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Double and Triple Fully Airborne Phases in the Gaits of Racing Speed Thoroughbreds Jeffrey A. Seder, AB, JD, MBA, and Charles E. Vickery, III, BS INTRODUCTION tary gallop, often seen in a horse coming out of the starting Current literature suggests that during the gallop, there gate. The rotary gallop is generally seen in the counter- is normally one airborne phase during a single stride,1,2 be- clock wise direction of LR, RR, RF, LF, and, unlike the ginning when the lead foreleg leaves the ground and ending switching of leads, the rotary gallop is often repeated for when the non-lead rear leg bears weight. During a normal more than one stride. transverse gallop stride pattern, the following step sequence This study documents the frequency of occurrence of occurs. Sequence numbers with corresponding occurrences additional airborne phases within a single stride between include: the lead rear leg and non-lead foreleg and between the 1. Left rear leg (LR) bears weight. This leg would be forelegs (these air phases respectively referred to as “dou- considered the non-lead rear leg of a horse on its ble-air-P2” and “double-air-P3”). right lead. We refer to horses that used more than one airborne 2. A few hundredths of a second before the left rear leg phase within a single stride as “double-air” horses. We refer stops bearing weight, the right rear leg (RR) bears to horses that used 3 airborne phases within a single stride weight. In this instance, the right rear leg is called the as “triple-air” horses. Figure 1 presents step diagrams de- “lead rear leg,” and the horse is said to be on its scribing the “single-air,” “double-air-P2,” “double-air-P3,” “right lead.” and “triple-air” running patterns. 3. A few hundredths of a second before the right rear The extension variables studied in this paper (P1, P2, leg stops bearing weight, the non-lead left foreleg and P3) are a measure of how stretched out a horse is. We (LF) bears weight. measured this extension between the pairs of legs shown in 4. A few hundredths of a second before the left foreleg Figures 2 through 4. Figure 2 shows extension between the stops bearing weight, the lead right foreleg (RF) rear legs. We call this extension P1. We have never seen an bears weight. airborne phase between these legs. Figure 3 shows exten- 5. The right foreleg (lead foreleg) stops bearing weight sion between the lead rear and the non-lead foreleg. We and the horse is fully airborne until the non-lead left refer to this extension as P2. If there is an airborne phase rear leg (LR) again bears weight, thus starting an- between these legs (as exists in this panel), we say the horse other stride cycle. is double-air-P2. Figure 4 shows extension between This sequence could be shown as LR, RR, LF, RF. A forelegs. We refer to this extension as P3. If there is an air- horse on its left lead would have the sequence: RR, LR, RF, borne phase between these legs (as exists in this panel), we LF. say the horse is double-air-P3. Among single airborne phase stride patterns, there are A technical definition of double-air would be that ex- two common exceptions to the above stride pattern. One actly as one leg stops bearing weight, the next leg bears exception occurs when a horse switches leads from the weight. In this case, there would be little or no overlap be- right to the left, or vice versa. The other exception is the ro- tween those legs, and the horse would be said to be 100% extended (or totally stretched out) between those legs. If a period of time exists between the time the first leg stops bearing weight and the next leg bears weight, the horse is Copyright © EQB, Inc, Unionville, Pennsylvania. considered to be more than 100% extended. It is so Reprint requests: EQB, Inc, 501 Hicks Rd, Unionville, PA 19390. 1- 800-223-7014; E-mail: [email protected]; Web site: www.eqb.com. stretched out that it cannot bring the next leg down before doi: 1053/jevs.2003.50 it lifts the previous leg. Volume 23, Number 5 S73 Fig 1: Step Diagrams: The solid dot indicates the start of ground contact and stance phase of the limb, while the open circle represents the end of ground contact for that step. Overlap is denoted by the diagonally shaded area. Airborne phases are noted in each panel. MATERIALS AND METHODS Computer analysis was done with a Prime 2450 minicom- Approximately 2.5 strides of more than 6500 different puter (Prime, Natick, Mass) and SAS statistical software Thoroughbred racehorses were filmed with Lo-Cam 16- (SAS Institute, Cary, NC). For the purposes of this study mm cameras (Redlake Corporation, Campbell, Calif) at a we used only the 5724 filmings, representing 