The Gait Patterns of Olympic Dressage Horses

Transcription

1 INTERNATIONAL JOURNAL OF SPORT BIOMECHANICS, 1990, 6, The Gait Patterns of Olympic Dressage Horses Nancy R. Deuel and longdin Park Limb contact variables of the gaits of dressage horses were determined for competitors at the 1988 Seoul Summer Olympic Games in the team and individual dressage competitions. Two 16-mm motion picture cameras f1ming at 100 fps were aimed perpendicular to the plane of equestrian motion along the HXF and MXK diagonals of the standard dressage arena. Eighteen competitors in team dressage were filmed during the Grand Prix test while executing the extended walk, extended trot, and left lead extended canter. Fifteen horses selected as finalists for individual dressage medals were filmed during the Grand Prix Special test executing the extended trot, one-stride canter lead changes, two-stride canter lead changes, and the left lead extended canter. Velocities of the extended walk, extended trot, and extended canter were positively related to stride length. Velocities of the Grand Prix extended walk and Grand Prix Special extended trot were positively related to stride frequency. Limb contact patterns of the extended walk stride appeared to have relatively little importance in scoring. Certain characteristics of the extended trot and extended canter were strongly related to scores attained in Grand Prix Special dressage tests, with highest scores achieved by horses with the longest, fastest strides. For canter strides involving lead changes, no limb contact variables were detected that were significantly related to scores. This study provided the first objective documentation of the limb contact patterns of the walk, trot, and canter of world-class dressage horses. The biomechanics of the symmetrical quadrupedal walk and trots have been studied in a variety of species (Adrian, Roy, & Karpovich, 1966; Dagg & de Vos, 1968; Drevemo, Dalin, Fredricson, & Hjerten, 1980; Hildebrand, 1967; Zug, 1972), but the most detailed studies have been conducted on the domestic horse (Hildebrand, 1965; Taylor, Tipton, Adrian, & Karpovich, 1966; Wentink, 1978). Relatively few studies have been devoted to the asymmetrical canter and gallop gaits used predominantly during athletic competitions of horses (Deuel, Groppel, & Lawrence, 1983; Deuel & Lawrence, 1984, 1986, 1987a, 1987b, N.R. Deuel is with the Department of Animal and Nutritional Sciences at the University of New Hampshire, Durham, NH J. Park is with the Department of Physical Education at Pusan Sanub University, Taeyun-dong, Nam-gu, Pusan, Korea 608.

2 Olympic Dressage Horses c; Hildebrand, 1977; Leach & Dagg, 1983; Leach & Sprigings, 1979; Pratt & O'Connor, 1978). The biomechanics of the locomotion of competitive athletic horses have been studied most extensively in Standardbred racehorses (Drevemo, Dalin, Fredricson, & Bjorne, 1980; Drevemo, Dalin, Fredricson, & Hjerten, 1980; Drevemo, Fredrickson, Dalin, & Bjorne, 1980), and to a lesser extent in Thoroughbred racehorses (Leach & Dagg, 1983; Pratt & O'Connor, 1978). However, there has been little objective study of the gait kinematics of riding horses. Dressage horses receive the most lengthy training of any type of riding horse, typically a minimum of 7 years of training before entering top-level competition. Elite dressage horses display gait patterns that are the most highly developed by human training of any animal. Many excellent texts have discussed the practical aspects of gait characteristics desirable in a dressage horse (e.g., Jackson, 1967; Podhajsky, 1967). However, there has been little scientific documentation of the gait characteristics of successful dressage horses and particularly few objective studies of the kinematics of world-class competitors. Likewise, there is little research literature pertaining to the kinematics of the equine canter (Deuel et al., 1983) and none that concerns the canter of world-class dressage horses. Furthermore, little is known about the complex motion patterns that occur as a horse executing the transverse canter or gallop switches from one lead to the other (Leach & Dagg, 1983). Also, relatively little is known about the interrelationships between stride length, stride frequency, and velocity for the wide variety of equine gait patterns (Deuel & Lawrence, 1986; Leach & Dagg, 1983; Ratzlaff, Shindell, & White, 1985). The major purposes of this study were to document the walk, trot, and canter stride-timing characteristics of Grand Prix-level dressage horses for the first time, to appropriately diagram those gait patterns, and to identify relationships between stride length, stride frequency, and velocities for each gait. Another goal was to determine the limb timing patterns typical of canter lead changes. A final objective was to associate alterations in certain limb contact variables of each gait pattern with scores in world-class dressage performances at the 1988 Seoul Summer Olympic Games. This study of equine gaits will be confined to velocities, stride lengths, limb contact sequences, and temporal variables delimited by limb impacts and liftoffs, since these represent the summary result of al rotational and translational movements of body limb segments through the stride cycle. Filming Procedure Materials and Methods Limb contact variables were determined for the gaits of dressage horses competing in the 1988 Summer Olympic Games at Seoul Equestrian Park. All horses were filmed with two 16-mm motion picture cameras (100 fps), aimed perpendicular to the plane of equestrian motion along the HXF and MXK arena diagonals, while executing prescribed movements in a standard 20-m x 60-m dressage arena (Figure 1). The exposure time was 1/300 slframe. The cameras' field of view was 14 to 18 m. Eighteen of the 53 competitors in the team dressage competition were filmed during the first day of dressage competition on September 24,1988, during completion of the 7-min Grand Prix (GP) test while executing Movement

