**2. Review of studies undertaken on "artificial" laterally coordinated horse gaits**

Square ipsilateral horse gaits are those in which all four limbs operate relatively independently and involve a lateral footfall sequence of left hind (LH), left front (LF), right hind (RH), and right front (RF). The slowest and most basic square ipsilateral gait of the horse is the walk (see **Table 1**), an evenly-timed four-beat lateral-sequence and lateral-couplet gait, and so with a footfall sequence that can be demarcated with en dashes (�) indicating longer passages of time (LH–LF–RH–RF) and wherein ipsilateral limbs contact the ground closest together in time [1, 25, 26]. The walk typically occurs at speeds of 0.9 to 2.1 m/s, with a stride or cycle duration of 1.0 to 1.5 seconds, a stride frequency of 0.7 to 1.1 strides per second, and a stride or cycle length of 1.3 to 1.9 meters [2–5, 20, 22, 30–32]. On account of its slow speed and long stride duration there are no whole suspended phases where all four limbs are off the ground at once, or even contralateral suspended phases where both front limbs or both hind limbs are off the ground together, and so the hind limb makes contact with the ground for 55–75% of the stride or cycle length (i.e. a duty factor of 0.55 to 0.75), yielding support structures containing lots of three-feet support phases (54%), alternating with bilateral (24%) then diagonal (22%) support phases (see gait diagram a in **Figure 1**), i.e. 3-2D-3-2 L [3, 4, 22]. In the typical walk the


*Laterally Coordinated Gaits in the Modern Horse (*Equus ferus caballus*) DOI: http://dx.doi.org/10.5772/intechopen.106490*

**Table 1.**

*Temporal and linear kinematic parameters of the ipsilaterally coordinated gaits of horses reported in previous studies.*

front foot duration of ground contact is 0.95–1.04 that of the hind foot, the timing of the steps are fairly even (lateral advanced placement of 0.20–0.24 of the stride length and diagonal advanced placement of 0.26), independent of each other or square (lateral advanced liftoff of 0.25 and ipsilateral overlap of front and hand limbs for 44% of the stride), and with each foot remaining flat on the ground as the one after it comes down [6, 7]. The hind feet often cap and so overlap the vacated location of the ipsilateral front feet when they land or slightly overstep them up to a

#### **Figure 1.**

*Measurements taken of horse trackway (LH = left hind; LF = left front; RH = right hind; RF = right front). FW = footprint width; FL = footprint length; ISD = ipsilateral step distance; DSD = diagonal step distance; LO = lateral offset. IS = interior straddle; SL = stride length.*

hoof-length, or more technically by 3–19 cm or 0.01 to 0.10 of the stride length, resulting in footprints in lateral pairs that are generally parallel with each other and just to the side of the centerline [5, 7, 8, 22, 32]. In gaited horse breeds the walk may be extended with the hind legs overstepping the ipsilateral front legs somewhat, in which case it is often called a flat walk or dog walk.

Most horse breeds, and the zebra, transition to the diagonal intermediate speed gait of the trot at around 2.0–2.5 m/s, but select horse breeds display other intermediate "artificial" square ipsilateral gaits. One such gait is the running walk (common to Tennessee Walking Horses, as well occurring at times in other horse breeds, such as the American Bashkir Curly Horse, Florida Cracker Horse, Kentucky Mountain Saddle Horse, Peruvian Paso Horse (paso llano), Smokey Valley Horse, Spotted Saddle Horse, and the Walkaloosa. Like the walk, the running walk is a fairly evenly timed four-beat lateral-sequence and lateral-couplet gait (see **Table 1**).

#### *Laterally Coordinated Gaits in the Modern Horse (*Equus ferus caballus*) DOI: http://dx.doi.org/10.5772/intechopen.106490*

