Exercising in the cold inhibits growth hormone secretion by reducing the rise in core body temperature.

Objective: Ambient temperature alters exercise induced GH secretion. It is unknown whether temperature affects GH secretion at exercise intensities above the anaerobic threshold when other factors may override the relationship seen at lower intensities.

Design: Cross-over study of ambient temperature on exercise induced GH in swimmers and rowers.

Setting: St Thomas Hospital, London.

Subjects: Ten healthy men (age 21.7+/-0.8 yrs). Five swimmers and five rowers.

Intervention: Forty-minute exercise test at 105% of anaerobic threshold at room temperature (RT) and at 4 degrees C.

Measurements: Cutaneous and core body temperature. Serum GH concentration.

Results: Cutaneous body temperature increased during exercise at RT but decreased in the cold. Although core temperature rose in both settings, the rise was greater at RT (p=0.021). GH increased at both temperatures but the onset was delayed by the cold. Peak GH tended to be higher at RT (17.4+/-3.6 microg/L vs. 9.5+/-1.5 microg/L, p=0.07). Total GH secretion was greater at RT (353.3+/-99.1 microg min/L) than 4 degrees C (128.3+/-21.0 microg min/L), p=0.038. Change in core temperature correlated with log peak GH (r=0.66, p=0.039) and log incremental GH (r=0.67, p=0.032) when exercising at 4 degrees C. There was no difference between swimmers and rowers.

Conclusions: Exercise at 4 degrees C reduces GH secretion during exercise at intensities above the anaerobic threshold. A change in core body temperature may be one mechanism by which exercise induces GH secretion. The difference in GH between swimmers and rowers during their respective events relates to the conditions under which they compete.