title: Individual Differences in Diurnal Preference and Time-of-Exercise Interact to Predict Exercise Frequency.
abstract: BACKGROUND
  Diurnal preference (and chronotype more generally) has been implicated in exercise behavior, but this relation has not been examined using objective exercise measurements nor have potential psychosocial mediators been examined. Furthermore, time-of-day often moderates diurnal preference's influence on outcomes, and it is unknown whether time-of-exercise may influence the relation between chronotype and exercise frequency.
  
  
  OBJECTIVE
  The current study examined whether individual differences in diurnal preference ("morningness-eveningness") predict unique variance in exercise frequency and if commonly studied psychosocial variables mediate this relation (i.e., behavioral intentions, internal exercise control, external exercise control, and conscientiousness). Moreover, the study sought to test whether individuals' typical time-of-exercise moderated the impact of diurnal preference on exercise frequency.
  
  
  METHODS
  One hundred twelve healthy adults (mean age = 25.4; SD = 11.6 years) completed baseline demographics and then wore Fitbit Zips® for 4 weeks to objectively measure exercise frequency and typical time-of-exercise. At the end of the study, participants also self-reported recent exercise.
  
  
  RESULTS
  Diurnal preference predicted both self-reported exercise and Fitbit-recorded exercise frequency. When evaluating mediators, only conscientiousness emerged as a partial mediator of the relation between diurnal preference and self-reported exercise. In addition, time-of-exercise moderated diurnal preference's relation to both self-reported exercise and Fitbit-recorded exercise frequency such that diurnal preference predicted higher exercise frequency when exercise occurred at a time that was congruent with one's diurnal preference.
  
  
  CONCLUSIONS
  Based on these findings, diurnal preference is valuable, above and beyond other psychological constructs, in predicting exercise frequency and represents an important variable to incorporate into interventions seeking to increase exercise.
authors.affiliation: Department of Psychology, Iowa State University, Ames, IA, USA. hislerg@iastate.edu.
authors.forename: Garrett C
authors.initials: GC
authors.lastname: Hisler
authors.affiliation: Department of Psychology, Iowa State University, Ames, IA, USA.
authors.forename: Alison L
authors.initials: AL
authors.lastname: Phillips
authors.affiliation: Department of Psychology, Iowa State University, Ames, IA, USA.
authors.forename: Zlatan
authors.initials: Z
authors.lastname: Krizan
mesh_terms: D000293:Adolescent; D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D015444:Exercise / Q000523:psychology*; D005260:Female; D000072936:Fitness Trackers; D006801:Humans; D007206:Individuality; D008297:Male; D057566:Self Report; D012890:Sleep / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult
keywords: Chronotype; Diurnal preference; Exercise; Morningness; Physical activity