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Wien. Tierärztl. Mschr.- Vet. Med. Austria 97 (2010), 55 - 64
From the Centre for Applied Sport and Exercise Sciences, University of Lancashire1, Preston, UK, from the Department
of Physical Therapy, The University of Tennessee and Chattanooga2, Chattanooga, USA, from the School of Public Health
& Clinical Sciences, Faculty of Health, University of Central Lancashire3, Preston, UK, from the Department of Large Ani-
mal Clinical Sciences, Michigan State University4, East Lansing, USA, and from the Department of Exercise, Sport and
Leisure Studies, University of Tennessee at Knoxville5, Knoxville, USA
Motion analysis and its use in equine practice and research
S.J. HOBBS1, D. LEVINE2, J. RICHARDS3, H. CLAYTON4, J.TATE5and R. WALKER2
received July 8, 2009
accepted for publication November 27, 2009
Keywords: equine locomotion, kinematics, kinetics, for-
ces, horses.
Summary
Motion analysis techniques have been used in vete-
rinary research for the measurement of normal and patho-
logical gait in horses since the late 19th century.Many of the
early studies involved capturing moving images in 2
dimensions, and these techniques are still commonly used
in field based research and clinical practice. In recent
times, more advanced methods employed in human medi-
cine have been adopted to measure forces and motion in
3 dimensions along with other aspects of locomotion in
horses. This paper describes kinematic and kinetic techni-
ques that are currently used in equine veterinary research
and reviews normative and clinical data that have been
obtained using these methods.
Schlüsselwörter: Lokomotion des Pferdes, Kinematik,
Kinetik, Kräfte, Pferd.
Zusammenfassung
Bewegungsanalyse und deren Nutzen in Pferdepraxis
und -forschung
Die Methoden der Bewegungsanalyse werden seit dem
späten neunzehnten Jahrhundert in der veterinärmedizini-
schen Forschung für die Messung des normalen und
pathologischen Ganges des Pferdes genutzt. Viele dieser
frühen Studien beinhalteten die Aufnahme von Bildern in 2
Dimensionen - diese Techniken werden oftmals auch heute
noch in der Feldforschung und klinischen Praxis verwendet.
In letzter Zeit wurden in der Humanmedizin fortschrittlichere
Methoden angewendet und auch für die Messung von Kräf-
ten und Bewegungen in 3 Dimensionen aber auch anderen
Aspekten der Bewegung bei Pferden adaptiert. Dieser Arti-
kel beschreibt kinematische und kinetische Messtechni-
ken, die heutzugtage in der Forschung beim Pferd ver-
wendet werden, und bewertet normative und klinische
Daten, die mit diesen Methoden erhalten werden.
Introduction
In the late 19th century the first motion picture cameras
recorded faster gait patterns of locomotion for both
humans and animals. In 1877 Muybridge demonstrated,
using photographs, that when a horse is moving at a fast
trot there is a moment when all of the animal's feet are off
the ground. It took him 5 years to develop the capabilities
to capture these movements with a series of single lens
cameras.
The 20th century saw the development of systems capa-
ble of automated and semi-automated computer-aided
motion analysis using both manual and automatic marker
identification techniques. Both the hardware and software
that these systems use has developed rapidly in the last 10
years and a large variety of different methods can now be
used to track movement in two (2-D) or three-dimensions
(3-D). Most systems use either image based or signal
based tracking with one or more cameras or receivers to
record the image or signal. All systems require the volume
of interest to be calibrated and the number of cameras or
receivers used by the system and their capabilities will
influence the accuracy of the measurements recorded.The
popularity of motion analysis systems in veterinary research
is evident from the number of studies conducted since the
work of Fredricson and Drevemo in the 1970s.
The latter half of the 20th century has also seen the intro-
duction of other methods of recording movement, including
instrumented walkmats, accelerometers and electrogonio-
meters, which have all contributed to our current knowled-
ge of movement. However these systems have been used
sparingly in veterinary medicine due to the cost, and the
challenges of adapting software created for bipeds to hor-
ses. Veterinary colleges around the world now utilize this
technology although it is still an emerging field of research.
