Biological Explanation Revealed


Hindsight is a wonderful thing and we can't help but wonder why we didn't think of this before: a University of Iowa study has found a biological link between fatigue and pain that explains in large measure why a great deal more women than men end up being diagnosed with chronic conditions involving pain and fatigue such as chronic fatigue syndrome and fibromyalgia.

Kathleen Sluka, Ph.D., professor in the Graduate Program in Physical Therapy and Rehabilitation Science in the UI Roy J. and Lucille A. Carver College of Medicine discovered that a protein that is implicated in muscle pain works together with testosterone, the male hormone, to protect mice against muscle fatigue.

Medical science has long been aware that fatigue and chronic pain tend to coexist with as many as 3 out of every 4 people with chronic pain reporting high levels of fatigue while 94% of those with chronic fatigue syndrome tell us they have muscle pain. We also know that diseases like fibromyalgia and chronic fatigue syndrome have an overwhelming preponderance of female sufferers.

In order to establish the link between fatigue, pain, and sex-based influence, the Iowan scientists induced muscle fatigue in both male and female mice with exercise. Some of the mice were given an ion channel protein known as ASIC3 that is activated by acid and has been shown to be implicated in pain that is musculoskeletal in nature.

It was found that 3 one-hour runs brought on varying levels of fatigue in the designated groups of mice. This was measured through the temporary loss of muscle strength as brought on by the selected activity.

Testosterone Treatment?

Female mice showed more fatigue than male mice given ASIC3. What proved informative here was the fact that the male mice with no ASIC3 protein displayed fatigue levels comparable to those of the female mice and certainly higher than those levels of normal male mice. Perhaps the most exciting finding was that when female mice with ASIC3 were treated with testosterone, their muscles resisted fatigue at levels comparable to normal male mice. Of significance was the fact that the muscle strength of the female mice not given the protein did not increase when they were given testosterone.

Says Sluka, "The differences in fatigue between males and females depends on both the presence of testosterone and the activation of ASIC3 channels, which suggests that they are interacting somehow to protect against fatigue. These differences may help explain some of the underlying differences we see in chronic pain conditions that include fatigue with respect to the predominance of women over men."

The study gives every indication that muscle pain and fatigue are conditions that are linked and codependent. Sluka feels that pain and fatigue may share a common circuit that is blocked somehow in the case of the various chronic musculoskeletal pain syndromes. The research team hopes to continue this vein of thought by investigating the idea that pain may increase fatigue in females more than in males. Finding a way to reduce the chronic fatigue that keeps so many people from work and normal social activities would indeed be a marvelous deed.


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