A pilot study was conducted to describe the reaction to lack of daylight and different training times of circadian rhythms and sleep in a subject arriving in Alta (Northern Norway) from Milan (Italy) in the darkness period. Monitoring sessions by heart rate (HR) monitor and actigraph were performed after four conditions: MS1, no training in Italy; MS2, no training in Alta (lack of daylight); MS3, evening training in Alta; and MS4, morning training in Alta. Midline Estimating Statistic Of Rhythm (MESOR) for activity was lower in MS2 than in MS1, MS3 and MS4, and decreased progressively for HR. Acrophases were advanced in MS2 and MS4 compared to MS1 and MS3 for both activity and HR. Sleep Efficiency was higher in MS2, MS3 and MS4 compared to MS1, coinciding with low values in the Mean Activity Score and Movement and Fragmentation Index. It could be seen that lack of daylight induced a decrease of the activity state in the subject, advancing the acrophase and leading to increased sleep.After the exercise sessions the activity state of the subject increased and the circadian structure was influenced according to the time at which the training was performed.

The potency of exercise as a nonphotic time cue compared to the solar cycle in influencing entrainment (organism synchronization within the 24-h period) has yet to be defined. Above the Arctic Circle during winter the sun remains below the horizon for several weeks and during summer remains above the horizon for several weeks. The goal of the present study was to investigate the effects related to exercising time on the circadian structure under conditions of lack of daylight and continuous daylight. The experiments were carried out at 70° North, above the Arctic Circle. Ten healthy females (age 24±5 years) were divided into two groups: an exercise and a control group. The subjects in the exercise group performed the same exercise routine at two different times of day (0900 and 1800 hours) both in January (twilight period) and in May (continuous daylight period). Continuous heart rate data were collected and analysed by the cosinor method. The acrophase values were significantly modified in the exercise group during evening exercise in January showing a delay compared with morning exercise and compared with the control group (3 h and 1.5 h, respectively), while in May this effect was not seen. The results indicate that in continuous daylight, the potency of exercise in modulating the circadian phase seems to be suppressed. However, these findings need to be verified in a larger poulation.