75 years (Mitchell et al 2012). Older adults share numerous overlapping pathways and risk factors for disability such as decreasing physical function, increasing number of chronic medical conditions and impaired vision (Rosso et al 2013).…”

Comprehensive proteome analysis of human skeletal muscle in cachexia and sarcopenia: a pilot study

“…Based on their responses to previously published health selection criteria,7, 24 all individuals were healthy and did not engage in any form of physical training. Based on DXA, these individuals were classified as non‐sarcopenic healthy elderly or age‐related sarcopenic.…”

“…In elderly people, several of these conditions may co‐exist, and the cause of muscle wasting could not easily be allocated to a single condition. Hence, a molecular description of these different groups may hold the key to unequivocally differentiate between normal age‐related muscle loss and chronic disease‐related muscle wasting 5, 6, 7. Weight loss and muscle wasting as a result of chronic disease such as cancer, heart failure, renal failure, or chronic obstructive pulmonary disease is termed cachexia 8.…”