1st Joint ESMAC-GCMAS Meeting - Análise de Marcha

O-49
THE INFLUENCE OF FOOTWEAR SOLE HARDNESS ON THE PROBABILITY OF
SLIP-INDUCED FALLS IN YOUNG ADULTS
Tsai, Yi-Ju, M.S., P.T., Powers, Christopher, Ph.D., P.T.
Musculoskeletal Biomechanics Research Laboratory
Department of Biokinesiology and Physical Therapy, University of Southern California,
Los Angeles, CA, USA
Summary/conclusions
The results of this study demonstrate that the probability of a slip-induced fall was not
influenced by footwear sole hardness. These findings do not support the premise that persons
wearing harder soled shoes are at greater risk for a fall once a slip is initiated. It is likely that
recovery from a slip event is more related to one’s ability to generate an effective response
strategy rather than shoe sole hardness.
Introduction
Slips have been recognized as a significant cause of falls and are one of the most common
causes of occupational accidents [1]. Several biomechanical factors have been shown to be
associated with slip-induced fall events including slip distance and foot velocity during the slip
event [2-4]. Once a slip is initiated, prevention of a potentially injurious fall depends on the
available friction of shoe/floor interface (i.e., dynamic friction) and the ability of an individual
to generate a recovery response [5]. With respect to shoes, harder soled shoes have been shown
to provide less dynamic friction than softer soled shoes based on mechanical testing [6]. This
would imply that persons wearing harder soled shoes could be at greater risk for falling once a
slip has been initiated. Theoretically, a shoe that provides less dynamic friction could result in
a greater slip distance and foot velocity, thereby limiting the ability of an individual to generate
an effective recovery response. The purpose of this study was to investigate the effects of
footwear sole hardness on the probability of slip-induced falls in young adults. It was
hypothesized that persons who wear harder soled shoes would demonstrate greater slip
distances, slip velocities, and a higher proportion of fall events compared to those who wear
softer soled shoes.
Statement of clinical significance
Information provided by this study is important in contributing to our understanding of the
factors that may influence slip and fall events and for the design of footwear aimed at reducing
slip and fall related injuries.
Methods
Forty healthy young adults between the ages of 22 and 36 years participated in this study. Each
was randomized into one of two shoe groups: soft sole hardness (N = 20) and hard sole
hardness (N = 20). Two sets of commercially available Oxford style dress shoes (Bates
Footwear Inc., Rockford, MI) that differed only in outsole hardness were used in this study.
The material and appearance of the uppers of two pairs were identical, and the outsole of each
pair was made from Styrene Butadiene Rubber (SBR). One set of shoes had a sole hardness of
Shore 75A and was used for the soft shoe group testing, while the other set of shoes had a sole
hardness of Shore 54D and was used for the hard shoe group testing. All subjects ambulated at
a self-selected fast walking speed across a slippery floor surface consisting of a Teflon panel
combined with a soapy water contaminate. The SATRA physical test method (SATRA
PM144) revealed that the dynamic frictions for the hard and soft soled shoes on a Teflon
surface with soapy water contaminate were 0.09 and 0.16 respectively. A fall arresting harness
was used for all walking trials. Slip and fall events were documented using a VICON motion
analysis system (120 Hz). In addition, a load cell (Omega Engineering Inc. Stamford, CT)
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