If repeated cellular damage can cause cancer but that’s also how muscle is built, why isn’t weight lifting a cancer risk?


To build muscle you are tearing the muscles and letting it heal. Does this not increase risk of mutations that might turn into cancer like how repeated damage to skin or lung cells can cause cancer?

I don’t think it is a cancer risk but I would like an explanation as to why.

In: Biology

Cancer is less about cellular damage and more about protein damage.

Repeated cellular damage does cause an increase in replication, which can lead to cancer risks, but not nearly as much as carcinogenic factors, which can damage the actual DNA of a cell, and make it replicate without stopping.

Genetic damage is what causes cancer. Your cells have a system in place to “commit suicide” if they stop functioning correctly. Through genetic damage this system can break down and the cells will fail to die gracefully. Thankfully your immune system will clean them up. You get cancer fifty to a hundred times per day. Unfortunately, sometimes the genetic damage causes the cell’s behavior to change such that it doesn’t die and it avoids the immune system. Now you’ve got a clinical case of cancer.

Cells can suffer genetic damage from ionizing radiation. For example, your body is full of radioactive potassium-40 that is constantly causing genetic damage to your cells. It can also occure when cells multiply: each time cells split, about three base pairs are accidentally changed. The former cause is why sunburns can lead to cancer. The latter cause is why children suffer disproportionately from cancer compared to young adults. But such baseline levels of genetic damage isn’t usually harmful.

Since exercise isn’t causing genetic damage and is boosting your cancer-fighting immune system, it isn’t a cancer risk.

There’s some debate around the topic but it’s largely agreed that muscles grow by hypertrophy and not hyperplasia.

Hypertrophy is when existing cells get bigger, hyperplasia is when new cells are added to the mix through cell division.

The number of muscle cells you have is predetermined by genetics. Working out produces damage to the muscles that you described.

This damage produces a signalling cascade that stimulates muscle stem cells – myosatellite cells – to turn into immature muscle cells – myoblasts – which then fuse with existing muscle cells in the damaged area, making those muscle cells larger without actually adding a new muscle cell into the mix.

So there’s not actually a whole load of cell divisions going on when it comes to muscle growth. It’s high rates of cell division that increase the risk of cancer.

The damage incurred by muscle building is more about tearing groups of cells apart. The cells themselves are largely fine, they simply repair their connections to one another, stronger than they were before. Cancer, on the other hand, is damage to each individual cell, causing them to go haywire and replicate without anything stopping them.

Consider: you have a concrete bridge. Muscle growth would be like tearing down the bridge piece by piece and building a bigger, stronger bridge in its place. Cancer would be more like replacing the construction crew with out of control robots that constantly pour concrete, never stopping for anything. Only more concrete. Forever.

Your muscles are essentially a rope that’s made out of millions of protein fibers that are all wrapped together. Its those fibers that are the functional unit of a muscle, not the muscle cells, and each fiber will pass through thousands of cells from start to finish.

Muscle cells are sort of wrapped around those fibers. The cells themselves don’t provide any structural support to the muscle – its all the fibers doing that. What those cells are doing is maintaining the fibers and providing the proper chemical environment to allow the fibers to expand and contract.

What this means is that when you put force on a muscle 100% of that force goes into the fibers, none actually goes into the cells. So when you “damage” a muscle during exercise you aren’t actually damaging the cells, you’re damaging the fibers. What causes your muscle to grow is the cells repairing the damaged fibers and building new ones.

Muscle cells, like most other cells in your body, cannot replicate once you’ve hit adulthood and have an extremely limited ability to repair themselves.

So only specific damage increases cancer risk. If the cell is damaged it is okay as long as the DNA remains untouched. This is because a damaged cell with good DNA will either die or heal and be fine. When the DNA is damaged the damage will propagate as the cell divided and will be inherited by all daughter cells. This happens enough the right combination of DNA damage can occur to produce cancer.