Proceedings of the 2018 IEEE International
Conference on Intelligence and Safety for Robotics
Shenyang, China, August 24-27, 2018

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained forall other uses, in any current or future media, including reprinting/republishing this material foradvertising or promotional purposes, creating new collective works, for resale or redistribution toservers or lists, or reuse of any copyrighted component of this work in other works.

Rigid Material on Top of a Compliant Flooring Effectively Reduces
the Impact Force In The Event of a Forward Fall
Nader Rajaei, Member, IEEE, Saeed Abdolshah, Member, IEEE, Yasuhiro Akiyama, Member, IEEE, Yoji
Yamada Member, IEEE, Shogo Okamoto Member, IEEE,

Abstract— The biomechanical studies have proposed several
forward fall arresting strategies to reduce the impact forces in ahuman-robot collaboration environment. A proposed strategy isusing a compliant flooring for an environment because it can
reduce the stiffness of the ground. In this study, we proposed that
if a rigid layer is mounted on a compliant flooring (double-layer
flooring), the impact force is further reduced. In order toinvestigate this goal, we designed two subjective laboratory
experiments. In experiment 1, the subjects were instructed
falling to the ground where was covered by a single layer ofcompliant material (a foam pad). In experiment 2, the subjects
fell on double-layer flooring when one rigid layer (a wood
surface) was mounted on the compliant layer. The impact forceswere measured for two short forward fall heights onto theoutstretched hand. The results showed that the profile of the
impact forces consists of two peaks. The first peak has a higher
magnitude, and it is followed by the second peak with a lower
magnitude. Comparing the magnitude of the first peak between
two experiments shows a reduction of the impact force inexperiment 2. In contrast, the magnitudes of second peaks are
identical for both experiments. Therefore, we concluded thatusing a double-layer flooring, i.e.one rigid layer and one
compliant layer can be an effective strategy for considerably
reducing the impact force, and preventing the wrist fracturesduring the forward fall.

I.

INTRODUCTION

Fall is a common incident that can seriously threaten thehealth of humans. A fall leads to physical consequences, or
psychophysical, and social consequences, or both [1]-[4]. The
physical consequences of fall cause either fatal or non-fatal
injuries and exert a significant financial burden on thehealthcare system. For example, it has been estimated that in
the United States direct cost of occupational fall-related
injuries reaches $43.8 billion by the year 2020 [5]. Therefore,
it is important to reduce the number of fall-related injuries byeffective methods, especially in the occupational
environments [6] where humans and robots collaborate and acollision between them may lead to a fall.
There are several types of fall in which a forward fall is
one of the most frequent one [7]. It occurs mainly due to an
unexpected perturbation of human balance or a failure in
his/her recovery strategy[8] when tripping or slipping occurs
during their walking [9]-[10]. The forward fall leads to mostcases a severe injury or a bone fracture in the upper extremity.
The Colles’ fracture (distal radius fracture) is one of thecommon forward fall-related fractures [11]-[13] because
humans spontaneously use their hands to avoid injury to thehead or trunk when a forward fall occurs. A worst-caseforward fall scenario is when the human descends with theoutstretched hand position which leads to approximately 90%of the Colles’ fracture [14].
A wide range of biomechanical studies has attempted to
identify the range of forces that lead to a distal radius fractureusing cadaveric hands (the in vitro studies) [14]-[17].
Moreover, the in vivo studies, the profile of impact forces
applied to the hand was identified during low-height forwards
fall onto the outstretched hand [18]-[19]. By using
mathematical models, the real impact forces during a forward
fall from a standing position were estimated [18], [20]-[21]where the in vivo studies have shown limitations due to safety
considerations for the subjects when falling from a largeheight.
In addition, the attention of the biomechanical researchers
has also attracted to find the effective biomechanical factorsthat can probably reduce the impact force in the event of aforward fall. A recent study showed that the natural reactionof the human during a forward fall has an important role inpreventing injuries [22]. Other studies showed that using atypical fall arresting strategy is an effective method for
reducing the fall-related fractures [23]-[26].
One of the newfound methods for preventing fall-related
injured is using a compliant flooring [27]. A compliant
flooring is a floor covering to reduce the stiffness of theground. In one early study, the impact forces applied to hands
was measured when the subjects fell on a rigid surface andfell on several compliant surfaces with different stiffness [28].
The result showed that the compliant surfaces led to aconsiderable reduction in the impact force in comparison with
the impact force on a rigid surface. Another additional study
investigated the magnitude of impact forces when the young
adults fall for different playground surface materials. The
study results showed a moderate but considerably reductionin the peak of forces for lower stiff materials in comparison
with rigid materials [29].
In this study, we investigated the effect of using a doublelayer flooring on the magnitude of the impact forces during aforward fall. In order to examine this, a series of subjective
laboratory experiments were conducted. We measured theimpact forces during fall onto the outstretched hand position
from short fall heights to avoid the risk of a fracture of thesubjects’ hand. We compared the impact forces when thesubjects fall on only one layer of a compliant surface andwhen they fall on a double-layer surface in which a rigid layer
is mounted on the compliant layer. We hypothesize that theN. Rajaei, S. Abdolshah, Y. Akiyama, Y. Yamada and S. Okamoto arewith Department of Mechanical Science and Engineering, Nagoya
University, Nagoya, Japan (e-mail: nader.rajaei@mae.nagoya-u.ac.jp).

