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There are many reasons for feeling unusually tried during a training program. Anemia, overtraining, and dehydration are all common culprits. However, there is an additional reason for fatigue that often goes unnoticed by runners: an under active thyroid (also called hypothyroidism). Having a properly functioning thyroid is absolutely essential for runners hoping to run to the best of their abilities.
The human thyroid is located in the lower front of the neck and it plays a critical role in influencing metabolism, assisting in growth and development of the human body, and regulating the body’s temperature. The thyroid accomplishes these actions by releasing hormones called triiodothyronine (T3) and thyroxine (T4).
The release of T3 and T4 by the thyroid is actually the last part of a long chain reaction in the body. This chain reaction begins when the brain’s hypothalamus, which controls body temperature, hunger, thirst, and fatigue, senses that the body needs more T3 and T4 hormones. The hypothalamus will then release a substance called thyrotopin-releasing hormone (TRH). TRH’s role is to stimulate the pitutary gland to release a hormone called TSH, which is the substance that causes the thyroid to release T3 and T4. This complicated process can be summarized as follows: (1) hypothalamus detects fatigue in the body and releases TRH, (2) TRH causes the pituitary gland to release TSH, and (3) TSH causes the thyroid to release T3 and T4.
So what’s the point of all of this? Well, if the thyroid does not release a proper amount of T3 and T4, the body will be fatigued. Fortunately, T3 and T4 can be produced synthetically and, if there is a deficiency in the body, those hormones can be supplied through a pill. The most popular thyroid medication is called “Synthyroid,” but there are many other generic brands on the market (some less effective than others).
To determine if a person needs synthetic T3 and T4, a doctor will take a blood test and measure the amount of TSH in the body. As the above discussion of the “chain reaction” shows, if there is a large amount of TSH in the body, the hypothalamus must really want the thyroid to release more hormones. If there is not much TSH in the body, the thyroid must be doing its job.
Therefore, the “TSH numbers” in the blood are critical when determining whether a runner has a hypothyroid. There is a fierce debate in the medical community about the “normal” range for TSH. Generally, physicians agree that a TSH level of .5 to 4.5/5.0 mIU/L is within normal levels. However, many now say that anything over 3.0 means that a patient has hypothyroidism. The best advice is for a runner to see a doctor and get a blood test if he or she feels lethargic and discuss the results of the test with the physician. Taking action against an under active thyroid could very well change your running for the better.