An Investigation of Various Measures Used in Football Helmet Evaluation

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Abstract

The purpose of this study has been to evaluate and compare certain measures used in the evaluation of football helmets. This was accomplished by relating the findings of the medical research on brain injury to the information secured from the impact test data.

Thirty-nine football helmets were impacted by a pendulum striker at four velocities (12, 15, 18, and 21 feet/sec.). The helmets, mounted on a wooden head, were struck at four positions; front, back, side, and top. Two accelerometers, one placed on the back of the pendulum and the other inside the wooden head were employed. The output from the accelerometer circuits was fed into a dual trace oscilloscope. A Polaroid camera, mounted on the face of the instrument, was used to record the acceleration-time curves for both acceleration of the head and deceleration of the pendulum striker.

The photographs were projected and plotted on graph paper. Pour measures were determined for both acceleration and deceleration: (1) peak or maximum acceleration, (2) rate of change of acceleration, (3) time duration of acceleration, and (A) kinetic energy.

The interrelationship of these four measures for acceleration of the head was determined from the plots of the six combinations or pairs of measures. The acceleration values were plotted against those for deceleration to determine to what degree they are related.

It is concluded that, the front and back positions responded similarly as did the top and side. Peak acceleration, rate of acceleration, and kinetic energy increased with an increase in impact velocity, while the fourth measure, time duration of acceleration, decreased. A positive relationship was noted for peak, rate, and kinetic energy. These three measures were negatively correlated with time duration of acceleration. These findings indicate that the measurement of peak acceleration alone is sufficient under these testing conditions. The acceleration values were directly related to those for deceleratiOn. This was especially true of time duration, peak acceleration, and rate. 0n the basis of these results, it is concluded that observing the phenomenon of deceleration of the striker at impact is unnecessary for this type of helmet testing.

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