Coordination Dynamics of the Horse-Rider System

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<ul><li><p>This article was downloaded by: [University of Ulster Library]On: 13 November 2014, At: 09:32Publisher: RoutledgeInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK</p><p>Journal of Motor BehaviorPublication details, including instructions for authors and subscription information:</p><p>Coordination Dynamics of the Horse-Rider SystemJ. Lagarde a , C. Peham b , T. Licka b &amp; J. A. S. Kelso ca Florida Atlantic University Center for Complex Systems and Brain Sciences Boca Ratonb University of Veterinary Medicine Vienna Clinic of Orthopedics in Ungulates Wien, Austriac Florida Atlantic University Center for Complex Systems and Brain Sciences Boca RatonPublished online: 07 Aug 2010.</p><p>To cite this article: J. Lagarde , C. Peham , T. Licka &amp; J. A. S. Kelso (2005) Coordination Dynamics of the Horse-Rider System,Journal of Motor Behavior, 37:6, 418-424, DOI: 10.3200/JMBR.37.6.418-424</p><p>To link to this article:</p><p>PLEASE SCROLL DOWN FOR ARTICLE</p><p>Taylor &amp; Francis makes every effort to ensure the accuracy of all the information (the Content) containedin the publications on our platform. However, Taylor &amp; Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor &amp; Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.</p><p>This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms &amp; Conditions of access and use can be found at</p><p></p></li><li><p>Coordination Dynamics of the Horse~Rider System</p><p>J. LagardeCenter for Complex Systems and Brain SciencesFlorida Atlantic UniversityBoca Raton</p><p>C. PehamT. LickaClinic of Orthopedics in UngulatesUniversity of Veterinary Medicine ViennaWien, Austria</p><p>ABSTRACT. The authors studied the interaction between riderand horse by measuring their ensemble motions in a trot sequence,comparing 1 expert and 1 novice rider. Whereas the novicesmovements displayed transient departures from phase synchrony,the experts motions were continuously phase-matched with thoseof the horse. The tight ensemble synchrony between the expert andthe horse was accompanied by an increase in the temporal regu-larity of the oscillations of the trunk of the horse. Observed differ-ences between expert and novice riders indicated that phase syn-chronization is by no means perfect but requires extended practice.Points of contact between horse and rider may haptically conveyeffective communication between them.</p><p>Key words: coordination dynamics, dressage, expertise, phase syn-chronization</p><p>adward Muybridges (1899) high-speed photographsprovided an early picture of animal gaits, themselves a</p><p>beautiful example of biological coordination that hasreceived considerable analysis by biologists (Grillner, 1985;Hildebrand, 1965; Holst, 1973; Hoyt &amp; Taylor, 1981; Shik&amp; Orlovsky, 1976), mathematicians (Collins &amp; Stewart,1993; Golubitsky, Stewart, Buono, &amp; Collins, 1999; Rand,Cohen, &amp; Holmes, 1988; Stewart &amp; Golubitsky, 1992), andphysicists (Schner, Jiang, &amp; Kelso, 1990). The inherentrhythmicity of animal gaits has afforded a deep understand-ing of their coordination dynamics; in furtherance of thatunderstanding, investigators have used the mathematicaltheory of weakly coupled oscillators (Collins &amp; Stewart,Rand et al.), group symmetry arguments (Golubitsky et al.;Stewart &amp; Golubitsky; Schner et al.), and the concepts ofsynergetics (Haken, 1977; Kelso, 1995; Schner et al.).However, the nature of the coordination between the riderand the horse, a partnership that has spanned centuries(Minetti, 2003), remains elusive. Adding the rider to the</p><p>horse raises some new problems. What are the essential fea-tures of the functional coordination between two such high-ly complex systems that differ on so many dimensions, oneof which (the rider) must adapt to the horses motion at thesame time as he or she tries to gain and achieve control?Skill of the rider and training of the horse are ubiquitouscomponents of that particular cooperation. The results ofprevious work have shown that a skilled rider is able to sta-bilize a horse trotting on a treadmill (Peham, Licka,Schobesberger, &amp; Mescham, 2004), but, thus far, no one hasstudied the mutual interaction between rider and horse interms of their coordination dynamicsthat is, as an infor-mationally coupled dynamical system. For that reason, wecompared two riders of different skill levels, one an expertin dressage and the other a hobby rider who occasionallypractices dressage at a lower level.