50-Year-Old Muscles Just Can’t Grow Big Like They Used To – The Biology of How Muscles Change With Age

How the body builds muscle

The exercise I study is the type that makes you stronger. Strength training includes exercises like pushups and situps, but also weightlifting and resistance training using bands or workout machines.

When 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 as 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 a 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.

These cellular pathways also turn on genes that code for specific proteins in cells that make up the muscles contracting machinery. This activation of gene expression is a longer-term process, with genes being turned on or off for several hours after a single session of resistance exercise.

The overall effect of these many exercise-induced changes is to cause your muscles to get bigger.