Thyroid Hormones: What T4 & T3 Thyroid Hormones Love Muscle & Hate Fat!..

Thyroid Hormones

Learn how to manipulate and understand thyroids

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Maybe it's a well-kept secret that nobody wants to share, or perhaps it's a rare jewel that lies hidden and awaits discovery. Regardless of the reason, if you're a bodybuilder who is interested in hormones that affect growth and metabolism, this baby could be the Holy Grail. The nectar that awaits in this cup is called the thyroid hormones, and they can unleash the power of metabolism in muscles. But why is it that nobody has yet to realize its importance to the sport of bodybuilding?

The most likely explanation for people not talking much about the thyroid and its hormones is that it has just been taken for granted. The close association between the thyroid hormones and metabolism has long been recognized in the field of medicine. If a person is hypothyroid-a condition where one produces too lithe thyroid hormone-there is a loss of appetite, they become easily fatigued, have weak muscles, suffer from weight gain and have a low body temperature due to their reduced metabolism. On the other hand, if one is hyperthyroid and produces too much thyroid hormone, they tend to lose weight despite a good appetite due to their increased metabolism. They are also restless, unable to sleep and have higher body temperatures.

These two extremes show just how powerful the thyroid hormones are. In fact, it should make one stop and consider whether this awesome power should be tampered with at all. But these two conditions represent disease states where the thyroid gland has gone out of control. What we are interested in is optimizing the body's daily output of thyroid hormone to our advantage. Like all glands that produce hormones, the thyroid produces its hormones within a normal range that varies from high to low. Our goal is to increase this gland's normal production of thyroid hormones and keep them in the high end and working to maintain our anabolic edge.


The thyroid is a gland that wraps itself around the larynx just behind the trachea. It produces two active hormones known as triiodothyronine and thyroxine. Triiodothyronine and thyroxine are each composed of two amino acids of tyrosine and only differ by the amount of bound iodine. Triiodothyronine has three iodides bound to it while thyroxine has four. This is why they are called T3 and T4.

T3 and T4 are released by the thyroid into the blood where they bind to specialized proteins that carry them to other parts of the body. for the most part, both hormones have identical functions but must be released from their binding proteins to be active. T3 is the more powerful of these twins; although it is present in amounts that are 30-60 times lower than T4. However, many cells are capable of removing one of the iodides from T4 and converting it to the more active T3.

Once these hormones reach the muscles, they are released from their binding proteins and are carried inside the cells by receptors on the cell membrane. Inside the cell, there are two targets where T3 can exert its effect. One is the nucleus where it can bind to the genes and increase protein synthesis. The other is the mitochondria, which are the power factories that burn calories in the presence of oxygen to produce adenosine triphosphate (ATh). It is believed that T3 can increase the mitochondria's ability to burn calories and thus raise the basal metabolic rate (BMR). In addition, T3 will also cause an increase in the number and size of the mitochondria, which will further serve to increase BMR.


The effects of the thyroid hormones are many and can be most advantageous to the bodybuilder. Every bodybuilder knows that muscles look their best when you're ripped and there's no excess bodyfat to obscure the striations. This is where T3 really excels by helping a person burn away those puffy little fat cells. T3 increases the BMR in nearly every cell of the body, especially the muscles, It does so by causing the fat cells to release free fatty acids into the bloodstream where they are taken up by the tissues. Here they are burned by the hyperactive mitochondria to make the ATP that drives muscle contractions. This energy can then be used to support muscle contractions for exercise and protein synthesis for growth. Another benefit is that although T3 increases the level of free fatty acids in the blood, it lowers cholesterol and triglyceride levels.

T3 is so effective at cranking up the metabolic fires and using fat to feed these fires that it can actually increase the BMR by 60- 100%. So if one can increase their T3 levels just a little it can have a profound effect on metabolism. Since one of the bodybuilder's prime concerns is keeping off bodyfat, T3 easily earns its title of master of metabolism for bumping up the BMR. even if it did nothing else at all.

But T3 does more than function as a terminator for fat cells. Another site of action for T3 is the muscles, where slight increases in this hormone causes the muscles to react to increased resistance with greater vigor. It accomplishes this by increasing the number of sarcoplasmic reticulum, which control contractions, and the energy- producing mitochondria that provide the muscle with the energy to do work. T3 has also been shown to cause an increase in the muscle's production of myosin, which is one of the major contractile proteins in muscle. Much of this accomplished by T3's ability to activate genes and cause an increase in protein synthesis in the muscles.

Nothing escapes the influence of T3, since it can also stimulate almost all aspects of carbohydrate metabolism. It can increase the absorption of glucose by the intestinal tract, increase the uptake of glucose by the cells, and increase glucolysis. In glycolysis, the excess glucose that is not needed for glycogen production is broken down and burned by the mitochondria to produce even more ATP.

T3 also has the ability to influence other hormones. Because it can cause blood sugar levels to rise, this causes a release of insulin from the pancreas to deal with the flood of glucose. As we have seen in the previous parts of this series, rapid rises in insulin can lead to hypoglycemia, which induces the production and release of growth hormone. T3 also causes a greater release of lactate and a lowering of blood pH. Acidic blood conditions are another mechanism by which growth hormone is induced. The induced growth hormone in turn causes the synthesis of insulin-like growth factor several hours later. All these hormones working in concert can produce an anabolic environment that will give maximum support to muscle growth and repair after an intense workout.

