Effects of exercise, altitude, and food on blood hormone and metabolite levels.

Measurements of blood glucose and plasma free fatty acids (FFA), thyroxine (T4), free thyroxine (FT4), triiodothyronine (T3), and thyroid-stimulating hormone (TSH) were made on samples taken from fed and fasted human subjects while at rest and immediately after 20 min moderate exercise. Six subjects were studied on successive weeks before (LA1), during (HA1, HA2, HA3), and after (LA2) a 3-wk sojourn at high altitude (3,650 m). The subjects and location were the same as those used for the energy expenditure measurements described in the preceding paper (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 45:345--349, 1978). The most marked effect of altitude was to potentiate the rise in FFA due to exercise. This effect was most noticeable in fed subjects during HA1 and HA2. Changes in the plasma levels of the thyroid hormones correlated with the FFA changes and, once again, exercise at altitude caused the greatest increase in circulating levels. Possible causes of the parallel changes in FFA and thyroid hormone levels and their relationship to changes in energy metabolism are discussed.