The motion analysis laboratory typically contains sever-
al pieces of equipment. The first is usually an array of
infrared cameras, at least 2 but more typically 5 or more
depending on the complexity of the biomechanical model
used. Data is acquired at speeds varying from 50 Hz to
1,000 Hz, depending on the speed of the activity. Activi-
ties such as gait analysis at walk only require camera
speeds of 50 Hz but analyzing activities such as trot, gal-
lop, or a jump require higher speed acquisition to obtain
valid data as the angular velocities involved in these activi-
ties are much higher. The typical motion capture space
(usually termed capture volume) is comprised of an area in
which data can be seen by 2 or more infrared cameras.
The horse has reflective markers attached to the body at
Abbreviations: BM = body mass;EMG = electromyography; GRFs =
ground reaction forces
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Wien. Tierärztl. Mschr.- Vet. Med. Austria 97 (2010)
predetermined landmarks that will be used to calculate
joint angles (Fig. 1). At least 3 markers are required per
body segment to create a local coordinate system. These
markers can be as small as 1mm or as large as 25 mm,
are lightweight and are easy to replace if they are dislod-
ged. Typically the larger the marker, the better the camera
resolution but larger markers may interfere with the move-
ment being observed and it may be difficult to differentiate
multiple large markers attached to small body segments.
As the horse moves through the capture volume, infrared
light emitted from the cameras is reflected off of the mar-
kers and back into the camera lens, striking a light sensitive
plate that creates a video signal. Computers collect these
signals and determine the position of each marker in 3-D
space. These systems can also be used in the field with
active (light emitting) markers, but wires from the markers
to a control device must be attached to the horse.
If markers are impractical, such as in an underwater
treadmill, swimming, or on a racetrack, a video-based
system can be utilized. Multiple video cameras on tripods
collect data, which are transferred to a computer. The
points can later be manually or automatically labeled and
angles then calculated. The accuracy may suffer, and
approximately 10 cubic meters is realistically the largest
volume that can be captured, but the versatility is excep-
tional using these methods. For field work signal based
techniques, such as ultrasound emitting diodes can also
be used. Often they only require one receiver, but for these
systems the emitters must be attached to the horse using
wires, which can limit their use at faster gaits. Precision of
one system was reported by CHATEAU et al. (2004) to be
0.3 mm and 0.5 degrees for distance and angle measure-
ments, respectively.
Measurements produced from motion analysis systems
include displacements of segments, joints angles and their
derivatives (velocity and acceleration). These data inhe-
rently include errors which are recorded along with the real
movement and these errors are removed using filters.
Commonly low pass digital filters (such as Butterworth fil-
ters), fourier analysis or splines are used to filter equine
movement data. The frequencies contained within the
recorded measurement will depend on the speed of the
movement, the capture frequency and the systematic and
random errors that are present. Filters are usually applied
to the labeled marker data or the calculated displacement
data to remove errors before any derivatives are calcula-
ted, as errors are amplified during velocity and accelerati-
on calculations if they have not previously been removed.
Together with a motion analysis system, many labs now
contain other commercially available, complementary
equipment. One or more force platforms can be embedded
into a walkway or measurement volume to collect ground
reaction forces together with synchronized motion data,
from which muscle forces can be estimated. Muscle activi-
ty can be measured during movement using electromyo-
graphy, transient shock can be measured at foot strike
using accelerometry and pressure mats can be used to
determine the foot positions or pressure distribution under
the foot. In addition, prototype equipment is emerging from
veterinary colleges and universities to answer more chal-
lenging questions, such as the ultrasound equipment deve-
loped by CREVIER-DENOIX et al. (2009) to estimate ten-
don strain.
