This is a spicy topic. If you are in a healing phase and have a health crisis - for example Hashimoto's or Graves - You want to reduce cortisol and overall stress. Cortisol decreases Thyroid Stimulating Hormone (TSH) --> which will lower thyroid hormone production. Cortisol also inhibits the conversion of T4 to T3 (active thyroid hormone), and increases the conversion of T3 to reverse T3.
Dr. Jen recommends:
Weight lifting 3 times per week
Walking 3-4 times per week
Yoga 2 times per week
Avoid HIIT work outs as these tend to spike cortisol which we don't want while in the healing phase.
Once you are in remission and thyroid is balanced- you may add in HIIT workouts once a week.
Why weights? Weight lifting is going to help balance blood sugar which will put less strain on the adrenals and thyroid.
Why not swimming? You can mix in swimming; however, be sure to rinse off well! Chlorine can have negative effects on iodine levels.
Some favorite youtube account for routines.