3 Deuel and Park DRESSAGE ARENA Figure 1 - Standard dressage arena used for Olympic competition, with locations of Cameras 1 and 2 depicted with focal axes perpendicular to planes of subject motion. The center of the arena was designated location X, so motion along the diagonals was described as along FXH or HXF (filmed by Camera 1) or along MXK or KXM (filmed by Camera 2). 2, extended trot; Movement 9, extended trot; Movement 11, extended walk, and Movement 23, extended canter (left lead). Fifteen of the 19 contenders for individual dressage medals (finalists) were filmed during completion of the 7.5-min Grand Prix Special (GPS) test on September 27, 1988, while executing Movement 2, extended trot; Movement 19, canter lead changes every two strides; Movement 20, canter lead changes every stride; and Movement 21, extended canter (left lead). The centermost strides in the film image were analyzed per sequence. It should be noted that the horse and rider always compete as a team in Olympic equestrian events and it was therefore impossible to differentiate the effects of specific riders on equine gaits in this study. It should also be noted that at this level of dressage competition riders do not post (rise and fall in the saddle) at the trot.

4 Olympic Dressage Horses 201 Film Data Collection Limb contact timing variables were calculated from frame-by-be determinations from projected film images of limb impacts and liftoffs on film, utilizing previously established methods and nomenclature (Deuel & Lawrence, 1986, 1987a, 1987b, 1987~). Projected film image sizes were between 4.6 and 6.8 real cmlprojected m of image. AU linear and temporal measurements reported herein were demarcated by the impact or liftoff of one or more hooves. The hoof impact frame was defined as the first frame following partial obscuring of the hoof sole and preceding rapid dorsiflexion of the metacarpo-phalangeal joint. The hoof liftoff frame was defined as the first frame after limb contact in which the metacarpo-phalangeal joint plantar-flexed beyond a relative angle of 180". Linear distances were calculated from conversions of projected image distances utilizing a reference meterstick filmed in the plane of motion. Stride lengths were determined by converted linear measurements between successive impact locations of the toe of the hind right or hind trailing limb. Stride frequencies were determined by counting the number of frames for an entire stride, then dividing by 100 framesls to yield stride duration, then calculating the inverse to obtain stride frequency. Velocities were calculated as the product of stride length and stride frequency. Data Analyses Interrelationships between scores, velocity, stride length, and stride frequency were examinedfor each gait pattern by means of multiple linear regression techniques. Limb contact data were subjected to multiple linear regression analyses of variance (SAS, 1985) to segregate and individually determine the effects of the horse, stride length, and stride duration on stride variables. Total GP score or finishing place, or GPS score, was also included in multiple linear regression analyses as a covariable to determine possible linear relationships between stride variables and dressage scores. In addition, the inclusion of score, stride length, and stride frequency as covariables permitted the calculation of least-square m&s for canter kinematic variables on an equivalent-score and equivalent-velocity basis. All comparisons of canter variables were also made on the basis of a standard (average) canter lead effect (Deuel & Lawrence, 1987~). If covariables in the mdtip!e!inear regression model were related to the dependent kinematic variable at a significance level of P<.05, simple linear regression equations were then calculated for those two variables. No data smoothing techniques were employed. Combinations of temmral variables associated with high GP and GPS scores for the trot and canters we;e determined by stepwise multiple regression (Leach, Ormrod, & Clayton, 1984; SAS, 1985), using the maximum R2 improvement method with a P<. 15 level for inclusion in the model and a P>. 15 level for deletion. Models selected and presented herein are those in which the number of variables most closely approached the C statistic (SAS, 1985). It is important to point out that Phe horses involved in this study belonged to a relatively homogeneous group of elite athletes selected for world-class competition. The R2 values represent the proportion of variability in one characteristic that can be associated with another, with no cause-andeffect relationship necessarily implied. Due to the homogeneity of the population, statistically significant relationships found in this study should be considered meaningful for world-class

5 202 Deuel and Park dressage horses, even though some R2 values may appear low at first inspection. One might expect higher R2 values from a more heterogeneous population that included horses of all ability levels. Judges' scores for the individual movements were requested but, unfortunately, were unavailable. Each judge used a scoresheet (Federation Equestre Internationale, 1983, 1987) while viewing the test. A preset number of points for a theoretical "perfect" performance were accorded to each movement, and the judges rated each competitor on each movement of the prescribed test on the basis of correctness, cadence, regularity, and the qualities of extension or collection. Judges also awarded additional points in the category of "collective marks" for overall impressions of the horse's lightness and freedom of movement, impulsion, suppleness, and submission to the rider, and the rider's position and use of aids. The percentages of each dressage test score accorded by the scoresheets to the various gaits are shown in Table 1 (FEI, 1983, 1987). The scoresheet points allocated for any individual movement presented herein represent 2.4 to 4.9% of the total score. Therefore, any statistically significant R2 value exceeding.05 that relates stride variables from a single movement with score may indicate a kinematic variable or combination of variables more strongly associated with judges' scores than one might anticipate by the scoresheet points accorded to that movement. Similarly, R2 values exceeding -12 (GP) or.07 (GPS) for walk variables,.43 (GP) or.45 (GPS) for trot variables, and.31 (GP) or.28 (GPS) for canter variables may indicate gaits given a relatively greater emphasis in the scoring than would be anticipated by the total scoresheet points assigned to movements involving that particular gait. The stride lengths, stride frequencies, and velocities that are encompassed by the various gaits of the many different breeds of horses are depicted in Figure 2. Each gait pattern characteristic of equine locomotion may be placed within a certain range on the plot. The results of this study and ongoing research in equine gait analysis will locate ranges on the plot for the most common horse gait patterns. Results and Discussion Total score for team competitors fdmed averaged 1,315 f 12 points for the Grand Prix (GP) test out of a theoretical perfect score of 2,050 points. Total score for finalists' Grand Prix Special (GPS) dressage tests averaged 1,354f 11 points, out of a theoretical perfect score of 2,050 points. The top scoring horselrider team in both phases was Rembrandt 24 (a bay Westfalian gelding) ridden by Nicole Uphoff of the Federal Republic of Germany, receiving 1,458 points in the GP test and 1,521 points in the GPS test. Extended Walk Stride of Team Competitors The extended walk of team dressage horses was similar to that of most quadrupeds (Dagg & de Vos, 1968) and other horses studied (Hildebrand, 1965; Wentink, 1978), with a lateral hoof impact sequence and contact sequences alternating between bipedal and tripedal contact (Table 2 and Figure 3). According to the nomenclature of Hildebrand (1965), the strides observed would be termed those of a fast lateral sequence diagonal couplet walk. On the average, bipedal contact accounted for 61 % of the total stride duration while tripedal contact accounted for the remaining 39% of the stride duration. The average extended walk stride