The running walk, however, occurs at a faster velocity than the regular walk and involves a lot of hind-leg extension and a bit more lateral coordination. Hence it can be demarcated with a hyphenated footfall sequence of LH-LF-RH-RF. The running walk typically occurs at a speed of 2.7–4.5 m/s, although it can be even faster in a few horses, with a stride duration of 0.68–0.75 seconds, a stride frequency of 1.3–1.5 strides per second, a stride length of 2.0 to 2.2 meters, and a hind-leg duty factor of 0.52–0.58 [1, 9, 10, 22]. At slower speeds the running walk is maintained via front legs pulling the horse forward while the hind longs engage in an extended stride with one hind foot lifting off while the other hind foot is still on the ground whereas the front feet employ shorter strides with one front foot coming down just as the other one is going up. Hence at slow speeds the running walk has a support structure with periods of tripedal, followed by diagonal then bilateral support, i.e. 3-2D-2L-3-2D-2L, though with much less three-limbed and more two-limbed support structures than in the standard walk, namely 15–23% tripedal, 50–67% bilateral, and 16–27% diagonal. At faster speeds the running walk can even have periods of single-foot support as both front feet are off the ground at the same time, though there is no period wherein both hind feet or all four limbs are off the ground. Thus at fast speeds the running walk has a support structure of 3-2D-1-2 L-3-2D-1-2 L, with a stride possessing 5–11% tripedal, 55–58% bilateral, 25–26% diagonal, and 2–8% single foot support structures [8–10]. At slow speeds the running walk has a lateral advanced placement of 0.22, a lateral advanced liftoff of 0.18, a diagonal advanced placement of 0.29, and a diagonal advanced liftoff of 0.35 the stride duration, while, at fasts speeds, these values reach 0.12, 0.10, 0.37, and 0.39, respectively, indicating more lateral coordination and less evenness to the gait [8–10]. Because the running walk involves a long hind-leg extension and the hind legs often scissoring out in an arc, two key kinematic features separate it from the standard walk. In the first place the front limbs are on the ground less than the hind limbs are, so there is a lower front to hind limb stance duration ratio of 0.86–0.92. Secondly, there is a very large overstep of hind feet over ipsilateral front feet of 15–50 cm, or around 15–25% of the stride length [8, 22]. Indeed typically the hind feet land near or just beyond the mid-point of the prior location of the front feet yielding footprint pathways of four insolated and almost evenly-spaced prints rather than prints with lateral or diagonal pairs. The running walk is a very smooth gait with little side-to-side or up and down movement of the horse's back, though it often involves the horses head nodding up and down with the movement of the hind limbs (Tennessee Walking Horse) or the forelimbs moving in a swinging arc (termino of the Peruvian Paso), and a slight rocking fore-to-back motion in the saddle.

Other gaited horse breeds transition from the slow walk to the intermediate "artificial" laterally coordinated gait of the rack or tölt. Such a racking gait is famous in the American Saddlebred, Icelandic Horse, Kentucky Mountain Saddle Horse, Mountain Pleasure Horse, North American Single-Footing Horse, Racking Horse, Rocky Mountain Horse, Smokey Valley Horse, Spotted Saddle Horse, and the Tennessee Walking Horse, but it also occurs in such breeds as the Aegidienberger, American Bashkir Curly Horse (curly rack with quick stride duration but lots of tripedal support), Garrano Horse (paso travado), McCurdy Plantation Horse (plantation gait), Mangalarga Marchador (marcha picada), Morgan Horse, Tiger Horse, as well as various Asian breeds [1, 10, 20, 33–36]. The rack or tölt is another fairly square and evenly-timed four-beat gait (see **Table 1**), with a footfall sequence of LH-LF-RH-RF, but one that involves more collection and quickness with a stride duration of 0.42–0.66, and a fair amount of lateral coordination, with the front limbs touching down close behind the hind limbs in time and remaining down until just after the opposite hind limbs contacts the ground, while the hind limbs of the

