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Interrelationships between moisture content of the track, dynamic properties of the track and the locomotor forces exerted by galloping horses
Refereed
INTERRELATIONSHIPS BETWEEN MOISTURE CONTENT OF THE TRACK, DYNAMIC PROPERTIES OF THE TRACK AND THE LOCOMOTOR FORCES EXERTED BY GALLOPING HORSES Marc H. Ratzlaff, DVM, PhDl; Martha L. Hyde, PhD3; David V. Hutton, PhD 2 Rhonda A. Rathgeber, DVM, PhD4; Olin K. Balch, DVM, PhD 5
SUMMARY
Three methods were used to examine the relationships between the dynamic properties of a track and the locomotor forces exerted by galloping horses. The impact resistance and the percentage of energy returned by the track were determined using a trailer mounted track testing device. Vertical forces were measured from instrumented horseshoes nailed to all four hooves and the velocities of each of the six horses galloping in a track straight-away were determined from slow-motion films. The moisture content of the track was altered by the addition of water. These data were analyzed to determine the relationships between changes in moisture content on the energy returned by the track, impact resistance of the track and locomotor forces exerted by the horses. There was a strong linear relationship between impact resistance and the percentage of energy returned by the track. Changes in moisture content of the track cushion Authors' addresses: 1Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology. 2Department of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164. 3Department of Biology, California State University, 9001 Stockdale Highway, Bakersfield, CA 93311.4Hagyard, Davidson and McGee Equine Medicine and Surgery, 42550 Ironworks Road, Lexington, KY 40511. 5Department of Anatomy, School of Veterinary Medicine, Tuskegee University,Tuskegee,AL 36088 Acknowledgements: This study was supported by the Grayson-Jockey Club Research Foundation, C.N. Ray Foundation and the Equine Research Program at Washington State University. The authors thank Dr. John E. Hamell, (Department of Plant and Soil Sciences, University of Idaho, Moscow, Idaho 83843) for his advice and assistance in the interpretation of the data and Kathryn Kunka, Sarah Christian, Cody Ames and Stuart Nelson for their assistance during these studies. The authors also thank Larry Miller, Mitch Almeida and David Tibbals for the design and construction of many of the electronic components in the instrumentation used in this study.
Volume 17, Number 1, 1997
resulted in similar changes in both the percentage of energ 2 returned and the impact resistance of the track. Energ 2 return and impact resistance decreased at 8% moisture ant progressively increased from 8.5 to 14% moisture. The horses were divided into two groups based upor their speed during each trial (Group I: 14.5 to 15.4 m/se~ and Group II: 15.5 to 16.5 rn/sec). Changes in the moistur~ content of the track cushion altered the forces exerted b 3 the horses. Forces were lowest at 8% moisture content fo~ Group 1 and at 12% moisture for Group II. Changes in th~ percentage of energy returned and the impact resistance ol the track also affected the forces exerted by the horses. FoJ the horses in Group I forces increased as energy return and impact resistance increased. Conversely, horses in Grour 11exhibited a decrease in force as energy return and impacl resistance increased. These results suggest that the dynamic properties of the track may be suitable for horses traveling at relatively narrow ranges of velocity and tha! when horses work at speeds outside of this range, pronounced changes in locomotor forces will occur.
INTRODUCTION
The relationship between track conditions and injuries in Thoroughbred racehorses has been addressed in a series of studies based upon track surveys. 1-3 In these reports, the condition of the track was based upon estimated moisture contents and each track was rated as fast, good, sloppy, or muddy. It was found that the incidence of lameness was higher on the "fast" and "sloppy" tracks. The definitions of track conditions in these studies were subjective and other factors such as soil composition, length of race, and individual variations between horses may have also contributed to the incidence of injuries. Another report 4 concluded 35
Figure 1. Trailer-mounted
track testing device. A. Recorder B. Amplifiers and power supply C. Battery D. Impact head.
