The role of chronotype in the participation and performance of South African and Dutch marathon runners

Includes bibliographical references.Introduction: Our circadian rhythms are internal biological rhythms of approximately (circa) 24 - hours (dies) allowing us to synchronize our internal biological “clock” with external time cues. Many innate biological functions are dependent on time-of-day, such as secreting adrenaline and cortisol in the mornings and melatonin in the evenings. The time-of-day at which these and other physiological functions are active, change or reach a certain level may influence a person’s diurnal preference, i.e. preference for mornings (morning-types) or evenings (evening-types), and is referred to as ‘chronotype’. Many different factors may affect a person’s chronotype, including age, sex, physical activity, ethnicity and geographical location. Certain clock-related genotypes have also been shown to be associated with chronotype. For example, some studies have found that the 5-repeat allele of the PER3 variable number tandem repeat (VNTR) polymorphism (PER35) is associated with a preference for mornings. Recent research has shown a high prevalence of morning-types and PER35VNTR allele carriers in trained South African runners, cyclists and triathletes. It was proposed that the early morning start-times of these endurance events might select people with a preference for mornings, since morning-types may cope better with rising early and being physically active in the early morning. Alternatively, the habitual early waking for training or endurance events may have conditioned the athletes to adapt to become morning-types. However, the geographical location of South Africa (i.e. climate and day length) and the fact that each group was physically active may also have contributed to this finding. Comparison of South African and Dutch runners would allow us to explore the effects of race start time and geography on this observation, since marathons in The Netherlands on average start at 11:41, and since the two countries differ significantly in latitude and as such have noticeable differences in daylight exposure. Aims: The aims of this study were 1) to compare the PER3VNTR genotype and chronotype distribution of South African and Dutch recreational marathon runners and active but non-competitive controls; 2) to investigate the relationship between the PER3VNTR genotype and chronotype in both the Dutch and South African samples; and 3) to determine whether marathon race time is associated with chronotype and PER3VNTR genotype in Dutch and South African marathon Methods: Ninety-five trained South African male marathon runners, 97 South African male active but non-competitive controls, 90 trained Dutch male marathon runners and 98 Dutch male active but non-competitive controls completed a questionnaire capturing demographics, training and race history, including personal best and most recent full and half-marathon race time (if applicable) and the Horne-Östberg morningness-eveningness personality questionnaire (HÖ-MEQ, a tool to assess a person’s chronotype). Each participant provided a buccal cell swab from with total genomic DNA was extracted to determine his PER3VNTR polymorphism genotype. The official race time from each runner who completed the designated marathons in South Africa or the Netherlands was collected from the event websites. Results: The South African and Dutch runners were more morning-orientated than their respective control groups and the South African runners were more morning-orientated than the Dutch runners. The PER3 VNTR polymorphism distribution was similar between the four groups and was not associated with chronotype. The marathon performance of the morning-type South African runners was better than the evening-types, and a higher HÖ-MEQ score (morningness) correlated with better personal best and most recent half-marathon race time. Similar observations were not found in the Dutch runners. Discussion: Since a higher prevalence of morning-types in South African marathon runners compared to Dutch marathon runners was found, it is proposed that the early marathon start-times in South Africa may favour morning-types, who are able to cope with those early morning start times. Alternatively, one could argue that through repetitive early-morning racing (i.e. participating in competitive running events), the chronotype of South African runners may be conditioned to that of a morning-type over time. It is proposed that this ability to cope with early morning marathon start times may lead to better marathon performances for morning-types than neither-types and evening-types in the South African running group. This effect does not occur in the Netherlands, where marathons start later in the morning and do thus not favour a certain chronotype. The difference in daylight exposure between the two countries as a function of latitude does not seem to affect chronotype, since the active but non-competitive control groups did not differ significantly between South Africa and the Netherlands. Unlike the findings from a previous study, the PER35allele was not more prevalent among the South African runners, but rather the distribution wasi n line with what has been described in most, but not all, other populations. No association between the PER35VNTR xpolymorphism and chronotype was found in any of the four groups. Since the four groups investigated in this study comprised physically active individuals, it is proposed that this lack of association may be due to the habituation effects of physical activity and early morning start times of marathon events(for only the South African runners). Conceivably,this habituation may even shift the diurnal preference of those with the PER34/5 and PER34/4VNTR genotypes towards morningness, disassociating any relationship between chronotype and the PER3VNTR genotype. Conclusion: The early morning start time of South African marathon events may favour morning-types, due to their ability to cope with being physically active in the early morning. We propose that the PER3VNTR genotype cannot solely explain the higher prevalence of morning-types in the South African runners in this study, however, it is very likely that the PER3VNTR genotype does play an important role in the chronotype distributions found in the study of Kunorozva et al.(2012). Since the PER3VNTR genotype was not associated with chronotype in any of the four groups, it is proposed that habituation to early-morning marathon racing may be the causal effect of the high number of morning-types in the South African runners group, and the apparent disassociation between chronotype and the PER3VNTR genotype. We also propose that the habituation effect of physical activity and training time-of-day on chronotype in the other groups may dissociate the PER3VNTR genotype with chronotype in a similar manner to which the early-morning start times of South African endurance events dissociates the two. No effect of geographical location on chronotype was found when comparing the Dutch and the South African groups. The morning-orientated South African runners seem to perform better in marathon running than the more evening-orientated runners do, which may be caused by their ability to cope with these early-morning marathon events. Further studies may explore whether marathon performance in later chronotypes can be improved by training-based habituation

