Diurnal variation: effect on immune function and athletic performance in elite middle distance runners
  Purpose: To investigate the physiological, immunological and psychological response to an intense bout of exercise performed by highly trained individuals at 09:00 hs and 16:00 hs (Chapter 5) and at 09:00 hs and 18:00 hs (Chapter 6). Methods: Using a crossover randomized design, 7 and 13 well trained runners (range V̇O2max 61-79 ml.kg-1min-1) performed a 10 km time trial run, in two contrasting environments: cold (6°C) and hot (28°C and 70% relative humidity), at 2 different times of day (09:00 hs and 18:00 hs or 16:00 hs). 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- and 1h post-trial. Core body temperature, heart rate, power, strength and flexibility as well as RPE, mood, arousal and alertness were measured pre-, post-trial and 1h post- trial at both times of the day. Results: The time taken to complete the trial was not significantly different in both studies but was faster at 09:00 hs under hot environmental conditions. During the time trial, core body temperature was significantly higher at 18:00 hs (P < 0.05) under hot and humid conditions, whereas, heart rate and core body temperature were higher at 09:00 hs in the cold environment. A significant diurnal difference (P < 0.05) was found for total WBC, neutrophil and lymphocyte counts with higher values at the evening in both studies. Plasma CC16 and total RBC and RBC variable counts were not affected by the time of the day in the cold condition. Resting IL-6 and CC16 as well as HSP70 at 1 h post-trial were significantly higher in the morning, whereas, HSP70, total RBC and RBC variables counts were not affected by the time of the day in hot and humid conditions. Similarly no significant differences were observed in power, strength or flexibility in these conditions. Most psychological measures were not affected by the time of the day in either environmental condition. However, recovery arousal at 09:00 hs was significantly higher (P < 0.05) in the hot and humid condition. Conclusion: a 10 km time trial run, in both environmental conditions, can cause different physiological and immunological responses dependent on the time-of-day in which it is performed. Nevertheless in highly trained runners this variation was not enough to impact on their performance. Despite no statistically significant difference in diurnal running performance in the hot and humid condition a 19 second mean difference in completion time would decide the race winner or even new records.

  • Dates:

    2009 to 2015

  • Qualification:

    Doctorate (PhD)

Project Team