Kinematic or motion analysis of gait is a powerful tool
that can be used to measure movement patterns during
gait and other activities, such as jumping. As 3-D motion
analysis systems are very expensive and require extensi-
ve training to use there is limited information in the vete-
rinary literature regarding 3-D gait analysis. 2-D systems
are less expensive, and have a place in clinical gait analy-
Fig. 1: Photograph (left) and stick figure (right) of a horse walking over a series of force plates; the left hind, right hind
and left front limbs are in the stance phase, with each hoof contacting a different force plate. The grey arrows on the stick
figure represent the ground reaction force vectors. The marker set shown in this figure is suitable for 2D, sagittal plane
analysis. Reflective markers are placed in the following locations: 1: facial crest, 2: wing of atlas, 3: 6th thoracic vertebra,
4: 1st lumbar vertebra, 5: 1st coccygeal vertebra, 6: tuber spinae scapulae, 7: greater tubercle of humerus, 8: lateral hume-
ral epicondyle, 9: ulnar carpal bone, 10: lateral metacarpal epicondyle, 11: ventral part of tuber coxae, 12: cranioventral
part of greater tuberosity, 13: lateral femoral epicondyle, 14: talus, 15: lateral metatarsal epicondyle.There are 3 markers
on each hoof: midlaterally on the coronet, mid-dorsally on the coronet and mid-dorsally 3 cm distal to the coronet. Hoof
markers are proximally located to reduce the risk of contact with the other hooves.This is why the point of application of
the ground reaction force at the hoof-ground interface appears is below the position of the hoof markers. (Photo credit:
Britt Larson)
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Wien. Tierärztl. Mschr.- Vet. Med. Austria 97 (2010)
sis for studying sagittal plane motions (flexion and extensi-
on movements).To date they have been used more exten-
sively in laboratory and field based studies of equine loco-
motion, but as rotations are not limited to flexion and exten-
sion it may be beneficial in some studies to analyze 3-D
movements. Also the additional time and effort required for
a full 3-D analysis are substantial and may not be justified
if flexion-extension are the movements of primary interest.
Kinematic (motion) analysis of gait
in horses
Many research questions are still answered in relation
to equine locomotion using 2-D techniques. Sagittal plane
kinematics are commonly collected using a variety of late-
ral marker sets which often simplify the lower limbs, due to
the small size of the pastern segments. Consequently the
definition of what constitutes a joint in terms of angle cal-
culation varies between methods. Joint movement is also
reported to be overestimated due to soft tissue artifacts
(WEEREN et al., 1992; DREVEMO et al., 1999; CLAYTON
et al., 2002).
Despite this concern, little variation is found for intra-
individual stride characteristics in the sagittal plane using
2-D methods, provided speed is controlled. Greater varia-
bility is documented for inter-individual stride characteri-
stics, particularly where differences in breed and confor-
mation are evident (GALISTEO et al., 2001). BACK et al.
(1996) studied the kinematics of walk (1.6 m.s-1) and rela-
ted stride length, joint angles and range of motion of joints
at trot (4.0 m.s-1) on a treadmill using a CODA-3 system.
For 24 Dutch Warmblood horses stride length at trot (2.7
m) was 1.6 times that of walk and the increase was due to
an increase in protraction of 1.6 degrees in the forelimb
and 1.4 degrees in the hind limb. Except for the fetlock
joint, similar patterns were reported for joint angle time dia-
grams for the limb joints at walk and trot. However, absolu-
te differences in temporal and spatial kinematics were
observed. In walk 2 extension maxima were recorded whe-
reas at trot there was only one maximum.Variability in ran-
ge of motion in both limbs was highest in the higher moti-
on joints, so the range of motion (mean, SD) for the
forelimb fetlock, forelimb carpus and hind limb fetlock joints
were 80.6 ± 7.1, 90.8 ± 7.1 and 85.0 ± 7.7 degrees, res-
pectively, at trot. Forelimb joint angles are illustrated in Fig.
2 for one full stride at trot.
Recent studies have reported detailed 3-D kinematics
for the digital joints, including pastern joint rotations (CHA-
TEAU et al., 2004; HOBBS et al., 2006; CLAYTON et al.,
2007a,b). Flexion of the pastern joint occurs early in the
stance phase. The joint then extends to a peak at the start
of breakover after which rapid flexion is seen to toe off. As
the range of motion is small the variability is greater.
HOBBS et al. (2006) reported a coefficient of variability of
22 % for stance phase range of motion for this joint at walk
for 4 horses. CHATEAU et al. (2004), who studied 4 trot-
ters, reported inter-individual variability for the lower limb
Fig. 2: Forelimb joint angles during one stride at
trot starting with hoof contact; the stick figures
are taken at the instants of hoof contact, mid-
stance, lift off, midswing and the next hoof
contact. The forelimb segments corresponding to
the graphs are drawn in black. The arrows
beneath each stick diagram indicate the corre-
sponding time during the stride. The joints repre-
sented from the top down are the shoulder,
elbow, carpal, metacarpophalangeal and distal
interphalangeal.