</p><p>Method</p><p>We measured the motion of the horse and the riders for aworking trot, with the rider sitting on the saddle throughout.The two riders were instructed to perform a trot on differenttrials (N = 8) with the same horse, as if they were compet-ing in a dressage competition. To analyze the movement ofthe horse and the rider, we recorded and digitized, respec-tively, a set of 10 and a set of 8 markers, the locations ofwhich are shown in Figure 1A. We used the sagittal planespanned by the horizontal (x) and vertical (z) axes of thelaboratory frame of reference to represent the motion of themarkers.</p><p>Correspondence address: J. Lagarde, Center for Complex Sys-tems and Brain Sciences, Florida Atlantic University, Boca Raton,FL 33431-771, USA. E-mail address:</p><p>E</p><p>418</p><p>Journal of Motor Behavior, 2005, Vol. 37, No. 6, 418424</p><p>J. A. S. KelsoCenter for Complex Systems and Brain SciencesFlorida Atlantic UniversityBoca Raton</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Uni</p><p>vers</p><p>ity o</p><p>f U</p><p>lste</p><p>r L</p><p>ibra</p><p>ry] </p><p>at 0</p><p>9:32</p><p> 13 </p><p>Nov</p><p>embe</p><p>r 20</p><p>14 </p></li><li><p>Horse~Rider Coordination Dynamics</p><p>November 2005, Vol. 37, No. 6 419</p><p>Riders and Horse</p><p>The horse was ridden at a working trot, with the riders sit-ting according to definitions of the Federation EquestrianInternationale (1995). A male professional rider (age = 33years, body mass = 65 kg) and a female recreational rider(age = 30 years, body mass = 65 kg) rode the horse at aworking trot. During the riding measurements, a ridinginstructor judged the performance of horse and rider with a10-point scoring system, according to Federation EquestrianInternationale guidelines.</p><p>Markers</p><p>We attached spherical markers coated with a reflexivefoil to the right temporal region of the rider and to theriders right shoulder, elbow, hand, hip, and knee, as well ason the heel and the tip of the right boot (Figure 1A). On the</p><p>horse, we placed similar markers on the median line of thenasal bone and on the frontal bone. Two markers wereplaced on the sacral bone, one on the lateral side of the rightcarpal joint, one on the lateral side of the right tarsal joint,and one on each of the two right fetlock joints. Two hemi-spherical markers, each with a diameter of 7 cm, wereplaced on the right fore and hind hoofs. We accomplishedplacement of the markers by using textile adhesive tape,Velcro straps, or both. To minimize unilateral influence onthe motion, we similarly taped the described locations onthe left side of the horse.</p><p>Data Recording and Processing</p><p>For the measurements, the horse was ridden on a 12-m-long pressed-sand track in an indoor riding arena. Six cam-eras (sample rate = 120 Hz, resolution = 240 833 pixels)</p><p>FIGURE 1. Time series of vertical displacement. A. Locations of the 18 markers on the bodiesof the rider and the horse, recorded on the xz plane (axes shown). B. Representative time seriesof the oscillations along the z coordinate. Top. Riders. Bottom. Horse. Left. Novice rider. Right.Expert rider. The displacements are shown with an offset for clarity. From bottom to top, eachtrajectory represents, for the riders, motion of the toe, heel, knee, hip, wrist, elbow, shoulder, andhead; and for the horse, motion of the right hind hoof, right hind fetlock, right hock, right forehoof, right fore fetlock, right carpal joint, sacral bone back, sacral bone front, nasal bone, andfrontal bone. C. One cycle of vertical oscillation of the shoulder, elbow, and wrist for the two rid-ers, isolated from the data shown in B. For the novice rider, the oscillations were synchronizedtogether at the maxima of vertical displacement, whereas at the minima, corresponding to theextension of the horse, an increasing phase shift evolved from the shoulder to the wrist. For theexpert, the synchronization was maintained during the entire cycle.</p><p>A</p><p>B</p><p>Cz</p><p>x</p><p>z</p><p>500 ms</p><p>Novice</p><p>Horse</p><p>Expert</p><p>Horse</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Uni</p><p>vers</p><p>ity o</p><p>f U</p><p>lste</p><p>r L</p><p>ibra</p><p>ry] </p><p>at 0</p><p>9:32</p><p> 13 </p><p>Nov</p><p>embe</p><p>r 20</p><p>14 </p></li><li><p>placed along the right side of the measurement track record-ed the marker positions with the ExpertVision System(Motion Analysis Corp., Santa Rosa, CA). Eight trials wererecorded. We realized and optimized the calibration of thespace volume by using a cube with eight markers and awand of known length (1.5 m). We used the sagittal planeso that parallax and perspective errors would be minimized.We filtered marker motions by using a Butterworth low-pass filter with a cutoff frequency of 5 Hz, except for thefore hoof marker, which we filtered with a cutoff frequencyof 20 Hz because of different maximum speeds of markermotion.