that track conditions did not influence the occurrence of racing injuries in Thoroughbred horses in New York. However, a more recent study 5 reported that breakdowns on the New York Racing Association tracks were related to the specific track and track composition, as well as season of the year and inherent factors within the horses. The dynamic properties of the track surface vary with its moisture content, composition and compaction. The moisture content of the base of the track remains relatively constant, however, the water content of the track cushion may fluctuate widely. 6 Several studies have shown that the composition of the track surface alters the dynamic responses of the soil 7,8 and that the compaction of the track surface may vary widely over different areas of the same track. 6-1~A study 11 on the impact and shear resistance of turf racing surfaces, using two mechanical devices, found that turf roots were responsible for increased impact resistance (hardness) and resistance to shear. Additionally, these investigators reported that changes in soil moisture altered the soil properties and that soil composition affected the resistance to shear. The dynamic responses of the surfaces of five racetracks were measured with an impact testing machine and these results were compared with the incidences of lameness in horses working on these tracks. 12 These investigators concluded that the dynamic responses of the soil were related to the water content and depth of cushion and that the incidences of lameness on these tracks could have been related to the hardness of each track. Studies 1~ using accelerometers attached to the hooves of horses have demonstrated that both the compaction and composition of the track surface dramatically affect hoof impact deceleration. Lower compaction and higher percentages of organic matter result in lower impact forces. Another study 15using instrumented horseshoes, showed that as moisture content of the track surface increased, the variation in the magnitude of vertical forces between successive strides decreased. This study was undertaken to determine the effects of 36
Figure 2 . Track testing device in the transport position. A. Linear variable differential transformer B. Accelerometer C. Load cell D, Impact head.
changes in moisture content of the track cushion on the dynamic responses of the track surface, the locomotor forces exerted by galloping horses and the interrelationships of the locomotor forces and the physical properties of the track. Two procedures were performed concurrently; a trailer mounted device was used to measure the physical properties of the track and instrumented horseshoes were used to record the vertical forces exerted by the hooves as horses galloped through a track straightaway.
MATERIALS AND METHODS
A trailer-mounted track testing device (TTD), modified after the drop-hammer device used by Cheney, et al.12 was used to measure the dynamic response of the track surface to impact loading. This machine, designed to simulate the vertical force exerted by a galloping horse, consisted of an 80 pound (36.4 kg) weight dropped in free fall from a height of 5.0 inches (12.7 cm) and is shown in Figures 1 and 2. The weight consisted of a stainless steel disc, 5 inches (12.7 cm) in diameter, bolted to a steel ram. The instrumentation for the TTD consisted of a load cell, a accelerometer, b linear variable differential transformer, c amplifiers, d power supply, d and recorder, e The force, displacement and acceleration of the weight at impact with the track surface were recorded from 10 sites for each trial. A typical recording of these parameters is shown in Figure 3. The impact force, impact resistance (deceleration at impact) and the rebound energy, expressed as a percentage of the initial impact energy, were determined. The rebound energy was determined from the rebound height which was calculated using the formula: aModel 9011, Kistler InstrumentCorporation, Amherst, NY bModel EGAXT-*-25, Entran Devices, Inc., Fairfield, NJ CModel0246-000, Trans-Tek, Inc., Ellington, CT dElectronics Division, College of Veterinary Medicine,Washington State University, Pullman,WA eTEAC R-61 Cassette Data Recorder, B.J. Wolfe Enterprises, North Hollywood, CA JOURNAL OF EQUINE VETERINARY SCIENCE
Displacement
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Figure 3. Force, acceleration and displacement traces
Figure 4 . Instrumented horseshoe with piezoelectric transducers located at the toe (A) and both sides of the heel (B). The leads (C) from the transducers exit the lateral side of the shoe.
recorded from the track testing device. 1 G = 9.8 m/sac 2
1) Where:
H = 1/2 gt 2 H = rebound height g = acceleration of gravity t = one-half of the time the weight was in the air between the initial impact and the rebound impact
The percentage of rebound energy returned was determined by the formula:
2) Where:
U=mH x 100 mP U = % energy returned m = mass of the weight H = rebound height P = total drop height of the weight
Since force is directly proportional to acceleration (F = m-a), and the mass remained constant, impact resistance (deceleration at impact) and the percentage of energy returned by the soil were used to characterize the dynamic responses of the track surface to impact loading. A straightaway of a track f was harrowed to a depth of two and one-half inches. On each day, tests were conducted sequentially under four conditions:
soil samples were weighed, dried in an oven at 100~ for 24 hours and reweighed to determine the percentage of water in each sample. The textural classification of the track cushion was loamy sand and the soil composition is presented in Table 1. Six conditioned Thoroughbred horses, two mares and four geldings, were used to determine the effects of changes in moisture content of the track cushion on the locomotor forces exerted by these horses as they galloped through a track straightaway. The hooves of each horse were shod with instrumented shoes containing piezoelectric transducers located at the toe and both sides of the heel (Figure 4). 16-19The leads from the transducers in each shoe were connected to preamplifiers dtaped to the lateral aspect of the distal end of the metacarpus/metatarsus of each limb. The cables from the preamplifiers were taped to each leg and connected to a multichannel recorderg carried in a backpack by the rider. The vertical forces exerted on each transducer were recorded from six consecutive strides for each trial as each horse galloped through the straightaway. The forces exerted on each of the 12 transducers were stored digitally in the recording unit. These data were transferred to a Table
1. Soil composition of the
track*
1: track harrowed, no water added; 2: track harrowed, water added; 3: additional water added, track harrowed; and 4: additional water added, track harrowed. The physical properties of the track surface were recorded from 10 sites using the TTD and the moisture contents of the soil were determined on a dry matter basis from samples collected immediately after each trial. The
Very coarse sand 15.2 Coarse sand 23.1 Medium sand 19.3 Fine sand 13.7 Very fine sand 5.8 Silt 15.8 Clay 7.1 Organic matter 1.1 *Soils laboratory, College of Agriculture, University of Idaho, Moscow, Idaho. U.S. Departmentof Agricultureclassification.