horse land close to but behind the contralateral front limbs in space, resulting in a bowed or wave-like footprint pattern, i.e. undulating, comprised of diagonal pairs [3, 4, 11–13]. At lower velocities of 2.7–3.8 m/s the rack is often labeled a mountain, pleasure, saddle, slow, stepping, style, or trail gait and possesses a 3-2D-3-2 L support structure–with 2–37% tripedal support, 25–46% bilateral support, and 16–48% diagonal support–a hind limb duty factor of 0.50–0.66, and a stride length of 1.7 to 2.2 m [11–13, 22, 36]. At such slow speeds the rack or tölt has a lateral advanced placement of 0.20–0.30, a lateral advanced liftoff of 0.27–0.29, a diagonal advanced placement of 0.23–0.28, and a diagonal advanced liftoff of 0.26, as well as a lateral overlap of 0.30 of the stride cycle, with the front feet having a stance duration 0.85–0.95 that of the hind feet [10, 13–16, 28]. At very slow speeds the rack often has ipsilateral feet forming footprint pairs on the ground or isolated prints resembling a running walk. At faster speeds of 3.9–7.6 m/s the rack or tölt is often called a performance, racing, road, show, or speed gait (or the contrarily labeled pleasure gait of the Rocky Mountain Horse), tends to become more animated with the front legs high-stepping or pitching out in an arcing motion, and bears 3-2D-1-2 L-3-2D-1-2 L or even 2D-1-2 L-1 support structures. A fast rack is hence often called a single-foot gait, especially in the North American Single Foot Horse and Racking Horse, and displays periods of single-leg support from 8 to 65% of the stride cycle depending whether there is contralateral suspension in the front alone (half rack) or both the front and hind feet (full rack), bilateral support of 22–40%, diagonal support of 3–14%, and lacking tripedal support structures. At such high speeds the rack or tölt possesses a lateral advanced placement of 0.18–0.30, a lateral advanced liftoff of 0.13–0.20, a diagonal advanced placement of 0.22–0.24, and a diagonal advanced liftoff of 0.30, as well as a hind limb duty factor of 0.36 to 0.49, fore feet on the ground only 0.62– 0.87 the duration of the hind feet, and a stride length of 2.2–3.2 m [10, 13–17, 22, 28]. At these high speeds the rack lays down prints with diagonal pairs and consequently an undulating pattern of prints. The rack often exhibits some up-and down movement of the rear of the horse (seen in croup and tail), due to the horse pushing off forcefully from the hind feet, while the rider in the saddle can experience a slight side to side motion due to the increased lateral coordination of the limbs.

Many gaited horse breeds can also engage in a stepping pace, amble, or broken pace, i.e. an unevenly-timed shuffling 4-beat laterally coordinated gait, rather than an even 4-beat gait, so having a footfall pattern of LH-LF–RH-RF (see **Table 1**). A stepping pace, in particular, occurs in the Asturcón, Campolina (somber paso), Columbian Criollo Paso, Icelandic Horse (skeith tölt), Florida Cracker Horse (coon rack), Paso Fino (andadura), Racking Horse, Spotted Saddle Horse, and Tennessee Walking Horse. Such a gait has been little studied as it is usually not considered a desirable gait by breeders or horse breed associations, and, in fact, is often named depreciatively as a piggy-pace, slick pace, or pacey rack or pacey tölt, perhaps as it is somewhat uncomfortable for the rider since the horse's neck and back move from side to side. In the Peruvian Paso Horse, however, it is considered a desirable gait and named the sobreandando (agulillo; pasiamblado), and it is also prized in the Tiger Horse (glider gait or lateral Indian shuffle) and Virginia Highlander. In the stepping pace there is a large amount of lateral coordination of limbs as ipsilateral hind and front limbs lift off the ground just after each other and contact the ground just after each other and cause side-to-side motion for the rider. The stepping pace occurs around 3.8–7.4 m/s, with a stride duration of 0.54–0.62, a stride frequency of 1.6–1.9, a stride length of 2.0 m or more, and hind limbs remaining in the stance phase 0.80– 0.98 as long as the hind legs. It possesses a lateral advanced placement of 13–24, lateral advanced liftoff of 10–16, diagonal advanced placement of 32–34, and diagonal advanced lift-off of 37–42. The stepping pace or sobreandando at slow speeds has a support structure of 15–25% tripedal support, 48% bilateral support, and 27%

#### *Laterally Coordinated Gaits in the Modern Horse (*Equus ferus caballus*) DOI: http://dx.doi.org/10.5772/intechopen.106490*

diagonal support at slower speeds, or a 3-2 L-3-2D support structure, and at higher speeds there can be some single-foot support with alternating contralateral front and hind suspensions, i.e. 2 L-1-2 L-1, or even occasional suspension of all four legs from 1 to 10% of the stride duration with a 2 L-0-1-2 L-0-1 support structure [10, 15].