6 Olympic Dressage Horses Table 1 Scoring of Dressage Tests and Movements Filmed at the 1988 Summer Olympic Games Movements Grand Prix Grand Prix Test Special Test Diagonal Relative Diagonal Relative filmed' score (Oh) filmed* score (010) Walk Collected Extended Trot Collected Medium Extended Passage Piaffe Canter Collected Extended Single-stride lead changes Double-stride lead changes Pirouette Collective marks Freedom and regularity Impulsion and engagement Attention, lightness Submission Rider Position Use of aids Total KXM (4.9) MXK (2.4) HXF (2.4) HXF (2.4) KXM (4.9) HXF (2.4) *Order of letters indicates direction of motion along the arena diagonal (see Figure 1). Adjacent percentage value in parentheses represents the points allotted to that motion pattern in the overall score. duration of 1.03 s, equivalent to a tempo of 58 strideslmin, was only slightly longer than that of.98 s observed in ponies and horses walking at 1.4 to 1.8 m/s (Wentink, 1978), with briefer hoof contacts and longer noncontact durations in this study. Since extended walk velocities averaged 1.88 mls in this study, stride lengths were longer than those observed by Wentink (1978). Velocity, stride length, and stride duration of the extended walk were not significantly related to GP score or finishing place. Therefore it would seem that the characteristics of the extended walk were relatively unimportant in the overall score of the Grand Prix test. The velocity of the extended walk was not significantly related to stride duration, but varied with stride length such that velocity =.882

7 204 Deuel and Park - A 3.5 I W V) " 2.5 > VELOCITY (M/SECI Y 2.0 W M LL U) 4 t 2 O l ; ; b STRIDE ; d LENGTH 7 ; (MI ;! 0 Figure 2 - Plot of stride frequency, stride length, and resultant velocities within the extent of the limits of equine locomotion (stride length) (R2 =.45, P<.001). Extended walk stride duration and stride length were positively related such that stride duration = (stride length) (R2=.42, P<.OOl). Extended Trot Stride of Team Competitors and Finalists The trot is a moderate-velocity gait of quadrupeds in which diagonal limb pairs move in synchrony (Hildebrand, 1965). A depiction of trot motion patterns of an Olympic dressage gold medalist is provided in Figure 4. The extended trot of team competitors had an average velocity of rnls (mean f SE), range 4.09 to 6.07 mls; stride length m, range 3.02 to 4.68 m; stride duration.763f.004 s, range.680 to.820 s. This equates to a tempo of 79 strideslmin. The tempo cited for the working trot of 154 strideslmin for Grand Prix horses by Cohen (1989) must actually refer to a step frequency, equivalent to a tempo of 77 strideslmin. Extended trot velocity was strongly related to stride length, such that velocity = (stride length) (R2 =.88, P<.0001). Stride duration was not significantly related to stride length, but velocity and stride duration were negatively related such that velocity = (stride duration) (R2=.30, P<.oOol). For team competitors, limb contact durations and limb noncontact durations both increased with trot stride duration, such that mean limb contact duration = (stride duration) (R2 =.22, P<.05); and mean limb noncontact duration = (stride duration) (R2 =.33, P<.01). For finalists, mean limb contact durations did not vary significantly with stride duration, but limb

8 Olympic Dressage Horses Table 2 Limb Contact Variables of the Extended Walk Stride of Olympic Team Dressage Horses Variable Mean SE Min. Max. Range Velocity (mls) Stride length (m) Stride duration (s) Limb contact durations (s) Hind right Hind left Fore right Fore left Limb impact intervals (s) Left lateral (HL- FL) Right lateral (HR- FR) Left diagonal (HR-FL) Right diagonal (HL-FR) Fore (FL- FR) Hind (HR-HL) Bipedal contact durations (s) HR + FL HR + FR HL + FR HL + FL Total Tripedal contact durations (s) HR + HL + FR HR + HL + FL HR + FR + FL HL + FR + FL Total Limb noncontact durations (s) Hind right Hind left Fore right Fore left All temporal measurements are presented on the basis of an average stride duration and GP score. N = 36 strides of 18 horses. Abbreviations: H = hind, F = fore, L = left, R = right. noncontact durations were found to increase with stride duration such that mean limb noncontact duration = (stride duration) (R2=.42, P<.0001). Limb contact durations and limb noncontact durations of the extended trot did not differ between limbs for team competitors and finalists. However, impact intervals between ipsilateral limbs were significantly longer on the right side than on the left side of the body for both team competitors (P<.0001) and finalists (P<.01).

