Diurnal variation in variables related to cognitive performance: a systematic review.

PURPOSE: The aim of this review was to assess current evidence regarding changes in cognitive function according to time-of-day (TOD) and assess the key components of research design related to manuscripts of chronobiological nature. METHODS: An English-language literature search revealed 523 articles through primary database searches, and 1868 via organization searches/citation searching. The inclusion criteria were met by eleven articles which were included in the review. The inclusion criteria set were healthy adult males, a minimum of two timepoints including morning and evening, cognitive measures of performance, and peer-reviewed academic paper. RESULTS: It was established that cognitive performance varies with TOD and the degree of difference is highly dependent on the type of cognitive task with differences ranging from 9.0 to 34.2% for reaction time, 7.3% for alertness, and 7.8 to 40.3% for attention. The type of cognitive function was a determining factor as to whether the performance was better in the morning, evening, or afternoon. CONCLUSION: Although some studies did not establish TOD differences, reaction time and levels of accuracy were highest in the evening. This implies that cognitive processes are complex, and existing research is contradictory. Some studies or cognitive variables did not show any measurable TOD effects, which may be due to differences in methodology, subjects involved, testing protocols, and confounding factors. No studies met all requirements related to chronobiological research, highlighting the issues around methodology. Therefore, future research must use a rigorous, approach, minimizing confounding factors that are specific to examinations of TOD.

Daily variation in performance measures related to anaerobic power and capacity: A systematic review.

Numerous functional measures related to anaerobic performance display daily variation. The diversity of tests and protocols used to assess anaerobic performance related to diurnal effects and the lack of a standardized approach have hindered agreement in the literature. Therefore, the aim of the present study was to investigate and systematically review the evidence relating to time-of-day differences in anaerobic performance measures. The entire content of PubMed (MEDLINE), Scopus, SPORTDiscus® (via EBSCOhost) and Web of Science and multiple electronic libraries were searched. Only experimental research studies conducted in male adult participants aged ≥ 18 yrs before May 2021 were included. Studies assessing tests related to anaerobic capacity or anaerobic power between a minimum of two time-points during the day (morning vs evening) were deemed eligible. The primary search revealed that a total of 55 out of 145 articles were considered eligible and subsequently included. Thirty-nine studies assessed anaerobic power and twenty-five anaerobic capacity using different modes of exercise and test protocols. Forty-eight studies found several of their performance variables to display time-of-day effects, with higher values in the evening than the morning, while seven studies did not find any time-of-day significance in any variables which were assessed. The magnitude of difference is dependent on the modality and the exercise protocol used. Performance measures for anaerobic power found jump tests displayed 2.7 to 12.3% differences, force velocity tests ~8% differences, sprint tests 2.7 to 11.3% differences and 5-m multiple shuttle run tests 3.7 to 13.1% differences in favour of the evening. Performance measures for anaerobic capacity found Wingate test to display 1.8 to 11.7% differences and repeated sprint tests to display 3.4 to 10.2% differences. The only test not to display time-of-day differences was the running based anaerobic sprint test (RAST). Time-of-day variations in anaerobic performance has previously been partially explained by higher core-body and/or muscle temperature and better muscle contractile properties in the afternoon, although recent findings suggest that differences in methodology, motivation/arousal, habitual training times and chronotypes could provide additional explanations. There is a clear demand for a rigorous, standardised approach to be adopted by future investigations which control factors that specifically relate to investigations of time-of-day.

Daily variation in time-trial sporting performance: A systematic review.

Few functional measures related to time-trial display diurnal variation. The diversity of tests/protocols used to assess time-trial performance on diurnal effects and the lack of a standardised approach hinder agreement in the literature. Therefore, the aims of the present study were to investigate and systematically review the evidence relating to time-of-day differences in time-trial measures and to examine the main aspects related to research design important for studies of a chronobiological nature. The entire content of Manipal Academy of Higher Education electronic library and Qatar National Library, and electronic databases: PubMed (MEDLINE), Scopus and Web of Science were searched. Research studies published in peer-reviewed journals and non-peer reviewed studies, conducted in male adult participants aged ≥18 y before November 2021 were screened/included. Studies assessing tests related to time-trials in any modality between a minimum of 2 time-points during the day (morning [06:30-10:30 h] vs evening [14:30-20:00 h]) were deemed eligible. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) process was used to assess the evidence to inform recommendations. The primary search revealed that a total of 10 from 40 articles were considered eligible and subsequently included. Six were conducted using cycling, two using running and two using swimming as the mode of exercise. Distances ranged from 1 to 16.1-km in distance or 15 to 20-min time in the cycling and running time-trials, and 50 to 200-m in the swimming time-trials. Only four studies found one or several of their performance variables to display daily variations, with significantly better values in the evening; while six studies found no time-of-day significance in any variables assessed. The magnitude of difference ranged from 2.9% to 7.1% for performance time to complete a cycling time-trial, while running and swimming did not find any differences for performance time. Power output during a 16.1-km time trial in cycling also found evening performance to be significantly better by 10%. The only other observed differences were stroke rate and stroke length during a swimming time-trial and stroke rate (cycles.min-1) during a cycling time-trial. The magnitude of difference is dependent on exercise modality, individual chronotype, the training status of the individual and sample size differences. The lack of diurnal variation present in the majority of studies can in-part be explained with some of the methodological limitations and issues present related to quality and control. It is paramount that research assessing diurnal variation in performance uses appropriate session timings around the core body temperature minimum (~05:00 h; morning) and maximum (~17:00 h; evening). Although, differences in motivation/arousal, habitual training times, chronotypes and genotypes could provide an explanation as to why some studies/variables did not display time-of-day variation, more work is needed to provide an accurate conclusion. There is a clear demand for a rigorous, standardised approach to be adopted by future investigations which control factors that specifically relate to investigations of time-of-day, such as appropriate familiarisation, counterbalancing the order of administration of tests, providing sufficient recovery time between sessions and testing within a controlled environment.