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Wien. Tierärztl. Mschr.- Vet. Med. Austria 97 (2010)
segments and joints to be greater than intra-individual
variability for all rotations at walk. Sagittal plane hoof rota-
tions were reported to vary at foot strike by 5.2 degrees
and landing kinematics of the hoof together with global
adduction of the limb were thought to be mainly responsi-
ble for out of plane movements of the distal joints (CHA-
TEAU et al., 2004; HOBBS et al., 2006; CLAYTON et al.
2007a,b).
3-D kinematic analyses and correction algorithms for 3-D
skin displacement have been described for the tibia, third
metatarsus (LANOVAZ et al., 2004) and the radius
(CLAYTON et al., 2004; SHA et al., 2004). Bone fixed mar-
kers were used as a reference to model the 3-D displace-
ment patterns of 6 markers on the skin of the equine radi-
us by SHA et al. (2004) and 6 markers on the skin of the
tibia and third metatarsus by LANOVAZ et al. (2004). Skin
displacements were greater at the proximal end of the seg-
ments, often due to greater musculature, and SHA et al.
(2004) found the largest skin movements in the longitudi-
nal direction, which supports the findings of WEEREN et
al. (1992).
Clinical studies using kinematic
techniques
As motion analysis systems advanced towards the end
of the 20th century 2 prominent research groups carried out
a number of 2-D kinematic clinical studies with horses.
Hilary Clayton investigated clinical lameness conditions
using high speed cinematography, some years later a team
from Utrecht investigated changes in gait factors due to
experimentally induced lameness with a CODA-3 system.
In both studies temporal patterns and relationships bet-
ween stride variables and lameness were explored over-
ground (CLAYTON, 1986a,b, 1987a,b, 1988) and using
treadmills (BUCHNER et al. 1995a,b, 1996a,b).
Lame horses that are led in hand tend to reduce varia-
bles such as stride length and stride duration so their over-
all speed is reduced (CLAYTON, 1986a; BUCHNER et al.,
1995a), whereas on treadmills where speed can be con-
trolled, the lame horse maintains speed using shorter,
quicker strides than a sound horse moving at the same
speed (BUCHNER et al., 1995a; KEEGAN et al., 1997). In
supporting limb lameness a shortening of the swing phase
and increased stance duration is usually seen in both lame
and sound limbs (BUCHNER et al., 1995a). Head and
neck motion in forelimb lameness and croup motion in hind
limb lameness are asymmetrical; vertical displacement
increases during stance of the sound limb and decreases
during stance of the lame limb (BUCHNER et al., 1996a).
In addition, the suspension phase following stance of the
lame limb is reduced at trot (CLAYTON, 1986a; BUCHNER
et al., 1995a) and placement of the lame forelimb usually
precedes the diagonal hind limb. In the lame horse there is
a need to reduce load on the lame limb and compensate
for this by redistributing the load to the other limbs (WEIS-
HAUPT, 2008). Passive distal joint rotations reflect the
reduction in loads upon them, with flexion of the coffin joint
and extension of the fetlock joint being reduced during
weight bearing of the lame limb (BUCHNER et al., 1996b).
For this reason fetlock joint rotation is often used as an
indicator of supporting limb lameness, which is supported
by evidence indicating a direct relationship between fetlock
joint extension and magnitude of the peak vertical force
(McGUIGAN and WILSON, 2003). However, PELOSO et
al. (1993) found that fetlock extension did not consistently
characterize lameness. Proximal joints then actively con-
trol braking and act as load dampers through active increa-
ses in flexion of the shoulder and tarsal joints (BUCHNER
et al., 1996b).
