The Effect of Racetrack Design on Gait Symmetry of the Pacer

W.H. Crawford and D.H. Leach*

ABSTRACT

A survey of a western Canadianracetrack determined the supereleva-tion and transition curves to be lessthan the cited design standards. High-speed cinematography was used tofilm seven Standardbred pacers asthey proceeded around one curve ofthe track at racing speed and for eachhorse 19 temporal stride parameterswere obtained from these films using afilm analyzer system. Average veloci-ties were calculated and the meanstride length was found to vary from5.08 m to 5.77 m. In all frames ana-lyzed the hind foot was observed tocontact the track surface prior to theipsilateral forefoot and all horses dis-played significant (p < 0.05) contra-lateral asymmetry of some temporalstride parameters. Fifteen temporalstride parameters were significantlydifferent (p < 0.05) when comparedbetween horses but only three tem-poral stride parameters were signifi-cantly different (p < 0.05) when theirvalues were compared between seg-ments of the curved portions of thetrack. It is suggested that temporal gaitasymmetry should not be used to judgethe standards of racetrack design.

Key words: Pacer, locomotion, gaitanalysis, temporal stride characteris-tics, stride length, racetrack design.

RESUME

L'investigation d'une piste decourses de l'Ouest canadien revela quesa surelevation et ses courbes de transi-tion etaient en de'a des normes stan-dards. Les auteurs utiliserent la cine-matographie ultrarapide pour filmersept ambleurs Standardbred, alorsqu'ils negociaient une courbe de la

piste, a la vitesse de course et, pourchacun d'eux, ils obtinrent ainsi, araide d'un analyseur approprie, 19parametres temporels de leursenjambees. Ils calculerent aussi lavitesse moyenne de ces ambleurs etconstaterent que la longueur moyenned'une enjambee variait de 5,08 a 5,77metres. L'analyse de leurs films lesamena aussi a constater que le piedposterieur des ambleurs touchait le solavant le pied anterieur ipsilateral etqu'ils affichaient tous une asymetriecontralaterale significative (p < 0,05)de certains parametres temporels deleurs enjambees. Quinze de ces para-metres affichaient une difference ap-preciable (p < 0,05) d'un cheval a l'au-tre, mais seulement trois se revelerentsignificativement differents (p < 0,05)lorsque les auteurs comparerent leurvaleur, entre les segments des courbesde la piste. Les resultats de cette inves-tigation indiquent qu'il ne faudrait passe referer a l'asymetrie temporelle de lademarche, lors de l'elaboration desnormes standards du trace d'une pistede courses.

Mots cles: ambleur, locomotion, ana-lyse de la demarche, caracteristiquestemporelles d'une enjambee, longeurd'une enjambee, trace d'une piste decourses.

INTRODUCTION

There is concern regarding the inci-dence of equine lameness in the horseracing industry (1,2,3,4,5) and the fac-tors involved in racing injuries havebeen investigated (4,6,7,8,9,10,1 1).Incorrect curvature and supereleva-tion of racetrack turns have beenimplicated as major contributing fac-tors to the incidence of lameness (8,12). Fast moving trotters exhibit

asymmetric limb placement whenmoving through inadequately designedracetrack curves (12,13,14). These gaitasymmetries are reduced by the transi-tion curve, located between thestraight and true curve portions of thetrack, which permits a gradual changein the superelevation and degree ofcurvature (8).

Linear and temporal gait character-istics have been described for trottersin Sweden moving on straight sectionsof racetracks (15,16,17,18) and Jordan( 19) reported linear gait characteristicsfor pacers and trotters travelling in astraight line. However, there is noinformation on the temporal gaitcharacteristics of racing pacers. Thepurpose of this study is to investigatethe temporal gait characteristics of fastmoving pacers travelling on thestraight and curved portions of a trackdesigned with transition curves.

MATERIALS AND METHODS

RACETRACK DESIGN

The racetrack studied was located atNorthlands Park in Edmonton,Alberta. It is a 1000 meter (5/8 mile)(Fig. 1) course on which the east andwest turns have transition curves at thebeginning and end of the true curve.The west turn of the racetrack wasused in this study. A land survey wasconducted using standard surveyingtechniques to determine the superele-vation of this turn.

