The IL-6 signalling pathway: potential biomarkers for training load, performance, and health status in endurance runners?

Interleukin-6 (IL-6) is a cytokine with many functions, including mediating immune, inflammatory, and metabolic responses to exercise. IL-6 signalling can have both beneficial and deleterious effects on an athlete’s ability to take part in training and competition; IL-6 promotes energy availability for muscle contractions and is implicated in the anti-inflammatory effects of exercise, however it can also induce fatigue, mood disturbances and act in a pro-inflammatory manner. 

The current thesis aimed to describe the IL-6 signalling response to acute exercise and long?term training in a group of highly trained endurance runners. Specifically, the objective was to assess whether IL-6 signalling components had potential as biomarkers for exercise  stress, training adaptations and tolerance of a training programme. The acute IL-6 response  to a standardised treadmill run was characterised before and after an 8-week period of self?selected training. During the training period, resting levels of IL-6 signalling components  were measured weekly and compared to training characteristics and markers of perceived wellbeing. Participants were also genotyped for a single nucleotide polymorphism of the IL-6 receptor gene (rs2228145) which has been shown to influence IL-6 signalling responses. There was an acute increase in IL-6 in response to the treadmill run before the training  period, the magnitude of which was associated with perceived exertion during exercise. Following the training period, the IL-6 response was attenuated, with the degree of attenuation correlating with the total training volume completed. During the training  period, resting levels of IL-6 signalling components were associated with perceived muscle soreness, mood, and mental wellbeing. Genotype frequency for rs2228145 appeared  different in the current highly trained cohort compared to that expected within the general  populations. Genotype also seemed to effect plasma levels of IL-6 receptor, illness  frequency during the training period, and perceived exertion during exercise. 

Overall, the work in the thesis has increased the understanding of the interaction between  IL-6 signalling, exercise tolerance and health status in an athlete population. Monitoring of  IL-6 signalling and the genotyping of rs2228145 may be of value to applied practitioners in  helping to optimise training prescription.