Studies of alterations in hoof balance, on sagittal and
out of plane distal joint rotations have been carried out at
walk and trot (NILSSON et al., 1973; WILLEMEN et al.,
1999; SCHEFFER and BACK, 2001; CHATEAU et al.,
2006; PEHAM et al., 2006). Heel or toe wedges are com-
monly recommended for various orthopaedic conditions
and knowledge of their effects on distal joint rotations is
important although conflicting results exist in relation to
fetlock joint rotation. Earlier 2-D studies using simpler non-
invasive modeling techniques (NILSSON et al., 1973;
WILLEMEN et al., 1999; SCHEFFER and BACK, 2001)
reported a decrease in maximum fetlock extension using
heel wedges during gait. A more recent study using ultra-
sound emitting diodes and invasive techniques found an
increase in maximal flexion of the pastern and coffin joints
and no significant differences in maximal extension of the
fetlock joint for heel wedges and generally the opposite
(except for pastern joint extension) using toe wedges
(CHATEAU et al., 2006). In addition, heel and toe wedges
appear only to influence sagittal plane and not out of pla-
ne joint rotations (CHATEAU et al., 2006; HOBBS et al.,
2009). In another study using a 3-D 6 camera system and
non-invasive techniques PEHAM et al.(2006) reported that
hind limb heel wedges increase flexion of the coffin and
hock joints and decrease extension of the fetlock joint
during the stance phase. Differences in these results may
relate to different marker sets, soft tissue artefacts present
using non-invasive markers and/or the effects of using
invasive techniques. Confirming the changes in maximal
joint rotations are important as increasing or reducing a
joint angle will alter tendon and ligament strain (LAWSON
et al., 2007) and therefore influence the success of treat-
ment, rehabilitation and pain management.
As the spine is central to the body, lameness forcibly
affects motion of the trunk and vertebrae (GOMEZ ALVA-
REZ et al., 2008) and using 3-D motion capture systems
researchers are beginning to take advantage of this tech-
nology to explore lateral bending and axial rotation
together with flexion-extension. One study of the effects of
induced hind limb lameness (GOMEZ ALVAREZ et al.,
2008) found increased axial rotation of the pelvis together
with an overall increase in thoracolumbar flexion-extension
at walk, whereas at trot there was reduced flexion-extensi-
on in the lumbosacral spine. Another study of limb and
trunk motion developed kinematic indices to quantify loco-
motion symmetry using sound and lame horses (AUDIGIE
et al., 1998). Markers used to detect body and limb motion
were successfully used by STROBACH et al. (2006) to
detect coordination competence in ataxic horses and
baseline data of horses with stringhalt have also been
measured using similar techniques (KAUFMANN et al.,
2008).
Currently 2-D motion analysis is more commonly used
as a diagnostic tool, as it is more versatile and as an exam-
ple has been documented recently to aid clinical farriery
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Wien. Tierärztl. Mschr.- Vet. Med. Austria 97 (2010)
treatment (WOODALL et al., 2008). In contrast 3-D techni-
ques are mainly used in research to extend knowledge and
understanding of clinical conditions and treatment. Howe-
ver, more novel studies are emerging such as the study by
CLAYTON et al. (2008) where the effect of tactile stimulati-
on on gait was explored. These and other work investiga-
ting the benefits of physical therapies may, in time, enhan-
ce equine rehabilitation methods.
Kinetics (measurement of forces)
in horses
Force plates or instrumented horseshoes are the 2
types of force transducers commonly used to measure
GRFs during equine locomotion. Force plates are consi-
dered a basic and fundamentally important tool for gait
analysis. The first recording of force measurements dates
back to the late 19th century when MAREY (1873) used a
wooden frame on rubber supports. ELFTMAN (1939a)
used a similar method with a platform on springs. However,
it was not until the advancement of computers and electro-
nic technology that the readings could be accurately mea-
sured. In 1965, PETERSEN and co-workers developed
one of the first strain-gauge force plates. A plethora of
publications now exists on the applications of such devices
in both clinical research and sports. Since 1965 forces pla-
tes have undergone considerable development by 3 inter-
nationally accepted manufacturers, Kistler Instruments,
AMTI and the Bertec Corporation. Advances have made
the plates more accurate (reducing crosstalk), with increa-
sed sensitivity (increasing the natural frequency), and bet-
ter portability (RICHARDS and THEWLIS, 2008).
Force plates simply measure forces as the limbs strike
them (ground reaction forces [GRFs]) and relay the infor-
mation to the computer as analog data. This analog data is
a continuous measure of voltage as the sensors in each
corner of a force plate generate a voltage as they are
deformed. The sensors are typically stacked in each cor-
ner (3 high, one for each axis). This data is then converted
to digital data (though mathematical equations), which allows
it to be viewed as a unit of force. The digital data can be
reported as force components; vertical forces (z), longitu-
dinal or braking and propulsive forces (y), and medio-late-
ral forces (x), and can be displayed as a 3-D force vector
making it helpful for visualization of the effects. A number
of measurements can be reported from the force graphs
produced, which include peak forces, times to peak forces,
averages force over the stance phase, limb loading rate
and impulse (force multiplied by time).
