Unlike linear acceleration (measured in Gs), which tracks straight-line forces (like being hit from the front or side), rotational velocity (measured in radians per second, rad/s) captures the twisting motion of the brain inside the skull.

This rotational force is particularly significant because the brain is a soft tissue suspended in fluid; when the head rotates rapidly, different regions of the brain move at varying speeds, creating shear stresses between layers of brain tissue.

In head impacts, rotational velocity is strongly associated with the risk and severity of brain injuries, including concussion, diffuse axonal injury (DAI), and long-term degenerative diseases like Chronic Traumatic Encephalopathy (CTE).

While a single high linear impact can be dangerous, it is often the rotational component that leads to the most severe neurological disruption. For HIT users, tracking rad/s provides critical insight into
invisible but damaging forces, particularly in sports with frequent or unexpected collisions (e.g., rugby, diving, hockey).

Research suggests that concussion risk increases significantly when rotational velocities exceed approximately 30–40 rad/s, though this threshold may vary by individual and impact context (Rowson & Duma, 2013; Gennarelli et al., 1982).

By monitoring rotational data, athletes, coaches, and clinicians can make informed decisions about rest, assessment, or intervention to better safeguard brain health.