Two-dimensional kinematics of the flat-walking Tennessee Walking Horse yearling

Equine and Comparative Exercise Physiology 3(2); 101 108 DOI: 10.1079/ECP200685 Two-dimensional kinematics of the flat-walking Tennessee Walking Horse yearling MC Nicodemus 1, * and HM Holt 2 1 Department of Animal & Dairy Sciences, Mississippi State University, P.O. Box 9815, MS 39762, USA 2 Department of Animal Science, Auburn University, 210 Upchurch Hall, AL 36849, USA * Corresponding author: mnicodemus@ads.msstate.edu Submitted 13 January 2006: Accepted 16 March 2006 Research Paper Abstract Gaited horse research is limited, with the majority of the research focusing on the measurement of the temporal variables of adult-gaited horses. The objective was to measure the fore and hind limb kinematics of the flat-walking Tennessee Walking Horse (TWH) yearling. Four TWH yearlings were filmed at 60 Hz being led at a consistent flat walk that followed breed standards. Reflective markers attached along palpation points of the joint centres of the fore and hind limbs were tracked for five strides for each yearling. During stance, the elbow (154 ^ 38), carpal (185 ^ 38), fore (222 ^ 9 and 221 ^ 98) and hind fetlocks (216 ^ 118), hip (111 ^ 38), stifle (157 ^ 48) and tarsal (167 ^ 98) joints demonstrated peak extension with the forelimb fetlock joint having double peaks of extension. During swing, the same joints demonstrated peak flexion with the elbow (109 ^ 38) and hip (88 ^ 68) peak flexion occurring later in the swing phase. The carpal (54 ^ 48) joint demonstrated a greater range of motion than the tarsus (40 ^ 98) with less vertical displacement. The hind fetlock (60 ^ 108) had greater range of joint motion compared with the forelimb fetlock (45 ^ 88), but lacked the double peak of extension during swing. Kinematic measurements will assist in objectively defining the gait for both clinical and performance applications. Keywords: gaited horse; Tennessee Walking Horse; flat walk; kinematics; yearling Introduction Although the Tennessee Walking Horse (TWH) is one of the fastest growing horse breeds in the United States, locomotive research concerning the TWH has been lacking. The TWH is known for performing faster variations of the walk called the flat and running walks 1. Friends of Sound Horses, Inc. (FOSH) define the flat and running walks as symmetrical, four-beat stepping gaits with a lateral footfall sequence, a pronounced head nod and an over stride from the hind legs 2. The running walk is performed at a faster speed with a longer stride. The gaits should be free and loose with penalties given for artificial execution of the gaits. However, the rhythm of the running walk has been found to be influenced by the conformation of the horse 3. During growth, the TWH experienced variations within the gait in which weanlings performing the flat walk demonstrated differences between support phases and advanced placement; half of the weanlings performed a more lateral gait, both in the duration of lateral support and in the timing of lateral advanced placement, compared to the other weanlings performing a stepping gait that was more even in timing and limb support 4. Velocity may also be a consideration in gait variations as earlier studies concerning walking non-gaited adult horses found durations and limb support were influenced by velocity 5,6. The TWH running walk was found to demonstrate differences in limb support and rhythm with changes in velocity in that, as velocity increased, the lateral bipedal support increased and the lateral advanced placement decreased 7. Breed differences have also been cited as influencing the kinematics of qcab International 2006

102 the walk 8,9. Andalusians and Dutch Warmbloods were noted as having more limb animation at the walk 9, while German horses were found to have greater regularity and propulsion at the walk compared with Spanish and French breeds 8. Without consistency in the stepping gaits and in the definition of the stepping gaits, performance and clinical evaluations will be limited in clearly identifying the normal and abnormal gaits of the gaited horse. Understanding the normal gait of the TWH is critical with the passing of the Horse Protection Act (HPA) in 1970 10. HPA is a federal law directed towards the use of shoeing and action devices in the TWH industry that causes soring in the horse. Soring is any type of practice associated with the horse s limbs that causes distress or pain in order to accentuate the horse s gaits. The United States Department of Agriculture (USDA) established an accreditation programme through the Animal and Plant Health Inspection Services (APHIS) for designated-qualified persons (DQP) in which the DQP is present at sanctioned TWH and racking horse shows to examine both physical and locomotive characteristics, looking for any sign of soring. USDA publishes horse protection training materials for the DQP that includes restrictions on the weight of action devices (beads, bangles, rollers and chains) around the pastern to no more than 6 ounces and in which the device must be smooth and uniform, with only one device per limb 11. USDA