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Relationship between linear and rotational head acceleration in various activities.

James R Funk¹, Joseph M Cormier, C Edward Bain

¹Biodynamic Research Corporation, San Antonio, TX, 78249, USA.

Biomedical Sciences Instrumentation

|January 15, 2009

Summary

This study determined the effective radius of rotation for head impacts across various activities. Results show this radius varies significantly, from 84 mm in boxing to 376 mm in voluntary hand strikes, aiding head injury prediction.

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Area of Science:

Biomechanics
Injury Biomechanics
Human Kinematics

Background:

Head injury prediction commonly uses linear and rotational acceleration criteria.
Linear acceleration is often easier to measure than rotational acceleration.
Peak rotational head acceleration (a_peak) can be estimated from peak linear head acceleration (a_peak) using an effective radius of rotation (r).

Purpose of the Study:

To empirically determine the effective radius of rotation of the human head across diverse impact scenarios.
To provide statistical characterization of the effective radius of rotation values for different activities.

Main Methods:

Collected linear and angular head acceleration data from 20 human volunteers during various activities (e.g., soccer ball impact, self-shaking, drops).
Utilized existing literature data for American football, boxing, and automotive impacts.
Calculated effective radius of rotation values and statistically analyzed their distribution (median, 50%, 95% ranges).

Main Results:

Median effective radius of rotation values varied widely, from 84 mm (boxing) to 376 mm (voluntary hand strikes).
Statistical ranges (median, middle 50%, middle 95%) were determined for each activity.
The effective radius of rotation is an empirical relationship, not a precise kinematic model.

Conclusions:

The effective radius of rotation provides a simplified empirical link between linear and rotational head acceleration.
Head kinematics are complex, and the center of gravity does not rotate around a fixed point at a constant radius in most studied activities.
This empirical relationship can be a useful tool for head injury prediction models.