Comparison of different methods to extract the required coefficient of friction for level walking

Abstract

The required coefficient of friction (RCOF) is an important predictor for slip incidents. Despite the wide use of the RCOF there is no standardised method for identifying the RCOF from ground reaction forces. This article presents a comparison of the outcomes from seven different methods, derived from those reported in the literature, for identifying the RCOF from the same data. While commonly used methods are based on a normal force threshold, percentage of stance phase or time from heel contact, a newly introduced hybrid method is based on a combination of normal force, time and direction of increase in coefficient of friction. Although no major differences were found with these methods in more than half the strikes, significant differences were found in a significant portion of strikes. Potential problems with some of these methods were identified and discussed and they appear to be overcome by the hybrid method.

Practitioner Summary: No standard method exists for determining the required coefficient of friction (RCOF), an important predictor for slipping. In this study, RCOF values from a single data set, using various methods fromthe literature, differed considerably for a significant portion of strikes. A hybrid method may yield improved results.

Keywords:

• required coefficient of friction
• cross method comparison
• human locomotion
• friction demand

Acknowledgments

The authors wish to thank Edmund Correa, Lauren Gwozdz, Richard Holihan, Jennie Jackson, Mary F. Lesch, Niall O'Brien, Margaret Rothwell and Peter Teare for their assistance during the course of this study.