1. A computer-readable non-transitory medium comprising computer-readable code physically embodied thereon which, when executed by a processor, causes the processor to perform a method comprising: receiving inertial sensor data directly from one or more inertial sensors attached to a person's shank that performs a quantitative timed-up-and-go (QTUG) test, the inertial sensor data being measured by the one or more inertial sensors and including shank angular velocity data comprising measured gait parameters related to the person sitting, walking, and turning; receiving, at a time subsequent to receiving the inertial sensor data from the QTUG test, additional inertial sensor data indicative of cognitive function of the person directly from the one or more inertial sensors, including shank angular velocity data comprising gait parameters related to the person sitting, walking, and turning measured during a subsequent QTUG test; determining an indication of cognitive decline in the person based on a difference between the inertial sensor data indicative of cognitive function and the received additional inertial sensor data including a difference between the gait parameters; generating a classifier function that associates the received inertial sensor data with the determined indication of cognitive decline in the person as a prediction for cognitive decline in other persons; after generation of the classifier function, collecting inertial sensor data directly from the one or more inertial sensors from another person that performs the QTUG test; using the generated classifier function, associating the collected inertial sensor data from the QTUG test from the another person to an indication of cognitive decline in the another person; and providing, using the association from the generated classifier function, to a user a prediction of whether the another person will experience cognitive decline based on the inertial sensor data collected from the another person, wherein the prediction provided to the user comprises a classification of the another person as either having cognitive decline or being cognitively intact.