Exercise versus Sarcopenia in Mice
Exercise helps to slow the age-related loss of muscle mass and strength known as sarcopenia, something we should all bear in mind as we age. This open access paper reporting on a study of exercise and aging in mice is one of a number to provide evidence on this topic. Beyond helping to slow the onset of physical frailty, exercise also improves numerous other aspects of our cellular biochemistry and organ function over the long term. There is no available medical technology, as yet, that can do anywhere near as much for overall health, and thus it is a very good idea to put in the effort to make and maintain good lifestyle choices as best as possible while we await the arrival of future rejuvenation therapies. A few years here or there might make the difference between living to benefit from these technologies or missing out.
In men and women, the annual rate of muscle mass loss is reported as approximately 0.9 and 0.7%, respectively, after the age of 75 years. Sarcopenia can be greatly accelerated by physical inactivity and poor nutrition, and loss of function is more pronounced in the muscles of the lower limbs. Sarcopenia can result in severe muscle weakness and contributes to frailty, reduced mobility, diminished independence, and an increased susceptibility to falls and fractures, with escalating costs to the global healthcare system. Resistance exercise is an effective intervention used to counteract the detrimental effects of sarcopenia. In humans aged 60 years and older, marked gains in strength, muscle mass, functional mobility, muscle protein synthesis, and mitochondrial function have been observed after progressive resistance training programs that range from 8 weeks to 1 year. These studies provide evidence that elderly men and women (including nonagenarians) are physiologically capable of adapting to progressive loading, and in some instances have reported relative gains in muscle strength and mass that are comparable to younger individuals and between sexes.
Voluntary wheel running (endurance or aerobic exercise) is often used to monitor the long-term benefits of exercise, with rodent models being widely used due to their relatively short lifespan; a 24-month-old mouse is considered roughly equivalent to a 70-year-old human. Although an age-related decline in voluntary wheel running is well documented in mice and rats, relatively small amounts of physical activity can have many benefits. Beyond the protection of muscle mass, long-term voluntary wheel running has a variety of physiological benefits including decreased weight gain, restoration of neuromuscular junction (NMJ) architecture, and preserved muscle innervation, increased mitochondrial biogenesis and autophagy, improved oxygen uptake (VO2 max), and the overall metabolic enhancement of the skeletal muscle. Investigations in young men and elderly women (aged 22 to 75 years) show that combined resistance and endurance training can contribute to greater gains in muscle strength and/or mass, compared with endurance exercise alone. Whether resistance exercise (with progressive loading of voluntary wheel running) can increase the hypertrophic potential of aging muscles has not been thoroughly tested in rodents.
The present study investigates the effect of 34 weeks of voluntary resistance wheel exercise (RWE) initiated from mid-life (15 months of age) on skeletal muscle mass and function in male and female C57BL/6J mice (aged 23 months). Overall, our data show that the introduction of resistance wheel running from middle age was effective in preventing sarcopenia in the hindlimb muscles of both male and female mice. Specifically, weights of the exercised quadriceps, gastrocnemius, and EDL muscles at 23 months were maintained at values similar to 15 months, while mass of the soleus muscles increased. The maintenance of muscle mass into old age was accompanied by striking changes to morphological and molecular parameters of the muscles, including myofiber size and type, with some increased markers of mitochondrial and autophagic activity. Since exercising muscles produce many factors with systemic effects, it is possible that other tissues may subsequently feedback and contributes (indirectly) to the prevention of sarcopenia, by exercise. This study shows that aging mice of both sexes have a good capacity for such resistance exercise and that this exercise helps to maintain healthy old muscles.