title: Critical Difference and Biological Variation in Biomarkers of Oxidative Stress and Nutritional Status in Athletes.
abstract: The longitudinal monitoring of oxidative stress (OS) in athletes may enable the identification of fatigued states and underperformance. The application of OS biomarker monitoring programs in sport are hindered by reliability and repeatability of in-the-field testing tools, the turnaround of results, and the understanding of biological variation (BV). Knowledge of BV and critical difference values (CDV) may assist with data interpretation in the individual athlete.
  
  
  METHODS
  We aimed firstly to assess the repeatability of the clinical point of care redox test, Free Oxygen Radical Test (FORT) and the Free Oxygen Radical Defence (FORD) in trained participants and elite athletes and secondly to calculate the analytical, BV, CDV and index of individuality (II) for FORT, FORD, red blood cell glutathione, lutein, α and γ-tocopherol. Part 1: Fifteen elite athletes were sampled in duplicate for calculation of the repeatability of the FORT and FORD tests. Part 2: Twelve well-trained athletes had venous samples drawn every 2 hours from 0800 to 1800 for calculation of BV, CDV, II for FORT, FORD, RBC GSH, lutein, α-tocopherol and γ-tocopherol.
  
  
  RESULTS
  Repeatability of the FORT and FORD assay was 3.9% and 3.7% respectively. Biomarker CDV ranged from 12.8% to 37%, with a circadian effect for FORT, α-tocopherol and γ-tocopherol (p<0.01), with all biomarker indices of individuality < 0.8 arbitrary units.
  
  
  CONCLUSIONS
  We report that the use of the novel redox test in athletes is practical, and the generation of BV and CDV for biomarkers of OS enhances the interpretation of physiologically meaningful changes in individuals above the use of clinical reference ranges alone.
authors.affiliation: English Institute of Sport, Athletes Training Village, University of Bath, Bath, United Kingdom.|School of Sport, Health and Applied Science, St Mary's University, Twickenham, London, United Kingdom.|ORRECO, Institute of Technology, Sligo, Ireland.
authors.forename: Nathan A
authors.initials: NA
authors.lastname: Lewis
authors.affiliation: ORRECO, Institute of Technology, Sligo, Ireland.|School of Mathematics, Applied Statistics and Mathematics, National University of Ireland, Galway, Ireland.
authors.forename: John
authors.initials: J
authors.lastname: Newell
authors.affiliation: English Institute of Sport, Athletes Training Village, University of Bath, Bath, United Kingdom.|School of Sport, Health and Applied Science, St Mary's University, Twickenham, London, United Kingdom.|ORRECO, Institute of Technology, Sligo, Ireland.
authors.forename: Richard
authors.initials: R
authors.lastname: Burden
authors.affiliation: Department of Sport, Exercise and Rehabilitation, Northumbria University, Newcastle, United Kingdom.|Water Research Group, School of Environmental Sciences and Development, Northwest University, Potchefstroom, South Africa.
authors.forename: Glyn
authors.initials: G
authors.lastname: Howatson
authors.affiliation: School of Sport, Health and Applied Science, St Mary's University, Twickenham, London, United Kingdom.|ORRECO, Institute of Technology, Sligo, Ireland.|Cardiovascular Performance Program, Massachusetts General Hospital, Boston, Massachusetts, United States of America.
authors.forename: Charles R
authors.initials: CR
authors.lastname: Pedlar
mesh_terms: D000328:Adult; D056352:Athletes; D015415:Biomarkers / Q000097:blood; D015444:Exercise; D005260:Female; D005978:Glutathione / Q000097:blood; D006403:Hematologic Tests / Q000379:methods*; D006801:Humans; D014975:Lutein / Q000097:blood; D008297:Male; D009752:Nutritional Status; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D015203:Reproducibility of Results; D055815:Young Adult; D024502:alpha-Tocopherol / Q000097:blood; D024504:gamma-Tocopherol / Q000097:blood
chemical_list: D015415:Biomarkers; D024504:gamma-Tocopherol; D005978:Glutathione; D024502:alpha-Tocopherol; D014975:Lutein