Systemic Inflammatory Response To Consecutive Days of Exercise In The Heat

Abstract

PURPOSE: The purpose of this study was to determine the LPS-mediated SIR to acute bouts of exercise in the heat and any adaptive response that occurs during consecutive days of exercise in the heat. METHODS: 8 healthy males (Age = 24 ± 3 yrs, VO2max = 55.3± 3.6 ml*kg-1*min-1) were asked to run (~78% VO2max) in a hot environment on 5 consecutive days. Participants ran each day until core temperature (Tc) was elevated 2°C above rest or volitional exhaustion. Blood samples were obtained pre-exercise, post-exercise, 1 h post-exercise, and 3 h post-exercise on the 1st, 3rd, and 5th day of exercise. RESULTS: Resting Tc (P < 0.05) was significantly decreased on Days 4 and 5 as compared to Day 1. Heart rate (resting and exercise) and Physiological Strain Index were not significantly altered by 5 consecutive days of exercise in the heat. Exercise time was not significantly different among days. Plasma [IL-6] was significantly elevated post-exercise each day (14.8 pg/ml vs.10.6 pg/ml) as compared to resting values. No significant difference in the IL-6 response was detected among days. Plasma [TNF-α] was not significantly elevated above rest after exercise on any day though mean plasma concentrations were significantly lower on Day 5 at 1h (3.1 pg/ml vs. 4.7 pg/ml; P = 0.01) and 3 h (3.5 pg/ml vs. 4.7 pg/ml; P = 0.05) post exercise as compared to Day 1. Plasma [IL-10] was significantly (0.9 pg/ml vs 0.5 pg/ml; P < .01) elevated from baseline at 1 h post exercise with no difference among days. Plasma LPS activity significantly increased post-exercise (1.4 EU/ml vs. 0.9 EU/ml; P < 0.01) each day as compared to rest. No difference was detected among days for LPS activity. CONCLUSION: These data indicate that consecutive days of exercise in the heat results in a less pro-inflammatory (TNF-α) response to exercise and this adaptation may be a result of an increasing LPS tolerance.