A BIOMECHANICAL MODEL OF THE SPACING AND WIDTHEFFECTS OF ANTI-SLIP STRIPS
Hanatsu Nagano1, W.A. Sparrow1, Richard Bowman2, and Rezaul Begg1
1

Victoria University, Institute of Sport, Exercise and Active Living, Melbourne, Australia
2
Intertile Research Pty Ltd, Brighton East VIC 3187

The current research tested an ‘anti-slip’ strip product at two spacings (20cm and26cm) on a very low friction, vegetable oil-contaminated surface (CoF = 0.070.10). Kinematic data were collected from 80 walking trials using an Optotrak 3Dmotion capture system to sample shoe-mounted infra-red light emitting diodes(IREDS) at 100Hz. No slipping was observed when the foot directly landed on thestrip, accounting for 43% of trials at 20cm-spacing and 28% at 26cm-spacing.
While maximum potential slipping distance could be hypothesised to equal thestrip spacing, results indicated maximum slipping distances up to foot contact withthe strip of only 1.71cm and 3.15cm for 20cm- and 26cm-spacing, respectively.
Following strip contact the foot travelled a further 4.2cm (20cm-spacing) and
5.25cm (26cm-spacing) until it decelerated. In summary, 20cm spacing was
superior to 26cm spacing in minimising the frequency and severity of slipping.

Introduction
Minimization of slip-related injuries is an important consideration in both occupational andresidential settings, as 20% of cases lead to absence from work for more than one month (Chiouet al., 2003; Leclercq, 1999; Yoon and Lockhart, 2006). For the older population (over 65 years)
slipping is a major contributor to hip fracture, with negative effects on morbidity and mortality,
especially in developed countries where a demographically ageing population is exacerbating
ageing and health concerns (Cassell and Clapperton, 2008; Hung et al., 2012; Sherrington andMenz 2003).
One approach to reducing slipping risk is to retrospectively apply ‘anti-slip’ strips to thefloor to increase slip-resistance. In applying these products one critical decision for the clientand supplier is determining adequate and cost-effective spacing to provide a high degree ofsafety with minimum labor and materials. Previous studies of slipping biomechanics (e.g.
Leclercq, 1999) suggested that the strip-spacing should be less than 10cm. This
recommendation is reasonable on the assumption that the heel slips up to 10cm without any
reflexive foot-flattening response. Spacing greater than 10cm was, however, considered viable
when taking into account the frequency of either direct foot contact with the strip, more anterior
part of the foot first contacting the strip or immediate foot-flattening that would reduce slipping
distance to less than the strip spacing.
The aim of this project was to test the spacing effect (20 cm and 26 cm) of an abrasive slipresistant strip on the biomechanical characteristics of foot-ground contact when walking on an oil
contaminated smooth Perspex surface wearing a soft soled walking shoe and a hard soled dress
shoe, see Figure 1.

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Testing Protocol
Two physically active, healthy male participants (30 years and 38 years) performed 10 walking
trials at each strip spacing (20 cm and 26 cm). Start position was adjusted such that the third
step would allow right foot contact with the forceplate. Vegetable-based cooking oil was used tocontaminate the Perspex plate to provide a coefficient of friction (CoF) of 0.07-0.10 as
measured using Four S rubber (400 P abrasive power: AS/NZS 4586, 2004), Four S rubber (400P abrasive paper: BS 7976-2, 2002) and TRL rubber (400 P abrasive paper: AS/NZS 4586,2004), defined as an extremely slippery walking surface (Nagano et aql., 2013). The plate wasretouched following each trial. The above procedure was undertaken with both shoes. Following
10 trials with 20 cm spacing, the plate was rotated to provide a 26 cm margin from the frontedge of the plate to the strip (Figure 1 C).

Figure 1. (A) Bottom sole: walking shoe (left) and dress shoe (right). (B) Marker locations,a walking shoe (top) and dress shoe (bottom) both 27cm in length. Marker
1 = forefoot (10cm anterior to mid-foot); marker ‫ۑ‬
2 = mid-foot (8.8cm‫ۑ‬
3 = heel. (C) Strip attachment on Perspex.
anterior to heel); and marker‫ۑ‬(D) Experimental setup.

- 106 -To capture foot kinematics an Optotrak ® optoelectic motion capture system (NorthernDigital Inc., Canada) with 3 camera towers tracked the 3D position (100Hz) of 3 light-emitting
diodes placed on the proximal inferior surface of the outer sole of the shoe (Figure 1). Raw
position-time data were low-pass filtered using a 4th order zero-lag Butterworth Filter with acutoff frequency of 15 Hz.

Figure 2. SI (Slip Initiation), SC (Strip Contact), and ST (Slip Termination) taken by highspeed camera (A): for the rubber soled walking shoe and (B): dress shoe.
Parameterisation
Slipping distances between the following four events were measured to assess the effectivenessof anti-slip strips on falls prevention due to slipping. Figure 2 visualized the four events
monitored by high-speed camera (Photoron SA3) at 500Hz.
As illustrated in Figure 3, Slip Initiation (SI) was defined kinematically as the first positiveacceleration following heel contact (Lockhart et al., 2003); Strip Contact (SC) occurred when
any part of the shoe contacted the strip, confirmed by the three markers’ 3D coordinates on
Perspex relative to the anterior-posterior location of the strip. The Strip Effect (SE) was when
the strip first took effect as reflected in negative acceleration (i.e. slowing) and peak horizontal
velocity following strip contact. At Slip Termination (ST) horizontal acceleration and velocity
approximated zero (i.e. the foot had stopped).

