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Abstract
The circadian variation of athletic performance has been observed to coincide with daily peaks in body temperature. Chronotypes (CT) take into account inter-individual variations in circadian rhythms, yet there is discord regarding the relationship between CT and athletic performance. This may be due to the most common chronotyping method, the Morningness-Eveningness Questionnaire (MEQ), lacking validity for athletic populations. PURPOSE: The purpose of this study was to develop and validate an athlete specific CT index (ACTi). METHODS: 297 athletes completed a CT questionnaire in MEQ (19) and newly-developed questions (15). Principle component analysis (PCA) was used to identify common themes and reduce the final number of questions. 10 respondents from each CT category, as determined by the MEQ, then participated in a 24-hour laboratory study. Participants abided by their typical sleep/wake cycle, provided hourly saliva samples (for dim light melatonin onset (DLMO) analysis) whilst awake and hourly core body temperature (CBT) readings (ingestible thermistor) for the 24-hours. Stepwise multiple linear regression analysis to predict DLMO onset and CBT was used to further refine the ACTi. RESULTS: PCA of the extended ACTi responses were performed, identifying 7 themes. Multiple regression identified 11 questions that explained DLMO (r2=0.81), forming the final ACTi. DLMO CT differences were observed between MEQ morning-type (MT) and intermittent-type (IT) (64±61.6 min, p=0.02); and MT and evening-type (ET) (114±71.2min, p=0.002). No CT differences were observed in CBT for MEQ or ACTi. Cohen’s Kappa revealed moderate CT classification changes between MEQ and ACTi (0.62). CONCLUSION: The ACTi is an 11-point index that enhances CT determination of athletes versus MEQ, based on the criterion measure DLMO. The ACTi may be used in team-sports to examine the impact of CT upon performance, monitoring of training responsiveness and athlete wellbeing.
Published Version
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