</p><p>Data Analysis</p><p>We extracted the instantaneous phases of the verticalmotions of the horse and the riders by using the Hilberttransform (Bendat &amp; Piersol, 1985). A peak-to-peak esti-mation of the relative phase gave similar results. We calcu-lated mean and standard deviation of the phase differenceby using circular statistics (Batschelet, 1981).</p><p>Results</p><p>Obviously, the periodic nature of the motions plays animportant role in the analysis and understanding of thecoordination between the horse and rider as a coupleddynamical system. As can be seen in Figure 1B, the timeseries of the two bodies displayed fairly regular oscillatorymovements along the vertical axis, particularly the head andthe back of the horse and the entire body of the rider.Because the horse moves the rider up and down throughtranslational motion, the rider must continually adjust his orher movements to accommodate the mechanical interactionwith the horsea kind of impedance matching (Hogan,1985). The very nature of the task of riding is information-ally linked to the horses locomotion through various pointsof contact, such as the saddle (bottom), the trunk (legs), thestirrups (feet), and the reins (hands). Note the essential rec-iprocity of those points of contact. For example, the horsesgait may be altered subtly by the shape of the saddle(Fruewirth, Peham, &amp; Scheidl, 2002; in equestrian circlesthey say a horse is sensitive enough to detect a fly on itsback and good riding is all about feel). Observed oscilla-tions in the movements of the horse and the riders can bedirectly related to the relative timing of the limbs in a char-acteristic trot; that is, one pair of diagonal legs moves inphase and half a period out of phase with the other diagonalpair (homologous limbs are antiphase). As a result, for eachcycle of a given pair of diagonal legs, there are two verticaloscillations of the trunk, giving rise to a 2:1 frequency ratio(the so-called two-beat pattern; for comparison, walk andgallop are four beats and canter is three beats). Notice inFigure 1B that the vertical oscillations of the riders were ofthe same magnitude as the oscillations of the sacrum andthe head of the horse. A closer look at the riders motionsreveals that the joints from the shoulder to the wrist of theexpert (Figure 1C, right time series) oscillated together in</p><p>time. By contrast, the movements of the hobby rider (Figure1C, left time series) exhibited a delay that traveled andappeared to grow from the shoulder to the wrist. That delaybegan at the lowest point of the cycle, which correspondedto the beginning of limb extension in the horse. As a result,the expert was able to keep the motion of all the joints of theupper body closely synchronized with the horses trunk,whereas for the novice, that synchrony was disrupted ateach vertical extension of the horse.</p><p>To quantify the coordination between the horse and therider, we calculated the mean and standard deviation of therelative phase (Batschelet, 1981) between a reference mark-er located on the sacrum of the horse and each marker onthe rider (Figure 2). As shown in Figure 2A and B, the meanrelative phase across the markers differed between the rid-ers, F(1, 14) = 8.23, p &lt; .05. In particular, the novice riderexhibited a larger phase lag relative to the horses sacrumthan the expert did. But the interaction between the skill ofthe rider and the riders ensemble motions (given by theanatomical markers) was also significant, F(7, 98) = 52.95,p &lt; .01. Whereas the experts shoulder, elbow, and wristwere aligned (the so-called straight-line position indicativeof excellent balance), the novices motions displayed a sys-tematic phase shift (cf. shaded regions in Figure 2A and B).Those mean changes in relative phase were accompanied bya consistent increase in relative phase variability, a measurethat has been shown to index the stability of coordination(Kelso, 1984), F(7, 98) = 3.41 p &lt; .01 (Figure 2C and D).The insets in Figure 2C and D show the distribution of therelative phases for the wrist marker for both riders and thecorresponding power spectra for a representative trial. Thesharper peak displayed by the expert (Figure 2D) suggeststhat strong phase synchronization is achieved only afterextended practice and learning.</p><p>An inspection of the mean relative phase between thesacrum of the horse and sensors located on the lower bodyof the rider revealed additional differences between the rid-ers. For the expert rider, the heel went up much later thanthe toe, whereas heel and toe moved more closely togetherin the novice (Figure 2A and B). Those rider-specific phas-ing patterns suggest that the expert used ankle flexion todamp vertical oscillations of the horse, whereas the novicekept her ankle joint still and stiff. Later activation of theheel relative to the toe may also...</p></li></ul>