A related, but opposite, "artificial" gait, is the broken trot, which is usually called the fox trot and found in the Missouri Fox Trotter and the Marsh Tacky (swamp fox trot), or the marcha batida and found in Mangalarga Marchador horses (with occasional quadrupedal support phases). Though often described as a diagonal gait it is technically a lateral-sequence [LH–LF-RH–RF] diagonal-couplet gait, one in which the front limb lifts off just before the ipsilateral hind limb lands, giving the impression of the horse kicking its front legs forward with its hind legs [21, 27, 36]. As a broken trot, the fox trot also possesses an uneven four-beat cadence with some foreto-back motion for the rider. It is also found in Icelandic Horses (brokk tölt), Paso Fino horses (paso corto and paso largo), Peruvian Paso horses (pasitrote), Columbian Criollo Paso horses (trocha), Spotted Saddle horses, and in the Nez Perce, Nokota Horse, the Tiger Horse (where it is called the glider gait or diagonal Indian shuffle), the Walkaloosa (Indian shuffle), and wild Mustangs. At high speeds it is sometimes called the fox rack or flying fox trot.

While most horse breeds switch from the trot to the gallop at around 4.0 m/s some horse breeds engage in the hard, straight, or true pace, the fastest lateral gait which involves heavily coordinated ipsilateral legs. The pace is a two-beat gait wherein ipsilateral legs lift-off and touch the ground simultaneously allowing for long stride lengths and great speed where it is called the flying pace or speed pace (see **Table 1**). The pace is found in Standardbred, Peruvian Paso (huachano), and Icelandic horses (flug skeith) and typically occurs at speeds of 8.0–12.3 m/s, and possess a stride duration of 0.34–0.54, a stride frequency of 1.9–2.9 strides/second, a lateral advanced placement of 0.07–0.17, a lateral advanced liftoff of 0.08–0.24, a front to hind limb stance duration ratio of 0.93–1.02, and a stride length of 3.5–4.8 meters [1, 4, 18, 19, 23, 24, 29, 37]. The pace has a hind-limb duty factor of 0.27– 0.44 and a suspension phase of 7–37% of the stride wherein all four limbs are off the ground [16, 20]. The pace thus has a support structure of 2 L-0-2 L-0. Like the rack and stepping pace it forms footprints in the sand of diagonal couplets in an undulating pattern as the hind feet come down just behind the contralateral front feet. The lift-off and set down of the limbs can be somewhat asymmetrical (8%) between the right and left sides of the horse and the pace also produces considerable side-toside rolling motion for the rider.

### **3. A study of laterally coordinated gaits in modern horses**

In order to add to our knowledge of artificial laterally coordinated horse gaits the authors undertook a study of the linear, temporal, and footprint parameters of twenty horses. This study remeasured some of the parameters described in the investigations mentioned above, completed them by measuring missing variables such as the diagonal advanced lift-off, and finally introduced new parameters useful in elucidating different aspects of a gait, such as temporal evenness, linear symmetry, and gauge width (interior straddle).

#### **3.1 Materials and methods**

To elucidate the temporal and linear parameters of the various lateral gaits of living horse breeds, studies were undertaken on twenty horses comprising various gaited breeds, seven Tennessee Walking Horses, four Icelandic Horses, three

Peruvian Paso Horses, two Mangalarga Marchador Horses, two Rocky Mountain Horses, an American Saddlebred Horse, and a Spotted Saddle Horse (see **Table 2** below for additional details concerning the horses studied). The horses were ridden by professional trainers selected by the owners of breed-specific horse farms in the lateral gaits specific to the breed, including the walk, flat walk, running walk, rack, and stepping pace of the Tennessee Walking horse, the paso llano, sobreandando, and huachano of the Peruvian Paso horse, the tölt of the Icelandic horse, the marcha picada of the Mangalarga Marchador, the slow gait and rack of the American Saddlebred Horse, the running walk, rack, and fox trot of the Spotted Saddle Horse, and the show and pleasure racking gaits of the Rocky Mountain Horse.

We did not investigate other four-beat lateral gaits such as the classic paso fino of the Paso Fino horse which most often lays down tracks of understepping ipsilateral pairs, the lope or slow canter of Western horses which lays down footprints in contralateral pairs that angle the same way, or the mixed canter of the Tennessee Walker or Missouri Fox Trotter wherein the horse canters in front with contralaterally coordinated legs but walks in the rear (aubin, broken rocking chair canter, valhopp, wicky wack) or the reverse (traquenard).

The horses were videotaped in these lateral gaits at 60 frames per second (or 30 frames per second at the European horse farms where the speed was usually below 3.0 m/s) with advanced cellphone cameras located perpendicular to the plane of motion and five to ten meters back so that all of the horse's body was visible and foot contact with and lift-off from the ground could be observed. These videos were


**Table 2.** *Information regarding modern horses studied (Original data).*

#### *Laterally Coordinated Gaits in the Modern Horse (*Equus ferus caballus*) DOI: http://dx.doi.org/10.5772/intechopen.106490*

analyzed frame-by-frame via Frame Player software to determine the timing of the lift-off and set-down of each of the horses' feet through a series of two stride cycles. From this recorded data various temporal parameters of the horses' gait could be determined such as stride duration and lateral advanced placement.

