The two main aims of the study were to compare the dominant and non-dominant hand with regard to circadian rhythms of accuracy of performance at a task that required eye-hand coordination and sub-maximum muscle contraction, as well as to investigate if there were differences between the dominant and non-dominant hands in the associations between circadian rhythms of performance and core temperature and time awake. The task consisted of using a larger counter to flick a set of 20 smaller counters to land as near as possible to the center of a target. The nearer to the center of the target a counter landed, the higher the score awarded. Three measures of accuracy were calculated: the total score, the number of times the counter missed the target altogether, and the mean score for those counters that hit the target. Seventy-eight healthy participants performed the task at each of six test sessions distributed every 4 h throughout the day (at 08:00, 12:00... . 04:00 h), the participants then having been awake for about 1, 4... . 20 h, respectively. Before each test session, sub-lingual temperature (an estimate of core temperature) was measured, and estimates of the individual's alertness and fatigue were obtained. Temperature, alertness, and fatigue all showed circadian rhythms that were phased conventionally. Measures of accuracy of performance also showed significant circadian rhythms that were phased closer to the rhythms of alertness and fatigue than to that of oral temperature. In addition, and in support of our previous work, there were significant associations between performance and temperature (positive) and time awake (negative) for most measures of accuracy. Even though circadian rhythms of performance accuracy and effects of oral temperature and time awake were generally very similar between the dominant and non-dominant hand, there was a suggestion that time awake affected some aspects of performance of the non-dominant hand to a greater extent. There was little evidence to support the view that the 24-h rhythmicity was less marked in the non-dominant hand, which argues against internal desynchronization, at least for the task used in this study.
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