Muscle Quality in Aging: a Multi-Dimensional Approach to Muscle Functioning with Applications for Treatment

Abstract

Aging is often accompanied by declines in physical functioning which impedes older adults' quality of life, sense of independence, and ability to perform daily tasks. Age-related decreases in skeletal muscle quantity, termed sarcopenia, have traditionally been blamed for these physical decrements. However, recent evidence suggests that the quality of muscle tissue may be more functionally relevant than its quantity. 'Muscle quality' has been emerging as a means to elucidate and describe the intricate intramuscular changes associated with muscle performance in the context of aging and sarcopenia. While muscle quality has most commonly been defined in terms of muscle composition or relative strength, at the core, muscle quality really describes muscle's ability to function. Skeletal muscle displays a strong structure-function relationship by which several architectural characteristics factor into its functional capacity. This review describes the structural, physiological, and functional determinants of muscle quality at the tissue and cellular level, while also introducing other novel parameters such as sarcomere spacing and integrity, circulating biomarkers, and the muscle quality index. Muscle qualitative features are described from the perspective of how physical exercise may improve muscle quality in older adults. This broad, multidimensional perspective of muscle quality in the context of aging and sarcopenia offers comprehensive insights for consideration and integration in developing improved prognostic tools for research and clinical care, while also promoting translational approaches to the design of novel targeted intervention strategies designed to maintain function and mobility into late life.

Muscle mass and association to quality of life in non‐small cell lung cancer patients

“…In elderly patients, it is demonstrated that muscle waste has to progress to a point below 30% of the mean of young adults before decrease in functional abilities are observed 21, 38. It has also been shown that physical performance is not solely dependent on muscle mass but also muscle strength 22, 39. Muscle strength, in turn, is reported to be independently associated with muscle radiodensity,40 and in accordance with our findings, greater muscular fat infiltration is found to increase the risk of immobility in older men and women 41…”

“…The significant association between SMD and dyspnoea may support this assumption. As documented in geriatric patients, elevated fat content in the skeletal muscle may affect muscle strength more than plain muscle waste 21, 22…”

“…Increased fat content within the skeletal muscle may affect the muscle quality and influence both muscle strength and function 21, 22. The fat content in muscle is reflected by the skeletal muscle radiation attenuation also known as skeletal muscle radiodensity (SMD) 23.…”

Efficacy of Age-Specific High-Intensity Stretch-Shortening Contractions in Reversing Dynapenia, Sarcopenia, and Loss of Skeletal Muscle Quality

“…Further, physiological assessments have primarily utilized skeletal muscle mass as a primary outcome metric for improving function in aged populations, yet results continue to be equivocal. More recently, muscle quality, defined as skeletal muscle performance per unit muscle mass, has been suggested and supported by data from basic, applied, and epidemiological research as being a more specific and sensitive outcome metric with respect to aging (and with respect to exercise training as well) [9,59,60].…”

“…It is chronic resistance exercise loading, or training, that is unique in promoting restoration or improvements in skeletal muscle performance (i.e., strength, work capacity, fatigue resistance, etc.) and skeletal muscle mass [83,84], as evidence for these findings exist in both human [57,71,83] and animal studies [66]; yet, little evidence exists for improving skeletal muscle quality in various populations, including aged populations [7,59]. There are numerous human studies that have suggested that resistance exercise training is beneficial in countering distinct components of musculoskeletal health and aging [71,83,84]; however, no translational study has shown that resistance exercise training can restore musculoskeletal health with aging to youthful states entirely.…”