How many of you are over 30?
This article is not just directed at the elderly! You start losing muscle at that age and by the time you are 60 up to a quarter of you will have thinner arms and legs than you did when you were young and all because you have lost muscle.
The trouble is that once this starts to happen, you find doing things becomes that bit more difficult – even things like getting out of a chair or up stairs or cleaning the house. This can encourage us to do less and that leads to even more muscle loss.
When you lose muscle, you start to fall more easily and this can lead to all sorts of problems.
The good news is that exercise can stave off and even reverse muscle loss and weakness. But while scientists know a lot about what goes wrong in aging, and know that exercise can slow the inevitable, the details of this relationship are just starting to be understood.
The role of muscle stem cells
Both muscle growth and repair are made possible only by the presence of muscle stem cells.
In 1961, Rockefeller University biophysicist Alexander Mauro, using electron microscopy, first described muscle stem cells, calling them “satellite cells” because of their position at the edge of the muscle fibres.
Subsequently, researchers have demonstrated that satellite cells are the only cells able to repair muscle—which explains why recovery from muscle injuries among the elderly is slow and often does not happen fully because the number of satellite cells falls from 8 percent of total muscle nuclei in young adults to just 0.8 percent after about 70 to 75 years of age.
However, it is possible to grow elderly human satellite cells in culture as well as those from young people, therefore it seems that declining function of satellite cells is not the problem; there are just fewer of them in muscle to do the job of repair and growth.
Other likely culprits of muscle aging are the mitochondria, the “powerhouses” of muscle. To work efficiently, skeletal muscle needs a sufficient number of fully functional mitochondria. These organelles represent around 5 percent to 12 percent of the volume of human muscle fibers, depending on activity and muscle specialization (fast-twitch versus slow-twitch). And research suggests that abnormalities in mitochondrial morphology, number, and function are closely related to the loss of muscle mass observed in the elderly.
In 2013, researchers found that as rats aged, there was a decline in the function of these “powerhouses” and therefore muscle loss ensued, suggesting that mitochondrial dynamics are also perturbed during muscle aging.
Protein quality control
Even if you eat plenty of protein, you often cannot maintain muscle mass, probably because our bodies cannot turn proteins into muscle fast enough to keep up with the natural rate of the breakdown of muscle tissue.
In 2005, Stanford University stem cell biologists found that there are factors in the blood of young mice that meant they were able to rejuvenate muscle repair in older mice.
It is now well known that the levels of circulating hormones and growth factors drastically decrease with age and that this has an effect on muscle aging. Indeed, hormone replacement therapy can efficiently reverse muscle aging, in part by activating pathways involved in protein synthesis.
How Can We Fight Muscles Ageing?
Fortunately, exercise can combat muscle aging, likely by reversing many of the age-related physiological changes at the root of this decline.
Proteins produced by the muscle when it contracts flow into the blood stream. These proteins can act locally on muscle cells or other types of cells in your body to coordinate muscle physiology and repair.
Human muscle fibers secrete up to 965 different proteins and researchers have only just begun to understand their role in muscle aging.
Exercise to combat muscle aging
Although the causes of muscle loss are numerous and complex, there is now a huge amount of evidence to suggest that exercise may prevent or reverse many of these age-related changes, whereas inactivity will accelerate muscle aging.
Earlier this year, for example, researcher in the University of Birmingham and King’s College London examined the muscles of 125 male and female amateur cyclists and showed that a lifetime of regular exercise can slow down muscle aging: there were no losses in muscle mass or muscle strength among those who were older and exercised regularly.
Exercise’s influence on muscle health likely acts through as many mechanisms as those underlying age-related muscle loss and weakness.
For example, the number of satellite cells can be increased by exercise, and active elderly people have more of these cells than more-sedentary individuals do. This is the reason why exercise prior to hip and knee surgery can speed up recovery in the elderly.
Physical activity also affects the muscle’s mitochondria. A lack of exercise decreases the efficiency and number of mitochondria in skeletal muscle, while exercise promotes mitochondrial health.
High-intensity aerobic interval training has been found to reverse many age-related differences in muscle composition, including restoring mitochondrial protein levels so all is not lost if you have got older; become more sedentary and you are reading this thinking ‘Help, I’ve had it’!
Exercise also improves muscle function. In one study, the older adults were 59 percent weaker than the younger adults before training, and only 38 percent weaker afterward.
Different types of exercise can trigger variable but specific responses in the muscle. For example, whereas strength training is efficient at making muscle, high intensity interval training in aerobic exercises such as biking and walking had the greatest effect at the cellular level at combating age-related loss and weakness.
Exercise may prevent or reverse many of these age-related changes, whereas inactivity will accelerate muscle aging.
In older women, one hour of brisk walking produced elevated insulin sensitivity on the following day.
Therefore, it is never too late to exercise to try to combat the consequences of muscle aging.
At the Avenue Clinic, therefore, we will continue to emphasise the benefits of regular exercise combined with good nutrition as being the most effective way to fight muscle loss, and possibly aging overall.
A. Mauro, “Satellite cell of skeletal muscle fibers,” J Biophys Biochem Cytol, 9:493–95, 1961.
B.M. Carlson, J.A. Faulkner, “Muscle transplantation between young and old rats: Age of host determines recovery,” Am J Physiol, 256:C1262–66, 1989.
W. Liu et al., “Loss of adult skeletal muscle stem cells drives age-related neuromuscular junction degeneration,” eLife, 6:e26464, 2017.
C. Ibebunjo et al., “Genomic and proteomic profiling reveals reduced mitochondrial function and disruption of the neuromuscular junction driving rat sarcopenia,” Mol Cell Biol, 33:194–212, 2013.
A. Pannérec et al., “A robust neuromuscular system protects rat and human skeletal muscle from sarcopenia,” Aging, 8:712–28, 2016.