Background: . Mental practice through motor imagery improves subsequent motor performance and thus mental training is considered to be a potential tool in neuromotor rehabilitation.
Objective: . The authors investigated whether a circadian fluctuation of the motor imagery process occurs, which could be relevant in scheduling mental training in rehabilitation programs.
Methods: . The executed and imagined durations of walking and writing movements were recorded every 3 hours from 8 AM to 11 PM in healthy participants. The authors made a cosinor analysis on the temporal features of these movements to detect circadian rhythms. Temporal differences between executed and imagined movements as well as their variability during the day were also quantified.
Results: . Circadian rhythms were detected for both the executed and the imagined movements. Furthermore, these rhythms covaried between them and with body temperature. The participants' ability to internally simulate their movements also fluctuated significantly during the day. The isochrony between the executed and the imagined movements was exclusively observed between 2 PM and 8 PM. In the morning (8 AM and 11 AM) and the evening (11 PM), the durations of the imagined movements were significantly longer than the durations of executed movements.
Conclusions: . Predictive internal models fluctuate in a circadian basis, as do many other physiological parameters. It could be important to take into consideration the time of day in the planning of rehabilitation programs using physical or mental training.