fHitchcock EquineResearchTrack, WashingtonStateUniversity,Pullman, WA
gData Logger,Scientech,Inc. Pullman,WA
V o l u m e 17, N u m b e r 1, 1997
37
138
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computer h and analyzed i to determine the maximum vertical force exerted on each transducer and the sum of the peak forces exerted on the transducers in each shoe during the support period of the limbs. This sum was expressed as a percentage of body weight. A high-speed 16mm cameraJ was used to photograph each horse as it galloped through the straightaway. Each trial was filmed at 300 frames per second using black and white film. k The running line was marked with lime and 2 reference stakes, 5 meters apart, were positioned behind the running line. The rails and posts were removed from the inner railing of the track to provide an unobstructed view of the horses as they traversed the course. The films were analyzed to determine the velocities of each horse during each trial. The physical properties of the track, moisture content, forces exerted by the horses and films of the horses were obtained for each trial. These data were analyzed ~ and polynomial equations fitted to determine relationships between changes in moisture content on the energy returned by the track, impact resistance of the track and locomotor forces exerted by the horses.
RESULTS The relationships between changes in the moisture content of the track cushion and the physical properties of the track are presented in Figures 5-7. Changes in moisture content resulted in changes in the percentage of energy returned following impact of the head of the TTD on the track surface (Figure 5). Energy return decreased at 8% moisture and progressively increased from 8.5 to 14% moisture. This relationship between moisture content and hDeskpro286, Compac Computer Corp., Houston,TX iASYT version 3.0, Asyst SoftwareTechnologies,Inc., Rochester,NY JModel 1PL, InstrumentationMarketing, Inc., Burbank, CA kTri-X 7278, Eastman Kodak Co., Rochester,NY ISigma-PIot,version 3.10, Jandel Scientific,Corte Madera, CA
16
. . , , 18
% Water
Water
Figure 5 . R e l a t i o n s h i p b e t w e e n t h e p e r c e n t a g e of energy returned and the moisture content of the track cushion. r=0.64, y=3,622-0,399x +0.027x 2.
38
..... 2
16
Figure 6. Relationship between the impact resistance and the moisture content of the track cushion, r=0.58, y=138.362-2.405x+0.161x 2.
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Figure 7. Relationship between the impact resistance and the percentage of energy returned from the track, r=0.92, y=-I 6.270 + O.143x 2.
energy return was not strong (r=0.64). The relative change in soil recoil approximated a two-fold increase; however, the actual increase in the energy returned was low, averaging less than 2.5% of the initial energy applied to the track. Changes in the moisture content of the cushion had a similar effect on the impact resistance of the soil (Figure 6). Impact resistance decreased at 8% moisture and gradually increased from 8.5 to 14% moisture. This relationship was low, r=0.58. A strong direct linear relationship (r=0.92) occurred between changes in impact resistance and percentage of energy returned by the track (Figure 7). The horses were divided into two groups based upon their speed during each trial. Horses in Group I were traveling at a moderate gallop at speeds between 14.5 and 15.4 m/sec and horses in Group II were running at a fast gallop at speeds between 15,5 and 16.5 m/sec, a~ The effects of changes in moisture content of the track cushion on the vertical forces exerted by all four limbs of the horses are presented in Figures 8 and 9. These relationships were relatively strong (r=0.81). Horses galloping at JOURNAL OF EQUINE VETERINARY SCIENCE
80
95 9o
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Figure 8. Relationships between the forces exerted by the horses galloping at velocities of 14.5-15.4 m/s (Group I) and the moisture content of the track cushion. Forces were recorded from transducers in the instrumented shoes nailed to each hoof. r 0.81 y=97.620-8.367x + 0.515x 2.
