Exercise in hot and cold environments: differential effects on leukocyte number and NK cell activity.
BACKGROUND
Exercise and environmental temperature have been reported to affect the immune system, but few studies have examined the combined effects of very hot or cold temperatures during exercise in the same group of subjects. Therefore, the purpose was to examine the immune responses following exercise combined with exposure to hot and cold environments.


METHODS
There were 10 men who completed 2 60-min cycle ergometry (60% VO2peak) trials: hot (HT: 38 degrees C, 45% RH) and cold (CD: 8 degrees C, 50% RH). Rectal core temperatures (Tc), average skin temperatures (Tsk), and HR were recorded every 15 min of exercise. Venous blood was collected before (PRE), immediately after (POST), 2 h after (2 h), and 24 h after exercise (24 h). Physiologic strain index (PSI) was calculated. Total and differential leukocytes were determined by manual counting (adjusted for plasma volume shifts). Natural killer cell activity (NKCA) was determined by a whole blood 51Cr-release assay.


RESULTS
Tsk, Tc, and PSI were significantly lower in the CD than HT trial (p < 0.05). Total leukocyte count was greater POST (40%) and 2 h (74%) than PRE and 24 h in both conditions (p < 0.05). Neutrophil count was greater POST (49%) and 2 h (132%) than PRE and 24 h in both conditions (p < 0.05). Lymphocyte count was greater POST (24%) in HT than CD (p < 0.05). NKCA was greater POST (38%) than PRE, 2 h, and 24 h in both conditions (p < 0.05). HT caused significant increases for Tc and Tsk above those observed for CD (p < 0.05). PSI was greater in HT (9.92 +/- 0.93) than CD (4.24 +/- 0.56) (p < 0.05).


CONCLUSIONS
Exercise in HT produced more physiological stress than CD; however, this difference was not manifested in the immune system response. Heat and cold stress in combination with exercise produce similar disturbances in immunity during recovery from exercise.
McFarlin
Brian K
BK
Department of Kinesiology, Texas Christian University, Fort Worth, TX 76129, USA. bkmcfarlin@att.net
Mitchell
Joel B
JB
D000328:Adult; D001831:Body Temperature; D001833:Body Temperature Regulation / Q000502:physiology*; D003080:Cold Temperature; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006358:Hot Temperature; D006801:Humans; D007694:Killer Cells, Natural / Q000502:physiology*; D007958:Leukocyte Count; D008297:Male