How Does Chemotherapy and Radiotherapy Affect Muscle? Advice from a Nutritionist in Bristol

As a Nutritionist in Bristol who has been through the cancer joureny I know the score. Cancer treatment often involves rigorous and aggressive approaches to eradicate cancerous cells, with chemotherapy and radiotherapy being two of the most common methods. Chemotherapy is not classed as a targeted therapy because it doesn’t differentiate between cancerous and noncancerous cells—hence the harsh side effects that come along with it1. Radiotherapy is a targeted therapy, as it is literally aimed at the cancerous site. Although considered less damaging than chemotherapy, it has its own set of side effects such as, but not limited to, burning of the skin and fatigue2.

While these treatments can be lifesaving, they come with a range of side effects—including significant impacts on muscle health, which is what we are going to discuss in this article.

Personally, I found post-chemotherapy I was able to start exercising again, but my muscular strength and endurance were diminished, leaving me feeling frustrated, demotivated, and very self-conscious. I felt that part of the core of my very being was taken away. With this core belief about myself stripped away, I felt violated in many ways. Who was I? Will I be the same again? How do I move forward?

Anyway, enough about me—let’s look into why this happens and how to get past it…

Chemotherapy and Muscle Health Low down from a Nutritionist in Bristol

Chemotherapy involves the use of potent drugs to kill rapidly dividing cancer cells. However, these drugs also affect healthy cells, including muscle cells, leading to various muscular issues3. Not to mention the effect they have on your body as a whole. When considering exercising in a public space, you might face niche challenges—as I did—like a running nose, IBS, hot flushes (if you’ve been put into menopause), or "chemo brain" (i.e. wandering around the gym forgetting what you’re doing), just to name a few. Not ideal—but honestly, I don’t think anyone even noticed.

Muscle Weakness

One of the most common side effects of chemotherapy is muscle weakness. Chemotherapy drugs can cause direct damage to muscle fibres and disrupt the balance of proteins involved in muscle contraction and maintenance3. This results in reduced muscle strength and endurance.

Muscle Atrophy

Prolonged chemotherapy can lead to muscle atrophy, which is the wasting or loss of muscle tissue. This occurs because chemotherapy can decrease the body’s ability to synthesise new muscle proteins while increasing the rate of muscle protein breakdown. Consequently, patients may experience significant muscle loss, particularly if they are less physically active during treatment4.

Fatigue

Chemotherapy-induced fatigue is another factor that indirectly affects muscle health. The persistent tiredness and lack of energy can discourage physical activity, further contributing to muscle weakness and atrophy5.

Neuropathy

Certain chemotherapy drugs can cause peripheral neuropathy, a condition where nerves are damaged, leading to pain, tingling, and numbness in the extremities. This can make it difficult for patients to engage in physical activities, thereby affecting muscle strength and coordination2. If you are struggling with this in terms of grip ability check out my artcile; 3 Ways of Adding Weight to Your Exercises When You Have Peripheral Neuropathy.

Radiotherapy and Muscle Health

Radiotherapy uses high-energy radiation to kill cancer cells. Like chemotherapy, it can impact surrounding healthy tissues—including muscles2. I had already forced myself to start back at the gym when my time for radiotherapy came up. I thought it would be a walk in the park compared to chemotherapy, which it was in many ways—but the side effects are not to be underestimated.

I recommend taking a break from vigerous exercise during your radiotherapy. You can still do light activity, but it may not be the right time to chase a personal best.

Radiation-Induced Fibrosis

This condition involves scar tissue forming in muscles and connective tissues due to radiation exposure2. It can cause stiffness, pain, and reduced range of motion. If you’ve had an operation and experienced cording or limited movement, this could worsen it.

Muscle Weakness and Atrophy

Similar to chemotherapy, radiotherapy can lead to muscle weakness and atrophy, particularly in the areas directly exposed to radiation. The radiation can damage muscle fibres and blood vessels, reducing oxygen and nutrient delivery to the muscles, which are essential for maintaining muscle mass and function2.

Fatigue

Radiotherapy can also cause significant fatigue, making it challenging for patients to stay active. This fatigue can be a result of the body’s response to the radiation, the energy required for tissue repair, and the overall stress of cancer treatment5.

