Variability in physical activity assessed with accelerometer is associated with the disease in elderly with Parkinson´s disease

The aim if this study was to explore the relationship between various aspects of physical activity (PA) and physical function, depression, Quality of Life and disease in elderly with Parkinson´s disease (PD). Participants wore an Actigraph GT3x+ accelerometer for one week. PA outcomes were total counts, time spent in various intensities and measures of variability. The analysis focused on episodes with high recorded activity, which was identified by calculating a rolling mean. From these measures of variability were calculated: skewness, kurtosis and interquartile range (IQR). Disease related outcomes were measured using the Unified Parkinson Disease Rating Scale (UPDRS)-motor and ADL-part. Physical function was measured by means of step length, velocity and cadence and by balance performance (Mini-BESTest). Depressive symptoms were assessed using the Geriatric Depression Scale (GDS) and Health related quality of life using SF-36. Principal components analysis (PCA) of PA variables and clinical variables were performed on 89 elderly with mild-moderate PD. The PCA revealed a high degree of covariance, with >60% of the total variance explained by the first two principal components. The PA variables formed three distinct clusters of highly correlated variables, one with skewness, kurtosis and sedentary time, one with various measures of intensity along with high intensity time named as peak activity and a third with measures of total PA. When the clinical variables were superimposed on the PCA of the accelerometer-derived variables disease related outcomes and symptoms of depression covaried with the accelerometer-derived measures of variability (skewness and kurtosis). In contrast, measures of physical function co-varied with accelerometer-derived variables representing aspects of peak activity. This study showed that novel features of variability of PA derived from accelerometer data were associated with disease related outcomes in elderly with mild-moderate PD.