gms | German Medical Science

Wearable devices, such as accelerometers, have become widely used tools to measure physical activity. Time series of acceleration magnitude are argued to reflect the circadian rhythm. Sleep-wake disturbances are often a prodromal feature preceding the onset of Alzheimer’s disease (AD) [1].

Different regression methods such as the function-on-scalar approach [2], functional mixed models [3] or two stage models [4] were proposed to analyze time-series from wearable devices. However, all regression methods have in common that they are only able to detect associations between covariates and activity levels but fail to identify activity patterns that could indicate a disturbed circadian rhythm.

Since time series from accelerometers are rather noisy, most regression models use a smooth of the data. We propose smoothing with wavelets [5] and compared this novel approach with different other smoothing techniques. Moreover, coefficients from wavelet transform are apt to train a neural network for pattern recognition. Wavelet coefficients are particularly suitable for pattern recognition in time series since they are localized weighted averages at various scales [5].

We demonstrate the different analysis approaches with simulated data and with real data from a study with 62 young, 66 old and 31 mildly cognitive impaired participants who wore an accelerator sensor (ActiGraph GT3X ™) for seven consecutive days. In particular, the simulation study demonstrated that neural networks are able to recognize various patterns that could indicate a disturbed sleep-wake rhythm, a possible precursor of AD.

The authors declare that they have no competing interests.

The authors declare that an ethics committee vote is not required.