Repeated damage to cells can cause cancer, so do muscle cells?💪💪💪

Chronic injury and inflammation are major risk factors for cancer. Carcinogenic factors such as eating hot food, drinking hot tea, smoking, and air pollution are all due to their repeated damage to human tissues. But why does repeated tissue damage lead to cancer? Although the mechanism of this carcinogenesis is complex, one of the more easily understood reasons is that the repair of damaged tissue requires cell division. Every time a cell divides, a gene may mutate. Repeated tissue damage increases the number of cell divisions, which increases the probability of mutation into an oncogene. At this time, fitness enthusiasts may think that muscle fibers are constantly damaged and repaired during muscle exercise. Will it also increase the risk of cancer?

Does muscle building increase the chance of a genetic mutation?

Its answer is of course not. Muscle building does not increase your risk of cancer. The main reason is that with or without exercise, muscle tissue rarely develops tumors. Lung cancer, breast cancer, liver cancer, etc. are all common, but muscle cancer is rare. It is because the muscle tissue rarely develops tumors. Although this does not mean that muscle tissue is completely tumor-free, for example, rhabdomyosarcoma is a tumor with muscle tissue characteristics. However, it is not caused by muscle building. Rhabdomyosarcoma is a common childhood tumor. Congenital or early developmental genetic mutations are its main cause. Adults over the age of 30 generally do not have rhabdomyosarcoma. 

Why do muscles rarely get cancer?

Long-term muscle building can lead to repeated muscle growth and injury, but why do muscles rarely get cancer? Because of the special structure of skeletal muscle, it has its own anti-cancer function. 

The structure of muscle.

As it can be seen from the above figure, a skeletal muscle cell is also called a muscle fiber. It has two main features:

1. Most cells in the human body generally have only one nucleus. However, a myofibroblast will have many nuclei. It belongs to multinucleated cells.
2. Muscle cells, which are multinucleated cells, do not divide and proliferate by themselves. They do not go from one muscle fiber directly to two muscle fibers.

So how does muscle training make muscles stronger without splitting muscle fibers? This makes muscles stronger both by making the muscle cells bigger and by fusing more muscle cells. Muscles tend to get bigger because each muscle fiber cell gets bigger, not because there are more of them. Myofibroblasts use nutrients in the body to synthesize more protein when stimulated by exercise. It makes muscle cells larger, but does not proliferate. 

Muscle building

How do muscles repair after muscle damage?

Muscle stem cells are responsible for muscle repair. Although myofibroblasts cannot divide and proliferate, muscle stem cells can. Muscle stem cells usually only attach to the surface of muscle fibers and do not proliferate. Muscle stem cells are activated if the muscle is growing or repairing damage. They divide and proliferate to create new muscle cells. Most stem cell divisions produce new cells that fuse with old myofibroblasts and repair damaged muscle fibers. The rest retain the properties of muscle stem cells and attach to the surface of muscle fibers.

Muscle Repair.

Why doesn't the division and proliferation of muscle stem cells increase cancer risk?

One of the main reasons is that most muscle stem cells fuse into muscle fibers after they divide and proliferate. When these stem cells fuse into muscle fibers, they lose their ability to divide and proliferate. They do not accumulate mutations. Although a single muscle stem cell division may lead to cancer-causing mutations, one mutation is not enough to generate cancer cells. Adults generally need to accumulate multiple mutations to form cancer cells. And in many cases, specific mutation types and sequences are required to cause cancer. The process is also relatively long. And when a muscle stem cell has an oncogene mutation, it is quickly fused into the muscle fiber. Even if the muscle is damaged by the next exercise, it will not divide and grow again. Normally, it does not accumulate into cancer cells and cause cancer. This biological feature is the anticancer function of skeletal muscle. In addition, a number of studies have shown that regular muscle training does not increase cancer risk but significantly reduces cancer incidence.