In addition, the footprint patterns left by eleven of these horses in the sand were photographed and measured in order to determine various linear parameters of the gaits such as stride (cycle) length and overstep amount. This was accomplished by raking smooth a 6x10 meter rectangular area in the sandy arena and using a tape measure or yardstick to measure various distances between the footprints after the horses performed gaits over it (see **Figure 1** for an illustration of measurements taken). Key physical parameters of each horse were also taken including height at the withers, and hoof length (see **Figure 2**).

The velocity of the horses was determined by noting how long it took on the videotape for the horse to complete a measured stride length as well as on occasion additionally timing the distance it took the horses to travel between cones or strips placed three to ten meters apart with a stopwatch. The first method was found to be the most accurate as it was difficult to accurately note when horses crossed various horizontal markers due to limitations of human perception as well as angular effects of distance of viewer from the markers. Hence the second method of using a stopwatch and delineated markers to measure speed was abandoned after the first six horses studied.

The temporal and linear parameters of the horse gaits were determined through videotape analysis or footprint measurements based upon the following definitions (modified from [38]):

Stride duration: Time in seconds taken to complete a stride cycle, i.e. time between successive left hind ground contacts. The stride duration tends to decrease in faster gaits.

Stride frequency: Number of strides per second, i.e. 1/stride duration.

Front stance phase: Percent of the stride duration the front limbs are on the ground.

Hind stance phase [here considered to be the duty factor]: Percent of the stride duration the hind limbs are on the ground.

#### **Figure 2.**

*Measurements taken of horse. HW = height at withers; HL = hoof length; IGA – Intergascular angle (maximum angle during gait).*

Average stance phase: Average value of front and hind stance phase. A value over 0.50 indicates there is no suspension phase where all four-limbs are off the ground simultaneously.

Front stance/Hind stance ratio: Front stance phase value divided by hind stance phase value. A value near or over 1.0 tends to indicate a slower walking gait is occurring.

Time between ipsilateral steps: Time in seconds between the ground contact of ipsilateral hind and front hooves.

Time between diagonal steps (s): Time in seconds between the ground contact of contralateral front and hind hooves.

Ipsilateral/diagonal step time ratio: Average value of time between ipsilateral steps divided by time between diagonal steps. This ratio relates to evenness of the steps and hence is 0.75–1.25 in even gaits, and less than 0.50 or above 1.50 in asynchronous gaits. A value below 1.0 indicates lateral coordination of limbs and above 1.0 diagonal coordination of limbs.

Ipsilateral swing phase overlap: Percent of stride cycle ipsilateral limbs are off the ground together. This indicates degree of lateral coordination and exceeds 0.75 in highly laterally coordinated gaits.

Ipsilateral stance phase overlap: Percent of stride cycle ipsilateral limbs are on the ground together.

Overall ipsilateral overlap: Average value of ipsilateral swing phase overlap divided by ipsilateral stance phase overlap. Higher values indicate strong coordination between ipsilateral limbs wherein ipsilateral hooves lift off and set down close in time to each other.

Swing/stance phase overlap ratio: Average value of ipsilateral swing phase overlap divided by ipsilateral stance phase overlap. A lower value of 0.60 or lower indicates a slow gait with a long stance phase while a higher value indicates a faster gait with increased swing phase time and less stance phase time.

Lateral advanced placement [Limb phase]: Time between contact of ipsilateral hind and front limbs, expressed as percent of stride cycle and so divided by stride duration. This value is 0.20–0.25 in square gaits with limbs operating relatively independently, less than 0.20 in gaits with ipsilateral limb coordination and lateral couplets, and 0.30 or higher in diagonally coordinated gaits with diagonal couplets.

Lateral advanced lift-off: Time between lift-off of ipsilateral hind and front limbs, expressed as percent of stride cycle, so divided by stride duration. This value is below 0.20 in highly laterally coordinated gaits and above 0.30 in highly diagonally coordinated gaits.