shoeing restrictions cover the length of artificial toe extensions, the type of pad materials and packing and the shoe weight, including weight attached externally to the shoe. Restrictions specific to yearlings prohibit shoeing devices that elevate the heel angle more than 1 in. and additional weight added to the limb and hoof other than a keg shoe weighing no more than 16 ounces. According to USDA training materials 11, any sign of unsoundness would lead to the loss of showing privileges. However, federal regulatory publications do not include any definition of lameness or of normal movement in the TWH. Therefore, the objectives of this study were to measure the fore- and hindlimb kinematics of the flatwalking TWH yearling. Methods Horses This experiment was conducted at the Mississippi Agriculture and Forestry Experiment Station (MAFES) Horse Unit at Mississippi State University (MSU). The Department of Animal and Dairy Sciences provided the subjects, a group of four TWH yearlings (two male and two female; age, 12 14 months; weight, 283 ^ 38.5 kg; height, 140.1 ^ 4.0 cm). All of the yearlings were sired by horses that have placed at breedrecognized shows. Subject numbers were small as MC Nicoemus and HM Holt the subjects were limited to horses with nationally recognized bloodlines that were available for research. The age of the subjects was limited to yearlings, as at this stage of training the practice of padded shoeing and pastern chain weights has not been implemented 12. These unique training practices are currently lacking study as to the influence on the stepping gait. While these training practices are common in the industry, they are controversial and strictly regulated by the HPA 10. The research study restricted any shoeing or action devices applied to the limbs before or during the study, which limited the subjects available for participation. All yearlings were raised at the MAFES Horse Unit and trained by a nationally recognized gaited horse trainer in a manner similar to a typical TWH yearling training regime as described by Joe Webb in The Care and Training of the Tennessee Walking Horse 12. Recording techniques Circular retro-reflective markers, 3.5 cm in diameter, were glued to palpable, anatomically defined locations of the hoof and skin over the fore- and hindlimbs as described by Leach 13 and along the skin over the skull and thoracic spinal processes as described by Audigie et al. 14. Eight anatomic landmarks were placed on the lateral side of the right forelimb: the proximal end of the spine of the scapula; the posterior part of the of the tuberculum majus of the humerus; the transition between the proximal and the middle thirds of the lateral collateral ligament of the elbow joint; midway between the site of attachment of the lateral collateral ligament of the carpal joint and the styloid process; the site of attachment of the lateral collateral ligament of the fetlock joint; the hoof wall over the estimated joint centre of the rotation of the coffin joint; and the proximal and distal aspects of the lateral hoof wall 13,15. Eight markers were placed on the following anatomical landmarks along the lateral side of the right hindlimb: the ventral part of the tuber coxae; lateral part of the greater trochanter; lateral condyle of the femur; talus; metatarsal attachment of the lateral collateral ligament of the fetlock joint; the hoof wall over the estimated centre of rotation of the coffin joint; and the proximal and distal aspects of the lateral hoof wall 13,16. The use of the marker location at the hoof wall over the estimated centre of rotation of the coffin joint for calculating fetlock joint motion may not give the truest measurement of the fetlock joint, but it is a common practice applied for kinematic measurement of performance horses outside the clinical environment 13. Care must be taken when interpreting fetlock joint measurements performed in this manner. Three markers were placed on the spinous processes of the vertebral column: (1) along the

Two-dimensional kinematics of Tennessee Walking Horse 103 thoracic vertebrae, approximately along the withers (sixth thoracic spinal process); (2) the lumbo sacral junction (18th thoracic spinal process, loin); (3) and the tuber sacrale (point of the croup) 14. One marker was placed on the right side of the zygomatic process of the temporal bone 14. Lines connecting the markers define the limb segments and the angles between adjacent segments define the joint angles. Data collection Sagittal plane video data (60 Hz) were collected using a JVC GR-DVL 9500 VHS camcorder (US JVC Corp., Wayne, NJ, USA). The zoom lens was adjusted manually to produce a field of view for measuring one full stride. The camera was set at a 908 angle from the runway and the centre of the camera was 705 cm from the centre of the runway. The camera was equipped with a 300 W light source to illuminate the markers on each yearling. The field of view was calibrated using a rectangular frame encompassing the area of analysis. An experienced handler familiar with the yearlings led each yearling at a consistent velocity at the flat walk along