title: Factors to consider when assessing diurnal variation in sports performance: the influence of chronotype and habitual training time-of-day.
abstract: OBJECTIVE
  The aim of this study was to compare morning and evening time-trial performance, RPE and mood state of trained swimmers, taking into account chronotype, habitual training time-of-day and PERIOD3 (PER3) variable number tandem repeat genotype.
  
  
  METHODS
  Twenty-six swimmers (18 males, age: 32.6 ± 5.7 years) swam 200 m time trials (TT) at 06h30 and 18h30 in a randomised order.
  
  
  RESULTS
  There was no difference between morning and evening performance when the swimmers were considered as a single group (06h30: 158.8 ± 22.7 s, 18h30: 158.5 ± 22.0 s, p = 0.611). However, grouping swimmers by chronotype and habitual training time-of-day allowed us to detect significant diurnal variation in performance, such that morning-type swimmers and those who habitually train in the morning were faster in the 06h30 TT (p = 0.036 and p = 0.011, respectively). This was accompanied by lower ratings of perceived exertion (RPE) scores post-warm-up, higher vigour and lower fatigues scores prior to the 06h30 TT in morning-type swimmers or those who trained in the morning. Similarly, neither types and those who trained in the evenings had lower fatigue and higher vigour prior to the 18h30 TT.
  
  
  CONCLUSIONS
  It appears that both chronotype and habitual training time-of-day need to be considered when assessing diurnal variation in performance. From a practical point of view, athletes and coaches should be aware of the potentially powerful effect of training time on shifting time-of-day variation in performance.
authors: MRC/UCT Research Unit for Exercise Science and Sports Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa, Dale.Rae@uct.ac.za.
authors: Dale E
authors: DE
authors: Rae
authors: Kim J
authors: KJ
authors: Stephenson
authors: Laura C
authors: LC
authors: Roden
mesh_terms: D000293:Adolescent; D000328:Adult; D054874:Athletic Performance; D002940:Circadian Rhythm; D005260:Female; D006184:Habits; D006801:Humans; D008297:Male; D056950:Period Circadian Proteins / Q000235:genetics; D017440:Photoperiod; D013550:Swimming
chemical_list: C512644:PER3 protein, human; D056950:Period Circadian Proteins
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