How an underactive thyroid affects athletic performance

Photo: Jonathan Chng/Unsplash. Design: BOOST Thyroid.

Photo: Jonathan Chng/Unsplash. Design: BOOST Thyroid.

The role of the thyroid in professional sports

Professional athletes’ bodies must be in exceptional shape to achieve top results while performing at a competitive, paid level. It’s crucial to have well balanced thyroid hormone levels to maintain such physical fitness levels.

According to research, the very first sign of an underactive thyroid in professional athletes is fatigue (1).

Impact of the thyroid on athletic performance

Thyroid hormones regulate the size and performance of muscles (1). The thyroid needs to be substantially active to allow a rapid increase in thyroid hormone levels when muscles are performing. As TSH values increase, exercise intensity can increase as well (2).

Several fitness problems are connected with an underactive thyroid:

  1. Reduced amount of blood the heart can pump with each beat—this decreases the amount of oxygen and food that is brought to the working muscles, reducing their performance (3).

  2. Reduced quantity of fat extracted from cells—this means there’s not enough fats delivered to muscles. Fat is a crucial substrate for muscle contraction during exercise. Lack of fat in muscles makes muscles weaker (4).

  3. Reduced insulin sensitivity—making it increasingly difficult to get sugar from blood, which is necessary for muscles to work effectively (5).

  4. Interference with normal bone metabolism—bone formation and resorption normally happens when people exercise. Poor bone metabolism makes bones more brittle and prone to breaking (6).

  5. Slowed down the rate of recovery for muscle injuries and tears—this means it takes longer to recover from injury and go back to exercise (7).

Injury recovery

After recovering from an injury, doctors advise to measure thyroid hormones before restarting exercise. It’s important to gradually increase intensity of exercise and measure thyroid hormones at certain intervals as performance increases.
Doctors usually take a blood sample when an athlete reaches 90% of their maximum heart rate—this is to make sure there is an appropriate intensity of exercise relative to an athlete's fitness (2).

Endurance sports

High endurance sports (compared to other forms of exercise) impact the thyroid the most as they are the ones that  require a well balanced thyroid the most. For example, in minutes and hours after the marathon, TSH, T4, and reverse T3 levels usually increase. They return to normal 1-4 days after the exercise (8, 9).

Performance enhancing drugs

Using performance enhancing drugs (PEDs) is a common practice in both amateur and professional sports. In professional sports it’s known as “doping” and is illegal.

Using PEDs can be very dangerous for overall health. PEDs affect some of the same bodily functions as the thyroid, including insulin resistance and changes in sugar metabolism (10).

There are several categories of PEDs—anabolic drugs are the most used ones. They increase muscle and reduce fat. Reports show that there is an increase in the use of anabolic steroids to improve athletic performance, which can be especially dangerous for people with thyroid conditions.

Thyroid hormones are sometimes used as PEDs, as they may help burn fat and reduce body water content. Taking thyroid hormones as PEDs can increase the risk of overtreatment and hyperthyroidism—with first symptoms being excessive sweating, heart palpitations, and hand tremor.

If you’re a professional athlete diagnosed with an underactive thyroid

talk to your doctor about your sport performance and make sure your T3 levels are okay. T3 hormone promotes type II muscle fibers (also known as fast fibers) and are needed for sport performance (7).Proper nutrition and being free of infections should also help to keep your athletic performance up.Some research reports that taking zinc might help restore thyroid hormone levels after exercise (11).

Track your lab tests, physical activity, and any symptoms you experience in the BOOST Thyroid app. This will help you when visiting your doctor and determining the best course of treatment to support your athletic performance.


  1. Caiozzo VJ, et al. The influence of hyperthyroidism on the maximal shortening velocity and myosin is form distribution in slow and fast skeletal muscles, 1991

  2. Ciloglu F, et al. Exercise intensity and its effects on thyroid hormones, 2005

  3. Duhig T, et al. Thyroid Disorders in Athletes, 2009

  4. Ranallo RF, et al. Lipid metabolism during exercise, 1998

  5. Canaris GJ, et al. The Colorado thyroid disease prevalence study, 2000

  6. Maïmoun L, et al. The intensity level of physical exercise and the bone metabolism response, 2006

  7. Salvatore D, et al. Thyroid hormones and skeletal muscle — new insights and potential implications, 2014

  8. Sander M, et al. Influence of marathon running on thyroid hormones, 1988

  9. Refuse HE, et al. Serum thyroxine, triiodothyronine and thyroid stimulating hormone after prolonged heavy exercise.

  10. Oliveira D, et al. Performance-enhancing drugs and adverse endocrine effects, 2018

  11. Kilic M, et al. The effect of exhaustion exercise on thyroid hormones and testosterone levels of elite athletes receiving oral zinc, 2006