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Quantitative characterization of biological age and frailty based on locomotor activity records
We performed a systematic evaluation of the relationships between locomotor activity and signatures of
frailty, morbidity, and mortality risks using physical activity records from the 2003‐2006 National Health and
Nutrition Examination Survey (NHANES) and UK BioBank (UKB). We proposed a statistical description of the
locomotor activity tracks and transformed the provided time series into vectors representing physiological
states for each participant. The Principal Component Analysis of the transformed data revealed a winding
trajectory with distinct segments corresponding to subsequent human development stages. The extended
linear phase starts from 35−40 years old and is associated with the exponential increase of mortality risks
according to the Gompertz mortality law. We characterized the distance traveled along the aging trajectory as a
natural measure of biological age and demonstrated its significant association with frailty and hazardous
lifestyles, along with the remaining lifespan and healthspan of an individual. The biological age explained most
of the variance of the log‐hazard ratio that was obtained by fitting directly to mortality and the incidence of
chronic diseases. Our findings highlight the intimate relationship between the supervised and unsupervised
signatures of the biological age and frailty, a consequence of the low intrinsic dimensionality of the aging
dynamics.