CGA FAQ: Effect of walkway carpeting on gait data

from CLGAIT-L 14/6/96
Here is the text of a paper I presented at the East Coast Clinical Gait
Analysis Meeting, held at the Mayo Clinic, Rochester, Minnesota, USA, May
5-8, 1993.  On re-reading the paper, I think that the statistics suffer from
an "error rate problem", and that a Bonferroni adjustment to alpha should
have been made.  On this basis, only the three variables which showed p <
0.01 should be regarded as "statistically significant".

Mike Whittle


Michael W. Whittle*# and Karen J. Ferris#

* The University of Tennessee at Chattanooga
# Siskin Hospital for Physical Rehabilitation, Chattanooga,
Tennessee, USA

     With the recent growth in clinical gait analysis, there has
been a move towards improving the appearance of gait laboratories
(Gage, 1983), which in many cases includes carpeting the walkway,
including the force platforms.  The assumption is generally made
that this does not affect the data obtained, but there do not
appear to have been any publications on this topic.  The present
paper describes a study to test the hypothesis that the presence of
carpeting on a gait analysis walkway does not make a significant
difference to a range of commonly measured gait variables.

     The study was performed using a 12m walkway equipped with two
Bertec 4060H force platforms and a five-camera Vicon system.  Ten
adult volunteer subjects (5 men, 5 women) with no known disorders
of the locomotor system participated in the study.  The ages of the
subjects were evenly spread across the range from 25 to 62 years. 
The standard protocol for the Vicon Clinical Manager software
(Oxford Metrics, 1992) was performed with the subjects walking
barefoot at a self-selected comfortable speed.  Three walks were
performed with the floor and force platforms covered by carpet
tiles and three walks with them uncarpeted.  Five of the subjects
were tested first walking on the carpet, then walking on the bare
floor.  The other five subjects walked first on the bare floor,
followed by the carpet.  The carpet tiles consisted of 6mm of a
dense looped pile and 2mm of stiff latex backing.

     Three categories of variable were chosen for analysis: the
general gait parameters, 11 measurements of sagittal plane joint
angle, and six components of the ground reaction force.  The
results from each leg, for all three walks under a given condition
(carpeted or uncarpeted), were averaged and compared, using the
paired t-test.

     No statistically significant differences were seen between the
carpeted and uncarpeted conditions for either the general gait
parameters or the components of force.  However, significant
differences were seen between the two conditions for five
measurements of sagittal plane joint angle (Table 1).

     It might be expected that carpeting the force platforms would
modify the ground reaction forces, so it is surprising that the
only differences noted between the two conditions were in the joint
angles.  The observed differences were small, all being less than
1.5 degrees.  It is possible that these results were due to random
variation, since if enough variables are examined, it is likely
that one or more will show significant differences.  Further
studies would be needed to confirm whether there are any real
differences between the test conditions for these variables. 
Whether or not these differences are real, however, none of them
was sufficiently large to be considered significant clinically.

     Since carpet is slightly resilient, it might be expected to
reduce the magnitude of the heelstrike transient, by increasing the
time to peak deceleration of the foot following initial ground
contact.  Although detailed measurement of the heelstrike was not
attempted in the present study, it was noted that most of the
subjects had a more marked heelstrike when walking on the bare
floor than when walking on the carpet.

     The present study suggests that while there may be slight
changes in gait analysis variables as a result of carpeting the
walkway, the changes are unlikely to affect the results of clinical
gait analysis.

Gage JR. (1983) Gait analysis for decision-making in cerebral
palsy.  Bulletin of the Hospital for Joint Diseases Orthopaedic
Institute 43:147-163.

Oxford Metrics (1992)  Vicon Clinical Manager Users Guide.  Oxford:
Oxford Metrics.

                                    CARPET    NO CARPET     SIGNIF
GENERAL GAIT PARAMETERS:                                          
Velocity (meters/sec)                1.39       1.41          N/S 
Cadence (steps/min)                   120        120          N/S 
Stride length (meters)               1.39       1.41          N/S

Hip at Heelstrike                    27.6       27.5          N/S 
Max Hip Extension                    13.6       15.0          **  
Max Hip Flexion                      28.5       28.7          N/S 
Knee at Heelstrike                    7.2        7.9           *  
Max Knee Flexion: Stance             18.2       20.8          N/S 
Max Knee Extension: Stance            4.5        4.2          N/S 
Max Knee Flexion: Swing              57.0       55.9          **  
Ankle Dorsiflexion at Heelstrike      9.3        8.8          N/S 
Max Ankle Dorsiflexion: Stance       19.6       18.9           *  
Max Ankle Plantarflexion: Stance      7.3        7.9          N/S 
Max Ankle Dorsiflexion: Swing        12.6       13.8          **