Diagonal advanced placement: Time between contact of front limb and contralateral hind limb, expressed as percent of stride cycle, so divided by stride duration. A value below 0.20 indicates a high level of diagonal-coordination of limbs while a value above 0.30 indicates a high level of lateral-coordination of limbs.

Diagonal advanced lift-off: Time between lift-off of front limb and contralateral hind limb, expressed as percent of stride cycle or divided by stride duration. A value below 0.20 shows strong diagonal-coordination of limbs while a value above 0.30 indicates strong lateral-coordination of limbs.

Foot couplet time differential: Time in seconds between closest contact of hooves whether ipsilateral, diagonal, or contralateral front or contralateral hind.

Tripedal support phase: Percent of stride cycle three limbs are on the ground at the same time whether two front and one hind or two hind and one front. This value can be 50% or more of the gait in slower gaits and missing in faster gaits.

#### *Laterally Coordinated Gaits in the Modern Horse (*Equus ferus caballus*) DOI: http://dx.doi.org/10.5772/intechopen.106490*

Bilateral support phase: Percent of stride cycle two ipsilateral limbs are on the ground at the same time whether left or right side. This value is less than 30% in diagonally coordinated gaits and above 50% in laterally coordinated gaits.

Diagonal support phase: Percent of stride cycle two diagonal limbs are on the ground at the same time, i.e. one front limb along with its contralateral hind limb. This value is less than 30% in highly laterally coordinated gaits and above 50% in a highly diagonally coordinated gait.

Unipedal support phase: Percent of stride cycle only one leg is on the ground, whether front or hind. Such unipedal support occurs in fast four-beat artificial gaits such as the running walk and rack or tölt.

Front contralateral suspension phase: Percent of stride cycle both front limbs are off the ground at the same time.

Hind contralateral suspension phase: Percent of stride cycle both hind limbs are off the ground at the same time.

Four-limb suspension phase: Percent of stride cycle all four limbs are off the ground together. This occurs in fast two-beat gaits, namely a trot or pace, and the canter and gallop.

Maximum rear intergascular angle: Inverted pendulum angle formed between contralateral gaskins (from stifle to hock) when both hind hooves are on the ground during gait (placement) or during protraction when both feet are in the air (suspension), or a combination of the two (see **Figure 2**). This value will be higher in gaits involving larger hind leg extension such as the running walk.

Stride length (cycle length): Distance in meters between the hoof top (toe) of successive left hind footprints. The stride length tends to increase as a gait gets faster.

Stride length/Horse height ratio: Dimensionless speed ratio found by dividing stride length by horse height at the withers. As gaits get faster this number increases. In walking gaits this value is usually less than 1.0, between 1.0–2.0 in intermediate speed gaits, while in very fast gaits it can be above 2.0.

Distance between diagonal steps: Measurement in centimeters between toe and heel of contralateral front and hind hoof prints.

Distance between ipsilateral steps: Measurement in centimeters between toe and heel of ipsilateral front and hind hoof prints.

Ipsilateral overstep/Stride length ratio: Distance between ipsilateral steps divided by the stride length. In the running walk with much hind leg extension as well as in fast laterally coordinated gaits such as the rack, stepping pace, and pace, the ipsilateral overstep can be 15–30% of the stride length.

Diagonal/Ipsilateral step distance ratio: Distance between diagonal steps divided by distance between ipsilateral steps. This value is below 0.50 in highly laterally coordinated gaits and above 1.0, often by a large margin, in highly diagonally coordinated gaits.

Average interior straddle [Gauge width]: Average distance in centimeters between quarters of contralateral front and hind hoof prints. In the walk and running walk this value is typically positive but in gaits with high-lateral coordination the hind limbs are free to come in or cross the centerline without interference and so this value is often negative.

Average foot pair lateral offset: Average distance in centimeters between quarters of closest hoof print pairs whether formed by ipsilateral, diagonal, or contralateral front or contralateral hind. This value is low when ipsilateral pairs of feet are close together but high when diagonal pairs are close together.

Foot pair lateral offset/hoof width: Ratio of average foot pair lateral offset divided by average width of hoof at quarters. This value is high for gaits with diagonal pairs landing close together in space but low for gaits with lateral pairs landing close together in space.

