Introduction: Interleukin 6 (IL-6) has been ascribed both positive and negative roles in the context of exercise and training. The dichotomous nature of IL-6 signaling seems to be determined by the respective concentration of its receptors (both membrane-bound [IL-6R] and soluble [sIL-6R] forms). The purpose of the present study was to investigate the response of sIL-6R to long-term training and to investigate the relationship between sIL-6R, self-reported measures of well-being, and upper respiratory symptoms in highly trained endurance athletes. Methods: Twenty-nine athletes provided resting blood samples and completed well-being and illness monitoring questionnaires on a weekly basis for a period of 18 wk during a winter training block. Results: Upper respiratory symptoms were not correlated to concentrations of sIL-6R or cortisol, but there was a nonsignificant trend (P = 0.08) for the most illness-prone athletes (as defined by self-reported illness questionnaire data) to exhibit higher average sIL-6R concentrations compared with the least ill (23.7 T 4.3 vs 20.1 T 3.8 ngImLj1). Concentrations of sIL-6R were positively correlated to subjective measures of stress (r = 0.64, P = 0.004) and mood (r = 0.49, P = 0.02) but were negatively correlated to sleep quality (r = j0.43, P = 0.05) and cortisol concentration (r = j0.17, P = 0.04). In a subgroup of 10 athletes, weekly training distance was quantified by coaching staff, and this negatively correlated with sIL-6R in the following week (r = j0.74, P G 0.005). Conclusion: The findings of the current study suggest that sIL-6R is responsive to prolonged periods of exercise training, with sIL-6R levels varying related to the volume of training performed in the preceding week. Importantly, our data indicate that changes in sIL-6R levels could be linked to common symptoms of overreaching, such as high levels of stress, and/or depressed mood.
Cullen, T., Thomas, A. W., Webb, R., Phillips, T., & Hughes, M. G. (2017). SIL-6R is related to weekly training mileage and psychological well-being in athletes. Medicine and Science in Sports and Exercise, 49(6), 1176–1183. https://doi.org/10.1249/MSS.0000000000001210