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Figure 3. Kinematic definitions of SI-SC, SC-SE, SE-ST.

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Results
Strip effectiveness was based on overall slipping frequency (slip or no-slip, Table 1) combinedwith the three slipping distances based on the above kinematic events (Table 2). Responses witha total slipping distance of less than 3 cm were not included as they are considered “micro-slips”(Liberty Mutual Group, 2004).
Slipping Frequency
With 20 cm spacing there was no recorded slip on 43% of trials whereas at 26 cm 28% of trials
were no-slip (Table 1). All non-slip trials were due to subjects stepping directly onto the strip.
As described in Table 1 strip contact with the heel was 10/ 80 (13%) of trials and of these 10
trials only two trials with an SC-SE distance exceeding 5 cm did not attain foot flattening.
Table 1. Frequency of slipping associated with three contact locations. Data presented as
frequency of slips/n of contacts (%). (e.g. In 20 cm spacing with walking shoe, mid-footcontacted strip 11 times and in 55% of cases ( n= 6) the shoe slipped)

StripSpacing
20cm
26cm
Total

Walking Shoe
Contact Location
Heel
Mid-foot Forefoot

0/0 (0)0/3 (0)0/3 (0)

6/11 (55)
7/9 (78)
5/5 (100) 9/12 (75)
11/16 (69) 16/21 (76)Dress Shoe
Contact Location
Heel
Mid-foot Forefoot

0/5 (0)2/2 (100)
2/7 (29)

5/5 (100)
3/6 (50)
8/11 (72)

5/10 (50)
10/12 (83)15/22 (68)Slipping DistanceSlipping distances are summarized in Table 2. Despite the 26 cm condition eliciting greater SISC slipping distance than the 20 cm condition, in both spacings SI-SC was considerably lessthan the maximum distance available (i.e. 20 cm and 26 cm). SC-SE indicates the slipping
distance from contact with the strip to when the strip took effect. There was no clear shoe-type
effect on this variable, with the dress shoe showing a short strip effect distance at 20cm but aconsiderably longer distance at 26cm while for the walking shoe SC-SE were more comparablefor the two spacings.
The distance required to completely stop the slip from when the strip began to take effect
was indicated by SE-ST. The 20 cm spacing demonstrated shorter SE-ST distance (by 1.6 cm)
for the walking shoe. Considerably shorter SE-ST distance was found for the dress shoe than thewalking shoe (3.3cm). In summary, for the walking shoe a reduction in strip spacing from 26
cm to 20 cm achieved approximately 20% less distance travelled from when the strip took effectto stopping while for the dress shoe the 20 cm spacing decreased the distance by approximately
50%.
Table 2. Slipping Distances (cm)

SI-SCSC-SESE-ST

Walking shoe
20cm
26cm
2.00 ± 1.56
3.54 ± 2.42
5.91 ± 4.97
4.31 ± 2.51
6.20 ± 1.88
7.82 ± 3.00

Dress shoe
20cm
26cm
1.43 ± 0.54
2.76 ± 4.33
2.49 ± 1.47
6.18 ± 4.63
3.19 ± 1.01
6.50 ± 2.64

Discussion
Narrower spacing remarkably increased the frequency of direct foot contact with the strips;- 109 -

when reducing the spacing from 26 cm to 20 cm, slip frequency was 15% lower. As all ‘no slip’
trials were confirmed as due to stepping directly onto the strip, reduced spacing between
multiple strips would be assumed to be effective in increasing the probability of direct contact.
Previously, a slipping distance of 10cm has been documented as the threshold for recovery
from posterior balance loss due to heel anterior slipping (Leclercq, 1999; Moyer et al., 2006;
Parijat & Lockhart, 2008; Strandbert & Lanshammar, 1981). In this project, however, slip
initiation to strip contact (SI-SC) averaged less than 10cm with strips spaced at 20 cm and 26
cm. This suggests that in everyday applications considerably wider spacing may be effective insignificantly reducing slipping distance.
In the above slipping model SC-SE distance is a potentially very useful variable fordetermining anti-slip strip width effects. If a strip is contacted at the most posterior point of theheel, and continues without foot flattening, SC-SE distance is required to be less than strip
width to effectively decelerate the foot. SE is when foot acceleration first becomes negative. As
Figure 1 indicates the mid-foot marker was located 8.8 cm anterior to the heel marker. When,therefore, strip contact occurred at mid-foot (34% of trials) the SC-SE distance threshold can beextended to 13.8 cm (5 cm + 8.8 cm). On 54% of trials strip contact occurred at the forefootmarker, providing a 23.8 cm SC-SE threshold. At 20 cm spacing, strip effect to slip termination(SE-ST) distance was reduced compared to 26 cm spacing. Narrower spacing is, therefore,effective in reducing slipping distance.
In summary, narrower spacing increased direct foot contact with the strip and reduced
slipping distance. In future work, using our slipping model, it would be informative to further
investigate strip width effects in addition to spacing. Biomechanical testing can be usefully usedin developing strategies for real-world falls prevention by determining the security achieved fora given application cost.

References
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Hung, W.W., Egol, K.A., Zuckerman, J.D., & Siu, A.L. (2012). Hip fracture managementtailoring care for the older patient. American Medical Association, 307 (20), 2185-2196.
Leclercq, S. (1999). The prevention of slipping accidents: a review and discussion of work
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Nagano, H., Sparrow, W.A., & Begg, R.K. (2013). Biomechanical characteristics of slipping
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Sherrington, C., & Menz, H.B. (2003). An evaluation of footwear worn at the time of fallrelated hip fracture. Age and Ageing, 32, 310-314.
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