HORSES

Ten sound Standardbred pacers,capable of racing 1600 m (1.0 miles) inless than two minutes and ten seconds,were selected for this study. A recenthistory of soundness and performancewas obtained from the trainer of eachhorse. Each horse, without bandagesor harness, was observed standing and

*Department of Veterinary Anaesthesiology, Radiology and Surgery (Crawford) and Department of Veterinary Anatomy (Leach), Western College ofVeterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan S7N OWO. Present address of Dr. Crawford: Department of SurgicalSciences, School of Veterinary Medicine, University of Wisconsin, Madison, Wisconsin 53706.

This work was supported by a grant from the Western College of Veterinary Medicine Equine Health Research Fund.

Submitted August 19, 1983.

Can J Comp Med 1984; 48: 374-380.374

Fig. 1. Plan of Northlands Park Racetrack,Edmonton, Alberta. 'Starting point of survey.bIngoing straight. Ingoing transition curve.true curve. eOutgoing transition curve. TOut-

walking and then, when harnessed to ajog cart, observed at a slow trot orpace. Each individual limb was thencarefully examined using palpation,passive flexion and extension. Forfilming each horse was numbered andthen driven by an experienced driver ina standard jog cart.

FILMING TECHNIQUE

Range poles and numbered identifi-cation cards were placed in designatedareas around the west turn and itsadjoining transition curves andstraightaways in order to identify thehorse's position on the racetrack as itappeared on the film. The distancebetween each pair of hubrail posts wasmeasured and recorded.Two high-speed 16 mm research

cameras (Locam, Model 164-50C, RedLake Laboratories Inc., Santa Clara,California) on tripods were placed

going straight. gJunction of ingoing straight andingoing transition curve at 60 m from 0 + 00.hJunction of ingoing transition curve and truecurve at 120.0 m from 0 + 00. 'Junction of true

1.5 m away from each other on separ-ate platforms elevated three metersabove ground level. The cameras werelocated at the centre of curvature forthe west turn of the racetrack (Fig. 1).Film speed was 300 frames per secondand timing lights located in eachcamera created a small area of expo-sure on the film at 0.10 second inter-vals to verify the film speed.

Each horse was jogged clockwisearound the track for 3200 to 4800 m asa warm-up exercise and then driven ina counter-clockwise direction 1.5 mfrom the hubrail, at the fastest possibleconstant speed over the surveyed seg-ments of the west turn. The drivers didnot urge the horses in any manner thatmight cause velocity changes, buthorse I would not maintain a constantspeed without excessive urging andwas withdrawn from the trial.The horses attained maximum

curve and outgoing transition curve at 353.3 mfrom 0 + 00. iJunction of outgoing transitioncurve and outgoing straight at 396.2 m from0 + 00.

speed at the one-mile starting pole(Fig. 1). Camera I was started whenthe horse was at a point 30 meters eastof station 0+00, thereby insuring thecamera to be running at a stabilizedspeed when the horse reached station0+00. This camera filmed the horse tothe midpoint of the west turn. Camera2 was started when the horse waslocated 30 meters prior to the mid-point of the turn and similarly filmedthe horse through the remaininglength of the west turn to a point 12meters beyond the southwest transi-tion curve. In some filming sequencesthe south straight section was notincluded or was incompletely filmeddue to limitations of film length. Eachhorse in the trial repeated the sequenceat least four times, while some of themcompleted five or six sequences. Allsequences for each horse were filmedon the same day with a time interval

375

=3 =

that varied from five minutes to onehour between each sequence.The fourth film sequence of horses

2, 3, 4, 6, 7, 8 and 9 was chosen foranalysis because it contained the max-imum amount of useable film footage,and by this sequence the horses werewell warmed up and familiar with theroutine. However, only for horse 6 wasdata available in the outgoing straight(OS). Horse I was withdrawn from thetrial because of inconsistent speed, thefilm quality was unsatisfactory for thefourth sequence of horse 5 and horse10 was injured in the third filmingsequence and was unable to continuethe trial.