978-1-5386-5546-7/18/$31.00 ©2018 IEEE273

double-layer flooring can further reduce the impact force of.
According to the best of the author's knowledge, the strategy
of falling on a double-layer flooring has not been investigated.
This rest of this paper is organized as follows. In Section
II, we introduce the method and protocol to be used for
conducting the experiments. Section III represents the average
results associated with impact force during the fall on a single
layer flooring and the fall on double-layer flooring. The paper
continues with further discussion and limitations regarding
this study in section IV. Finally, the conclusions are presented
in section V.

top of the foam pad to become a double-layer flooring (Fig.1.
(b)).
In order to prevent a wrist fracture during implementing
the experiments, we considered the amount of impact force
applied to each hand for two short fall heights (h = 3 cm and6 cm). The fall height was adjusted using the distance between
the palms and the upper surface of the foam pad and the woodlayer for the first and second experiment, respectively(Fig.1(c)). Every subject completed twelve trials (twoexperiments × two fall heights × three repetitions = twelve
trials).

a)II. MATERIAL AND METHOD
A. Subjects
Four young Japanese individuals (male) of ages 20-25
years (mean ± standard deviation [SD] = 23.75 ± 0.5 years),participated in this study. Their average height and body mass
were 174 ± 3 cm and 61 ± 5 kg, respectively. None of thesubjects reported any prior training, such as Jodo, martial arts
techniques, wrestling, or gymnastics. Moreover, they did nothave a history of major medical or neurological illnesses, suchas epilepsy, hand trauma, balance disorders, and falls. The
participants did not present bone disease or other conditions
that would increase the likelihood of a fracture occurrence. All
subjects signed a written informed consent prior to theexperiments. The experimental protocol was approved by theInstitutional Review Board of Nagoya University, Japan. All
experiments were conducted in accordance with the approved
guidelines.

b)

B. Experimental Protocol
The objective of this experiment was to measure the forces
applied to each hand during a forward fall while the ground iscovered by a single-layer and double-layer flooring.
The experiment was designed according to the protocol
utilized in most previous forward fall studies [18]-[19], [28][29]. This protocol was designed to be adopted in the in vitro
study design [14]. In this study, each subject wore an upper
body harness (Fig.1. (a)). The subjects were instructed to place
their knees on a soft pillow fixed to the ground and flex theirknees, allowing the subject to lean forward against the harness.
In this position, the thighs and the horizontal line parallel tothe ground created an angle of 30° (Fig.1).
A rope connected to the harness lifted the subjects to an
appropriate height from the ground. The subjects were
instructed to maintain at a position with their elbows fully
extended (the outstretched hand position). In this position, theangle between the subjects’ arms and the vertical line wasestablished at 15°. Two force plates (M3D Force plate, Tec
Gihan Corp.) were fixed to the ground beneath the subjects’
hands. Given that the surface of the force plates is considered
as a rigid surface with approximately infinite stiffness, in thefirst experiment, the surface of the force plates was covered bya single layer of foam pad (i.e. a compliant material) with 1 cm
thickness (Fig.1.(b)). In the second experiments, an additional
wood surface (rigid layer) with 1 cm thickness was inserted on

274

c)

Experiment. 1

Experiment. 2

Fig.1. (a). The experimental setup for the forward fall in the outstretchedhand position for fall heights of 3 cm and 6 cm. (b). Two material layer, left
side-foam pad, and right side-wood surface (c). Different types ofexperiments: experiment 1 is associated when the force plates were coveredby a single layer of the foam pad, experiment 2 is associated when one
additional wood layer was fixed on the foam pad.