the calibrated runway. The runway was 352 cm in length and was a straight, flat, dirt-packed track allowing for consistent, sagittal plane movement in which hoof contact and lift-off were easily detected. A trial was considered successful when the yearling was performing a flat walk according to the gait definition published in the FOSH judging manual 2, with the handler keeping the lead line loose and the yearling at a relaxed natural gait. Trials in which the handler interfered with the yearling or in which the yearling changed or interrupted its gait pattern 5 were not used for data analysis. Trials were excluded from the study if the horses were determined not to be performing the flat walk according to gait standards outlined by the FOSH judging manual 2,or were determined to be unsound according to clinical evaluations performed at the time of the data collection. Clinical unsoundness was determined by any sign of asymmetry in the head or hip motion 17. Five trials meeting these requirements for each of the yearlings were selected for this study. Data analysis The videotapes were analysed using an Ariel Performance Analysis System (Ariel Dynamics Inc., Trabuco Canyon, CA, USA). Each video frame was grabbed from which the markers on the yearling were automatically digitized. Digitizing and analysis techniques followed the guidelines outlined in Hodson et al. 15. Out-of-plane motions of the limbs during the stance phase were corrected using an algorithm based on the location of the distal hoof marker, the height of the camera and the distance of the camera from the yearling s plane of motion. The resulting data were transformed using a direct linear-transformation technique adapted for two-dimensional data 18 and smoothed with a fourth-order Butterworth digital filter with a cut-off frequency of 6 Hz. The instants of ground contact and lift-off were determined visually from the videotapes from which temporal measurements were determined. Initial ground contact of the hoof was taken as the first frame in which any part of the hoof made contact with the ground. Lift-off was the first frame in which the hoof was clear of the ground. From these frame numbers, temporal variables were calculated and expressed as a percentage of strides. Temporal variables measured included stride duration (time between successive impacts of the right hindlimb), stance duration (time from impact to lift-off of each limb), advanced placement (time between impacts of either the diagonal limbs or the lateral limbs), bipedal limb support (period during which either the diagonal or lateral limb pairs are on the ground) and tri-pedal limb support (period during which either the two forelimbs and one hindlimb or the two hindlimbs and one forelimb are on the ground) 7. The coordinates of the markers on the proximal aspect of the limbs were corrected for skin displacement in accordance with van Weeren et al. 19. Joint angles were measured on the anatomical flexor side of each joint, which is the palmar side for all forelimb joints except for the elbow, and the plantar side for all hindlimb joints except for the hip and tarsus. Joint angle time variations were normalized to percentage of stride. Statistical analysis Means (standard deviation) of temporal variables and joint motion and displacements of the five strides for each yearling were determined. Symmetry of the temporal variable of the flat walk was determined by performing paired t-tests (P, 0.05) on the left and right values of stance durations. Since there were no significant differences between left and right values, the yearling s flat walk was defined as symmetrical so that the left and right limb temporal values were collapsed into a single variable. Results The flat walk of the TWH yearling measured in this study was found to be a lateral footfall-sequenced symmetrical, four-beat stepping gait that had an irregular rhythm with lateral couplets (lateral advanced placement: 19 ^ 5%; diagonal advanced placement: 30 ^ 4%) and alternating periods of tripedal (38 ^ 3%) and bipedal (62 ^ 5%) support. The velocity was 1.66 ^ 0.21 m s 21 with a stride duration of 1.06 ^ 0.33 s and the majority of the stride spent in

104 stance (59 ^ 2%). Stride length (velocity stride duration) was 1.76 ^ 0.49 m. Hoof horizontal displacement was 1.57 ^ 0.11 m for the forelimbs and 1.52 ^ 0.08 m for the hindlimbs. The head and withers had a range of motion of vertical displacement throughout the stride of 0.11 ^ 0.02 and 0.08 ^ 0.02 m, respectively, with the head reaching the highest point of vertical displacement when the forelimbs made contact with the ground and reached the lowest point when the hindlimbs made contact with the ground. In the forelimb, the shoulder joint flexed through mid-stance while the carpus extended (Table 1; Figs 1 and 2). The fetlock demonstrated the first peak of extension at the beginning of stance followed by a second peak of fetlock extension towards the end of stance (Fig. 2). The elbow joint gradually extended throughout stance, reaching peak extension towards the end of stance (Fig. 1). During the swing phase, the fetlock, carpus and elbow