How muscles can change older ?
My colleagues and I have found in our research is that in young muscle, a little of exercise produces a strong signal for the many processes that trigger muscle growth. In older people’s muscles, by comparison, the signal telling muscles to grow is much weaker for a given amount of exercise. These changes begin to occur when a person reaches around 50 years old and become more pronounced as time goes on.
This recent study, we wanted to see if the changes in signaling were accompanied by any changes in which genes – and how many of them – respond to exercise. Using a technique that allowed us to measure changes in thousands of genes in response to resistance exercise, we found that when younger men exercise, there are changes in the expression of more than 150 genes. When we looked at older men, we found changes in the expression of only 42 genes. This difference in gene expression seems to explain, at least partly, the more visible variation between how young and old people respond to strength training.
This exercise I study is the type that makes you stronger. Strength training includes exercises like push ups and sit ups, but also weightlifting and resistance training using bands or workout machines.
Whenever you do strength training, over time, exercises that at first felt difficult become easier as your muscles increase in strength and size – a process called hypertrophy. Bigger muscles simply have larger muscle fibers and cells, and this allows you to lift heavier weights. As you keep working out, you can continue to increase the difficulty or weight of the exercises as your muscles get bigger and stronger.
It is easy to see that working out makes muscles bigger, but what is actually happening to the cells a muscles increase in strength and size in response to resistance training?
Any time you move your body, you are doing so by shortening and pulling with your muscles – a process called contraction. This is how muscles spend energy to generate force and produce movement. Every time you contract a muscle – especially when you have to work hard to do the contraction, like when lifting weights – the action causes changes to the levels of various chemicals in your muscles. In addition to the chemical changes, there are also specialized receptors on the surface of muscle cells that detect when you move a muscle, generate force or otherwise alter the biochemical machinery within a muscle.
In an healthy young person, when these chemical and mechanical sensory systems detect muscle movement, they turn on a number of specialized chemical pathways within the muscle. These pathways in turn trigger the production of more proteins that get incorporated into the muscle fibers and cause the muscle to increase in size.
The cellular pathways also turn on genes that code for specific proteins in cells that make up the muscle's contracting machinery.
Thus overall effect of these many exercise-induced changes is to cause your muscles to get bigger.
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