FORCES: (Newtons)                                                 
Medial/Lateral: Peak                   48         50          N/S 
Anterior/Posterior: Peak 1            145        147          N/S 
Anterior/Posterior: Peak 2           -158       -158          N/S 
Vertical: Peak 1                      821        832          N/S 
Vertical: Peak 2                      783        788          N/S 
Vertical: Trough                      485        490          N/S

Table 1: Results of measurements with and without carpet.
N/S: p > 0.05          *: p < 0.05          **: p < 0.01

from BIOMCH-L 23 Jun 1998 07:55:02 +0100

From:         Marietta van der Linden <>
Organization: University of Salford
Subject:      summary of labfloors
Dear all,
Thanks very much  to everybody who replied to my question on the
best colour and material for lab floors.
Below is a summary of replies.
Marietta van der Linden
Dep of Rehabilitation
University of Salford
Salford, UK
I use a dark cord carpet in the lab in Derby  It works very well and would
not hesitate to reinstall
Steve Attfield
Derby Gait Lab
Dear Madam
The swiss company Forbo makes a low reflection floor covering called
Sure Step which we use for the walkway we sell together with our
portable force plates. It has very low infrared reflection and excellent
slip resistance too. I am not sure about the availability in the UK. It
is expensive.
Best Regards
Christian Calame
Christian Calame, Product Manager Biomechanics
Kistler Instrumente AG Winterthur, P.O.Box 304,
CH-8408 Winterthur, Switzerland
Tel: +41 52 224 11 11, Fax: +41 52 224 14 14
In 1989 I built a new motion laboratory here at UT Southwestern, and had
the opportunity to construct the lab from the ground up.  I had similar
concerns to the ones you describe regarding floor reflectance.
I decided to use the middle support layer used to make indoor/outdoor
running surfaces common to many sports and fitness clubs in the US.  The
surface itself is a 1/4 inch synthetic rubber that comes in 4 foot wide
sheets, cut to length from 500foot rolls. Normally, this is placed as the
base of the running surface, and then sealed using a special urethane
sealant.  All I did was apply a heavy carpet glue to the concrete slab, and
then roll out 6-70 foot long sheets to cover the 24 foot width of the lab,
using a heavy weighted roller to ensure good contact.  No top coat sealant
was used.  We then just cut out around our forceplates, and shored up the
edges with some vinyl molding.  We are not of the belief that you should
try to conceal the existence of the force plates by covering them; the
subject knows they are there anyway, and it adversely affects shear
The floor itself has been remarkably robust, and has outlasted the tile
floor immediately adjacent to it; although it does attract dust.  It is
black and since it is rubber, has zero reflectance.  We have had children
and adults, patients and athletes, in dress shoes, running shoes, and
barefoot walk, run, and fall on it, without problem.  It is not cold to
bare feet, and is not easily damaged by moving heavy equipment across it.
Cleaning is rather simple; just vacuum it.
The cost, of course, is higher than conventional tile floors; but I think
it has been worth it.  When we built the lab, I ordered it from the
following vendor.  Not sure if they still are in business, or if they have
an European distributer.
Let me know what you decide.
Best regards,
Vendor: California Products Corporation
        169 Waverly St,  PO Box 569
        Cambridge, MA  02139
|  James J. Carollo, Ph.D., P.E.
|  Senior Research Scientist
|  Mobility Research and Assessment Laboratory
|  The University of Texas
|   Southwestern Medical Center at Dallas
|  9705 Harry Hines Blvd., Suite 105
|  Dallas, TX  USA    75208                             (214) 351-2041
I have just been through this process in planning a new motion lab, and
eventually settled on the "Nevamar" model MR-6-1 decorative HPL laminate
made by International Paper.  This panel is a neutral gray and has a light
reflectance value of 33.8%, versus 73.2% for the ST-6-1 "Gray Starlite"
model which is the color typically used for most raised computer floors.
 Hope this helps.
Terry Horn, Ph.D
Mississippi Methodist Rehabilitation Center
Hi Marietta
We have a MacReflex system.  Most of the laboratory is painted black.
Even so we found problems with reflections from cameras being detected
by cameras at the opposite end of the room.  The solution was to use
the sync-delay facility on the video processors to put the cameras at
the far end of the lab slightly behind those at the near end.
Ergonomics and Work Psychology Section
Health and Safety Laboratory, Broad Lane, Sheffield, S3 7HQ, UK
Tel +44 114 289 2594; Fax +44 114 289 2526
HSE home page:
Hello Marietta
Generally-speaking, the floors I have seen in most of the labs I have