ANALYSIS

All the strides available on the filmswere analyzed for the ingoing straight(IS), ingoing transition curve (IT),outgoing transition curve (OT) andoutgoing straight (OS) but for the truecurve (TC) a group of seven consecu-tive strides was chosen from itsmidpoint.The average velocity for each seg-

ment of the track was calculated fromthe time, determined by film framecounts, required for the horse to go aknown distance between designatedpositions on the hubrail (HR). Distan-ces determined in this manner are sub-ject to parallax errors in the IS and OSsegments of the track, therefore a cor-rection was applied using the methodshown in Figure 2. The parallax errorbecomes negligible as the angle aapproaches zero on the curved seg-ments of the track.A frame by frame film analyzer

(Vanguard Motion Analyzer, Model160, Vanguard Instrument Corp.,Melville, New York) was used todetermine the following temporalstride parameters (TSP): stride dura-tion, left stance phase duration, rightstance phase duration, left suspensionphase duration, right suspensionphase duration, stance phase durationfor each individual limb, the durationof the overlap period between ipsilat-eral limbs, the advance placementintervals and the duration of the singlesupport phase for each individual limb(20) (Fig. 3).A two-day analysis of variance (21)

was used to compare the TSP betweeneach horse over all the track segmentsand to examine the differences in these

Hubrail

acc

w

a = w tan a'

a'

m

a

bw

a = w tan a

error = a-a': true distance = 60 + w (tana - tan a')

Fig. 2. Calculation of correction due to parallax error for distance measurements over the ingoingand outgoing straight segments ofthe track when the distance is measured from films taken from thecentre of curvature of the turn. 'Center of curvature and camera location. bDistance of the horseaway from the hubrail.

parameters that occurred between theIS, IT, TC and OT segments of theracetrack. A one-way analysis of var-iance was used to compare the TSPbetween track segments for horse 6.The relationship between stride dura-tion and average velocity was exam-ined using a linear regression analysis.Average stride length in each tracksegment, for each horse, was deter-mined by multiplying the averagestride duration by the average cor-rected velocity for the segment. Pairedt-tests (22) were used to compare the

mean times of the stance and suspen-sion phases and to compare the stancephase and single support phase timesbetween ipsilateral limbs. To deter-mine if asymmetry was presentbetween the left and right side of thepacer as it proceeded around the turn,the mean values and standard error ofthe mean (SEM) for each parameteron each of the track segments weredetermined for each horse. The differ-ence between contralateral temporalparameter means and the standarderror of the difference (SED) between

376

GO

bIH

RIGHT STANCE

Time n frames (1 frame=.0033 s)FM

dRH

IF RF

LEFTSUSPENSION_

single Single single singleoverlp support support overlap port

LH LH-LF _ F RH RH-RF RF

stance of LF stance of RF

_stance of LH stance of RH

ad.-pl. advanced placement ad.-pl. advanced placement_,~~~a-LH La LF-RH RH-RF RF-LH

stride duration

LEFT STANCE

e-* Hoof contact with track surface. Hoof touches theground at Fi and leaves the ground at FE.

Fig. 3. Relationship of temporal stride parameters (TSP) to contact of horse's foot with the tracksurface. 'Advance placement. bLeft hind. cLeft fore. dRight hind. 'Right fore.

TABLE 1. Northlands Park Racetrack Survey Results. Superelevation and Elevations on the TrackSurface at the Hubrail (HR) and Lines Running Parallel to the Hubrail at 2.5 m, 5.0 m and 10.0 mfrom the HR

Track 2.5 m 5.0 m 10.0 mPosition H Ra from HR from HR from HR SuperelevationJO + oob 0oo.ooi 100.10 100.20 100.43 4.00STC 99.99 100.09 100.21 100.49 4.20mTCd 100.03 100.21 100.42 100.76 8.402 + 60e 100.06 100.24 100.43 100.80 8.60CT' 100.06 100.22 100.41 100.69 8.20TS5 100.00 100.09 100.19 100.43 3.084 + 40h 100.01 100.11 100.20 100.43 4.00

aHubrailbStarting point of surveycJunction of ingoing straight and ingoing transition curvedMidpoint of true curvee260 m along track surface from 0 + 00fJunction of true curve to outgoing transition curvegJunction of outgoing transition curve and outgoing straighth440 m along track surface from 0 + 00'Elevation (m) at the track surfaceJSuperelevation (%) calculated at a point 5 m into the track surface from the HR

these means were determined. TheSED between the means was expressedas standard deviation units (t ratio)away from a hypothesized mean dif-ference of zero (21). Differences wereconsidered significant (p < 0.05) whenthel t ratiol > 1.96.

