Purpose: To investigate the physiological and immunological response to an intense bout of exercise performed by highly trained individuals at 09:00hs and 18:00hs. Methods: Using a crossover randomized design, 13 well trained runners (range VO2max 61-79 ml/kg/min) performed a 10 km time trial run, at 2 different times of day (09:00hs and 18:00hs), in an environmental chamber (28°C and 70% relative humidity). Lung function tests and blood samples were taken immediately pre, post and 1h-post trial to determine, total WBC counts, WBC variables, total RBC counts, RBC variables, IL-6, CC16 and HSP70 levels. Nasal lavage procedure for the analysis of upper respiratory airway was conducted pre-, post-trial and 1h-post trial. Core body temperature, heart rate, power, strength and flexibility were measured pre-, post-trial and 1h-post trial. Results: The time taken to complete the trial was not significantly different. During the time trial, heart rate and core body temperature was significantly higher at 18:00hs (P < 0.05). A significant diurnal difference (P < 0.05) was found for total WBC, neutrophil and lymphocyte counts with higher values at 18:00hour (pre- trial: total WBC counts 22%, neutrophil 40% and lymphocyte 9%. Post-trial: total WBC counts 27%, neutrophil 38% and lymphocyte 20%. 1h post- trial: total WBC counts 36%, neutrophil 43% and lymphocytes 20%). Resting plasma CC16 and IL-6 was higher at 09:00hs compared to 18:00hs (23% and 87%, respectively), whereas, HSP70, total RBC and RBC variables counts were not affected by the time of the day. No significant differences were observed in power, strength or flexibility. Conclusion: a 10 km time trial run, in a hot and humid environment, can cause different physiological and immunological responses dependent on the time-of-day in which it is performed. Despite no statistically significant difference in diurnal running performance a 19 second mean difference in completion time would decide the race winner or even new records.
© Copyright 2014 19th Annual Congress of the European College of Sport Science (ECSS), Amsterdam, 2. - 5. July 2014. Published by VU University Amsterdam. All rights reserved.