Interleukin-6 (IL-6) is a pluripotent cytokine which has inflammatory properties. It is suggested to mediate a variety of processes including increased perception of fatigue during inflammatory states. In addition, prolonged exercise can cause a marked increase in circulating IL-6, and although there is a widely reported association between plasma IL-6 and fatigue in disease and inflammatory conditions, this relationship has remained relatively unexplored in healthy individuals during exercise. Therefore, the aims of this thesis were firstly, to develop a repeatable preload time trial in order to examine the variability of circulating IL-6 and other signalling molecules in response to an exercise challenge; secondly, to investigate the effect of plasma IL-6 and signalling molecules on fatigue and performance during a pre-loaded time trial; and thirdly, to evaluate the impact of nutritional interventions (glutamine intake during exercise, manipulation of pre-exercise diet and carbohydrate intake during exercise) on the response of circulating IL-6, IL-6 signalling molecules and biomarkers associated with IL-6 during exercise and their effect on preload time trial performance. Results from the studies determined that there was large variability in the plasma IL-6 and signalling receptors response to the pre-loaded time trial (8-20%) but that the exercise protocol was repeatable. Nutritional interventions did not alter the signalling receptor response, nor biomarkers associated with IL-6, including hepcidin. However, carbohydrate intake during exercise attenuated the circulating IL-6 response to exercise by 49% which correlated well with an improved time trial performance. Regardless of the intervention, a consistent finding in all studies indicated that a greater plasma IL-6 response to the preload exercise bout correlated well with a reduced relative exercise performance as a percentage of velocity at VO 2max during the subsequent time trial. To summarise, the findings from this thesis indicate that elevated levels of plasma IL-6 are associated with a decrement in exercise performance. Associated IL-6 signalling molecules are elevated in response to exercise but are not associated with performance and are unaltered by nutritional interventions.
|Publication status||Accepted/In press - 2012|