Immediate effects of heavy exercise on the circulating thyroid hormones.

Sera from 20 patients with suspected or known coronary artery disease were measured for thyroxine (T4), tri-iodothyronine (T3), tri-iodothyronine uptake ratio (T3UR), thyroid stimulating hormone (TSH), and reverse tri-iodothyronine (rT3), before and after maximal or near-maximal exercise. On the average the patients achieved 92% (rang 68-108) of the predicted maximum heart rate. There were no statistically significant differences between the pre- and the post-exercise serum levels of thyroid hormones. When five patients who achieved less than 90% of the predicted maximum heart rate were excluded, the results remained unchanged. It appears that the circulating thyroid hormones are not acutely affected after maximal or near-maximal exercise; however, the patient population was highly select.