9 Deuel and Park PIE GAIT DIAGRAM EXTENDED WALK STRIDE Figure 3 - Pie gait diagram of limb contacts of the walk contact sequence of Olympic dressage horses. Label values indicate for each limb contact phase the duration of the phase (s) and the proportion of the entire stride (%). Limb contacts, depicted counterclockwise in time: H = hind, F = fore, L = left, R = right. For team competitors, extended trot velocity, stride length, and stride frequency were not significantly related to GP score or finishing place. Two stride temporal variables of the extended trot of team competitors were found to have significant relationships with GP score. Impact intervals between limbs varied with GP score such that GP score = ,260 (right lateral limb impact interval) (R2 =.26, P<.05); and GP score = 1, ,460 (hind right-fore left limb impact interval) (R2 =.17, P<.05). A combination of three extended trot temporal variables was found to be most closely associated with increased GP scores by stepwise multiple regression (R2=.26, P<.001): a decreased hid left noncontact phase, an increased impact interval between right limbs, and a decreased interval between liftoffs of the right hind and fore left limbs. These findings indicate that in the extended trot, superior dressage horses tended to have an increased time interval between the hind right limb impact before the fore left diagonal limb impact, while liftoffs of those limbs tended to occur more simultaneously. In addition, superior horses had relatively longer intervals between the impact of the hind right limb and fore right limb. These may be indications of hind limb laterality in increased reliance upon the hind right limb in support at the extended trot.

10 Olympic Dressage Horses Extended trot Gold medalist Rembrandt Olympic Games Dressage Competition Figure 4 - Sequential depictions of nearly one-half stride (one step) of the extended trot of the 1988 Olympic dressage individual gold medalist. The stride depicted begins with hind left-fore right diagonal limb contact and would continue similarly after No. 4 with hind right-fore left diagonal limb contact. The extended trot strides of finalists tended to have higher velocities, longer stride lengths, and shorter stride durations than those of team competitors. This is an expected result of their more pronounced extension. The average tempo was 80 strideslmin for the extended trot of finalists. Every trot stride variable measured was found to differ among finalists (P<.OoOl). The limb contact patterns seem to be highly individualized features of the extended trot stride, which is in agreement with the findings of Drevemo, Dalii, Fredricson, and Hjerten (1980) in their study of trotting Standardbreds. This indicates potential for the use of individualized kinematic profiling for performance evaluation of the trot of athletic horses. Descriptive statistics for trot stride variables of finalists are listed in Table 3. Velocity of the extended trot of finalists was strongly influenced by stride length, such that velocity = (stride length) (R2 =.79, P<.0001), but was not closely related to stride duration, with velocity = (stride duration) (RZ =.14, P<.01). Stride duration and stride length of the extended trot were not significantly related in finalists.

11 Deuel and Park Table 3 Limb Contact Variables of the Extended Trot Stride of Olympic Dressage Finalists Variable Mean SE Min. Max. Range Velocity (mls) Stride length (m) Stride duration (s) Limb contact durations (s) Hind right Hind left Fore right Fore left Bipedal contact durations (s) Left diagonal (HR + FL) Right diagonal (HL + FR) Total Airborne durations (s) Before left diagonal contact (HR + FL) Before right diagonal contact (HL + FR) Total Limb impact intervals (s) Left diagonal (HR-FL) Right diagonal (HL-FR) Left lateral (HL-FL) Right lateral (HR-FR) Fore (FL-FR) Hind (HR-HL) Limb liftoff intervals (s) Left diagonal (HR- FL) Right diagonal (HL-FR) Unipedal contact (s) Total Limb noncontact durations (s) Hind right Hind left Fore right Fore left All temporal measurements are presented on the basis of an average stride duration and GPS score. N = 30 strides of 15 horses. Abbreviations H = hind, F = fore, L = left, R = right. Limb contact sequences of the extended trot showed variability even among this homogeneous group of horses (Figures 5 and 6). The most common exact limb contact sequence of the entire extended trot stride of finalists (9 of 30 strides) was (1) hind right unipedal contact, (2) hind right-fore left diagonal bipedal contact, (3) fore left unipedal contact, (4) airborne phase, (5) hind left unipedal contact,

12 Olympic Dressage Horses LIMB CONTACTS EXTENDED TROT STRIDE Figure 5 - Limb contact sequences of extended trot strides of finalist Olympic dressage horses. Each line segment between boxes represents 10% of contact sequences observed. Limb contact combinations indicated in boxes: H = hind, F = fore, L = left, R = right. (6) hind left-fore right diagonal bipedal contact, (7) fore right unipedal contact, and (8) airborne phase. This was also the most common exact limb contact sequence for the extended trot strides of team competitors (12 of 31 strides). In finalists, velocity and stride length of the extended trot were found to be positively related to GPS score, such that GPS score = (velocity) (R2=.53, P<.0001), and GPS score = (stride length) (R2=.55, P<.0001). These findings highlight the importance of an ability to produce an extremely long extended trot stride, well in excess of 4 m, producing a velocity above 5.4 rnls to obtain top scores in world-class dressage competition. Several temporal variables of the extended trot of finalists were found to have significant relationships with GPS score. Right fore contact duration varied inversely with GPS score such that GPS score = (fore right contact) (RZ=. 17, P<.05). Fore right noncontact duration, fore limb impact interval, right

