The effect of transverse shear force on the required coefficient of friction for level walking.

Objective: An enhanced methodology to extract the required coefficient of friction (RCOF) value was used to investigate the effects of the transverse shear component of the ground reaction force (GRF) on the RCOF.

Background: The RCOF is an important indicator for slip incidents. However,the extraction of the RCOF from GRF is not standardized. The transverse shear force is usually ignored in calculating the RCOF value.

Method: For this study, 40 participants performed four walking conditions. The RCOF values both with (RCOF2) and without (RCOF1) the transverse shear force were identified from each strike by the use of an enhanced method and were compared.

Results: A total of 24,851 strikes were collected. The transverse component increased the RCOF value by more than 10% in 7.2% of the strikes. In 10.4% of the strikes, the RCOF2 occurred at least 20 ms earlier and the RCOF value was on average 8.9% larger than RCOF1.

Conclusion: With this method, we were able to successfully identify the RCOF in a significantly large number of strikes across 40 participants. In a portion of the strikes, the transverse shear force increased the RCOF significantly. In a significant portion of the strikes, the RCOF2 occurred much earlier than RCOF1.

Application: Better estimates of the RCOF magnitude and instant of occurrence could potentially improve risk assessment and identification of critical instants in gait.