III. RESULTSa) 3cm

Fig.2 illustrates the average impact force to be experienced
by on hand for fall height of 3 cm (Fig.2. (a)) and 6 cm (Fig.2.
(b)). Each plot consists of the result of both the experiment 1(blue-dash line) and the experiment 2 (red-dash line). For bothexperiments, which is similar to the previous findings [18][21],[30] the impact force includes two peaks; the first one hasa higher magnitude, which is followed by the lower secondpeak.
In Fig.2. (a), the average magnitude for the first peak wasapproximately measured as 278N and 250N for the experiment
1 and experiment 2, respectively. The magnitudes of thesecond peaks demonstrated lower forces of around 240N forexperiment 1 and 243N for experiment 2. Once the fall height
was increased to 6 cm (Fig.2. (b)), the average magnitude forthe first and second peak in experiment 1 was approximately
measured as 349N and 244N and in experiment 2 was 308N
and 243N.

b) 6cmThe one-way analysis of variance (ANOVA), using the
SPSS software package (IBM Corp. Released 2016. IBM
SPSS Statistics for Windows, Version 23.0. Armonk, NY:
IBM Corp), illustrated that increasing the fall height from 3 cm
to 6 cm significantly increases the magnitude of both peaks (p< 0.00003) for both experiment 1 and experiment 2.
Additionally, increasing the fall height had a greater effect on
the first peak than the second peak (Fig.3).
We also implemented other statistical analyses to compare
the magnitude of impact force applied to the hand inexperiment 1 and experiment 2 as shown in Fig.3 (two bar
charts). The analyses indicated significantly attenuated in themagnitude of the first peak (p < 0.01 for height 3 cm (theyellow color-bar in Fig.3 (a)) and p < 0.05 for 6 cm (the yellow
color-bar in Fig.3 (b))) in experiment 2 than experiment 1
whereas there was no significant effect on the magnitude of thesecond peak for both experiments (p = 0.71 for height 3 cm
and p = 0.95 for height 6 cm (the blue color-bar in the Fig.3 (a)and (b)).
IV. DISCUSSIONSThe previous biomechanical studies reported that using acompliant flooring is a potential method for attenuating theimpact forces applied to the body during a fall [27]-[29],[31].
However, these studies have been focused on comparing theimpact forces during fall on the ground with fall on one layercompliant surface [28]-[29]. In the present study, weinvestigated whether using a combination of a compliant layer
and rigid layer (double-layer flooring) can reduce further the
impact forces during a forward fall. In order to achieve theobjective of this study, the impact forces for two different
experiments were measured. Initially, the impact forces were
measured when the ground was covered by a single layer of acompliant material (a foam pad). Next, the impact forces wereagain measured when one additional relatively rigid surface(a wood surface) was mounted on top of the first layer(double-layer surfaces). The experiments were conducted fortwo short fall heights (3cm and 6cm) to prevent the risk offracture for the subjects during conducting experiments.

Fig.2 The impact force profile during fall at (a) 3 cm and (b) 6cm. The
figure consists of the average magnitude of force for experiment 1 (bluedash line) and experiment 2 (red-dash line).

experiment 2) considerably are similar to the results
conventionally claimed in previous studies [18]-[20],[30] andincludes two peaks; the first peak consisted of a highmagnitude which was followed by a second peak with a lower
magnitude. The statistical analysis showed that the magnitudeof the first peak was significantly reduced in experiment 2
than in experimental 1 (Fig.3). A calculation represented thatthe first peak in experiment 2 was reduced approximately
10.7% and 13.3% for fall height 3 cm and 6cm, respectively.
Therefore, the magnitude of the first peak further decreased
by increasing the fall height. Since the first peak impact force
usually causes a fracture [32], the noticeable reduction of thefirst peak using a double-layer flooring including rigid layer
and a compliant layer can be a vital point for preventing thewrist fractures within a forward fall from standing position.
In addition, the experimental results indicated that
increasing the fall height caused a significant increase in themagnitude of peaks. Therefore, the findings of this study
provide additional evidence to support and confirm theprevious findings regarding the impact force during a forward
fall [18]-[20], [30].