flexed while the shoulder gradually extended (Figs 1 and 2). The fetlock and carpus reached peak flexion towards the beginning of swing, followed by the elbow towards mid-swing. Throughout the stride, the carpus and hoof had a vertical range of motion of 0.10 ^ 0.03 and 0.11 ^ 0.04 m, respectively. The range of joint motion throughout the stride for the carpus and fore fetlock was 54 ^ 4 and 45 ^ 88, respectively. The croup and loin had a vertical range of motion of 0.09 ^ 0.03 and 0.08 ^ 0.03 m, respectively, with both the croup and loin reaching the highest point of vertical displacement when the head reached the lowest point of displacement and the lowest point was reached when the head was at the highest point. The tarsus and hind hoof had a vertical range of motion of 0.13 ^ 0.03 and 0.10 ^ 0.02 m, respectively. In the hindlimbs, the hip, tarsus, and fetlock gradually extended throughout stance, reaching peak extension towards the end of stance (Table 1; Figs 3 and 4). Stifle peak extension occurred at the beginning of stance, and then the joint gradually flexed throughout stance (Fig. 3). At the start of swing, the fetlock reached peak flexion followed by the stifle, tarsus Table 1 Peak flexion and extension (mean, SD) joint angles and the percentage of stride at which the peak occurred of the flatwalking fore- and hindlimbs of the Tennessee Walking Horse yearling Peak flexion Peak extension Shoulder 108 ^ 48 (27%) 118 ^ 78 (89%) Elbow 109 ^ 38 (78%) 154 ^ 38 (55%) Carpus 132 ^ 68 (72%) 185 ^ 38 (37%) Fore fetlock 175 ^ 78 (65%) 222 ^ 98 (22%)/ 221 ^ 98 (48%) Hip 88 ^ 68 (84%) 111 ^ 38 (57%) Stifle 124 ^ 68 (75%) 157 ^ 48 (48%) Tarsus 127 ^ 98 (79%) 167 ^ 98 (50%) Hind fetlock 156 ^ 108 (66%) 216 ^ 118 (48%) Joint angle ( ) and hip (Figs 3 and 4). The range of joint motion throughout the stride for the tarsus and hind fetlock was 40 ^ 9 and 60 ^ 108, respectively. Discussion The TWH yearlings measured for this study were selected because of their demonstration of competitive show quality without the introduction of advanced TWH training and shoeing practices. While measuring adult TWH kinematics would have been more applicable to comparisons with current published walking and flat-walking studies, research concerning the influence of current TWH shoeing and training practices in the adult TWH in which the adult TWH flat walk has been found to be influenced by shoeing and training practices of the heavy shod TWH 20 is limited. Hoof kinematic research in the trotting non-gaited horse found that a longer toe increased break-over and the Joint angle ( ) 240 220 200 180 160 140 120 100 80 60 1 20 40 60 80 100 % of stride 240 220 200 180 160 140 120 100 Fetlock Elbow Carpus Shoulder MC Nicoemus and HM Holt Lift-off Lift-off Extension Flexion FIG. 1Mean (SD) joint motion for the shoulder and elbow joints during the flat walk of the Tennessee Walking Horse yearling Extension 80 Flexion 60 1 20 40 60 80 100 % of stride FIG. 2Mean (SD) joint motion for the carpal and forelimb fetlock joints during the flat walk of the Tennessee Walking Horse yearling

Two-dimensional kinematics of Tennessee Walking Horse 105 Joint angle ( ) likelihood of toe first landings 21. Adding pads to the hoof making the hoof length longer, similar to the practices of the TWH industry, has been shown to increase stride and stance durations, break-over and hoof flight arc at the trot 22. Another TWH shoeing practice is adding weight to the shoe, which was found in non-gaited horses at the trot to increase hoof flight arc, carpal and fetlock flexion and stride and swing durations 23. In addition to shoeing, training influences on gait kinematics have been reported in the non-gaited horse. Trotting kinematic research found Standardbreds increased stride length and stride and swing durations, along with becoming more regular in the rhythm of the trot with training 24. Andalusians demonstrated with training at the trot increased hip and stifle flexion 25. Dutch Warmbloods after 70 days of training compared with those horses left out to pasture for 70 days demonstrated at the trot decreased hindlimb Joint angle ( ) 240 220 200 180 160 140 120 100 80 60 240 220 200 180 160 140 120 100 80 60 Hip Fetlock Stifle Tarsus Lift-off 1 20 40 60 80 100 % of stride Lift-off Extension Flexion FIG. 3Mean (SD) joint motion for the hip and stifle joints during the flat walk of the Tennessee Walking Horse yearling Extension Flexion 1 20 40 60 80 100 % of stride FIG. 4Mean (SD) joint motion for the tarsal and hind limb fetlock joints during the flat walk of the Tennessee Walking Horse yearling stance duration and range of motion for the forelimb protraction/retraction, elbow, forelimb fetlock and tarsus 26. At the canter, Thoroughbreds increased stance duration and carpal and fetlock range of motion with training 27, but additional kinematic research at the canter found the type of training may create different kinematic responses 28. Racehorse training when compared with dressage training was found to create differences in the advanced placement of the diagonal limb pair and stance and suspension durations at the extended canter. As