Scales

Wasting away

Diet, injury and a lack of use can affect our muscles

Brown urine resulting from muscle damage

Brown urine resulting from muscle damage.

CC BY

Dr James Heilman via Wikipedia

Muscle can shrink as well as grow, and some reduction in muscular strength is a normal part of ageing. Exercise can slow this but not prevent it completely, and poor diet tends to speed it up. Serious age-related muscle wasting, or sarcopenia, usually involves the loss of myosin (as it is removed and not replaced) and the loss of some of the mitochondria, which produce the adenosine triphosphate (ATP) on which muscle power relies.

Malnutrition, especially getting too little protein to eat, can cause muscle wasting at any age. Kwashiorkor is one example of a childhood disease that involves muscle wasting, and predominantly affects children in low-income countries. A low-protein diet is among its causes.

Just a few weeks’ bed rest during illness can cause long-lasting muscle loss too, especially in older people. This is caused by the combination of a drop in the manufacture of new protein and an accelerated breakdown of existing muscle fibres. The effects are worst in the legs and back, which normally hold us up against gravity, and can quickly lead to immobility.

Rhabdomyolysis is the name given to the rapid breakdown of muscle and can be caused by many factors, including crush injuries (for example, when part of the body is squeezed between two heavy objects), cocaine abuse and exercise. It leads to the release of the pigmented protein myoglobin into the bloodstream. In severe cases, myoglobin in the blood can cause injuries to the kidneys by obstructing their tubules, leading to distinctive brown urine and even acute kidney failure.

The link between kidney failure and crush injury was first made by Professor Eric Bywaters, who noticed brown urine in people hurt during the London Blitz in World War II.

Case study: Cancer-related anorexia/cachexia

As previously mentioned, kwashiorkor most often affects malnourished children in low-income countries, but even in the West, where we have a plentiful supply of highly nutritious food and exceptional medical care, wasting conditions can still occur and be extremely harmful.

For example, cancer-related anorexia/cachexia (CAC) is a condition that affects over half of all cancer patients. A wasting disease, it results in extreme and rapid weight loss (including loss of muscle) and is resistant to normal therapies such as administering nutritional supplements. It is thought to be caused by cancer patients eating less than before they were ill (which can happen for a number of reasons) together with changes to their metabolism triggered by the cancer.

Often underestimated, CAC causes severe fatigue that can prevent sufferers from performing normal day-to-day activities. It also causes immense psychological suffering to both patients and their families, and can affect patients’ responses to anticancer treatments as well as their potential for survival.

Lead image:

Greg Wagoner/Flickr CC BY NC

References

About this resource

This resource was first published in ‘Exercise, Energy and Movement’ in January 2012 and reviewed and updated in August 2016.

Topics:
Physiology, Health, infection and disease
Issue:
Exercise, Energy and Movement
Education levels:
14–16, 16–19, Continuing professional development