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Introduction A lot of useful information about how a horse moves can be obtained just by watching it. With the advent of modern video and optoelectronic systems, we can quantify the motion (or kinematics) of the horse's limbs and study it in greater detail. However, external observations alone cannot directly answer the question: "How is the horse achieving the motion?" or, in other words, what's going on inside those powerful limbs? We would like to know things like: Which muscles are working to achieve a particular motion? When are these muscles active? What kind of forces are they producing? How do the activation patterns and forces of the muscles change with different activities? With lameness?
Our lab is working towards developing an understanding of the Joint Moment and Joint Power profiles in normal horses at walk, trot and canter. Armed with this knowledge, we can begin to asses the effects of factors such as lameness and specific sport movements on the normal locomotion patterns. We will also be combining our knowledge of net muscle function through
Joint Moments and Powers with information on muscle activity patterns during
a given motion. Muscle activation times are measured with a technique
known as electromyography
(EMG), which uses sensors to record the electrical activity in muscles.
When information describing which muscles are active at any given time
is combined with a knowledge of the anatomy of the horse, we can speculate
on how the horse creates different Joint Moment and Power profiles and
thus have a greater insight into how the horse moves!
Methods Data Collection Most of the original data for this project was collected from 1994 to 1997 at Utrecht University's Equine Biomechanics Lab in the Netherlands. The facility there is equipped with a high speed optoelectronic system (CODA-3) for collecting kinematic data, and a force platform (Kistler, Type Z4852C) for collecting external ground reaction forces. Our own 60 Hz video camera system was also employed to collect some kinematic data. Some additional data was collected at the Equine Performance Center at the Western College of Veterinary Medicine , University of Saskatchewan, Canada during the summer of 1997. At the Equine Performance Center, 60 Hz video was used to collect kinematic data and a force platform (AMTI, OR6-5) was used to collect ground reaction forces. In the future, data will be collected at Michigan State University's College of Veterinary Medicine using video based systems for kinematics and a force platform (AMTI, LG6-4) for ground reaction forces. As well, data will continue to be collected at Utrecht University and other sites, including Texas A&M University . Most of the current data focuses on the motion and forces in the sagittal plane of the horse. The motion of the limb during locomotion is assumed to be primarily two dimensional. Inverse Dynamics The technique used in this project to estimate the net muscle torque at the various joints is known as Inverse Dynamics. This method uses our simplified model of the horse's limb, the kinematic data describing the motion of the limb, information on the known forces at one end (in this case, the distal end of the hoof), and the inertial properties of the model to calculate the forces in the rest of the limb. The limb is modeled as a series of segments linked together by frictionless hinge joints. The net muscle forces are modeled as torque generators at each joint. The model is formulated in such a way that, if the forces are known at any instance in time at one end of a segment, they can be calculated for the other end. These newly calculated forces become the known forces for the end of the next segment and so on. When the limb is on the ground, the external forces acting on the distal end of the hoof are measured using a force plate. When the limb is in the air, the forces acting on the distal end of the hoof are also known, because they are zero. Thus, the forces in each joint of the model can be calculated. The method of inverse dynamics as it applies to equine gait analysis
was presented in Colborne et al, 1997a,
one of the first papers published from this project. There is also
an explanation
of inverse dynamics as it applies to human biomechanics in the Clinical
Gait Analysis FAQ page, part of Dr. Chris Kirtley's informative human
biomechanics site: Clinical
Gait Analysis.
Results The Walk - Fore Limb - Stance Phase Some initial data for this project was collected in October of 1994 at Utrecht University. Four Dutch warmblood horses were used. They were led in hand across the force platform while being recorded by two 60 Hz video cameras. The data from the force platform and the kinematics obtained from the video were combined and an inverse dynamics analysis was performed at the walk. The results were the basis of initial publications describing the methodology and preliminary analysis (Colborne et al, 1997a). As part of the development of the methodology, power flows were also calculated and reported Colborne et al, 1997b). Power flows use the results from the inverse dynamics analysis to examine how energy is being transferred between segments up and down the limb during locomotion. Finally, a complete paper presenting the walk data was given in
Colborne et al (1998).
Dr. Colborne
is now at the University of Bristol.
After the work on the walk, another set of data was collected on trotting horses. The subjects were also Dutch warmbloods and the data was collected once again at Utrecht University. In this study, six horses were used and mean data was obtained for the right fore limb. The results of the experiment were published in Clayton et al (1998).
The following are graphs showing the measured joint angles and calculated moments and powers for the fore limb during the stance phase of the trot. All of the joint angles were measured on the palmar/caudal side of the joint. The significant, repeatable peaks in the joint power profiles were labeled and will be used for future comparison with other data.
Future Work Hind Limb The joint moments and powers in the hind limb during normal gaits will be investigated. Lameness Data have been collected from horses with suspensory ligament strains and navicular problems. The joint moments and powers will be calculated and compared with data from the normal group to examine the differences in muscle action at different joints during the lameness. Dressage Movements Data have been and will continue to be collected on various dressage horse/rider combinations performing different dressage movements. The joint moment and power data from these activities will be examined to gain a better understanding into how the horse performs the movements. Swing Phase Data The picture of the normal joint moments and powers in equine gait will be more fully developed with the examination of the swing phase. Some possible additional data may include the effects of hoof weights (or heavy shoes) on the net joint moments. Electromyography (EMG) Collection of simultaneous EMG data with force plate and video data will enable
a more complete understanding of which muscles are involved in creating
the calculated net joint moments.
 For more detailed information about The McPhail Dressage Chair in Equine Sports Medicine, please visit the The McPhail Dressage Chair in Equine Sports Medicine Website at The McPhail Dressage Chair in Equine Sports Medicine
Dr. Hilary M. Clayton |
To
answer some of these questions, we must use our observations of the motion
and dig a little deeper. It is very difficult to measure forces produced
by a muscle directly, so we must find ways to indirectly estimate these
forces. To do this, we start by creating a simplified model of the
limb. We combine the kinematics with knowledge of the inertial properties
of the limb and any external forces to estimate the net effect of muscles
at various joints. These net muscle effects are known as Joint Torques
or Joint Moments since the muscles are modeled as generators of rotational
force or torque.
Having
estimated the net muscle effect at each joint, we can then study the energy
patterns of the muscle groups. When the net muscle effect is working
to move the joint, we say that the muscles are performing a 