RESULTS

TRACK SURVEY

There was a gradual increase in the

amount of elevation over the length ofthe transition curve (Fig. 4). Thesuperelevation was found to be con-stant at each survey station and there-fore the percentage of superelevationat 5.0 m from the HR was consideredto be representative. Table I shows themaximum superelevation was 8.60%occurring at station 2 + 60, thirtymeters beyond the mid point of thetrue curve (Station 2 + 30). The sharpincrease in elevation at station 3 + 80

(Fig. 4), 5 m from the inside rail,results from the transition curvesuperelevation being increased inorder to meet the relatively flat,straight chute incoming from a higherelevation at the southwest corner (Fig.1). The decrease in elevation on the TCsegment was the result of track main-tenance error (Fig. 4).

INTERINDIVIDUAL TEMPORALCHARACTERISTICS

Table II shows the mean correctedvelocity, mean stride duration andmean stride length for all the horses oneach segment of the track. The meanstride length for individual horsesranged from 5.08 m to 5.77 m, with anoverall mean of 5.41 m. In five of theseven horses the mean stride durationtended to become shorter as the horsesprogressed from the ingoing straightto the outgoing transition segments.Comparison by linear regression, ofstride duration to average velocity foreach horse in each segment of thetrack, shows a strong negative coeffi-cient of regression for horse 6 (r=-0.927) and horse 8 (r = -0.9914). Theremaining horses show poor negative(three horses) or positive (two horses)coefficients of regression.Mean of the mean values of TSP

obtained for horses 2, 3,4, 6, 7, 8 and 9are presented in Table III.The stance phase of the left and right

sides was significantly (p < 0.05)longer in duration than the suspensionphases and the hindlimb exhibits asignificantly (p < 0.05) longer stancephase and single support phase thanthe ipsilateral forelimb.

All horses placed the hind limb onthe ground in advance of the ipsilateralfore limb. The advance placementtimes range from 0.016 seconds to0.045 seconds and averaged 6.79% ofthe stride duration time.

Table IV presents the data of thehorses that have contralateral asymme-tries (CA) as demonstrated by signifi-cant (p <0.05) differences betweenthe mean values of contralateral tem-poral stride parameters. The tracksegments in which these differencesoccur are indicated. Examination ofTable IV shows that most of the CAoccur on the IT, TC and OT and thereappears to be more CA on the IT thanon the OT. The contralateral limbstance phases, LH-RH and LF-RF,

377

U'

RIGHT-SUSPENSION-

e-- o$ 10 meters from inside rail

9 O3 O 5.0 " " "

-+ I ++- 25 " "

6 a a inside roil

STa TCl=120.9b

. . ... . .

CT= 3+35.3c TS= 3- 96.2d*Kt i

0+00 0.20 0+40 0-tO u-8. 1.- .2.'. :-.: !-,I !-t. .2-.22 .'22C 2+4C ?-2.,8 ?8C .-) 3.20 3+40 3+.O 3+8004.0 4-.0 4+40

STATION ON INSIDE RAIL (METERS)

Fig. 4. Elevation of the racetrack surface adjacent to the inside rail (hubrail) 2.5 meters, 5.0 metersand 10.0 meters from the inside rail. aJunction of ingoing straight and ingoing transition curve at60 m from 0 + 00. bJunction of ingoing transition curve and true curve at 120.9 m from 0 + 00.cJunction of true curve and outgoing transition curve at 353.3 m from 0 + 00. dJunction of outgoingtransition curve and outgoing straight at 396.2 m from 0 + 00.

TABLE II. Mean Values and Standard Deviations of Stride Parameters Velocity, Stride Duration,Stride Length, RF-LH Advanced Placement, RF Stance Phase for Horses 2,3,4,6,7,8,9 at EachTrack Segment