13 Deuel and Park HL PIE GAIT DIAGRAM EXTENDED TROT STRIDE Figure 6 - Pie gait diagram of limb contacts of the most common extended trot contact sequence of finalists Olympic dressage horses. Label values indicate for each limb contact phase the duration of the phase (s) and the proportion of the entire stride (%). Limb contacts, depicted counterclockwise in time: H = hind, F = fore, L = left, R = right. lateral limb impact interval, and hind left-fore right diagonal contact duration all varied positively with GPS score such that GPS score = (fore right noncontact) (R2 =.17, P<.05); GPS score = -2, ,100 (fore limb impact interval) (R2 =.14, P<.05); GPS score = - 1, ,250 (right lateral limb impact interval) (R2 =.17, P<.05); and GPS score = 2,390-4,878 (hind left-fore right diagonal contact duration) (R2=.29, P <.01). These findings indicate that the extended trot of superior world-class dressage horses was characterized by a long time duration between the impacts of the two fore limbs and also a reliance upon right hind limb contact in the extended trot. Trot characteristics may account for up to 45% of the points awarded to the competitor, but the extended trot movements fdmed only account for 2 to 5 % of the total score. The R2 values relating GPS score and trot stride variables measured during the extended trot ranged between.14 and.29. This would indicate that the characteristics of the extended trot are of relatively great importance in the judges' scores for GPS movements involving the trot, or that these kinematic variables are also reflected in other trot movements and scored accordingly. However, the overall importance of these variables is within the range one might expect for scoring of the trot. It also seems that the limb contact variables of the trot are of greater importance in the GPS scores for finalists than in the GP scores

14 Olympic Dressage Horses 21 1 for team competitors, possibly reflecting a greater emphasis on qualities of gait after an initial selection of the most accurate, consistent, and correct performers. The combination of five extended trot temporal variables found to be most closely associated with increased GPS scores by stepwise multiple regression (R2=.37, P<.0001) were an increased fore right contact duration, an increased fore left noncontact duration, a decreased interval between hind left and fore right liftoffs, a decreased airborne phase following hind right-fore left diagonal contact, and a decreased hind left-fore right diagonal contact. The tendency for right limb kinematic variables to vary with judges' GPS scores highlights the presence and importance of laterality in equine gaits (Deuel & Lawrence, 1987~). The extended trot strides of this study would be termed those of a slow running trot, according to the terminology of Hildebrand (1965). Predictably, the trot stride durations measured in this study were much longer, stride lengths were shorter, and velocities were slower than stride durations of.46 s and stride lengths of 5.45 m measured in racing Standardbreds trotting at 12 mls (Drevemo, Dalin, Fredricson, & Hjerten, 1980), with the mean limb contact duration occupying approximately 31 % of the limb stride cycle in this study but approximately 25% of the limb stride cycle in standardbred racehorses. Extended Canter Stride of Team Competitors The canter is an asymmetrical gait common to quadrupeds (Hildebrand, 1977). The first limb of each pair mnd or fore) to impact is termed the trailing limb, while the second limb to impact is termed the leading limb. Horses generally utilize a transverse canter sequence in which the limbs' impact order for the right lead canter is (1) hind left, (2) fore left, (3) hind right, and (4) fore right (Deuel & Lawrence, 1984, 1986; Hildebrand, 1977). Similarly, the impact sequence for the left lead canter is (1) hind right, (2) fore right, (3) hind left, and (4) fore right. The extended canter is intended to display extension and impulsion while maintaining correct, attentive form. For team competitors, extended canter velocities averaged nds, range 5.42 to 7.74 nds; stride lengths m, range 3.39 to 4.72 m; and stride durations.604f.005 s, range.520 to.650 s. The tempo was 99 strideslmin, slightly faster than the 96 strideslmin cited by Cohen (1989) for canter work. Every canter stride variable measured was found to differ (P<.05) among team competitors, and therefore the limb contact characteristics of the gait are highly individualized features of the extended canter stride, just as they are in the gallop gait (Deuel & Lawrence, 1987b). This indicates potential for the use of individualized kinematic profiling for performance evaluation of the canter of athletic horses. A trend toward a positive relationship was detected between extended canter stride length and GP score, such that GP score = - 1, (stride length) (RZ=.12, P<.052). There was no significant relationship between extended canter stride length and finishing place, nor between stride duration or velocity and GP score or finishing place. The velocity of extended canter strides of team competitors was related to both stride length and stride duration. Stride length was strongly related to velocity in the range of 5.4 to 7.7 nds such that velocity = (stride length) (RZ=.69, P<.0001). Stride duration was less closely related to velocity such that velocity = (stride duration) (R2=.21, P<.01). Stride duration and