Our experimental results demonstrate that the profile ofimpact force for both experiments (experiment 1 and

275

500

wood layer. Therefore, based on these assumptions, theamount of force in the experiment 2 must be smaller thanexperiment 1 because in experiment 2 the total amount ofspring constant is calculated as if two-spring system
connected in series whereas in experiment 1 there is a single
spring constant. Subsequently, a simplistic linear spring
system can well describe that fall on a double-layer flooring
leads to a small amount of the impact forces applied to handin comparison with a fall on the single compliant flooring.

a)** P < 0.01
The first peak
The second peak

400

Force (N)

**
n.s

300

However, some limitations are worth noting. Even though
this study showed that the magnitude of impact force during
a forward fall on the double-layer flooring decreases further
in comparison with fall on a single compliant layer, morestudies such as using a mathematical model or mathematical
dynamic simulation are required to investigate results of using
one-layer and double-layer flooring for a real forward fallfrom a typical standing position. Moreover, in this study, it
was not investigated whether a double-layer flooring may
increase the human balance during walking by decreasing therisk of fall as was reported in some previous studies [27], [33][34]. In our future work, this issue can be further investigated.

200

100

0
One-layer

Double-layers

500* P < 0.05b)

V. CONCLUSIONS*

400

In this study, for preventing the forward fall-related
injuries, we demonstrated that using a double-layer flooring
where a rigid layer is mounted on a compliant layer, could
significantly reduce the impact force applied to the hand.

Force (N)n.s300This result was obtained after conduction two laboratories
experiments. In the first experiment, we measured the impact
forces applied to the subjects’ hands when they fell on one
single compliant flooring from short fall heights. In thesecond experiment, we repeated the experiments where
impact force was measured during the fall on the double-layer
flooring.

200

100

0
One-layer

Double-layers

Fig.3. Comparison between the magnitude of the first peak ( yellow-bar)
and the second peak (blue-bar) for one-layer and double-layer experiments
during the fall from height (a) 3 cm and (b) 6 cm. *- significant for p <0.05. **- significant for p < 0.01. n.s- no significant.

Furthermore, the experimental results of impact forces
can be interpreted using a serially connected two springmodel. According to Hook’s law, the amount of compression
force for a spring is calculated by multiplying the amount of
reduction in the length of a spring to the amount of spring
constant. Hence, each layer is modeled as a linear springwhere the stiffness of each layer is considered as a spring
constant and the amount of reduction in the length of springs
is equivalent to the amount of compression of the layer duringfall. In experiment 1, fall occurs on one layer (a foam pad),and the impact force is obtained from the behavior of a single
spring (one degree of freedom). In contrast, in experiment 2,
the impact force is calculated based on the behavior of two
springs to be connected in series (two degrees of freedom) byconsidering double layer; one foam pad and one wood
surface. In addition, the reduction of spring length is almost
equal for both experiments because, in experiment 2, thereduction in the length of spring is incredibly small for the

In addition, our results illustrated similar impact force
profiles for both experiments including two peaks; the firstpeak with a higher magnitude followed by a second peak witha lower magnitude of the force. More specifically, the doublelayer flooring decreased the magnitude of the first peak whichmainly causes a dorsal radius fracture during a forward fall.
In contrast, the double-layer flooring not effected on themagnitude of the second peak.
The study results also showed that the magnitude of thefirst peak reduction is correlated with increase fall height sothat by increasing the fall height from 3 cm to 6 cm, a further
reduction was observed for the magnitude of the first peak.
Hence, we can experimentally predict that fall form
approximately large fall height, i.e. fall from a typicalstanding position, on a double-layer flooring remarkably
decreases the first peak l. However, we have consideredvalidating this prediction by appropriate mathematical models
or mathematical dynamic simulation in our future studies.
ACKNOWLEDGMENT
This work was supported by JSPS KAKENHI Grant
Number 26750121, and METI “Strategic international
standardization
promotion
project:
International
standardization of human tolerance against fall injuries”.

