Abstract: An apparatus has a housing adapted for mechanical coupling with a skull of a human. A first sensor is positioned in the housing to collect linear motion signals. A second sensor is positioned in the housing to collect rotational motion signals. A processor is positioned in the housing connected to the first sensor and the second sensor. The processor is configured to process the linear motion signals and the rotational motion signals to derive a cumulative impact power measure of repetitive sub-concussive head impacts. The cumulative impact power measure is compared to a threshold indicative of the onset of neural tissue deformations corresponding to physiological changes from repetitive sub-concussive head impacts. An alert is supplied when the cumulative impact power measure is proximate the threshold.