Both the magnitude and the duration of the acceleration are critical to determining the severity of a TBI . For instance, the brain can sustain high accelerations without injury but only for a very short period. Conversely, relatively low accelerations over long periods can cause severe damage. Thus, the head impact criteria (HIC) is often used to measure the likelihood of head injury arising from an impact. To quantify the difference in impact response among various protection structures, we introduce the modified head impact criteria (mHIC), a dimensionless parameter that incorporates both the magnitude and duration of the acceleration :