Factors to consider when assessing diurnal variation in sports performance: the influence of chronotype and habitual training time-of-day.

PURPOSE: The aim of this study was to compare morning and evening time-trial performance, RPE and mood state of trained swimmers, taking into account chronotype, habitual training time-of-day and PERIOD3 (PER3) variable number tandem repeat genotype. METHODS: Twenty-six swimmers (18 males, age: 32.6 ± 5.7 years) swam 200 m time trials (TT) at 06h30 and 18h30 in a randomised order. RESULTS: There was no difference between morning and evening performance when the swimmers were considered as a single group (06h30: 158.8 ± 22.7 s, 18h30: 158.5 ± 22.0 s, p = 0.611). However, grouping swimmers by chronotype and habitual training time-of-day allowed us to detect significant diurnal variation in performance, such that morning-type swimmers and those who habitually train in the morning were faster in the 06h30 TT (p = 0.036 and p = 0.011, respectively). This was accompanied by lower ratings of perceived exertion (RPE) scores post-warm-up, higher vigour and lower fatigues scores prior to the 06h30 TT in morning-type swimmers or those who trained in the morning. Similarly, neither types and those who trained in the evenings had lower fatigue and higher vigour prior to the 18h30 TT. CONCLUSIONS: It appears that both chronotype and habitual training time-of-day need to be considered when assessing diurnal variation in performance. From a practical point of view, athletes and coaches should be aware of the potentially powerful effect of training time on shifting time-of-day variation in performance.

Chronotype and PERIOD3 variable number tandem repeat polymorphism in individual sports athletes.

A link between diurnal preference and a variable number tandem-repeat (VNTR) polymorphism in the PERIOD3 gene (PER3) has been demonstrated: the longer PER3(5) and shorter PER3(4) alleles with preferences for mornings and evenings, respectively. As many competitive events in South Africa for individual athletes are scheduled for the early mornings, we hypothesized that this might favor those athletes with a preference for morning activities. Self-selected white, male cyclists (CYC, n = 125), runners (RUN, n = 120) and Ironman triathletes (IM, n = 287) of European descent were compared with a control population of active, non-competitive individuals (CON, n = 96). The chronotypes of all CYC, RUN and CON participants and a sub-sample of the IM group (n = 49) were assessed using the Horne-Östberg Morningness-Eveningness Questionnaire, and the PER3 VNTR genotype for each participant was determined. The athlete groups contained more morning-type individuals than the CON group (CYC: 72%, n = 90; RUN: 67%, n = 80; IM: 59%, n = 29; CON: 41%, n = 39; p < .001). The prevalence of the PER3(5) allele was greater in the athlete groups (CYC: 61%, n = 152; RUN: 58%, n = 132; IM: 56%, n = 324; CON: 38%, n = 76; p < .001), and more athletes were genotyped as PER3(5/5) than CON individuals (CYC: 41%, n = 51; RUN: 23%, n = 26; IM: 28%, n = 81, CON: 9%, n = 8; p < .001). A strong relationship between chronotype and PER3 VNTR genotype was observed (p < .001). Finally, the time of day at which the athletes preferred to train was related to their chronotype (p < .001). This is the first study of its kind in a South African sporting population, and the results have not yet been replicated. These data suggest that white males of European descent participating in individual endurance sports in South Africa are more likely to be morning types. Furthermore, the PER3 VNTR may be one of the factors contributing to this observation.