title: A New Method to Individualize Monitoring of Muscle Recovery in Athletes.
abstract: OBJECTIVE
  Assessment of muscle recovery is essential for the daily fine-tuning of training load in competitive sports, but individual differences may limit the diagnostic accuracy of group-based reference ranges. This article reports an attempt to develop individualized reference ranges using a Bayesian approach comparable to that developed for the Athlete Biological Passport.
  
  
  METHODS
  Urea and creatine kinase (CK) were selected as indicators of muscle recovery. For each parameter, prior distributions and repeated-measures SDs were characterized based on data of 883 squad athletes (1758 data points, 1-8 per athlete, years 2013-2015). Equations for the individualization procedure were adapted from previous material to allow for discrimination of 2 physiological states (recovered vs nonrecovered). Evaluation of classificatory performance was carried out using data from 5 consecutive weekly microcycles in 14 elite junior swimmers and triathletes. Blood samples were collected every Monday (recovered) and Friday according to the repetitive weekly training schedule over 5 wk. On the group level, changes in muscle recovery could be confirmed by significant differences in urea and CK and validated questionnaires. Group-based reference ranges were derived from that same data set to avoid overestimating the potential benefit of individualization.
  
  
  RESULTS
  For CK, error rates were significantly lower with individualized classification (P vs group-based: test-pass error rate P = .008; test-fail error rate P < .001). For urea, numerical improvements in error rates failed to reach significance.
  
  
  CONCLUSIONS
  Individualized reference ranges seem to be a promising tool to improve accuracy of monitoring muscle recovery. Investigating application to a larger panel of indicators is warranted.
authors.forename: Anne
authors.initials: A
authors.lastname: Hecksteden
authors.forename: Werner
authors.initials: W
authors.lastname: Pitsch
authors.forename: Ross
authors.initials: R
authors.lastname: Julian
authors.forename: Mark
authors.initials: M
authors.lastname: Pfeiffer
authors.forename: Michael
authors.initials: M
authors.lastname: Kellmann
authors.forename: Alexander
authors.initials: A
authors.lastname: Ferrauti
authors.forename: Tim
authors.initials: T
authors.lastname: Meyer
mesh_terms: D000465:Algorithms; D056352:Athletes; D001499:Bayes Theorem; D015415:Biomarkers / Q000097:blood; D003402:Creatine Kinase / Q000097:blood; D005260:Female; D006801:Humans; D008297:Male; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000502:physiology*; D012016:Reference Values; D013177:Sports / Q000502:physiology*; D014508:Urea / Q000097:blood
chemical_list: D015415:Biomarkers; D014508:Urea; D003402:Creatine Kinase
keywords: distribution; individualization; reference range; sport