been to are a grey, matt-colored linoleum, of a thickness of 2-4 mm.
Since the floor-covering material is quite important, depending on the
type of research you are doing, you need to take into consideration the
durabillity of the material, the friction coefficients (for running
studies etc ...), it's washability (if you are sticking tape, or any
other material to the floor)). Motion Analysis can provide filters with
their systems, which will reduce all non-visible red reflections.
Daylight notch filters can be provided as well, for any outdoor
marker-based work - again removing all un-necessary light of specific
wavelengths . You may want to check with the APAS people if they have
such options available. Let me know if you need any more information.
Barry O'Flynn
European Sales and Support
Motion Analysis Corporation
London, U.K.
Tel: +44 (0)181 747-0396
Fax: +44 (0)181 742-8608
Cell: +44 (0)46 737-2084
Dear Marietta,
We use the APAS system too with 5 cameras. We put a black blanket (carpet?)
on the floor and painted the walls very dark blue. This works OK, the foor
does not reflect light. But you might notice that we direct all light
towards a white cealing.
Erik B. Simonsen
Erik B. Simonsen, Associate Professor, M.Sc. Ph.D.
Institute of Medical Anatomy section C.
Panum Institute. University of Copenhagen
Blegdamsvej 3., DK-2200 Copenhagen N
Phone:  +45 35 32 72 30 (work)   Fax: +45 35 32 72 17
Phone:  +45 45 89 45 86 (home)
I posed the same question about a year ago because we were building a new
human performance laboratory here at Duke University(which has just been
completed!)  Anyway, here are some of the factors to consider/summary of
responses/recommendations that I received.  We were also mounting force
plates underneath the floor.
1) Consider reflection.  Carpet surface good for that.
2) Light colored vinyl floor: problems - needs buffing to keep clean, needs
a mat surface which contrasts well with subject's skin color to get good
video recordings, reflections off the floor.
3) Nike lab seems to be asphalt base and rubber composite material on top -
feels like outdoor track runway.
4) Concrete with epoxy finish.  Epoxy is designed to have low reflectivity,
good resistance and wear characteristics.
5) Cement filled raised floor tiles
6) Commercial vinyl tiles.
7) Linoleum floor
8) Force plates in a pit, therefore they are flush with the floor.  Put in
a cable so wires are not all over the place.
9) Lab floor: concrete, forceplates mounted flush, then covered with
plastic tiles.
Here at Duke, we went with a Mondo track surface, which is similar to our
outdoor runway track.  I think it is similar or the same to what Nike has
(point #3).  We have a Motion Analysis system and do a lot of research in
running/cutting maneuvers.  So we wanted a surface with low reflectivity,
and good slip resistance which Mondo surface has.  It does seem to collect
dirt fairly easily, however.  If you are just doing gait analysis, you
might want to consider carpeting which is what we had when I worked in the
Gait Lab at the University of Virginia.
Hope this helps.
Scott Colby
Duke University Sports Medicine
        I am working with a motion capture system and had similar problems.
I used dark colored short pile carpet to eliminate the reflections.  You
want a dark fuzzy surface to make sure that the light is absorbed and
scattered by the surface.  If the surface is dark and smooth you will get
reflections just like asphalt at night.
Joseph McIntyre
Ph.D. Student in Mechanical Engineering
Auburn University, Auburn AL
Dear Marietta van der Linden,
I do not know how well your systems are working, but I think with
MacReflex you have to put markers on the object you want to analyse. Why
don`t you have a look at a marker-less system with very high accuracy ?
My experiences with this SIMI Motion Sytem are very good!
Just go to:
Yours sincerely
Wolfgang Pagani
PS: Let your floor not be too bright or to dark, try some grey colours
We have a Vicon system and don't seem to have a problem with our
It is a darkish grey lino material. Although it doesn't look
particularly attractive we have had no problems
Senior Lecturer in Biomechanics
Roehampton Institute, London
Tele: 0181 392 3541
Dear Marietta:
You might want to consider a durable carpet for your floor.  We have had
good luck with our gray "office buidling" carpet, which is comfortable
for our subjects and staff to walk and run on, and does not reflect
light.  The pictures of our lab on our web site might help.
- Glenn
Glenn S. Fleisig, Ph.D.
work phone: 205-918-2138
work fax:       205-918-0800
address:        American Sports Medicine Institute
                     1313 13th Street South
                     Birmingham, Alabama 35205
web site:

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