Track Velocity Stride Stride RF-LH Advanced RFSegmenta (mps)b Duration (s) Length (m) Placementc (s) Stanced (s)

is, 12.58 0.33 0.427 ± 0.014e 5.41 ± 0.21 0.184 ± 0.012 0.108 ± 0.004IT 12.49±0.40 0.428±0.016 5.34±0.22 0.188±0.010 0.105±0.009TC 12.81 0.56 0.422 ± 0.022 5.39 ± 0.38 0.185 ± 0.010 0.103 ± 0.008OT 12.84±0.70 0.423±0.022 5.39±0.28 0.181 ±0.013 0.102±0.011osg 13.74 0 0.408 ± 0.006 5.50 ± 0 0.176 ± 0.008 0.089 ± 0.006

alS = ingoing straight, IT ingoing transition, TC = true curve, OT= outgoing transition,OS = outgoing straightbMean velocity (mps) in each segment corrected for parallax errorcMean advanced placement time of the right fore limb over the left hind limb (s)dMean right fore stance phase time (s)eMean TSP ±SD calculated for each track segmentfValues based on observations from five horses onlygValues based on observations from one horse only

have the lowest incidence of CA andwhere suspension phase CA occur inthe IT and TC the left suspensionphase is of shorter duration than theright suspension phase.The two-way analysis of variance

showed that significant (p < 0.05) dif-ferences exist between horses over allthe track segments in all temporal gaitcharacteristics with the exception ofthe right suspension phase, stance ofthe left foreleg, advanced placement ofthe right fore foot over the left hindfoot and the single support phase ofthe left fore limb.

TRACK SEGMENT COMPARISONS OFTSP

Comparing only the curve segmentsof the track, IT, TC and OT, by atwo-way analysis of variance, there is asignificant difference (p < 0.05) instride duration, RF-LH advancedplacement time and RF stance phasetime. Table II shows the mean valuesof these TSP for all horses on eachsegment of the track. Inclusion of theIS with the curved segments in a two-way analysis ofvariance results in onlythe RF stance phase showing a signifi-cant difference (p < 0.05).

Film length limitations resulted ininsufficient data being collected in theOS for all horses except horse 6. Aone-way analysis of variance found nosignificant (p < 0.05) differences toexist in any of the TSP relating to thetrack segment for horse 6.Temporal gait characteristics that

have significant changes related totrack segments did not increase nordecrease predictably with specifictrack positions and no trend can be

TABLE III. Mean of the Mean Temporal Stride Parameters (TSP) for Standardbred Pacers Moving at Racing Speeds

StrideHorse Dura- Stance Phase Suspension Stance of Limb Overlap Advance Placement Single SupportNo. tion Left Right Left Right LH RH LF RF RH-RF LH-LF LH-LF LF-RH RF-RF RF-LH LH RH LF RF

2 0.418b 0.124 0.123 0.089 0.082 0.107 0.104 0.102 0.106 0.087 0.086 0.020 0.191 0.018 0.188 0.020 0.018 0.016 0.0183 0.458 0.143 0.143 0.086 0.087 0.116 0.114 0.108 0.110 0.081 0.080 0.036 0.194 0.033 0.197 0.036 0.033 0.028 0.0284 0.431 0.136 0.148 0.073 0.074 0.112 0.113 0.109 0.109 0.074 0.086 0.026 0.182 0.038 0.185 0.026 0.038 0.023 0.0356 0.416 0.130 0.127 0.076 0.084 0.098 0.097 0.096 0.098 0.068 0.067 0.031 0.172 0.029 0.179 0.031 0.029 0.030 0.0297 0.404 0.124 0.139 0.063 0.076 0.108 0.108 0.105 0.101 0.080 0.090 0.018 0.168 0.038 0.176 0.018 0.038 0.015 0.0328 0.423 0.135 0.126 0.078 0.081 0.109 0.104 0.103 0.097 0.077 0.077 0.032 0.181 0.029 0.177 0.032 0.029 0.026 0.0229 0.415 0.138 0.134 0.066 0.075 0.111 0.111 0.101 0.106 0.088 0.072 0.166 0.029 0.182 0.182 0.037 0.032 0.029 0.023

Range 0.408 0.114 0.119 0.057 0.063 0.088 0.092 0.087 0.089 0.059 0.059 0.016 0.158 0.017 0.168 0.016 0.017 0.010 0.014of - - - - - - - - - - - - - - - - - - -

MeansaO.462 0.148 0.154 0.097 0.092 0.123 0.118 0.114 0.113 0.105 0.097 0.043 0.202 0.045 0.020 0.043 0.046 0.032 0.041

aRange of mean values from track segments IS, IT, TC, OT, OSbMean TSP (s) calculated from the mean average TSP for track segments IS, IT, TC, OT, OC

