Morning-type vs. Evening-type: Scheduled race start time may influence participation and performance in South African and Dutch marathons
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Each person has a built-in biological clock that guides us in being active, perform specific tasks and sleep at specific times of day, known as our circadian clock. However, each individual’s circadian clock does not run synchronously with that of others. As a result, each individual prefers to be active, perform specific tasks and sleep at slightly different times, according to his or her circadian clock. This characteristic is what we call a person’s chronotype: morning-types (or early birds), evening-types (or night owls) and everything in between.
A study in 2012 found that South African runners, cyclists and Ironman triathletes were more likely to be morning-type compared to South Africans that do not participate in competitive sports but who do go to the gym to exercise. The South African athletes from that study were also more likely to be morning-type than most other populations around the world. We could think of three explanations for this: 1) because the athletes are more physically active than the gym-goers; 2) because South Africa has a warmer climate than the countries from the other populations around the world; 3) because of the early endurance race start times (approximately 6 a.m.) in South Africa. We set out to explore which of these explanations may be true by comparing males who run marathons to males who train in the gym for fitness but do not run, from South Africa (warm climate and early race start times) and the Netherlands (less warm climate and later race start times). All participants completed a questionnaire that captures demographics, training times, race times and chronotype.
First, we found that the marathon runners from both countries were more morning-orientated than the gym-goers from their respective country. This suggests that being more physically active may indeed contribute to a morning-type personality (explanation 1). Second, we found that the ratio of morning-types to evening-types in the South African and Dutch gym-goers groups was not different. Therefore it seems unlikely that the warm South African climate is an explanation for South Africans to be morning-types (explanation 2). Thirdly, we found that more South African marathon runners were morning-types compared to Dutch marathon runners. We suggest that the early marathon race start time in South Africa may indeed explain this observation – attracting morning types and discouraging evening-types from participating (explanation 3). The following image display the proportion of morning-types, neither-types and evening-types among each of the four groups.
As in interesting aside, we also found that early chronotypes among the South African marathon runners generally performed better than later chronotypes did. The following image shows that the early chronotypes (on the right-hand side) have a better marathon performance (bottom of graph) among the South African Runners (yellow spots). On the other hand, the early chronotypes did not perform better than the late chronotypes among the Dutch runners (blue spots).
The take home messages are: 1) being more physically active may make people feel more like morning-types; or morning-types may choose to be more active; 2) Scheduling events at extreme times of the day may either encourage or discourage participation by individuals with strong preferences for either morning or evening activity.
Rob Henst (MSc) (UCT’s Division of Exercise Science and Sports Medicine)
Dr. Dale Rae (UCT’s Division of Exercise Science and Sports Medicine)
Dr. Laura Roden (UCT’s department of Molecular and Cell Biology)
Dr. Richard Jaspers (MOVE Research Institute, VU University, Amsterdam)
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