Traction performance across the life of slip-resistant footwear

Slips, trips, and falls are a major cause of injury in the workplace.
Footwear is an important factor in preventing slips. Furthermore, traction
performance (friction and under-shoe fluid drainage) are believed to
change throughout the life of footwear. However, a paucity of data is
available for how traction performance changes for naturally worn,
slip-resistant footwear. Participants wore slip-resistant
footwear while their distance walked was monitored. Friction and
under-shoe fluid pressures were measured using a robotic slip tester under
a diluted glycerol contaminant condition after each month of wear for the
left and right shoes. The wear volume and the size of the worn region was
also measured. Prior to wearing shoes at work, participants completed dry
walking trials during which ground reaction forces were recorded across
different types of shoes. The peak normal force, shear force, and required
coefficient of friction (RCOF) were calculated. Friction
initially increased and then steadily decreased as the distance walked and
the size of the worn region increased. Fluid pressures increased as the
shoes were worn and were associated with increased walking distance and
size of the worn region. Consistent with previous research, increases in
the size of the worn region are associated with increased under-shoe fluid
pressures and decreased traction. These trends are presumably due to
reduced fluid drainage between the shoe-floor interface when the shoe
becomes worn. Wear rate was positively associated with peak RCOF
and with peak shear force, but was not significantly related to peak
normal forces. Traction performance changes with natural wear. The
distance walked in the shoe and the size of the worn region may be
valuable indicators for assessing loss of traction
performance. Current shoe replacement recommendations for
slip-resistant shoes are based upon age and tread depth. This study
suggests that tools measuring the size of the worn region and/or distance
traveled in the shoes are appropriate alternatives for tracking traction
performance loss due to shoe wear. The finding that shear forces
and particularly the peak RCOF are related to wear suggests that a
person’s gait characteristics can influence wear. Therefore, individual
gait kinetics may be used to predict wear rate based on the fatigue
failure shoe wear mechanism.