How Thyroid Can Affect Training Results


Despite near daily reference in mainstream media and the fitness industry at large, the metabolism is still the most widely misunderstood system of the human body.

Ask the average trainee about metabolic function, and they will throw around questions and statements like

“Doesn’t green tea speed that up?”

“Isn’t that how much food you can eat and not get fat?” or better yet,

“I don’t have to worry about it, my fat burner speeds it up.”

The fundamentals of this article are to stop thinking of your metabolism like it’s an “ON/OFF’ switch than certain foods or fads can dial up and down. The truth is that your ‘metabolism’ essentially refers to the functions of the thyroid gland and the Hypothalmus-Pituitary-Thyroid Axis (HPT Axis) as it regulates your bodies energy demand in real time through a highly complex hormonal web.

So let’s make the purpose of this article to cut through the over marketed and overwhelmingly misunderstood concepts of how your body produces cellular energy, and work to illuminate what the actual impact on your training is like when your metabolism is actually slow!

Basics of the HPT Axis:

The Thyroid gland works with given instruction from the Hypothalmus as it produces Thyrotropin-Releasing-Hormone (TRH), which then stimulates the Anterior Pituitary Gland to produce Thyroid Stimulating Hormone (TSH) which then works directly on the Thyroid Gland itsels to start churning out the parent Thyroid hormone Triiodothyronine (T4). T4 is then liberated into the blood stream and travels to cells all over your muscle, organs and tissue to attach to the Nuclear Receptor Sites where it is then converted to the far more potent T3. T3 is 100 times more potent at burning fat than T4. T2 is more potent than T3 again.

Basically, as you move down the chain of the Thyroid hormones from T4 to T3 to T2 the lipolytic action increases and it is this mechanism that dictates the rate at which your body produces cellular energy, and by the same token, what your caloric intake must be to provide said energy. Basically you cannot rev the engine without more regularly filling the tank! If you do slow the food intake, the engine must slow to adapt, and this is how chronic under eating can cause as much weight gain as over eating. Less input equals slowed output from your Thyroidal activity, means less energy produced and the cycle continues in a depressed manner, lowering your basal metabolic rate in the process and accumulating fat, fluid, causing hormonal issues and generally disrupting homeostasis.

So to summarise, HPT Axis is as follows:

Hypothalmus (TRH)à Anterior Pituitary (TSH)àThyroid (T4)àT3à T2*

*T3 and T2 conversion occur at cellular level in Nuclear Receptor sites where these Hormones bind to cells to illicit metabolic activity*

Impacts of a Sluggish Thyroid on Training:

So the basics of the Thyroids function are now covered off. The next step is to define what happens when this process is not functioning ideally and what that can do to your training!

A sluggish Thyroid can lead to digestive issues, gut health dramas, elevated cortisol levels and negatively impact hormonal balancing, in particular, increasing estrogenic activity. This sluggishness of the Thyroid is a result of either incorrect conversion pathways of T4 into Reverse T3 (rT3) which is actually metabolically inactive and binds up free T4, or due to actual issues with the signalling to the Thyroid to produce more hormone.

Causation aside, if you throw together that cocktail of gut health issues with elevated cortisol and increased estrogenic activity, essentially your training results can go from hero to zero scary fast!

Whether it is building muscle or burning fat, both require a certain degree of homeostasis that is thrown out of balance when the Thyroid slows your cellular energy production. Furthermore and of equal importantance, is the huge energy demands in the actual process of synthesising new muscle tissue. The amount of energy needed to build new muscle tissue from scratch is a monumental process which is very metabolically expensive to the body to do. Hence all muscle building programs involving a caloric surplus!

By the same token, to efficiently burn fat you need the lipolytic activities of your Thyroid hormones to be doing their job, thereby stimulating AMP-K and PPar pathways to name but a few, and encourage adipose tissue to be burnt as fuel.

So very quickly the picture becomes clear that if your Thyroid isn’t producing cellular energy efficiently then muscle building will be compromised as nutrient uptake and digestion is hampered, whilst fat loss is made nearly impossible by the inadequate lipolysis being signalled to take place by your sluggish Thyroid.

Now like all systems in the body, there are negative feedback loops and a slow system also back logs certain other biological processes in the process. Keeping it rudimentary, a slow system effects everything from your appetite via the actions of Ghrelin (hunger stimulating hormone), the rates of digestion and nutrient delivery/partitioning, the elevation of Cortisol as the system is under duress from an internal energy crisis, and finally the elevation of Estrogenic activity due to the decreased metabolic activity coupled with high Cortisol. Insulin sensitivity will also suffer.

Just by looking at Cortisol alone you will see increased visceral fat storage while promoting muscle wasting, anxiety and insulin resistance. This is a potent cocktail for building fat and losing muscle!

Estrogenic activity is the next issue for both the guys and gals! Gender aside, your ratio of Testosterone: Estrogen is referred to as your Androgen ratio. More Testosterone leads to increased muscle mass, burning fat at a faster rate and increased metabolic activity. Ergo, a slow Thyroid promoting excess Estrogen decrease this ratio, resulting in fat gain, increased fluid retention and decreased Thyroid hormonal output. Again, this will really put a hand brake on your training progress!

Finally, your gut health is widely recognised now as being a crucial part of the picture for overall health, and especially training progress.

You are not what you eat, but rather, what you absorb!

Your gut wall is 400 square metres, making it the largest organ in your body which regulates hormones, nutrient partitioning and brain chemistry. All of these factors obviously will really slow training progress if they are out of alignment, so let’s address what can be done to help this scenario from never preventing you hitting your next PB in the gym!

Correcting a Sluggish Thyroid:

There are several mechanisms to correct a sluggish Thyroid with the most acute treatments being supplementation.

  • Supplements to correct Hypo/Hyperthyroidism include adaptogens like Withania, Coleus Forskholii, Yerba Mate, as well as vitamins, minerals and trace elements like Selenium, Iodine, Zinc, Magnesium, Chromium, Vit D, Vit A, Vit K, the B Vitamins, and Tyrosine. These herbs, vitamins and amino acids work to correct the activity of Thyroid hormones from TSH to the more metabolically active forms T4, T3 and T2 as well as correcting any signalling issues that would otherwise prevent TSH stimulating the production of a healthy amount of T4.

These supplements can of course all be sourced individually, or they can all be found in one supplement with our new Thyroid health product, Metabolyz, in the exact doses your body requires!

  • In a longer term approach, there are mountains of data showing resistance training at an intensity of 70% and above (measured usually by heart rate) will illicit the most drastic increases in metabolic activity as well and increases in serum T4 and free T3 (1).
  • Nutrition of course plays a major factor as there is massive nutritive demand in the Thyroid conversion process as mentioned above, so a diet high in nutrient dense foods is crucial to allow efficient Thyroid function.
  • Finally, calorie intake is a powerful tool as well. As discussed in the body of the article, under eating for your energy requirements is a great way to slow your metabolic rate. Inversely, ensuring you consume as many calories as your body requires in a day will ensure you will keep your metabolic rate at a happy rate while you attempt to progress your training goals.

Take Home
A sluggish thyroid will lead to increased fat storage and compromise your ability to build and repair muscle. This can be corrected with supplementation, nutrition and exercise and will lead to fantastic improvements in energy, fat loss, muscle building and hormonal balance, ultimately making progress in body composition a much easier process! 


  1. Exercise Intensity and Its Effects on Thyroid Hormones, Ciloglu, F. Et al, Neuroendocrinol Lett 2005; 26(6):830–834