15 212 Deuel and Park stride length were not significantly related. These findings are in contrast to the strong positive relationship between velocity and stride duration in the upper velocities of the gallop of Quarter Horses, in the range of 10 to 15 mls (Deuel & Lawrence, 1986). Extended Canter Stride of Finalists For finalists, limb contact variables for each canter stride movement (extended, one-stride lead changes, two-stride lead change prechange, two-stride lead change postchange) are provided in Table 4 and Figures 7 and 8. A two-stride canter lead change sequence of gold medalist Rembrandt is depicted in Figure 9. The extended canter of finalists, in comparison with team competitors, had similar stride durations and a tempo that tended to be only two strideslmin greater at 101 strideslmin. However, finalists tended to canter at higher velocities as a result of longer stride lengths than team competitors, thus displaying a greater degree of extension while maintaining a fairly constant cadence. Velocity and stride length of the extended canter of finalists were positively related to GPS score, such that GPS score = 1, (velocity) (R2 =.13, P<.05) and GPS score = (stride length) (RZ=.20, P<.05). This indicates that extended canter stride lengths greater than 4.2 m and velocities above 7.1 m/s were necessary to achieve the highest scores in world-class dressage competition. Extended canter stride variables were significantly related to GPS scores at RZ values from.13 to.20. Similar to the findings for the extended trot, this would indicate that the characteristics of the extended canter are of relatively great importance in the judges' scores for GPS movements involving the canter, or that these variables are also reflected in other canter movements and scored accordingly. However, the overall importance of these variables is within the range one might expect for scoring of the canter. More kinematic variables of the canter are related to scores of finalists than to the scores for team competitors, possibly Table 4 Limb Contact Variables of Canter Strides of Olympic Dressage Finalists Variable 2-Stride lead changes 1-Stride Prechange Postchange changes Extended SD N strides Velocity (mls) Stride length (m) Stride duration (s) Limb contact durations (s)' Hind trail Hind lead Fore trail Fore lead

16 Olympic Dres~ge Horses Table 4 (Cont.) Variable 2-Stride lead changes Prechange Postchange 1 -Stride changes Extended Unipedal contact durations (s)' Hind trail Hind lead Fore trail Fore lead Total Bipedal contact durations (s)'s2 HT + HL HT + FT HT + FL HL + FT HL + FL FT + FL Total Tripedal contact durations (s)'12 HT + HL + FT HL + FT + FL Total Total quadrupedal contact duration (s)'.~ HT + HL + FT + FL Contact durations (s) Total hind Total fore Total contact Noncontact durations (s) Hind trail Hind lead Fore trail Fore lead Airborne phase Impact intervals (s)~ HT-HL HL-FT FT- FL FL - HT Contact ratios (s:s) Hind lead: total hind Fore lead: total fore Total fore: total hind 'All temporal measurements are at least-square means presented on the basis of an average stride duration, lead effect, and GPS score. Values without common superscripts within a row are different (P<.05). 'Abbreviations are H = hind, F = fore, L = lead, T = trail.

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18 Olympic Dressage Horses LIMB CONTACTS EXTENDED CANTER STRIDE Figure 8 - Limb contact sequences of extended canter strides of finalist Olympic dressage horses. Each line segment between boxes represents 10% of contact sequences observed. The dashed lines indicate observed strides representing less than 10% of the total. Limb contact combinations indicated in boxes: H = hind, F = fore, L = lead, T = trail. reflecting a greater emphasis in scoring on the pure qualities of gaits of finalists after an initial selection in the team competition of the most accurate, consistent, and correct performers. Stepwise multiple regression (R2=.90, P<.0001) revealed a combination of 11 extended canter temporal variables associated with higher total GPS scores: longer hind lead limb contacts, shorter fore lead limb contacts, shorter hind trail noncontact durations, longer intervals between impacts of hind lead and fore trail limbs, smaller ratios of hind lead contact to total hind contacts, greater ratios of fore lead contact to total fore contacts, greater ratios of fore contacts to hind contacts, longer unipedal contacts of the hind lead limb, shorter fore tripedal contacts, shorter simhltaneous contact of the two hind limbs, and longer airborne durations. These may reflect characteristics of the higher velocity extended canter of superior competitors.

19 Canter lead change Gold medalist Fkmbrandt Olympic Games Dressage Competition Deuel and Park?,& 3 4 & 3+ with Figure 9 - Sequential depictions of two strides during a canter lead change of the 1988 Olympic dressage individual gold medalist. The canter stride depicted in No. 1 through No. 5 begins with hind left limb impact and finishes with fore right limb contact (a right lead stride) and then the horse changes leads before the subsequent stride, No. 6 through No. 10, which begins with hind right limb contact and finishes fore left limb contact (a left lead stride). This sequence was traced from projections of a doublestride lead change sequence in Movement 19 of the Grand Prix Special dressage test. A practical interpretation of these findings is that the horses scored highest by the judges had relatively long, fast extended canter strides. In these strides the hind lead limb was used to a greater degree independently in support, with hind limb and fore limb contacts well separated in time. The top-scoring dressage horses thereby displayed the highest degree of extension at the canter. For each canter stride movement of finalists, stride length and velocity were strongly related,

