PURPOSE: To observe the effects of exercise in different environmental conditions on leukocyte counts and subsets. METHODS: Recreationally active Caucasian males (n=7; 23.9±2.4 yrs; 182.9±5.6 cm; 83.4±8.0 kg; 12.8±3.6 %BF; 47.3±5.9 ml·kg-1·min-1) completed an aerobic exercise protocol in low temperature (LT; 5°C), moderate temperature (MT; 22°C), and high temperature (HT; 35°C). The exercise protocol consisted of a 60-minute cycling trial at 60% VO2max, a 15-minute rest period, and a time to exhaustion trial at 90% VO2max (TTE). Blood draws were completed before (PRE) and after (60P) the 60-minute trial; immediately after TTE (90P), and one hour post-TTE (REC). Leukocyte count (WBC); lymphocyte number and ratio (LY# and LY%); monocyte number and ratio (MO# and MO%); and granulocyte number and ratio (GR# and GR%) were analyzed via hematology analyzer. Changes were analyzed using a time × trial within-subjects repeated measures ANOVA. RESULTS: For all trials, WBC increased at all time points relative to PRE (p’sp=0.015) and was elevated from PRE–90P in all trials (p’s=0.002-0.011). A time effect was observed for MO# (p=0.026) and GR# (ppp=0.001), and GR% (p<0.001). LY% decreased at REC (p>0.001); MO% decreased at all timepoints (p’sp’sConclusion: Temperature may not affect acute exercise-induced increases in total leukocyte counts. However, exercise in the heat (35°C) induces a greater increase in circulating lymphocyte counts when compared to exercise in moderate (22°C) and cold (5°C) temperatures.
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