title: sIL-6R Is Related to Weekly Training Mileage and Psychological Well-being in Athletes.
abstract: 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.
  
  
  
  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.
  
  
  
  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 ± 4.3 vs 20.1 ± 3.8 ng·mL). 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 = -0.43, P = 0.05) and cortisol concentration (r = -0.17, 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 = -0.74, P < 0.005).
  
  
  
  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.
authors.affiliation: 1Cardiff School of Sport, Cardiff Metropolitan University, Cardiff, UNITED KINGDOM; 2Institute of Sport and Exercise Science, University of Worcester, Henwick Grove, Worcester, UNITED KINGDOM; 3Cardiff School of Health Sciences, Cardiff Metropolitan University, Cardiff, UNITED KINGDOM; and 4University Hospital Wales Cardiff, Cardiff, UNITED KINGDOM.
authors.forename: Tom
authors.initials: T
authors.lastname: Cullen
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Thomas
authors.forename: Richard
authors.initials: R
authors.lastname: Webb
authors.forename: Thom
authors.initials: T
authors.lastname: Phillips
authors.forename: Michael G
authors.initials: MG
authors.lastname: Hughes
mesh_terms: D000339:Affect / Q000502:physiology*; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D015850:Interleukin-6 / Q000097:blood*; D008297:Male; D064797:Physical Conditioning, Human / Q000379:methods*; D010807:Physical Endurance / Q000502:physiology; D012141:Respiratory Tract Infections / Q000097:blood; D012420:Running / Q000502:physiology* / Q000523:psychology*; D012890:Sleep / Q000502:physiology; D013315:Stress, Psychological / Q000097:blood*; D011795:Surveys and Questionnaires
chemical_list: D015850:Interleukin-6; D006854:Hydrocortisone