276

REFERENCES[1]

Stenhagen, Magnus, Henrik Ekström, Eva Nordell, and Sölve Elmståhl.
"Accidental falls, health-related quality of life and life satisfaction: aprospective study of the general elderly population." Archives ofgerontology and geriatrics 58, no. 1, pp.95-100, 2014.
[2] Akyol, A. D. "Falls in the elderly: what can be done?." International
nursing review 54, no. 2 (2007): 191-196.
[3] Gillespie, Lesley D., M. Clare Robertson, William J. Gillespie,
Catherine Sherrington, Simon Gates, Lindy M. Clemson, and Sarah E.
Lamb. "Interventions for preventing falls in older people living in thecommunity." Cochrane Database Syst Rev9, no. 11 (2012).
[4] von Heideken Wågert, Petra, Yngve Gustafson, Kristina Kallin, Jane
Jensen, and Lillemor Lundin-Olsson. "Falls in very old people: thepopulation-based Umeå 85+ study in Sweden." Archives of gerontology
and geriatrics 49, no. 3 (2009): 390-396.
[5] Englander, Fred, Thomas J. Hodson, and Ralph A. Terregrossa.
"Economic dimensions of slip and fall injuries." Journal of Forensic
Science 41, no. 5, pp.733-746, 1996.
[6] Chang, Wen-Ruey, Sylvie Leclercq, Thurmon E. Lockhart, and Roger
Haslam. "State of science: occupational slips, trips and falls on the samelevel." Ergonomics 59, no. 7, pp. 861-883, 2016.
[7] C. E. de Putter, E. F. van Beeck, S. Polinder, M. J. M. Panneman, A.
Burdorf, S. E. R. Hovius, R. W. Selles, “Hand and Wrist Injuries byExternal Cause: A population-based study in working-age adults, 20082012,” Hand and Wrist Injuries, vol. 47, no. 7, pp. 1478–1482, 2016.
[8] K. Mitsuoka, Y. Akiyama, Y. Yamada, and S. Okamoto, “Analysis of
Skip Motion as a Recovery Strategy after an Induced Trip,” in Systems,
Man, and Cybernetics (SMC), 2015 IEEE International Conference on,pp. 911-916.
[9] T. W. O’Neill et al., “Age and sex influences on fall characteristics.,”
Ann. Rheum. Dis., vol. 53, no. 11, pp. 773–5, 1994.
[10] Nevitt, Michael C., and Steven R. Cummings. "Type of fall and risk of
hip and wrist fractures: the study of osteoporotic fractures." Journal of
the American Geriatrics Society 41, no. 11 (1993): 1226-1234.
[11] J. A. Baron et al., “Basic epidemiology of fractures of the upper andlower limb among Americans over 65 years of age.,” Epidemiology,
vol. 7, no. 6, pp. 612–8, 1996.
[12] L. M. Feehan and S. B. Sheps, “Incidence and Demographics of Hand
Fractures in British Columbia, Canada: A Population-Based Study,” J.
Hand Surg. Am., vol. 31, no. 7, pp. 1–9, 2006.
[13] Nevitt, Michael C., and Steven R. Cummings. "Type of fall and risk of
hip and wrist fractures: the study of osteoporotic fractures." Journal of
the American Geriatrics Society 41, no. 11 (1993): 1226-1234.
[14] G. Frykman, “Fracture of the distal radius including sequelae-shoulder-hand-finger syndrome, disturbance in the distal radio-ulnar
joint and impairment of nerve function. A clinical and experimental
study.,” Acta Orthop. Scand., vol. 6470, no. April, p. Suppl 108:38,
1967[15] E. R. Myers et al., “Correlations between photon absorption properties
and failure load of the distal radius in vitro,” Calcif Tissue Int, vol. 49,
no. October 2016, pp. 292–297, 1991.
[16] E. R. Myers, A. T. Hecker, D. S. Rooks, J. A. Hipp, and W. C. Hayes,“Geometric variables from DXA of the radius predict forearm fractureload in vitro,” Calcif. Tissue Int., vol. 52, no. 3, pp. 199–204, 1993.
[17] J. A. Spadaro, F. W. Werner, R. A. Brenner, M. D. Fortino, L. A. Fay,
and W. T. Edwards, “Cortical and trabecular bone contribute strength
to the osteopenic distal radius,” J. Orthop. Res., vol. 12, no. 2, pp. 211–
218, 1994.
[18] J. Chiu and S. N. Robinovitch, “Prediction of upper extremity impact
forces during falls on the outstretched hand,” Journal of Biomechanics,
vol. 31, no. 12, pp. 1169–1176, 1998.
[19] C. E. Kawalilak, J. L. Lanovaz, J. D. Johnston and S. A. Kontulainen,“Linearity and sex-specificity of impact force prediction during a fall
onto the outstretched hand using a single-damper-model,” J
Musculoskelet Neuronal Interact, vol. 14, no. 3, pp. 286-293, 2014.
[20] DeGoede, Kurt M., and James A. Ashton-Miller. "Biomechanicalsimulations of forward fall arrests: effects of upper extremity arrest
strategy, gender and aging-related declines in muscle strength." Journalof biomechanics 36, no. 3, pp. 413-420, 2003.
[21] Lo, JiaHsuan, and James A. Ashton-Miller. "Effect of upper and lower
extremity control strategies on predicted injury risk during simulated
forward falls: a study in healthy young adults." Journal ofbiomechanical engineering 130, no. 4, pp. 041015, 2008a.