A sleep behaviour intervention to improve cardiometabolic health in adults with overweight and obesity

Rob Henricus Petrus Henst was born on the 12th of March in Schaijk, the Netherlands. He graduated from pre-vocational secondary education (VMBO) in 2005 and continued to study process and laboratory technology at an intermediate vocational educational (MBO) institution. In 2009, Rob started with a Bachelor of Science degree, majoring in Life Science with a minor in Exercise Science. For his undergraduate thesis in 2012, he moved to South Africa where he was introduced to chronobiology in exercise science. In 2013, Rob continued to study in South Africa for his Master of Science (Exercise Science) degree and published his first peer-reviewed article in the Journal of Biological Rhythms. He then developed an interest in sleep and cardiometabolic health, specifically in the context of public health. In 2015, these interests were combined and lead to his current PhD thesis on a sleep behaviour intervention for the betterment of cardiometabolic health. In this year, he also co-founded the business unit Sleep Science within the Sports Science Institute of South Africa to help individuals sleep better. In 2019, Rob moved back to the Netherlands to write the final pages of his PhD thesis

Testing the cognitive and the communicative principles of relevance

The article reviews experiments that test consequences of the most central tenets of the theory, namely the cognitive and the communicative principle of relevance

Testing the cognitive and communicative principles of relevance

Outlines basic tenets of relevance theories and presents various experiments providing evidence about these tenet

Delayed cytokinesis generates multinuclearity and potential advantages in the amoeba Acanthamoeba castellanii Neff strain

info:eu-repo/semantics/publishe

Assessing the validity and reliability and determining cut-points of the Actiwatch 2 in measuring physical activity

Objective: The Actiwatch 2 (AW2) is a wrist-worn accelerometer typically used to measure sleep. Although it can measure physical activity, there is limited evidence supporting its validity. We assessed the validity and reliability of the AW2 to measure sedentary behavior and physical activity (light, moderate, vigorous intensities), and reported their respective count cut-points. Approach: Twenty-eight males and 22 females completed a task battery comprising three sedentary tasks and six randomized physical activity tasks at varying intensities, whilst wearing the AW2, a reference accelerometry device (Actigraph GT3X) and a cardiopulmonary gas analyzer on two separate occasions. Validity was assessed using correlations (AW2 counts versus GT3X counts and metabolic equivalent (MET) values), reliability using Bland–Altman analyses, and cut-points were determined using receiver operating characteristic (ROC) area under the curve (AUC) analyses. Main results: AW2 counts were positively correlated with GT3X counts (rho = 0.902, p < 0.001) and METs (rho = 0.900, p < 0.001). AW2-derived counts were comparable across independent assessment periods. Sedentary (AUC = 0.99, cut-point: 256 cpm) and vigorous activity (AUC = 0.95, cut-point: 720 cpm) were strongly characterized, and moderate activity (AUC = 0.66, cut-point: 418 cpm) was weakly characterized. Significance: The use of the AW2 in physical activity monitoring looks promising for sedentary behavior, moderate and vigorous activity, however, further validation is needed