378

102 r

(0LUILUI

z0

Li-jLUJ

99

100

TABLE IV. Horses Displaying Signifilcant (p < 0.05) Left Side to Right Side Asymmetry in Each Design Segment of Track

TrackSeg- L-R L-R Stance of Limb Overlapg Advance Placement Single Supportment Stancea Suspensiond LH-RH' LF-RF' (LH-LF) - (RH-RF) (LH-LF) - (RH-RF)h (LF-RH) - (RF-LH)' LH-RHi LF-RFk

4. (3.79) 9. (-4.61) 9. (3.12) 9. (3.11)IS 3. (-4.41)

4. (3.30)4.b (-3.75)C 3. (2.61) 8. (3.51) 8. (3.26) 4. (3.46) 4. (-3.70) 3. (2.58) 4. (-3.70) 3. (2.39)8. (2.29) 4. (-2.4) 7. (-3.40) 7. (-2.61) 6. (-3.10) 7. (-2.61) 4. (-3.61)

IT 6. (-3.74) 9. (-3.52) 7. (-2.51) 7. (-3.20)7. (-5.94) 8. (2.45) 9. (3.19)9. (-3.98) 9. (-4.99)

4. (-5.46) 4. (-3.23) 8. (3.37) 2. (2.07) 2. (2.71) 4. (-2.25) 4. (-6.68)7. (-5.03) 7. (-4.28) 4. (6.47) 4. (-6.15) 7. (-3.13) 4. (-6.21) 7. (-12.17)

TC 9. (1.99) 9. (-3.41) 7. (5.58) 6. (2.41) 9. (-2.70) 9. (-2.70)9. (-12.21) 7. (-5.76) 7. (-5.76)

3. (2.85) 2. (2.50) 3. (2.48) 8. (2.72) 7. (3.00) 3. (3.77) 9. (-2.12) 3. (3.77) 7. (-6.22)3. (1.98) 8. (2.23) 9. (-11.18) 7. (-2.48) 9. (3.66)

OT 7. (-2.61) 8. (-2.772) 9. (7.14) 7. (-2.48)8. (2.99)9. (2.81)

OS 6. (-2.60) 6. (-2.01)

aLeft stance phase minus right stance phasebHorse numberCt-ratio, p < 0.05 for It-ratiosl > 1.96dLeft side suspension phase minus right side suspension phase'Left hind stance phase minus right hand stance phasefLeft fore stance phase minus right fore stance phasegLeft hind and left fore overlap period minus right hind and right fore overlap periodhAdvanced placement of the left hind over the left fore minus advanced placement of the right hind over the right fore'Advanced placement of the left fore over the right hind minus advanced placement of the right fore over the left hindJLeft hind single support phase minus the right hind single support phasekLeft fore single support phase minus the right fore single support phase

seen related to track position for theparameters, RF-LH advanced place-ment and RF stance phase time.

DISCUSSION

The TC length (61 m) at NorthlandsPark Racetrack is shorter than the 75-100 m length recommended (8) fortrotters moving at 13.20 m/s on a1000 m track with a 2:1 curve tostraight ratio. It is of interest that thegait of the horse, pace or trot, does notaffect the geometric design of thetrack, since this is determined by thespeed and mass of the horse. The 8.6%maximum superelevation is less thanthe recommended 18% (8), but whentraditional track soil materials, sand,clay and loam are used, increasing thesuperelevation to the suggested levelsresults in increased maintenance costsdue to the surface material slidingtoward the hubrail during wet climaticconditions. Nontraditional construc-tion materials such as wood chips andsynthetic materials, have been used ona recently designed, all-weather trackhaving a maximum superelevation of

10%. This track is reported to be easilymaintained and have a lower incidenceof injuries to running Thoroughbredsthan tracks of traditional construction(1 1).The mean stride length for individ-

ual horses ranged from 5.08 m to5.77 m and there is no trend for thestride to become longer or shorter asthe horse moves from the straight tothe curved portions of the track. Theonly previous report on the stridelength of pacers is that ofa single horsepacing on a prepared straight segmentof the track at an unspecified speed inexcess of 12.4 mps having a stridelength of 6.3 m (19). The mean stridelength and mean velocity on the IS forfive pacers are shown in Table II.

