Three hundred forty elite athletes (males = 261, females = 79) were recruited for the present study. Athletes from basketball (n=12), rugby (n=22), wrestling (n=4), boxing (n=1), short track (n=5), swimming (n=14), squash (n=8), baseball (n=103), weight lifting (n=4), judo (n=6), soft tennis (n=11), rowing (n=34), canoe (n=9), tennis (n=1), fencing (n=6), field hockey (n=33), and handball (n=67) were recruited. All participants were screened for chronotype using the Korean versions of the Morningness - Eveningness Questionnaire (MEQ-K) by Horne and Ostberg : no definitely morning type (DM), thirteen moderately morning type (MM) (males = 11, females = 2), one hundred sixty-nine neither type (NT) (males = 136, females = 28), one hundred eleven moderately evening type (ME) (males = 75, females = 33), and sixty-one definitely evening type (DE) (males = 39, females = 16). There were no significant differences in age, height, weight, BMI and careers.
All subjects who agreed to participate in the study described the study to fully understand its purpose and the methods used in the ethical standards of the Declaration of Helsinki. In addition, all subjects signed an informed consent form prior to participation. This study was approved by Kangwon National University Review Board for Human Subjects (KWNUIRB-2020-03-007-002).
Morningness - Eveningness Questionnaire (MEQ)
The Korean Morningness - Eveningness Questionnaire (MEQ-K) from Horne and Ostberg was used to assess the circadian typology of each subject . MEQ has 19 items related to preferred time to participate in habitual physical and mental activities. MEQ scores range from 16 to 86, from extreme morning type to extreme evening type. The standard scores of the MEQ proposed by Horne and Ostberg were used to categorize the subjects as definitely morning type (DM), moderately morning type (MM), neither type (NT), moderately evening type (ME), and definitely evening type (DE)15. Cronbach’s alpha for the MEQ-K was 0.77, and the correlation coefficient between the MEQ-K scores for verifying the test-retest reliability was 0.898.
Pittsburgh Sleep Quality Index Questionnaire
The Pittsburgh Sleep Quality Index (PSQI) is a self-report questionnaire that evaluates sleep quality and quantity. The PSQI self-report questionnaire comprises of 19 items, yielding 7 component scores: (1) subjective sleep quality, (2) sleep latency, (3) duration, (4) habitual sleep efficiency, (5) sleep disturbances, (6) use of sleeping medication, and (7) daytime dysfunction. Each component is graded on a 0–3 severity scale based on the frequency of each disturbance and yields a global score with a range of 0–21 . A PSQI global score of 5 or greater indicates a clinically significant sleep disorder.
Wingate Anaerobic Test (WAnT)
WAnT was used following experiments performed by Kikuchi et al . The WAnT was performed on a cycle ergometer (Monark 824 E, Monark, Sweden) equipped a photoelectric sensor for recording 1.0 kg resistance basket and flywheel revolutions. Data for each 30-second WAnT were collected using POWER software (SMI, St Cloud, MN) and IBM-compatible microcomputer.
Each participant completed a self-selected stretching exercise and a five-minute cycle at the ergometer without applying a time limit. At the end of one minute of warm-up, each participant performed an "all-out" sprint for 4 to 5 seconds to simulate the actual test.
Before starting of the WAnT, the resistance for each participant was calculated using a body weight of kilograms multiplied by male 7.5% and female 5%, and the determined amount was placed in the basket. At the start of the test, the assistant lifted the resistance basket and no resistance was applied to the flywheel, and each participant was instructed to begin pedal to reach the maximum rpm at the end of the 5 second countdown. The resistance basket was released, and data collection began, subsequently ending after 30 seconds. After 30 seconds WAnT, participants were instructed to pedal against light resistance (1.0 kg) until they returned to their pre-test condition.
The SPSS statistical package version 25.0 for Windows (SPSS, Inc., Chicago, IL, USA) was used to perform all statistical evaluations. Means and standard deviations were computed for all variables, and normality was checked with the Shapiro Wilk test. Non-normal data were converted using square root or logarithmic transformations which achieved normality for all variables. Sleep state and wingate anaerobic power by chronotype were verified through a one-way analysis of variance (ANOVA). The relationships among variables were analyzed using Pearson’s correlation coefficients. Post-hoc analysis (Bonferroni test) was used to compare specific differences when significance was found. Statistical significance was accepted at the 0.05 level.