Force plates can also be used to measure the center of
pressure during stance, walking, trotting, or other activities
(see Fig. 3). Center of pressure analysis has been shown
to be a reliable tool for tracking movements of the horse's
center of pressure during standing (CLAYTON et al., 2003)
and this technique has been applied to assess the effects
of sedation with detomidine on the horse's balance
(BIALSKI et al., 2004). Center of pressure analysis is also
a promising technique for the detection of neurological
diseases (CLAYTON et al.,1999).
The force plate is either mounted within a raised plat-
form (Fig. 3) or embedded in the floor (Fig. 4) so that it is
even with the surface and unnoticeable to the horse. A
walkway of adequate length is essential to ensure a stea-
dy state gait pattern is achieved. Many systems have
timing lights that are triggered as the handler and horse
approach and cross the force plate to allow the calculation
of mean velocity and acceleration. Control of velocity and
acceleration within an appropriate range is essential for
repeatable data collection, because these greatly affect the
force placed on each limb (McLAUGHIN and ROUSH,
1995).
A force plate can be used to provide objective measures
of weight-bearing on limbs when proper technique is utili-
zed. Comparing the changes in forces over time is extre-
mely valuable to monitor the progression of a disease
(such as osteoarthritis), or to assess a conservative treat-
ment (such as an anti-inflammatory or analgesic medicati-
on), or surgery (DEULAND et al., 1977).
Force plates of varying sizes are usually concealed
under examination tracks and walkways (see Fig. 5)
(SCHRYVER et al., 1978;MERKENS and SCHAMHARDT,
1994; GUSTAS et al., 2004), arenas or treadmills (WEIS-
HAUPT et al., 2004), and have been used with a number
of different coverings (WILSON and PARDOE, 2001).
Inter-horse variability in GRFs between strides at a parti-
cular gait and speed is small (CLAYTON, 2005), but regu-
lating speed can be problematic. In addition, the size of the
plates will influence the ability to obtain successful foot stri-
kes at different speeds.WEISHAUPT et al. (2004) incorpo-
rated a force plate into a treadmill to overcome this pro-
blem, but as multiple hooves contact the force plate, indivi-
dual hoof forces must be derived mathematically. A draw-
back to this system is that only the vertical force compo-
nent is measured.
Instrumented or force shoes provide an alternative
method of force measurement, are able to record forces
during a number of strides (DALIN and JEFFCOTT, 1985)
and are particularly useful at higher speeds where stride
length may be over 5 m. Several designs have been deve-
loped and tested (BJÖRK, 1958; FREDERICK and HEN-
DERSON, 1970; RATZLAFF et al., 1987, 1993; HJERTEN
and DREVEMO, 1994; BARREY, 1990; ROLLOT et al.,
2004; ROBIN et al., 2009), but depending on the design,
differences in reliability and accuracy have been reported.
With the exception of the boot developed by BARREY
(1990) all of the instrumented horse shoes require some
farriery work in order that testing may take place, which
may limit their use for clinical gait analysis. Furthermore,
the weight of the force shoes, which tend to be considera-
bly heavier than steel horse shoes, may affect limb kine-
matics, especially in the swing phase.
During normal gait peak vertical forces (Fig. 6) were
found to be 6 body mass (BM) at walk (SCHRYVER et al.,
1978; RIEMERSMA et al. 1996), approximately 10 BM at
trot (SCHRYVER et al., 1978; HJERTEN and DREVEMO,
1994; MERKENS and SCHAMHARDT, 1994) and 17.5 BM
at gallop (RATZLAFF et al., 1993). At walk the vertical for-
ce profile has a double peak for both forelimbs and hind
limbs. The first peak occurs at about 20 % of the stance
phase and the point where the superficial digital flexor ten-
don experiences peak strain (JANSEN et al., 1993). At
midstance the centre of mass approaches its highest point,
decelerating the body in its upwards motion at which point
the vertical GRF reduces (MERKENS and SCHAM-
HARDT, 1994) and the suspensory ligament was found to
Wien. Tierärztl. Mschr.- Vet. Med. Austria 97 (2010)
60
Fig. 3: Horse standing on a platform with embedded 2 for-
ce plates to measure the location and movements of the
horse's center of pressure (Photo credit: Erin Grooms)
Fig. 4: Horse cantering over the force plate system in the
Mary Anne McPhail Equine Performance Center at Michi-
gan State University; the runway is viewed from behind the
screen of the Motion Analysis System (Motion Analysis
Corp., Santa Rosa, CA). The screen shows a real time
image of the horse as a stick figure, including the corre-
sponding ground reaction force vectors. 3 of the 10 infra-
red cameras arranged around the data collection volume.
