The friction plays an important role in human motion, either in gait and running. The characterization of Coefficient of Friction (COF) through the recognition of a pattern can held an essential
background to motion analysis of the athletes perfomance. The aim os this study was to obteined a preliminary analisys of coefficient of friction patterns in gait and running. Therefore, this analisys
focus on required coefficient of friction (RCOF) that is typically characterized by one or two peaks. Mainly, the first peak occurs at the end of the loading phase (after 5% of stance) as full body
weight is transferred to the supporting foot, while the second peak occurs later in stance (after 90% of stance) just prior to the beginning of the toe-off phase.
The Research Ethics Committee of the University of Campinas approved this study (No. 1.552.726). The participants were: 10 adults (20-35 years), both genders, without osteoarticular disease or
injuries that have left consequences for any movement. Participants performed 3 , valid trials on the force plates of both motions using footwear at self-selected speed. To acquire the data a Ground
Reaction Force (Kistler Mod. 9286) and the acquisition was performed using BioWare software (Version 4.0.x). Kinetic raw data were filtered using a 2nd order low-pass digital Butterworth filter with a
cut-off frequency of 10 Hz. Afterwards was held a cut for interest phase (stance), Fz > 20 N, based on the literature. Finally, it was necessary to transform Fx, Fy, Fz and |COFxy| cycle percentage
from the stance phase for analysis. The |COFxy| is calculated by dividing the horizontal components of the GRF, by the vertical component at the same instant. One or two peaks of the local maximum
values in the |COFxy| during the stance-phase are identified as the RCOF. The way that runners landed the foot on the ground affects the contact angle, thus directly influences the RCOF1. This is
followed by peak 2 under which the foot has a tendency to push backward. according to Blanchette et al. (2011).
The preliminary results were presented as mean and standard deviation of the follow variables: the |COFxy| magnitude at RCOF1 and RCOF2, and, their percentage occurrence in the stance-phase at RCOF1
and RCOF2, considering running and gait conditions. In the gait, RCOF1 and RCOF2 could be determined in all participants. For RCOF1 showed a mean of 0.18 (±0.03) occurring in 17.80% (±1.99%) of
stance-phase. In case of the RCOF2 showed a mean of 0.38 (±0.12), occurring in 97.2% (±2.7%). The running results for the 10 participants were: mean of RCOF1 was 0.21 (±0.14) occurring in 20.59%
(±13.5%), and, the RCOF2 was 0.57 (±0.29) occurring in 97.3% (±28.6%).
The pattern expected with RCOF1 and RCOF2 in the gait was not found for whole data, some of participants did not presented one of those peaks. However, these moments of RCOF were more frequent in gait
than running, furthermore, RCOF2 seems not appear in running for this preliminary data. In spite of this, the variability showed to be lower, either in |COFxy| as in occurrence percentage at stance