20 Olympic Dressage Horses 21 7 but stride duration and stride length tended to be unrelated. Stride duration and velocity were not significantly related for any canter stride movement, in contrast to the higher velocity gallop gait (Deuel & Lawrence, 1986). For the extended canter, velocity = (stride length) (RZ=.63, P<.0001). There was some variability in the limb contact sequences for extended canter strides of this homogeneous group of horses (Figures 8 and 9). The most common exact limb contact sequence for extended canter strides (19 of 40 strides) was (1) hind trail unipedal, (2) hind trail-fore trail bipedal, (3) hind trail-hind leadfore trail tripedal, (4) hind lead-fore trail bipedal, (5) hind lead-fore trail-fore lead tripedal, (6) hind lead-fore lead bipedal, (7) fore lead unipedal, and (8) airborne phase. Fewer than 5 % of extended canter strides had limb contact sequences typical of the gallop gait, that is, with a hind trail-hind lead bipedal contact, a unipedal hind lead contact, a unipedal fore trail contact, and a fore trail-fore lead contact. Therefore, nearly all strides filmed were those of a true extended canter. Extended Canter Strides Versus Canter Lead Change Strides of Finalists Elite-level dressage horses are intensively trained to readily change from one canter lead to the other (Jackson, 1967; Podhajsky, 1967) (Figure 9). Lead changes are a fairly difficult athletic maneuver for horses bearing a rider to accomplish smoothly and consistently, so they are only tested in the highest levels of dressage. All canter lead changes filmed were correctly executed first by the hind limbs. AU strides observed were those of the transverse canter (Deuel & Lawrence, 1983; 1987a), although horses are capable of switching leads only in the fore limbs and thereby executing rotary canter strides (Hildebrand, 1977), which are awkward for horses and are considered undesirable. In comparison with strides that involved canter lead changes, strides of horses moving at the extended canter had nearly twice the velocities and stride lengths, as well as shorter mean stride durations, even though the ranges of stride durations were similar for all movements. Canter movements with lead changes had an average tempo of 98 strideslmin, while extended canter movements had an average tempo of 101 strideslmin. Extended canter strides had shorter limb contact durations and longer limb noncontact durations for all four limbs. In addition, there were shorter total contact durations and longer airborne phases in extended canter strides. Total bipedal contact durations, total quadrupedal contact durations, total hind contact durations, and total fore contact durations were all shorter in extended canter strides than in strides involving lead changes. For all strides involving lead changes, velocities, stride lengths, and stride durations were not significantly related to GPS scores. Therefore it was likely that accuracy, consistency, and correctness of these difficult canter lead change maneuvers received the greatest emphasis by the judges in scoring rather than emphasizing pure qualities of gait kinematics. For one-stride canter lead changes, stride length and velocity were related such that velocity = OO (stride length) (R2=.53, P<.0001), and stride duration = I15 (stride length) (R2=.31, P<.0001). For two-stride lead change sequences, stride length and velocity were related such that, for the prechange stride, velocity = (stride length) (R2 =.68, P<.0001); and for the postchange stride, velocity = (stride length) (R2=.70, P<.0001). Stride durations were similar for onestride canter lead change strides and postchange two-stride lead change strides,

21 218 Deuel and Park each with a tempo of 97 strideslmin, but prechange two-stride lead change strides were of a shorter (P<.05) duration with a tempo of 99 strideslmin. These values are similar to the tempo of 96 strideslmin cited by Cohen (1989) for canter work. Two-Stride Canter Lead Changes of Finalists In comparison with canter strides following a lead change, canter strides preceding a lead change had lower velocities, shorter stride lengths, and shorter stride durations, even though ranges of stride durations were similar. In addition, they displayed shorter limb contact durations for the hind lead limb, fore trail limb, and fore lead limb (Figure 10). They also had longer noncontact durations for the hind lead limb and the fore lead limb, but shorter contact durations for the fore trail limb. In addition, strides preceding a lead change had shorter fore lead unipedal contacts, shorter hind trail-hind lead bipedal contacts, longer hind trailfore bipedal contacts, and shorter total contact durations and longer airborne durations, as well as longer intervals between impacts of the hind limbs and lower ratios of hind lead contact to total hind contacts. The most common exact limb contact sequence for canter strides immediately preceding a lead change (10 of 32 strides) was (1) hind trail unipedal, (2) hind trail-fore trail bipedal, (3) hind trail-hind lead-fore trail tripedal, (4) hind lead-fore trail bipedal, (5) hind lead-fore trail-fore lead tripedal, (6) hind leadfore lead bipedal, (7) fore lead unipedal, and (8) airborne phase (Figure 1 I). The most common exact limb contact sequence for canter strides immediately following a lead change (15 of 31 strides) was (1) hind trail unipedal, (2) hind trail-hind lead bipedal, (3) hind trail-hind lead-fore trail tripedal, (4) hind lead-fore trail bipedal, (5) hind lead-fore trail-fore lead tripedal, (6) hind lead-fore lead bipedal, (7) fore lead unipedal, and (8) airborne phase (Figure 12). The most pronounced difference between the limb contact patterns of prechange and postchange canter lead change strides was that strides preceding lead changes had the impact of the fore trail limb occurring before the impact of the hind lead limb, but in strides following lead changes the limb impact sequence was reversed. Canter strides preceding lead changes had a wide variety of limb contact patterns toward the end of the contact phase, with 3 1 % of strides having a fore trail-fore lead bipedal contact phase, 19% of strides having simultaneous liftoff of the hind lead limb and fore trail limb, and 50% of strides having a hind lead-fore trail contact phase. On the other hand, strides following lead changes consistently showed an exclusive reliance upon lateral support by the hind lead and fore lead legs toward the end of the contact phase. Stepwise multiple regression (R2=.44, P<.05) revealed a combination of seven temporal variables of the prechange canter stride that was associated with the highest total GPS scores: shorter fore trail contacts, shorter impact intervals between fore lead and hind trail limbs, longer hind trail unipedal contacts, longer bipedal contacts of the hind trail and hind lead, longer bipedal contacts of the hind lead and fore lead, longer hind tripedal contacts, and shorter quadrupedal contacts. These findings may be interpreted to mean that in the stride preceding a lead change, superior horses showed a higher degree of collection and longer hind limb contacts as they prepared to propel themselves into the air to execute the lead change. Stepwise multiple regression (R2=.38, P<.05) revealed a combination of five temporal variables of the postchange canter stride that was associated with

22 CANTER LEAD CHANGE PRE-CHANGE STRIDE POST-CHANGE STRIDE Figure 10 - Pie gait diagrams of limb contact phases of two-stride canter lead change strides for prechange and postchange canter strides of finalist Olympic dressage horses, standardized to similar stride durations. Label values indicate for each limb contact phase the duration of the phase (s) and the proportion of the entire stride (%). Limb contacts, depicted counterclockwise in time: H = hind, F = fore, L = lead, T = trail. N, a