Myopathy

Radiotherapy can sometimes result in a condition known as radiation-induced myopathy. This is characterised by inflammation and degeneration of muscle tissue, leading to muscle weakness and dysfunction2. Myopathy can develop months or even years after treatment and can be progressive.

Managing the Effects on Muscle

Despite the adverse effects of chemotherapy and radiotherapy on muscle health, there are strategies that can help mitigate these issues and promote muscle recovery.

1. Physical Activity and Exercise

Regular movement combats weakness and atrophy by stimulating muscle protein synthesis and improving circulation. Resistance training, walking, or stretching can all help. Start gently and increase intensity gradually—ideally with guidance from a qualified specialist in cancer rehab (ahemm… that’s me, a Nutritionist in Bristol with experience in post-cancer recovery!)

 

2. Nutrition

A balanced, protein-rich diet is essential for muscle repair and maintenance. Foods like fish, eggs, legumes, dairy, and nuts help provide the building blocks for recovery. And please, don’t just "go on a diet" post-treatment. Many people are overweight and deconditioned after treatment, but eating in a calorie deficit too soon can worsen muscle loss [4]. A Nutritionist in Bristol can help you tailor your nutrition to rebuild—not restrict.

As I discuss in my other article: Are You Eating Enough to Lose Weight?

3. Physical Therapy

Engaging with a physical therapist can provide personalised exercise programs tailored to the individual’s needs and capabilities. Physical therapists can also offer techniques to manage pain and improve mobility and function.

4. Medications and Supplements

Some may benefit from specific medications or supplements, but diet comes first. If you've googled “supplements for cancer,” you’ve probably been overwhelmed with misinformation and have encountered pleanty of myths surrounding diet and cancer. You ahve also been told not to take any supplements by your oncologist. But I know that the temptation is always there, so before spending loads of money, always ask a registered nutritionist before taking anything new.

5. Managing Fatigue

Addressing cancer-related fatigue involves a combination of strategies including proper rest, balanced nutrition, stress management, and physical activity. Techniques such as yoga, meditation, and mindfulness can also help manage stress and improve overall energy levels.

Conclusion

Chemotherapy and radiotherapy, while essential for treating cancer, can have significant effects on muscle health, leading to weakness, atrophy, and fatigue. Understanding these effects and implementing strategies to manage them can help you maintain muscle strength and improve your quality of life during and after treatment. Regular physical activity, proper nutrition, physical therapy, and supportive care are key components of effective muscle rehabilitation in cancer survivors. If you are ready to start your rehabilitation journey and want some support from a specialised cancer rehabilitaion personal trainer and registered nutritionist in Bristol get in touch and lets talk in through.

Disclaimer

The information on this blog is here to help and inspire, but it’s not meant to replace professional advice. Always check with a doctor before making any changes to your diet or lifestyle. The views shared are those of the author(s) and may not reflect those of any organisations involved. Rosy Nutrition & Personal Training can’t be held responsible for any outcomes from using this information.

References

1. Cancer Research UK. (n.d.). Chemotherapy side effects.  [Online] Avilable from: https://www.cancerresearchuk.org/about-cancer/cancer-in-general/treatment/chemotherapy/side-effects (Accessed 1st May 2025)

2. Macmillan Cancer Support. (n.d.). Radiotherapy side effects. [Online] Avilable from:https://www.macmillan.org.uk/cancer-information-and-support/treatment/types-of-treatment/radiotherapy/side-effects (Accessed 1st May 2025)

3. National Cancer Institute. (n.d.). Side effects of chemotherapy. [Online] Avilable from:https://www.cancer.gov/about-cancer/treatment/side-effects/chemotherapy (Accessed 1st May 2025)

4. American Cancer Society. (2021). Managing Cancer-Related Fatigue. [Online] Avilable from: https://www.cancer.org/treatment/treatments-and-side-effects/physical-side-effects/fatigue/managing-cancer-related-fatigue.html (Accessed 1st May 2025)

5. NHS. (n.d.). Living with and beyond cancer. [Online] Avilable from:https://www.nhs.uk/live-well/living-with-and-beyond-cancer/ (Accessed 1st May 2025)