The effects of circadian rhythmicity and time-awake on a simple motor task

The aim of the study was to assess if a simple motor task, one that required muscle contractions well below maximum, showed evidence of circadian changes and time-awake. The task consisted of using a larger counter to flick a number of smaller counters to land as near as possible to the center of a target. The closer a counter landed next to the center of the target, the higher the score obtained. Two distances from the target were used (long and short), and 20 counters were flicked at each distance. The task was performed by 72 diurnally active healthy participants at six test sessions distributed every 4 h throughout the day (08:00 h, 12:00 h, ... , 04:00 h), so covering a circadian cycle. When performing the sessions, subjects had been awake for about 1, 4, ... , 20 h. Before each test session, sublingual temperature was measured, and estimates of the individual's fatigue and alertness were made. Clear normally phased circadian rhythms (p<0.0001) in oral temperature and alertness with mean peak time (i.e., acrophases of 17.2 h and 15.9 h, respectively) and fatigue (i.e., mean acrophase of 3.4 h) were detected. The total scores for both the long and short distances also showed circadian rhythms that peaked slightly before the temperature rhythm (by 2.31+/-0.91 h and 1.77+/-0.77 h, mean+/-SE, respectively), and the number of occasions that the target was missed altogether showed rhythms that were in anti-phase (mean acrophases=3.8 h and 4.1 h for the long and short distances, respectively) to that of total scores (mean acrophases=16.0 h and 15.2 h for the long and short distances, respectively). With the long and, particularly, short distances, there were generally significant correlations (r<0.0005) between both the measures of accuracy (total score and number of misses) and body temperature and time-awake. The accuracy of performance at this task seems to show circadian and time-awake effects, and so makes it of potential value in protocols where repetitive measurements during the course of a day are required.