In addition to providing a rich anabolic setting for muscle growth, T3 has no tolerance for catabolic conditions. It acts directly on the liver to increase the rate of destruction of the adrenal glucocorticoids, such as cortisol, which are responsible for protein breakdown. This decrease in cortisol will allow for greater recovery and uninterrupted muscle growth.

There are other effects of T3 that are worth mentioning in brief. The increased BMR causes the muscles to demand increased oxygen to keep up with the greater burning of fats and energy production. To do this, T3 increases the respiratory capacity by increasing the depth of respiration and allows better oxygen utilization by the lungs. It also increases the strength of the heartbeat, increases blood volume and elevates blood pressure in the arteries. It also causes the vessels to expand and lower blood pressure. This decrease of blood pressure in the vessels offsets the rise in the arteries, so overall blood pressure remains unchanged. The result is greater amounts of oxygen-rich blood available to bathe the muscles with oxygen and nutrients and carry away waste metabolic by products.


As mentioned earlier, thyroid hormones have a normal range that varies from high to low. So to get the full benefits of T3, we must provide the body with conditions that will keep this hormone in the high range of production. One way to do this is through exercise. Most studies agree that intense exercise causes a rise in serum T3 and T4 levels. Repeated bouts of exercise cause an increased turnover of thyroid hormones. This means that the destructive process for thyroid hormones increases and signals the pituitary gland to release more thyroid stimulating hormone (TSR). The TSH causes the thyroid to produce more thyroid hormones.

This is somewhat of a slingshot effect, where the initial exercise pulls the thyroid hormones to the low end of the normal range. The body responds by cranking up the production of T3 and T4 to get levels back up to the normal range. This panic response by the body to the fall in thyroid hormones will result in their overproduction. and as the levels rise, they shoot past the midpoint and rise to the upper normal range. The result is that a person remains slightly hyperthyroid for a while until the turnover slows and thyroid levels fall back to the normal midrange.

As mentioned, intensity is necessary to get this process rolling. Studies of people who switched from a sedimentary lifestyle to one of moderate exercise showed no increase in their thyroid hormone levels. However, when the amount of exercise was doubled, there was a significant increase in thyroid hormone secretion. As we know there are two ways to increase the amount of exercise we perform-work longer or work harder. For bodybuilders the greatest advantage comes from working harder. or increasing the intensity of the workout.

Another factor that affects thyroid function is nutrition. People who go on a calorie-restricted diet cause the body to lower its BMR to conserve energy, and this causes a decrease in thyroid hormone production. If a person increases their food intake, thy- old hormone production increases to turn up the BMR and burn the extra calories. When a person exercises intensely, two independent changes occur. They burn calories during exercise and they increase their production of thyroid hormone, which raises their BMR and burns still more calories. However, if this energy burned during exercise isn't replaced, the production of thyroid hormones will decrease.

Also see that you get plenty of zinc in your diet. Zinc is thought to possibly play role in thyroid hormone metabolism and aid in the conversion of T4 to T3.

That's why it's important for bodybuilders to supplement their diets to replace expended energy. Two of the best nutrients for increasing the production of T3 and T4 are protein and complex carbohydrates. When people were led a protein/carbohydrate diet that was either low or high in fat. only the low-fat diet elevated thyroid hormone levels. It seems that carbohydrates and protein can stimulate T3 and T4, but fat inhibits their release. That's why sports supplements are an important tool in bodybuilding. They are designed to be high in protein and carbs, while extremely low in fat. This makes them obvious choices for replacing energy used during exercise and inducing T3 and T4.


Thyroid hormone loves muscle and hates fat. That's why it's a bodybuilder's best friend. Because muscles are the primary site of our body's BMR. T3 works to increase this lean mass so there will be increased BMR available to burn fat. To accomplish this, T3 virtually increases all aspects of protein synthesis in the muscles to allow growth to occur. It also increases the efficiency in which fat is burned. It can actually double the calories burned for each unit of work performed. That means twice the fat get burned while you train and grow. So as you can see, the thyroid hormones may well be one of bodybuilding's best kept secrets. And the good news is you don't have to travel to the distant ends of the earth like Indiana Jones to drink from this grail. Its benefits can always be summoned forth if one stimulates the muscles by using the principles and techniques of bodybuilding. while maintaining a proper diet that includes supplements. Do so. and the power of T3 will always be there for you.


As you conclude this five-pan series on the hormones that affect your metabolism and anabolic state, it should be clear that building a world-class physique doesn't depend on a single hormone. Many hormones work together as a team to influence muscular development and fitness. These hormones depend on each other to get the job done by providing a stimulus that aids in growth and recovery, while influencing each other's production. But most important, these hormones depend on you. Remember, they can't do their job unless you do yours. So plan your workouts and timing of supplementation to take full advantage of your anabolic hormones and there will be no limits to what your body can accomplish.

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