The Pattern of Physical Activity in Children

Complexity in the assessment of the dimensional pattern of physical activity has limited the understanding of short duration activity in children. Although many acknowledge that children's movement is sporadic and of short duration, this contention has been based on one observational study. Accelerometers provide multi-axial movement in both the laboratory and field settings. This thesis aims to characterize children's physical activity patterns using traxial accelerometry (the Research Track 3 or RT3). Six studies were conducted to develop a technique for assessing dimensions of the tempo of physical activity in children, and to uncover the physiological importance of activity of this nature. Following extensive calibration of the accelerometer device, a novel analytical program was written which provided detailed characteristics of the tempo of physical activity. Calibration of the RT3 provided thresholds for sedentary (< 5.2 RT3vmag .s-1 ) low-to-moderate (≥5.2 RT3vmag .s-1 to 60.0 RT3vmag .s -1 ) and vigorous activity (> 60.0 RT3vmag .s-1 ). The data processing programme utilized cluster recognition algorithms, showing children experience many clusters per hour, which are of short duration and are on average of low-to-moderate frequency. These tempo characteristics were found to differ markedly between the weekday and weekend. We found weekday physical activity pattern characteristics was related to cardiorespiratory fitness and dynamic exercise responses, whilst biomechanical efficiency was weakly related physical activity bouts. Markers of cardiovascular risk and obesity, namely high sensitive R-reactive protein (hsCRP), adiponectin and insulin resistance (IR) were investigated in relation to physical activity tempo characteristics. Dimension of short duration physical activity in children were inversely associated with hsCRP and IR (both p < 0.05). No significant relationship was found between adiponectin and physical activity (p > 0.05). In conclusion, the majority of an average day for a Hong Kong Chinese child is spent sedentary. The activity they engage in is of short duration and largely low-to-moderate intensity. Occasional spurts of high intensity are experienced. The variation of these short-duration bouts appeared to be important for fatness, cardiovascular and metabolic health. The mechanism underlying these relationships deserves further exploration.

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