When we talk about exercising, many women think about their beloved spin classes or a nice, crisp 5-mile run outside.

Unfortunately, when you live with hypothyroidism, these types of long, high-intensity cardio workouts can be really hard on the body and can sometimes set your thyroid hormones back even further.

Let’s talk about why this is.

Aerobic vs. anaerobic exercises

There are two general categories of exercises: aerobic and anaerobic.

Aerobic is what we often think of as “steady-state cardio”, as these types of exercises really work the heart. When your heart rate is continuously elevated (60-80-ish% of your maximum heart rate) for a long period of time (think 2-3 minutes or longer), this is an aerobic exercise.

In this state, your body is producing a lot of oxygen and burning a lot of calories. This type of exercise helps build endurance and strengthen your heart and lungs.

Anaerobic exercises are sprints - you’re using big but short bursts of energy to get your heart rate up to 80-90% of your maximum. Things like actual sprinting, weight lifting, circuit training and High-Intensity Interval Training are all forms of anaerobic exercise. 

This type of exercise helps build muscle. Because of that, it also helps boost your metabolism and burn fat.

What’s better for the thyroid?

When comparing these two forms of exercising, hands down anaerobic exercises are better for your thyroid.

When you’re in a constant aerobic state, your body may instinctively think you’re running for your life.

That’s right, the ol’ caveman part of our body actually switches on, releases our cortisol hormone, and puts us in a state of fight or flight. 

If too much cortisol is released over time and our body stays in this state of stress, it can start inhibiting thyroid hormone conversion. That cortisol may stop your body from converting T4 to T3, and instead, revert it to reverse T3, which is not what we want. 

Stress hugely impacts the thyroid, and while many women love going on long runs to clear their head, that constant aerobic state may actually be a stressor on the body and the thyroid. 

So, when you’re managing hypothyroidism, skip that steady-state cardio. Instead, stick to more anaerobic exercises. 

Where to find great thyroid-friendly anaerobic workouts

• I often post exercises and exercise tips on my YouTube and Instagram channels

• There are TONS of free fitness-focused accounts on YouTube. Just search “at home HIIT” or “Gym HIIT workouts”. My fave is Fitness Blender, as their workouts are simple but effective, and you often don’t need equipment

• Studios like Orange Theory and F45 cater to interval training

• Many of your other local gyms and community centres may have circuit training classes that you could join

What are your thoughts on aerobic vs. anaerobic training? Let me know in the comments below!