Aging of skeletal muscle fibers
Sarcopenia is the loss of lean body mass and muscle weakness associated with advancing age.
Muscle strength is a strong predictor of severe mobility limitation, slow gait speed, increased fall risk, risk of hospitalization, and high mortality rate.
Several recent studies show that factors such as changes in central nervous system drive, peripheral nerve dysfunction, alterations in the neuromuscular junction structure and function, fat infiltration, and a number of complex cellular and molecular changes at the level of single muscle fibers impair muscle force generation and power production.
This review discusses the cellular and molecular changes that underlie sarcopenia and may have implications for intervention, such as targeted exercise, nutrition and use of medication.
By 2050, the world's population over 60 years will double from about 11% to 22% and there will be 2 billion people aged 60 or older living on this planet. Approximately 400 million will be 80 years or older. Aging is associated with an increased incidence of chronic health conditions and, perhaps more importantly, with an increase prevalence of impairment and disability. Visual and hearing impairments, cognitive decline, musculoskeletal disorders, frailty, and sarcopenia all reduce activity and restrict participation. Muscle strength is a strong predictor of severe mobility limitation, slow gait speed, increased fall risk, risk of hospitalization, and high mortality rate.
Diagnosis is consisting of three criteria:
- muscle weakness (handgrip strength in men
- a lower muscle mass (determined by bioelectrical impedance or dual energy X-ray absorptiometry [DEXA]), men
- impaired performance (slow walking speed, <0,8 m/s).
Prevalence ranges between 4 and 27% worldwide.
The different physiological changes that take place in aging muscles are discussed:
- reduction in satellite cells (responsible for regeneration)
- decrease in size of muscle fibers of up to 40% (notably in type II)
- decrease in number of muscle fibres of 40%
- loss of excitability (decrease in receptors)
- decrease in myosin protein content (reduces the number of cross bridges and limit force)
- stiffness (reduction in elasticity)
- increased muscle fat content
- inactivity (affecting type I) and co-morbidities like cancer, diabetes and chronic heart failure (type II)
- loss of mitochondrial content and function (ATP production)
In short: age-related muscle changes are very complex and involve multiple features and mechanisms influenced both by intrinsic and environmental conditions.
Future research is needed to understand sarcopenia and to prevent or delay onset. Of particular interest is the relationship between sarcopenia, nutrition, exercise and use of medication.
Sarcopenia: a normal aging process or is targeted intervention such as tailored exercise feasible?
> From: Miljkovic et al., Ann Rehabil Med 39 (2015) 155-162(Epub ahead of print). All rights reserved to Korean Academy of Rehabilitation Medicine. Click here for the Pubmed summary.