for the young TWH, 30 days of round pen and halter training while being pasture housed did not influence the temporal variables of the flat walk 29 ; but the flat walk demonstrated increasing velocity and rhythm irregularity after 30 days of stalling without any form of turnout or training 30. Therefore, to report the kinematics of the natural flat walk and reduce the variability due to training and shoeing practices, TWH kinematics were measured and reported in this study using yearlings that were unshod and not participating in any training programme. Because of the lack of yearling of kinematic research for both gaited and non-gaited breeds, the majority of the discussion in this study was limited to adult comparisons. While age-related kinematic differences have been documented in non-gaited breeds 31, only differences in temporal variables between TWH foals and yearlings have been reported 32. Although non-gaited horse studies have reported calculations to adjust for size differences 31, these non-gaited horse calculations were not applied to this gaited horse study so that conclusions made through comparisons to adult studies within this discussion are done with the acknowledgement that age may be an influencing factor for the flat walk of the TWH. Research in foals 6 8 months of age performed the walk at a speed similar to the collected walk of the adult dressage horse using a shorter stride duration and length 33. While Back et al. 34 found coordination patterns of the Dutch Warmblood weanling that were indicative of adult gait, the Dutch Warmblood was determined to exhibit increase stride and stance durations with age. Unlike the Dutch Warmblood, Andalusian yearlings showed a decrease in stance duration at the trot with increasing age along with an increase in stride length, carpal and elbow range of motion and flexion, forelimb fetlock extension and hip and stifle range of motion 35. Similarly, Andalusians at 3 years of age compared with adults demonstrated a trot with greater flexion of the elbow, carpus, forelimb fetlock, hip and stifle 36. Therefore, future research like that performed in the non-gaited horse concerning age- and size-related kinematic differences is suggested for the TWH. Subject restriction to championship bloodlines and show quality without the use of shoeing or training

106 practices to accentuate the gait limited the number of subjects available for this study. Quality of the subjects used in a research study and the consistency of that quality across the subjects measured are necessary in kinematic research as earlier studies found differences between well- and poorly performing horses. Holmstom et al. 37 documented that Swedish Warmblood stallions judged as good performers compared with poor performers had increased stride duration, positive diagonal advanced placements and flexion of the elbow, carpus, hock and hind fetlock at the trot. Back et al. 38 found similar results in the Dutch Warmblood at the trot in that good performers had increased stride duration, forelimb fetlock extension and range of motion, and scapular retraction and range of motion. Clayton 39 documented variation in stride length and duration within a subject group of dressage horses, which was related to the variation in the level of training of the subjects as not all were of Olympic level. Holmstrom et al. 37 noted that large numbers of subjects of high-quality gait are neither practical nor economical, but studies using smaller subject numbers should be interpreted with care. Comparisons between the kinematics of other gaited breeds are limited due to the lack of research concerning gaited horses; and while the flat walk has been defined 4,32, kinematic variability due to breed differences has been reported in non-gaited horse studies. Andalusians, Anglo-Arabians and Arabians at the walk demonstrated differences in stride length, stride and stance durations, elbow flexion and extension, carpal flexion and fetlock extension 40. Andalusians were found to have a shorter over-tracking length at the trot compared with Dutch Warmbloods 9, Anglo-Arabians 40 and Arabians, which resulted in a more vertical trunk motion during the trot that was further indicated by the larger amounts of flexion of the forelimbs and of the tarsal and hind fetlock joints compared with that of the Anglo-Arabian and the Arabian 41. These kinematic findings in non-gaited breeds indicate the need for similar research in the gaited-horse breeds. Current research on the gaited horse flat walk has only focused on the adult Missouri Fox Trotter (MFT), in which the study did not measure hindlimb kinematics 42. Although the flat walk is suggested to be similar across breeds, the MFT had a regular rhythm flat walk with a velocity (1.75 ^ 0.06 m s 21 ) quicker than the TWH flat walk, which was produced by a longer stride length (1.95 ^ 0.05 m). The MFT demonstrated more forelimb animation with greater joint range of motion (carpus, 72 ^ 38; fetlock, 86 ^ 28), while showing a more distinct head nod (vertical displacement, 0.14 ^ 0.03 m) with flatter croup motion (vertical displacement, 0.04 ^ 0.01 m). Comparisons of