Biology of Muscle Growth



Roger Fielding, Associate Director of the Jean Mayer USDA Human Nutrition Research Center on Aging, Professor of Medicine, Tufts University, eloquently describes why we often see young adults in professional competitive sports like NFL, Olympics and others. He writes “This is because with every additional year spent on Earth, bodies age and muscles don’t respond to exercise the same as they used to“.

Old and young people build muscle in the same way. But as you age, many of the biological processes that turn exercise into muscle become less effective. This makes it harder for older people to build strength but also makes it that much more important for everyone to continue exercising as they age.

– Roger Fielding in The Conversation

In the article Fielding emphasizes the importance of Strength training like pushups and situps, weightlifting and resistance using bands or workout machines is important to become stronger.

Muscle Biology

Explaining the biology of muscle, Fielding writes:

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.

Screenshot source: The Conversation

Fielding says that when we move around, our muscles contact, by shortening and pulling with your muscles.

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.

During this contraction process some chemical pathways get activated which triggers more protein production and when more proteins are incorporated into the muscle fibers to increase its size. These cellular pathways also reported turn on genes that code specific proteins 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.

How Older Muscle Change?

Fielding explains the biological difference of muscle growth between the younger adults and people over 50s. Dr Fielding explains:

What my colleagues and I have found in our research is that in young muscle, a little bit 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.

… 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.

How to Stay Fit While We Age?

Dr Fielding emphasizes the older peoples should be encouraged to do more exercise than the young adults because of slower muscle gain when we age. He writes:

Exercise still remains one of the most important activities older adults can do for their health. The work my colleagues and I have done clearly shows that although the responses to training lessen with age, they are by no means reduced to zero.

… older adults with mobility problems who participate in a regular program of aerobic and resistance exercise can reduce their risk of becoming disabled by about 20%. We also found a similar 20% reduction in risk of becoming disabled among people who are already physically frail if they did the same workout program

“While younger people may get stronger and build bigger muscles much faster than their older counterparts, older people still get incredibly valuable health benefits from exercise, including improved strength, physical function and reduced disability,” writes Fielding.