[22] S. Abdolshah, Y. Akiyama, K. Mitsuoka, Y. Yamada and S. Okamoto,“Analysis of Upper Extremity Motion during Trip-Induced Falls,” inRobot and Human Interactive Communication (RO-MAN), 26th IEEE
International Symposium on Robot and Human Interactive
Communication, pp. 1485-1490, 2017.
[23] K. M. DeGoede and J. A. Ashton-Miller, “Fall arrest strategy affects
peak hand impact force in a forward fall,” J. Biomech., vol. 35, no. 6,
pp. 843–848, 2002.
[24] P. H. Chou, Y. L. Chou, C. J. Lin, F. C. Su, S. Z. Lou, C. F. Lin, and G.
F. Huang, “Effect of elbow flexion on upper extremity impact forces
during a fall,” Clinical Biomechanics, vol. 16, pp. 888–894, 2001.
[25] P. P-H Chou, H-C Chen, H-H Hsu, Y-P Huang, T-C Wu and Y-L Chou,“Effect of upper extremity impact strategy on energy distribution
between elbow joint and shoulder joint in forward falls,” Journal of
Medical and Biological Engineering, vol. 32, no. 3, pp. 175-180, 2012.
[26] J. Lo, G. N. McCabe, K. M. DeGoede, H. Okuizumi, and J. A. AshtonMiller, “On reducing hand impact force in forward falls: results of abrief intervention in young males,” Clinical biomechanics, vol. 18, no.
8, pp. 730-736, 2003.
[27] Lachance, Chantelle C., Michal P. Jurkowski, Ania C. Dymarz, Stephen
N. Robinovitch, Fabio Feldman, Andrew C. Laing, and Dawn C.
Mackey. "Compliant flooring to prevent fall-related injuries in older
adults: A scoping review of biomechanical efficacy, clinicaleffectiveness, cost-effectiveness, and workplace safety." PLoS one 12,
no. 2 , pp. e0171652, 2017.
[28] S. N. Robinovitch and J. Chiu, “Surface stiffness affects impact force
during a fall on the outstretched hand,” Journal of Orthopaedic
Research, vol. 16, no. 3, pp. 309–313, 1998.
[29] Choi, Woochol Joseph, Harjinder Kaur, and Stephen N. Robinovitch.
"Effect of Playground Surface Materials on Peak Forces during Falls."
CMBES Proceedings 34, no. 1, 2018.
[30] J. A. Ashton-Miller, “Biomechanical Factors Affecting the Peak Hand
Reaction Force During the Bimanual Arrest of a Moving Mass,” J.
Biomech. Eng., vol. 124, no. 1, p. 107, 2001.
[31] Lachance, Chantelle C., Valeriya O. Zaborska, Pet-Ming Leung, Fabio
Feldman, Stephen N. Robinovitch, and Dawn C. Mackey. "Perceptions
about Compliant Flooring from Senior Managers in Long-Term Care."
Journal of Housing For the Elderly, pp.1-17, 2018.
[32] Gustavsson J. Working in a nursing home with Impact Absorbing
Flooring: A qualitative study on the experiences of licensed practicalnurses [Internet]. Doctoral Dissertation, Karlstad University. 2015.
[33] Simpson, A. H. R. W., S. Lamb, P. J. Roberts, T. N. Gardner, and J.
Grimley Evans. "Does the type of flooring affect the risk of hip
fracture?." Age and Ageing 33, no. 3, pp.242-246,2004.
[34] Warren, Christopher J., and Hugh C. Hanger. "Fall and fracture rates
following a change from carpet to vinyl floor coverings in a geriatricrehabilitation hospital. A longitudinal, observational study." Clinicalrehabilitation 27, no. 3, pp.258-263, 2013.

277