joint motion patterns found the MFT forelimb lacked a double peak of fetlock extension at MC Nicoemus and HM Holt stance and had a carpal peak flexion occurring later in swing. While these kinematic differences in the flat walk may be attributed to the variation between breeds, other variables such as velocity and age may have an influence in these differences. The paso llano is another example of a faster four-beat stepping gait 43 performed by a gaited-horse breed, the Peruvian Paso. Unlike the TWH flat walk, the paso llano of the adult Peruvian Paso had a regular rhythm that was performed at a faster velocity (2.7 ^ 0.1 m s 21 ), with a similar stride length (1.7 ^ 0.1 m) and shorter stride duration (0.63 ^ 0.03 s). The Peruvian Paso is known for exaggerated rotational forelimb motion called termino, which is unique to the breed. While out-of-sagittal plane motion was measured for the Peruvian Paso due to the termino, this study only measured sagittal plane motion as the TWH is selected based on straightness of gait and frame 1. As for flexion and extension of forelimb joint motion, the carpus (106 ^ 108) and fetlock (108 ^ 118) ranges of motion due to the exaggerated motion of the termino was much larger than the TWH yearling flat walk. The flat walk is described as a faster variation of the walk 1. Hodson et al. 15,16 found a slower walking velocity in adult non-gaited horses (1.39 ^ 0.07 m s 21 ) than the flat walk, which was performed at a regular rhythm with a longer stride duration (fore, 1.27 ^ 0.08 s; hind, 1.27 ^ 0.07 s) and a similar stride length (1.75 ^ 0.09 m). Walking joint patterns were similar to the flat walk for the elbow, carpus, hip and stifle joints while a similar range of joint motion between flexion and extension peaks was found in the elbow, carpus, stifle, tarsus and foreand hindlimb fetlocks joints 15,16. Nevertheless, the walk had a more gradual return to shoulder extension towards the end of swing, less distinct double peaks of forelimb fetlock extension and a less distinct tarsal extension peak at the end of stance as compared with the yearling TWH flat walk. In comparison to the trot of 2-year-old Dutch Warmbloods, the hind fetlock joint motion at the flat walk demonstrated similarities to the trotting fetlock joint during stance 44. The hip and stifle joint range of motion at the flat walk was comparable to the slower trot of mature horses 16 while the range of motion of the vertical displacements of the tarsus and hind hoof was greater than that found in mature trotting European saddle horses (0.12 and 0.07 m, respectively) 45. While variations between studies measuring adult walking kinematics have been attributed to differences between breeds 15,16, velocity has also been attributed as a main source of variations between various types of four-beat stepping gaits and may explain some of the differences discussed in this study between the TWH yearling flat walk and other stepping gaits. Velocity was found to influence the temporal variables of the

Two-dimensional kinematics of Tennessee Walking Horse 107 walk 6, running walk 7 and toelt 46,inwhichdurationsand limb support varied with velocity in all of these four-beat stepping gaits. While Hodson et al. 15 did not find double peaks of fetlock extension during swing, those studies done on adult non-gaited breeds that measure a velocity similar to the TWH flat walk documented similar forelimb fetlock joint patterns 44,45. Since velocity is an important component of the definition of the flat walk and contributes to temporal variable and kinematic differences, future research in four-beat stepping gaits of gaited horses should consider velocity. Variations in gait kinematics have been attributed to lameness factors and identifying these variables in the TWH is critical for proper inspections made by the DQP at TWH shows. According to the USDA training materials, soring is indicated by lameness when the horse is walking, trotting or otherwise moving, but the definition of what constitutes lameness in the TWH is not defined 11. Forelimb hoof lameness in the non-gaited horse was identified by decreased diagonal advanced placements, suspension and swing durations in both the lame and sound forelimb at the trot with asymmetry particularly noticeable in the suspension phase in which the suspension phase was shorter after the lame hoof was on the ground 47. Timing of peak joint angles was delayed or became more gradual in the lame horse at the trot 48. Asymmetry due to lameness was more apparent in the timing and range of motion of the vertical displacement of the head and tuber coxae 17. Lameness associated with a specific joint caused decreased range of motion of the joint 49, but the general shape of the joint motion curves could still be identified using sound joint motion patterns 50. While these variables assist in identifying the kinematics of lameness, clinical lameness evaluations such as those used by the DQP inspectors at TWH shows consist of comparing the abnormal gait to the standard horse movements in which USDA standards 11 do not clearly identify what is standard in the TWH. Conclusion The