3008 unique frame rate of 300 frames per second. Digitizing was con- horses, which were on dry dirt surfaces and in which the ducted on more than 12,000 filmings (each horse filmed an horses were in an unimpeded transverse gallop (no lead average of 1.9 times) using motion analyzer projection changes or rotary gallops), at speeds from 44 to 66 feet per equipment (Vanguard Instrument Corporation, Melville, second (13.4-20.1 m/second or 15-10 seconds/furlong), NY; Lafayette Instrument Corporation, Lafayette, Ind; L-W and which had been in training for at least 60 days. All Athena International Corporation, Simi Valley, Calif). filmings used were made with professional jockeys who S74 Journal of Equine Veterinary Science May 2003 Fig 2: Extension between the rear legs. Fig 3: Extension between the lead rear and non-lead foreleg. were in normal riding positions and did not use their whip during the filming. The riders and trainers were working in- dependently of the authors, with no a priori-dictated be- havior with respect to this study. Most filmings (n = 4681: 2699 colts, 1982 fillies) were from early spring 2-year-old auctions. These horses were filmed during the final 16th mile of their work. Each cam- era filmed from 2.5 to 3 strides of each horse, depending on the facilities at each racetrack (which dictated how far back from the horses the cameras could be set up, and thus, their field of view). For about half of the filmings, the cameras were positioned to film a continuum of strides, such that as the horse left the field of view of the first camera, it entered the field of view of the second camera. The remainder of the filmings (n = 1043: 614 colts, 429 fillies) were of race age horses (some were 2-year-olds ac- Fig 4: Extension between the forelegs (Horse No. 6). tually in races in August or later, but most were at least into their 3-year-old year, often filmed in real races). These horses were generally filmed during the final one-sixteenth mile of their work but sometimes were filmed elsewhere in There were 2 clockers spaced approximately 330 feet their work or during races after they had gone approxi- apart, with the cameras and camera operators set up be- mately three-sixteenths to one half mile. Typically, during a tween them. Using “Equi-talk” FM wireless communica- Breeders’ Cup race or major stakes event, cameras were po- tion sets (EQB, Inc, Unionville, Penn), the first clocker sitioned at the “clocker’s stand” at the halfway point on the called the “on,” at which time both clockers started their backside of the racetrack. During these major events, the stopwatches. The second clocker called the “off,” at which point in the race filmed depended on the starting gate place- time both clockers stopped their watches. The 2 times on ment relative to the clocker’s stand position used for filming. the clockers’ watches were then averaged and, upon discre- Eighty percent of horses used their right lead. No more tion, were compared with the times taken directly from the than 3 consecutive strides were used to calculate the gait vari- film. Previous unpublished studies of this timing technique ables studied. Temporal measurements were used to describe conducted by EOB showed this technique to be accurate. It each horse’s gait characteristics in terms including extension, also solved the problem of being forbidden by racetrack au- stride length, stride frequency, overlap times between limbs, thorities to place electronic timing devices (which the au- and contact and non-contact times for the limbs. thors used in other studies) on the actual racetracks. Volume 23, Number 5 S75 Only a few people (digitizers) digitized the filmings locity dependence of the double-air running style. This used for this study. They had years of training and horse ex- analysis showed that double-air was the natural result of the perience. For practically all horses, the digitizers acted increase of P2 and P3 with increasing velocity. Table 2 pre- “blind.” That is, they did not know the sex, pedigree, value, sents regression equations and their R2 values. or ability of the horses they were digitizing. The digitizers Linear regression equations relating velocity to exten- identified each horse only by a hip number or a filming sion variables for thousands of horses showed low R2 values identification number. because of the high degree of individual variation from The unknowns in the data included soundness, condi- horse to horse. To eliminate this high degree of variation tioning levels, drugs administered, tack and rider weight, from one horse to the next, we calculated the averages of the and ability.

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