are visible behind the horse (Photo credit: Britt Larson)
Fig. 5: View of the data collection runway and alcove in the
Mary Anne McPhail Equine Performance Center at Michi-
gan State University; the horse is standing on the force
plates in the center of the data collection volume and
several cameras are visible distributed around this volume.
(Photo credit: Britt Larson)
Fig. 6: Vertical (above) and longitudinal (below)
ground reaction forces for a horse at walk (left
panel) and trot (right panel); black lines represent
the forelimbs, grey lines represent the hind limbs.
Forces are normalized to body mass (N/kg) and
time is normalized to stride duration (% stride).
61
Wien. Tierärztl. Mschr.- Vet. Med. Austria 97 (2010)
experience peak strain (JANSEN et al., 1993). The centre
of mass then lowers as the limb retracts.The second verti-
cal force peak and peak propulsion are found close to heel
off and during breakover, after which the limb is gradually
unloaded (MERKENS and SCHAMHARDT, 1994). At
faster gaits only a single vertical peak is observed
(SCHRYVER et al., 1978; RATZLAFF et al., 1993; HJER-
TEN and DREVEMO, 1994; MERKENS and SCHAM-
HARDT, 1994). Fig. 6 illustrates the force patterns and dif-
ferences in vertical and longitudinal force profiles between
fore and hind limbs at walk and trot.
Clinical studies using kinetic tech-
niques
Force data is useful to clinicians, as the lame horse will
modify its gait to reduce loads on the lame limb and com-
pensate by redistributing the load to the other limbs. In
addition, to provide the momentum for propulsion they will
increase the time the lame limb is on the ground as a
means of maintaining the impulse with a lower peak verti-
cal force.Force platforms measure the force produced over
time, so these adaptations can be captured from this
equipment. WEISHAUPT et al. (2001) compared force
measurements to the results of traditional orthopaedic
examinations and suggested that they were a helpful com-
plementary tool, but data should be carefully interpreted
and related to clinical observations. BOCKSTAHLER et al.
(2008) also suggested that force data alone was useful, but
had diminished value as an evaluation of joint fuction was
not possible.
For this reason laboratory based studies often collect
both force and motion data. One such study (CLAYTON et
al., 2000b) measured changes in force and motion of the
distal forelimb following induced superficial digital flexor
tendinitis. Lower peak vertical GRFs along with changes at
the pastern and fetlock joint were reported in the lame limb
and increased braking forces and impulse in the sound
limb. Another study investigated the effect of heel wedges
in horses with experimentally induced superficial digital
flexor tendinitis. Force and motion data were collected at
trot after the application of heel wedges (CLAYTON et al.,
2000c), tendon forces were then estimated from an in vitro
model (MEERSHOEK et al., 2002). Superficial digital ten-
don force was calculated to increase in the contralateral
sound limb and tendon forces did not decrease following
the application of heel wedges in either limb. The results
indicated that heel wedges are not beneficial in horses with
this condition and instead may exacerbate the problem.
Calculation techniques (known as inverse dynamics)
can also be used to estimate muscle and tendon forces at
each joint when force and motion data are combined. This
can be useful for studying normal locomotion (CLAYTON et
al., 1998), the effect of interventions such as farriery
(SINGLETON et al., 2003), the changes associated with
lameness (CLAYTON et al., 2000a) and the effects of the-
rapeutic interventions (CLAYTON et al., 2000c). McGUI-
GAN et al. (2005) used this method to estimate the deep
digital flexor tendon loads at trot in ponies with distal pha-
langeal rotation compared to normal ponies. GRFs were
reduced in the ponies with rotation, but more importantly
tension on the deep digital flexor tendon was zero for the
first 40 % of the stance phase and then increased to reach
a peak of 6.41 BM in the breakover phase.It was suggested
that treatment should aim to reduce forces during breakover
in horses with this condition.