### **3.2 Results**

Temporally the standard walk was characterized by a slow velocity (around 1.5 m/s), a stride duration over a second in length (1.16 seconds average), a front limb stance phase that is nearly as long as or even longer than the hind limb stance phase (1.02 front/hind limb stance phase ratio on average), a high ipsilateral/diagonal pair step time ratio (0.80 average), moderate ipsilateral swing phase overlap over the course of the stride (35.9% on average), and abundant tripedal support (52.9% of the stride duration) but not as much bilateral support (27.3%). The walk then is a relatively square and even four-beat gait with a lateral advanced placement of 21.6% and a lateral advanced lift-off of 24.1% of the stride cycle. The linear characterizations of the walk were not investigated here as previous studies have shown it to have a relatively short stride length (1.5–1.8 meters), with hind limbs that cap [forming direct register prints] or slightly overstep the front limbs (average intergascular angle of 33.3 degrees), and forming tracks in the sand characterized by lateral pairs in nearly parallel alignment if the horse is moving in a straight line [22] as can be seen in **Figure 3**. See **Table 3** and **Figure 4** below for additional temporal parameters and a gait diagram of the walk, as well as supplementary **Table S1**.

A few of the horse breeds exhibited the "artificial" lateral gait of the running walk, a faster variant of the walk emphasizing hind-limb extension (with an intergascular angle of around 59.0 degrees when both rear legs are on the ground), a pulling action with the front limbs, and often involving a counterbalancing mechanism such as nodding of the head and scissoring of the hind legs in the Tennessee Walking Horse, or an outward arcing path of the front limbs (termino) in paso llano of the Peruvian Paso Horse. The Spotted Saddle Horse, however, did not display much in the way of these counterbalancing mechanisms. The running walk is an even four-beat gait and is characterized temporally by a moderate stride duration (0.77 seconds on average, though a much quicker 0.58 seconds in the Peruvian Paso's paso llano), a high fore/hind stance duration ratio of 0.91 along with a high ipsilateral limb/diagonal limb step time ratio of 0.82, increased ipsilateral swing

#### **Figure 3.**

*Footprint patterns of various laterally-coordinated gaits in modern horses. In the fast walk (a) there is a small stride length with a small overstep of ipsilateral hind feed resulting in distinct lateral pairs of prints in roughly parallel lines and a diagonal step distance much larger than the ipsilateral one. The fox trot and true fast trot (B) forms a trackway similar to that of the walk with lateral pairs of prints lining up more or less in parallel but possesses a greater stride length. In the running walk (C) there is a large overstep yielding no obvious pairs of prints as the ipsilateral step distance is nearly equivalent to the diagonal one but wherein the ipsilateral step distances and diagonal step distances are roughly equivalent with themselves. This should be contrasted with the gallop (D) which also lacks obvious print pairings but which has a much greater stride length and in which there is greater variance within the ipsilateral and diagonal step distances and a sequence of contralateral feet. In the rack of tölt (E) the ipsilateral step length is much greater than the diagonal one resulting in diagonal pairs of prints that form a bowed pattern with a large stride length and hind impressions that often cross over the centreline. In the stepping pace and true pace (F) there is an even greater stride length and the diagonal pairs of prints occur very close together as the ipsilateral step distance is much larger than the diagonal one. The scale is in centimeters.*


### *Laterally Coordinated Gaits in the Modern Horse (*Equus ferus caballus*) DOI: http://dx.doi.org/10.5772/intechopen.106490*

## **Table 3.**

*Average temporal and linear kinematic parameters of ipsilaterally coordinated horse gaits (original data).*

phase coordination (61.6% of stride), and much less tripedal support (averaging 9.4% overall) and more bilateral support (55.5%). The lateral advanced placement in the running walk averaged 22.2% and the lateral advanced liftoff 17.3% of the stride duration reflecting the greater degree of lateral coordination than in the standard walk. The velocity of the running walk averaged 2.9 m/s, with a stride length of 2.3 meters, an ipsilateral overstep of the hind over the forefoot that

#### **Figure 4.**

*Gait diagrams of the walk, running walk, and paso llano of a horse.*

averaged 18.8% the length of the stride. The trackway of the running walk consistently produced four footprints separated from each other and located fairly equidistant from each other (diagonal/ipsilateral step distance ratio of 0.94; see **Figure 3**). See **Table 3** and **Figure 4** for more of the temporal and linear parameters of the running walk and paso llano as well as gait diagrams, as well as supplementary **Table S2**.

