Hierarchical organization of human physical activity.

Human physical activity (HPA), a fundamental physiological signal characteristic of bodily motion is of rapidly growing interest in multidisciplinary research. Here we report the existence of hitherto unidentified hierarchical levels in the temporal organization of HPA on the ultradian scale: on the minute's scale, passive periods are followed by activity bursts of similar intensity ('quanta') that are organized into superstructures on the hours- and on the daily scale. The time course of HPA can be considered a stochastic, quasi-binary process, where quanta, assigned to task-oriented actions are organized into work packages on higher levels of hierarchy. In order to grasp the essence of this complex dynamic behaviour, we established a stochastic mathematical model which could reproduce the main statistical features of real activity time series. The results are expected to provide important data for developing novel behavioural models and advancing the diagnostics of neurological or psychiatric diseases.

Phase-synchronization of daily motor activities can reveal differential circadian patterns.

The aim of the study was to determine any alteration of the 24 h motor activity pattern of a bipolar patient in different mood states. Actigraphic records were collected on an outpatient basis for a total of 387 days. The daily actograms were synchronized in phase to the time of morning awakening before averaging, which significantly enhanced the structure of the averaged traces. The actograms were divided into three groups based on total daily count. The daily motor activity patterns of the low- and high-activity days have a different circadian pattern. We propose it may have a relevance to the different mood states. The phase-synchronization of the 24h actograms to the patient's sleep-wake cycle, specifically to the time of awaking from the nighttime sleep, may help reveal differences in the daily temporal patterns of motor activity.