Navicular disease has also been studied using force
platforms and motion analysis. WILLIAMS (2001) carried
out a principal component analysis of force data from the
beginning and end of the stance phase in normal horses
and horses with navicular disease. Horses with navicular
disease were found to exhibit abnormal limb loading pat-
terns both before and after a palmer nerve block. WILSON
et al. (2001) used a force platform together with radio-
graphs and motion analysis to determine the contact area
between the deep digital flexor tendon and the navicular
bone and compressive stress on the navicular bone in vivo.
Stresses on the navicular bone were much higher in early
stance in horses with navicular disease, which was repor-
ted to be due to contraction of the deep digital flexor
muscle resulting in unloading of the heels. In another stu-
dy (McGUIGAN and WILSON, 2001) a bilateral palmer
digital nerve block was administered to horses with navicu-
lar disease. A reduction in compressive force on the navi-
cular bone was found throughout the stance phase, which
was thought to be a general response to a reduction in heel
pain, although force patterns did not return to the shape
reported for normal horses.
Other studies have found force platforms useful for dia-
gnostic purposes and to evaluate the effects of different
treatments. ISHIHARA et al. (2009) used a force platform
to differentiate between horses with hind limb lameness
and horses with spinal ataxia. From these results it was
suggested that peak lateral force and the variation in verti-
cal force could be used to differentiate between the 2 con-
ditions. The effects of different dosages of a COX-2 inhibi-
tor were evaluated in horses with osteoarthritis using a for-
ce platform to determine the optimal dose for reducing
lameness (BACK et al., 2009). Peak vertical force was
used to quantify lameness severity and found to be a relia-
ble measure. As no significant differences were found be-
tween 0.1 mg/kg and 0.25 mg/kg the lower dose was con-
sidered to be effective in the control of pain and inflamma-
tion.
Future Applications
Currently, the biggest need is to develop morphometric
models that can be used with inverse dynamic methods to
determine joint loading (that is, moments and joint reaction
forces). This research is currently underway and will
enhance the field of gait analysis in veterinary practice
greatly in years to come.
The use of either surface or fine wire electromyography
(EMG) is also in its infancy in veterinary motion analysis.
Fine wire needle electrodes are reported to affect gait or
other motions to a large degree whereas surface electro-
des developed for humans have been used more success-
fully equine studies to date (JANSEN et al., 1992; WIJN-
BERG et al., 2003, 2004, 2009; ZANEB et al., 2008). As
this technology develops, we can learn more about the
timing of muscles and when they are active in the gait cycle
or other activities. While EMG provides some quantitative
information about the force of a muscle contraction during
gait, the relationship between EMG activity and muscle for-
Wien. Tierärztl. Mschr.- Vet. Med. Austria 97 (2010)
62
ce is not linear and depends on many factors. What EMG
does provide is the timing of the firing sequences of the
muscles involved which provides a more complete picture
of how locomotion is achieved.
Motion analysis has been employed in human medicine
for decades and has been used for a variety of purposes
including surgical planning, evaluating the effectiveness of
surgery or implementation of treatment intervention, and
evaluating range of motion needed for a particular activity.
As the hardware systems and software applications advan-
ce, the usefulness of motion analysis within equine vete-
rinary medicine will continue to evolve.
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Authors´ address:
Sarah J. Hobbs, BEng (Hons), PG CERT, PhD, Jim Richards, PhD.
MSc., BEng, Darwin Building 110, Preston, PR1 2HE Lancashire,
UK; Hilary Clayton,BVMS, PhD, MRCVS, D202 Veterinary Medical
Center, East Lansing, MI 48824.1314, USA; Jeremiah J.Tate, PT,
MS, 1914 Andy Holt Avenue, 322 HPER Bldg, Knoxville, TN
37996-2700, USA; David Levine, PT, PhD, DPT, OVS, CCRP,
Randy Walker jr., PT, PhD, DPT, CMP, 615 McCallie Ave Dept #
3253, Chattanooga, TN 37403, USA.
e-mail: SJHobbs1@uclan.ac.uk