23 Deuel and Park LIMB CONTACTS TWO-STRIDE CANTER LEAD CHANGES PRE-CHANGE STRIDE Figure 11 - Limb contact sequences of two-stride lead change prechange canter strides of fialist Olympic dressage horses. Each line segment between boxes represents 10% of contact sequences observed. Limb contact combinations indicated in boxes: H = hind, F = fore, L = lead, T = trail. the highest total GPS scores: longer impact intervals between hind limbs, shorter impact intervals between fore limbs, longer bipedal contacts of the fore trail and fore lead, longer quadrupedal contacts, and longer total tripedal contacts. In the stride following a lead change, superior horses showed a higher degree of multiplelimb support for stability and maintenance of balance. One-Stride Lead Change Versus Two-Stride Lead Change In comparison with strides of horses executing two-stride lead changes, strides completed while executing one-stride lead changes had slower velocities, shorter stride lengths, shorter hind trail limb contact durations, and longer hind trail limb noncontact durations (Table 4). However, they had similar stride durations to

24 Olympic Dressage Horses LIMB CONTACTS TWO-STRIDE CANTER LEAD CHANGES POST-CHANGE STRIDE GALLOP STRIDE I CANTER STRIDE Figure 12 - Limb contact sequences of two-stride lead change postchange canter strides of fiialist Olympic dressage horses. Each line segment between boxes represents 10% of contact sequences observed. Limb contact combinations indicated in boxes: H = hind, F = fore, L = lead, T = trail. postchange strides of two-stride canter lead changes. In addition, one-stride lead changes involved longer hind trail-hind lead bipedal contact durations, shorter hind lead-fore lead bipedal contact durations, longer fore trail-fore lead bipedal contact durations, and shorter intervals between fore limb impacts than did strides involving two-stride lead changes. Two different limb contact sequences predominated in one-stride canter lead change strides. The most common lib contact sequence for one-stride lead change canter strides (15 of 51 strides) was (1) hind trail unipedal, (2) hind trail-hind lead bipedal, (3) hind trail-hind lead-fore trail tripedal, (4) hind lead-fore trail bipedal, (5) hind lead-fore trail-fore lead tripedal, (6) fore trail-fore lead bipedal, (7) fore lead unipedal, and (8) airborne phase. The second most common limb contact sequence for one-stride lead change canter strides (12 of 51 strides) was

25 Deuel and Park LIMB CONTACT ONE-STRIDE CANTER LEAD CHANGES Figure 13 - Limb contact sequences of one-stride lead change canter strides of finalist Olympic dressage horses. Each line segment between boxes represents 10% of contact sequences observed. Limb contact combinations indicated in boxes: H = hind, F = fore, L = lead, T = trail. (1) hind trail unipedal, (2) hind trail-hind lead bipedal, (3) hind trail-hind leadfore trail tripedal, (4) hind lead-fore trail bipedal, (5) hind lead-fore trail-fore lead tripedal, (6) hind lead-fore lead bipedal, (7) fore lead unipedal, and (8) airborne phase (Figure 13). One-stride canter lead changes showed a pronounced reliance upon simultaneous contact by two hind limbs at the initiation of support and a simultaneous contact by the two fore limbs near the termination of support (Figure 13). Thus the contact phases of the strides were initiated quite similar to strides following a two-stride lead change, but the strides were terminated with the most pronounced emphasis on bipedal fore limb contact of any of the canter strides filmed, similar to the limb contact pattern at the completion of gallop strides. Stepwise multiple regression W=.61, P<.0001) revealed a combination of seven temporal variables of one-stride canter lead changes associated with higher

26 Olympic Dressage Horses 223 total GPS scores: lower fore trail contact durations, lower fore lead contact durations, longer intervals between impacts of the fore lead limb and hind trail limb, longer total hind limb contacts, longer bipedal contacts of the hind lead and fore trail, shorter bipedal contacts of the hind lead and fore lead, and longer quadrupedal contacts. In single-lead change strides, higher scoring horses displayed a greater degree of hind limb contact and multiple limb contact, possibly contributing to balance, collection, and impulsion from the hind quarters. They also had an increased airborne time available to execute the lead change. Comparisons of Stride Lengths, Frequencies, and Velocities The stride length, stride frequency, and velocity characteristics typical of a number of equine gait patterns is depicted in Figure 14. On the plot are shown gaits of superior dressage horses from this study: the extended walk (Walk), the extended trot (Trot), the extended canter (Canter), and canter lead changes (Canter LC). The extended canter of Olympic individual dressage gold medalist Rembrandt was also indicated, with a notably long stride. The plot includes a variety of other equine gaits for comparison: the Standardbred racing pace (SB Pace) (Wilson, Neal, Howard, & Groenendyk, 1988); Figure 14 - Plot of stride frequency, stride length, and resultant velocities within the limits of equine locomotion, with regions typical of strides of a number of equine gait patterns indicated by ellipses. Olympic dressage horses: Walk = extended walk; Trot = extended trot; Canter = extended canter; Canter LC = canter lead changes. Standardbred harness racehorses: SB Pace = pace; adjacent Trot = trot. Thoroughbred flat racehorses: TB Gallop = gallop. Quarter horse flat racehorses: QH Gallop = gallop. Gaits of selected elite equine athletes indicated by solid dots.