The other common "artificial" lateral gait studied here was the rack found in the Tennessee Walking Horse and Rocky Mountain Horse and the similar gait of the tölt in the Icelandic Horse, which again is an even four-beat gait, though at a faster speed (averaging 3.8 m/s in the rack). In terms of temporal parameters, the rack or tölt is characterized by a relatively short stride duration (averaging 0.56 seconds), with a high ipsilateral/diagonal step time ratio of 0.79, a high forelimb over hindlimb stance duration ratio of 0.93, and a fair amount of lateral coordination (averaging 63.3% of the swing phase). The lateral advanced placement averaged 21.9% of the stride length and the lateral advanced lift-off 18.7%, while the hind limbs did not stretch forward as much at maximal protection as in the running walk (average intergascular angle of 41.0 degrees). Tripedal support was quite low (5.2% of stride cycle) while bilateral support was high (55.2%), and there was occasional

### *Laterally Coordinated Gaits in the Modern Horse (*Equus ferus caballus*) DOI: http://dx.doi.org/10.5772/intechopen.106490*

single foot support in some horses (around 13.2% of the stride cycle in fast racks). Perhaps the biggest difference, however, occurred in the prints themselves. At slower racking speeds, the ipsilateral feet form pairs with the hind foot overstepping the front foot (or on occasion form a trackway resembling a running walk with mostly isolated prints). In the fast rack, which had an average stride length of 2.2 meters, and an average ipsilateral overstep of 28.3% of the stride length, the footprint impressions are comprised of diagonal pairs with the hind foot understepping the front foot and forming a bowed or wave-like pattern in the sand (with a low diagonal/ipsilateral step distance ratio of 0.37). As observed in previous studies [22] there was very little distance separating the contralateral hoof impressions (see **Figure 3**), indeed when the rack is performed at fast speeds the hind foot understeps the front foot and due to lack of interference often crosses over the centerline and overlaps with its diagonal partner. This is reflected in a low interior straddle averaging �5.1 cm. **Table 3** and **Figure 5** display more of the temporal and linear parameters of the racking gait along with gait diagrams. See supplementary **Tables S3** and **S4**.

Some of the horses also engaged in the stepping pace characterized by an uneven four beat gait. Such a gait was very ipsilaterally coordinated with a lateral advanced placement averaging 15.6% and a lateral advanced lift-off 12.3%, along with an average ipsilateral swing phase overlap of 75.2%. Though the front/hind stance duration ratio was high (0.94), the ipsilateral/diagonal step time ratio was very low (0.46). Three-limb support was very also very low (3.6%), bilateral support very high (67.0%), and in some horses there was occasional single-foot support as well (for 9.6% of the stride length). The stepping pace took place at an average velocity of 3.7 m/s and had an average stride length of 2.1 m, ipsilateral overstep/stride length of 29.0%, an intergascular angle averaging 44.3%, and the footprint trackway in the sand occurred as close diagonal couplets as in the rack (0.24 diagonal/ ipsilateral step distance ratio; see **Figure 3** and supplementary **Table S5**). **Table 3** and **Figure 6** show additional temporal and linear parameters of the stepping pace.

**Figure 5.** *Gait diagrams of the rack or tölt of a horse.*

**Figure 6.**

Only two horses displayed a true or hard pace, i.e. an even two-beat gait with heavy ipsilateral coordination above 80% (with an average lateral advanced placement of 5–10% of the stride duration and 75–90% bilateral support through the stride cycle). This occurred at a relative slow speed for the pace, however, of around 3.4 m/s and so there were no suspension phases nor single-foot support structures (see **Figure 7** and supplementary **Table S6**).

Finally, three of the horses could also perform the fox trot gait, which is a lateralsequence but diagonal-couplet running gait occurring at around 3.3 m/s. Hence the fox trot is usually considered a diagonal gait. The fox trot has very unusual temporal parameters accordingly, and was characterized by a stride duration averaging 0.62, lateral advanced placement of 38.4% and lateral advanced lift-off of 31.7%. The forelimb/hindlimb stance duration ratio was low (average of 0.86) while ipsilateral/diagonal step time ratio was super large at 4.11 due to a delayed front step on each side. There was in addition a large amount of diagonal support (62.8% of the stride

**Figure 7.** *Gait diagrams of the pace and fox trot of a horse.*

cycle) and occasional single-leg support (2.8%), along with minimal ipsilateral swing overlap (27.1% of the cycle). See **Figure 7** for a diagram of some of the fox trots displayed by the horses and supplementary **Table S7**.