flat walk of the TWH yearling demonstrated several kinematic similarities with the non-gaited walk. However, basic timing of the joint motion curves and range of motion distinguished the flat walk from other stepping gaits. However, conclusions between comparisons made in this study are based on a limited subject number and with comparisons made between different breeds and age groups so that further research in this area is recommended. With federal regulatory bodies overseeing the training and shoeing practices of the TWH without an objective description of the normal and abnormal gaits of the TWH, this type of research is critical. Acknowledgements The authors thank the trainers who participated in the study by halter training and conditioning the horses and giving input on the gait performance. We are also grateful to the MAFES Horse Unit staff for their management and care of the horses during the study. References 1 Ziegler L (2005). Easy-Gaited Horse. pp. 39 42, 58 59. 2 Friends of Sound Horses, Inc. (2005). Independent Judges Association Rulebook. pp. 1 2. 3 Slade LM (1993). Conformation and gait characteristics of Icelandic, Tennessee walker and walkony horses. In: Proceedings of the International Workshop on Animal Locomotion and the Association of Equine Sports Medicine 2. Pasadena, CA: AESM Publications, 64 pp. 4 Holt KM and Nicodemus MC (2001). Temporal variables of the flat walk of the Tennessee Walking Horse weanling. Journal of Animal Science 79(1): 210. 5 Leach DH and Cymbaluk NF (1986). Relationships between stride length, stride frequency, velocity, and morphometrics of foals. American Journal of Veterinary Research 45: 888 892. 6 Nicodemus MC, Lanovaz JL and Clayton HM (2000). The effect of velocity on temporal variables of the equine walk. In: Lidner A (ed.), Conference on Equine Sports Medicine and Science: the Elite Show Jumper. Dortmund: Lensing Druck, 155 pp. 7 Nicodemus MC, Holt KM and Swartz K (2002). The relationship between velocity and temporal variables of the flat shod running walk. Equine Veterinary Journal Supplement 34: 340 344. 8 Barrey E, Desliens F, Poirel D, Biau S, Lemaire S, Rivero JLL and Langlois B (2002). Early evaluation of dressage ability in different breeds. Equine Veterinary Journal Supplement 34: 319 324. 9 Galisteo AM, Vivo J, Cano MR, Morales JL, Miro F and Aguera E (1997). Differences between breeds (Dutch Warmblood vs Andalusian purebred) in forelimb kinematics. Journal of Equine Science 8: 43 47. 10 United States Department of Agriculture (2004). Horse Protection Act Fact Sheet, Riverdale, Maryland. Animal & Plant Health Inspection Services, Animal Care Publications. 11 United States Department of Agriculture (2004). Horse Protection Training Material, Riverdale, Maryland. Animal & Plant Health Inspection Services, Animal Care Publications. pp. 9 12, 23 25, 31 37. 12 Webb J (1962). The Care and Training of the Tennessee Walking Horse. Searcy, AK: Webb Publishing. 13 Leach D (1993). Recommended terminology for researchers in locomotion and biomechanics of quadrupedal animals. Acta Anatomica 143(2 3): 130 136. 14 Audigie F, Pourcelot P, Degueurce C, Geiger D and Denoix JM (1998). Kinematics of the equine spine: Flexion-extension movements in sound trotting horses. Proceedings of the Fifth International Conference on Equine Exercise Physiology. Utsunomiya, Japan, 64 pp. 15 Hodson EF, Clayton HM and Lanovaz JL (2000). The forelimb in walking horses: 1. Kinematics and ground reaction forces. Equine Veterinary Journal 32: 287 294. 16 Hodson EF, Clayton HM and Lanovaz JL (2001). The hindlimb in walking horses: 1. Kinematics and ground reaction forces. Equine Veterinary Journal 33: 38 43. 17 Buchner HHF, Savelberg HHCM and Schamhardt HC (1996). Head and trunk movement adaptations in horses with

108 experimentally induced fore- or hind limb lameness. Equine Veterinary Journal 28: 63 70. 18 Abdel-Azis YI and Karara HM (1971). Direct linear transformation from computer coordinates into object coordinates in close-range photogrammetry. In: Proceedings of the ASPUI Symposium on Close-Range Photogrammetry. Falls Church, Virginia: American Society of Photogrammetry Publication, pp. 1 19. 19 Van Weeren PR, van den Bogert AJ and Barneveld A (1992). Correction models for skin displacement in equine kinematic gait analysis. Journal of Equine Veterinary Science 12: 178 192. 20 Nicodemus MC and Holt KM (2003). Walking temporal variables of the padded Tennessee Walking Horse. Journal of Animal Science 81(1): 263. 21 Clayton HM (1990). The effect of an acute hoof angulation on the stride kinematics of trotting horses. Equine Veterinary Journal Supplement 9: 86 90. 22 Balch OK, Clayton HM and Lanovaz JL (1994). Effects of increasing hoof length on limb kinematics of trotting horses. Proceedings of the Annual Convention of the American Association of Equine Practitioners 40, pp. 40 43. 23 Willemen MA, Savelberg HCCM and Barneveld A (1997). The improvements of the gait quality of sound trotting Warmblood horses by normal shoeing and its effect on the load on the lower forelimb. Livestock Production Science 52: 145 153. 