Previous reports (19,23) have statedthat the placement of the ipsilaterallimbs of the pacer occur simultane-ously. In the present study for allstrides analyzed on all segments of thetrack, the hind limb was placed priorto the ipsilateral fore limb. Drevemo etal ( 17) reports that racing trotters usu-ally place the fore limb in advance ofits weight-bearing partner, the con-

tralateral hind limb. However, photo-graphs of trotters taken in 1887 byMuybridge indicate that the place-ment order of the trotters' limbs is var-iable from one horse to another (24).

Contralateral asymmetry (CA) wasdemonstrated for each of the sevenhorses analyzed (Table IV). The factthat CA occurs more frequently in cer-tain segments of the track suggests itmay be due to the rate of change ofcurvature and inadequate supereleva-tion. During the filming procedure thedriver of horse 7 reported this horse tobe bearing out, or away from the left.Where asymmetry is present in thishorse (Tables III and IV) it is usuallythe left parameter that is of shorterduration. To determine if markedasymmetry, such as that exhibited byhorse 7, is the result of lameness on theleft side of the horse, or simply agreater biomechanical contributionfrom the left side, horses with knownlamenesses should be filmed andanalyzed.The existence of significant differ-

ences between horses in 15 of 19 TSPmeasured demonstrated the variability

379

that exists between horses. Size andconformation as well as differences inharness and shoeing contribute to theinterindividual variability.The findings of no significant inter-

individual differences for the rightsuspension phase, stance of the leftfore limb, advanced placement of theright fore limb over the left hindlimband single support phase of the leftfore limb may be the result of a rela-tively high variance of sample stridesand insufficient sample size.There is no clear trend to increase or

decrease those TSP stride duration,RF stance phase and RF-LHadvanced placement, which have sign-ificant differences between the curvedsegments (IT, TC, OT) of the track.Each horse may adjust to the turn in adifferent manner and the significantdifference in these TSP may reflect thisindividuality. It is possible the differ-ences that occur are not due to trackconfiguration factors such as degree ofcurvature and banking, but are due tosome other influence that occurs coin-cident with changes in position on theracetrack. Velocity is a factor thatcould have had a significant influenceon certain temporal gait characteris-tics. It has been reported that there is amoderate correlation between speedand the linear measurements of the lefthind step length in trotters (17). Veloc-ities over consecutive straight seg-ments of the track should be comparedwith the segments of the curve todetermine if variation in velocity is afunction of the horse or racetrack con-figuration. It may be difficult forhorses to maintain constant velocitywhen moving at near maximal speeds.Further statistical comparison byanalysis of variance is confounded byhaving average velocities for eachhorse on each track segment ratherthan a sample of velocities for each ofthe track positions.The values for stance phase of the

right fore limb and the advance place-ment time of the right fore over the lefthind varied significantly between tracksegments on the curved portion of thetrack. The duration of both theseparameters is related to the time ofplacement of the right fore foot. If theright fore is placed early both charac-teristics are increased and if the right

fore placement is delayed, the durationof these characteristics is shortened. Alinear regression analysis comparingthe values of the right fore stancephase and the advance placement timeof the right fore over the left hind onthe curved portions of the track doesnot demonstrate a consistent correla-tion between these parameters. It mustbe concluded therefore that changes inthese two parameters are not linearlyrelated to each other.

In spite of the fact that this track'ssuperelevation is less than 50% of therecommended amount (8), only minorand inconsistent changes occur intemporal gait characteristics as fastmoving pacers proceed through theturn of the track. This suggests thatinadequate track design may not bemanifested in temporal asymmetryand therefore judgement on trackdesign or suitability should not bemade on this basis. Angular asymme-try of gait in trotters has been reportedto be the tendency of the horse tocounteract centrifugal force on inade-quately designed curves, by leaningexcessively toward the center of curva-ture of the turn (13). This type ofasymmetry has been recorded, but notanalyzed, in pacers during races atNorthlands Park racetrack.The absence of temporal gait

changes in racing pacers should not beinterpreted that asymmetrical forcesare not present, but should beregarded as the horse's ability toaccommodate to changes in limb load-ing by methods other than timingchanges.

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method of investigating equine locomotion.Equine Vet J 1971; 3: 137-140.

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