Effect of exercise on thyroid parameters and on metabolic clearance rate of antipyrine in man

Serum concentrations of thyroxine, triiodothyronine, free-thyroxine-index, free-triiodothyronine-index and reverse-triiodothyronine (r-T3) were followed in nine normal men, aged 18 to 22 years, during a nights rest and during nine hours march (4.6 km/h). In addition antipyrine elimination was measured in the same periods after iv injection of 1 gram of antipyrine. No significant differences were found in any of the thyroid parameters during exercise except for a small increase in serum r-T3 after 3 hours. During rest a small but significant decrease was found in serum r-T3. Otherwise no significant differences were found except for a significant increase in free-T3-index after 3 hours rest. The mean value of total body clearance of antipyrine was identical at rest and during exercise.

Prolonged exercise does not change the metabolic clearance rate of antipyrine and does not elicit any major change in the serum concentrations of the thyroid hormones.