Measurement of impact acceleration: mouthpiece accelerometer versus helmet accelerometer

Abstract

Context: Instrumented helmets have been used to estimate impact acceleration imparted to the head during helmet impacts. These instrumented helmets may not accurately measure the actual amount of acceleration experienced by the head due to factors such as helmet-to-head fit.

Objective: To determine if an accelerometer attached to a mouthpiece (MP) provides a more accurate representation of headform center of gravity (HFCOG) acceleration during impact than does an accelerometer attached to a helmet fitted on the headform.

Design: Single-factor research design in which the independent variable was accelerometer position (HFCOG, helmet, MP) and the dependent variables were g and Severity Index (SI).

Setting: Independent impact research laboratory.

Intervention(s): The helmeted headform was dropped (n = 168) using a National Operating Committee on Standards for Athletic Equipment (NOCSAE) drop system from the standard heights and impact sites according to NOCSAE test standards. Peak g and SI were measured for each accelerometer position during impact.

Main outcome measures: Upon impact, the peak g and SI were recorded for each accelerometer location.

Results: Strong relationships were noted for HFCOG and MP measures, and significant differences were seen between HFCOG and helmet g measures and HFCOG and helmet SI measures. No statistically significant differences were noted between HFCOG and MP g and SI measures. Regression analyses showed a significant relationship between HFCOG and MP measures but not between HFCOG and helmet measures.

Conclusions: Upon impact, MP acceleration (g) and SI measurements were closely related to and more accurate in measuring HFCOG g and SI than helmet measurements. The MP accelerometer is a valid method for measuring head acceleration.

Figure 1. Modified National Operating Committee on Standards for Athletic Equipment (NOCSAE) headform with mouthpiece and headform center-of-gravity (HFCOG) accelerometers. The chin portion has been removed to show placement of accelerometer

Figure 2. National Operating Committee on Standards for Athletic Equipment impact test system. The helmeted headform was dropped from various heights onto the modular elastomer programmer (black pad)

Figure 3. National Operating Committee on Standards for Athletic Equipment (NOCSAE) impact testing sites and reference planes according to DOC 001-98. F indicates front; R, rear; FB, front boss; RB, rear boss, Ref. plane, reference plane. Reprinted with permission from NOCSAE, Overland Park, KS

Figure 4. Linear regressions of headform center of gravity (HFCOG) and helmet g measures, HFCOG and helmet Severity Index (SI) measures, HFCOG and mouthpiece g measures, and HFCOG and mouthpiece SI values (P < .01).