24 Leleu C, Cotrel C and Barrey E (2004). Effect of age on locomotion of Standardbred trotters in training. Equine and Comparative Exercise Physiology 1(2): 107 117. 25 Cano MR, Miro F, Diz AM, Aguera E and Galisteo AM (2000). Influence of training on the biokinematics in trotting Andalusian horses. Veterinary Research Communications 24: 477 489. 26 Back W, Hartman W, Schamhardt HC, Bruin G and Barneveld A (1995). Kinematic response to a 70 day training period in trotting Dutch Warmbloods. Equine Veterinary Journal Supplement 18: 127 131. 27 Corley JM and Goodship AE (1994). Treadmill induced changes to some kinematics variables measured at the canter in Thoroughbred fillies. Equine Veterinary Journal Supplement 17: 20 24. 28 Clayton HM (1993). The extended canter: A comparison of the stride kinematics of horses trained for dressage and for racing. Acta Anatomica 146(2 3): 183 187. 29 Holt KM and Nicodemus MC (2003). The influence of training on flat-walking temporal variables of Tennessee Walking Horse yearlings. Journal of Animal Science 81(1): 262. 30 Nicodemus MC and Holt KM (2004). Influence of a 30-day stalling period on Tennessee Walking Horse yearling flatwalking temporal variables. Equine and Comparative Exercise Physiology 1(2): A19. 31 Back W, Schamhardt HC, Hartman W, Bruin G and Barneveld A (1995). Predictive value of foal kinematics for adult locomotor performance. Research on Veterinary Science 59: 64 69. 32 Nicodemus MC and Holt KM (2003). Temporal variables of the flat walk of the Tennessee Walking Horse foal predicts yearling flat-walking performance. In: Nielson B (ed.), Proceedings of the World Conference on Animal Production IX, Porto Alegre, Brazil: Grafica UFRGS, 43 pp. 33 Clayton HM (1995). Comparison of the stride kinematics of the collected, medium, and extended walks in horses. American Journal of Veterinary Research 56(7): 849 852. 34 Back W, Barneveld A, Schamhardt HC, Bruin G and Hartman W (1994). Longitudinal development of the kinematics in 4-, 10-, MC Nicoemus and HM Holt 18-, and 26-month-old Dutch Warmblood horses. Equine Veterinary Journal Supplement 17: 3 6. 35 Cano MR, Miro F, Monterde JG, Diz A, Martin J and Galisteo AM (2001). Changes due to age in the kinematics of trotting Andalusian foals. Equine Veterinary Journal Supplement 33: 116 121. 36 Cano MR, Miro F, Vivo J and Galisteo AM (1999). Comparative biokinematic study of young and adult Andalusian horses at the trot. Journal of Veterinary Medicine 46: 91 101. 37 Holmstrom M, Fredricson I and Drevemo S (1994). Biokinematic differences between riding horses judged as good and poor at the trot. Equine Veterinary Journal Supplement 17: 51 56. 38 Back W, Barneveld A, Schamhardt HC, Bruin G and Hartman W (1994). Kinematic detection of superior gait quality in young trotting warmbloods. Veterinary Quarterly 16: S91 S96. 39 Clayton HM (1994). Comparison of the stride kinematics of the collected, working, medium and extended trot in horses. Equine Veterinary Journal 23(3): 230 234. 40 Galisteo AM, Morales JL, Cano MR, Miro F, Aguera E and Vivo J (2001). Inter-breed differences in equine forelimb kinematics at the walk. Journal of Veterinary Medicine 48: 277 285. 41 Cano MR, Vivo J, Miro F, Morales JL and Galisteo AM (2001). Kinematic characteristics of Andalusian, Arabian and Anglo- Arabian horses: a comparative study. Journal of Veterinary Medicine 47: 147 152. 42 Nicodemus MC and Clayton HM (2002). Forelimb kinematics of the flat walk of the Missouri fox trotter. In: Lidner A (ed.), Conference on Equine Sports Medicine and Science: The Elite Dressage and Three-Day-Event Horse. Dortmund, Germany: Lensing Druck, pp. 169 173. 43 Nicodemus MC and Clayton HM, (2001). Gait characteristics of the paso llano. In: Wickler S (ed.), Proceedings for the 21st Meeting of the Association of Equine Sports Medicine. Pasadena, CA: AESM Publications, pp. 94 99. 44 Back W, Schamhardt HC and Barneveld A (1996). Are kinematics of the walk related to the locomotion of a Warmblood horse at the trot? Veterinary Quarterly Supplement 18(2): S71 S76. 45 Robert C, Valette JP, Pourcelot P, Audigie F and Denoix JM (2002). Effects of trotting speed on muscle activity and kinematics in saddlehorses. Equine Veterinary Journal Supplement 34: 295 301. 46 Zips S, Peham C, Scheidl M, Licka T and Girtler D (2001). Motion pattern of toelt of Icelandic horses at different speeds. Equine Veterinary Journal Supplement 33: 109 111. 47 Buchner HHF, Savelberg HHCM, Schamhardt HC and Barneveld A (1995). Temporal stride patterns in horses with experimentally induced fore or hind limb lameness. Equine Veterinary Journal Supplement 18: 161 165. 48 Buchner HHF, Savelberg HHCM, Schamhardt HC and Barneveld A (1996). Limb movement adaptations in horses with experimentally induced fore or hind limb lameness. Equine Veterinary Journal 28: 63 70. 49 Back W, Barneveld A, van Weeren PR and van den Bogert AJ (1993). Kinematic gait analysis in equine carpal lameness. Acta Anatomica 146(2 3): 86 89. 50 Audigie F, Pourcelot P, Degueurce C, Geiger D and Denoix JM (2001). Kinematic analysis of the symmetry of limb movements in lame trotting horses. Equine Veterinary Journal Supplement 33: 128 134.