Figure 1 1. Relationships between the forces exerted by the horses galloping at velocities of 15.5-16.5 m/s (Group II) and the percentage of energy returned from the track. r=0.74, y= 131.557-34.276x +4.944x 2.
95
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Figure 9. Relationships between the forces exerted by the horses galloping at velocities of 15.5-16.5 m/s (Group II) and the moisture content of the track cushion. Forces were recorded from transducers in the instrumented shoes nailed to each hoof. r=0.81, y=152.606-13.216x 0.550x 2.
Figure 12. Relationships between the forces exerted by the horses galloping at velocities of 14.5-15.4 m/s (Group I) and the impact resistance of the track, r=0.79, y=3565.337+55.106x-0209x 2. 95
80
90
75 85
m 0C. 0
70 80 65
7s
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70
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Figure 10. Relationships between the forces exerted by the horses galloping at velocities of 14.5-15.4 m/s (Group I) and the percentage of energy returned from the track. r=0.60, y=24.739 + 33,168x-5.878x ~. Volume 17, Number 1, 1997
65 124
B
126
128
130
132
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138
Deceleration (m/sec 2)
Figure 13. Relationships between the forces exerted by the horses galloping at velocities of 15.5-16.5 m/s (Group II) and the impact resistance of the track, r=0.66, y=-1062.584 + 18.981 x - 0,078x 2. 39
40
speeds between 14.5 and 15.4 m/sec (Group I) exerted an average force of 72% of body weight at 4% moisture content; this decreased to 64% of body weight at 8% moisture and gradually increased to 68% of body weight at 11% moisture (Figure 8). Horses running at speeds between 15.5 and 16.5 m/sec (Group II) exerted average forces of 85% of body weight at 7.5% moisture which decreased to 73% of body weight at 12% moisture and increased slightly at 13.5% moisture (Figure 9). Relationships between the total forces exerted by the two groups of horses and the percentage of energy returned following impact of the head of the track testing device with the track surface are shown in Figures 10 and 11. For the horses traveling at 14.5 to 15.4 m/sec, total force increased as the percentage of soil recoil increased (r=0.60). Conversely, horses galloping at speeds between 15.5 and 16.5 m/sec exhibited a decrease in force as soil rebound increased (r--0.74). Similar relationships between the total forces exerted by the limbs and the impact resistance of the track were observed (Figures 12 and 13). Forces exerted by the horses in Group I (Figure 12) increased as impact resistance increased and plateaued at the higher resistances (r=0.79) Forces decreased as impact resistance increased (r=0.66) for the horses traveling at the higher speeds (Figure 13).
DISCUSSION
A study on racing surfaces suggested two important properties of the dynamics of hoof/substrate interaction: loading of the hoof while in contact with the track and the rotation of the toe of the hoof into the substrate in preparation for push-off. 11 The track surface presents compressive and frictional forces against the hoof during the support phase of the limb. The measurement of the impact resistance (hardness) of the track surface is a measurement of these forces. When compressive forces alone are considered, the difference between deformation of the track surface under load and when the load is removed represents rebound energy of the track. Since elasticity of the track surface may return energy to the hoof immediately before toe lift-off, the rebound energy occurring immediately after impact of the head of the TDD with the surface of the track may represent some of the energy that can be returned to the hoof if this energy is returned at the end of the support phase. The energy returned to the TTD occurred within 0.06 seconds following the initial impact. This energy, if returned to the hoof at this time, would be applied immediately after peak vertical force occurred on the hoof (Figure 14), while the hoof is in contact with the ground and the metacarpophalangealjoint is still maximally extended.~9 Rebound energy occurring at this time would not assist in elevating the foot from the ground and may, in fact, represent additional force which must be dissipated by the 40
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011
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0,3
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Figure 14. The relationship between the time of the peak rebound of the head of the TTD from the track surface as recorded from the linear variable differential transformer and the sum of the forces recorded from the three transducers in the instrumented shoe nailed to the hoof of the lead foreleg of Horse 4 galloping at 15.9 m/s. The hatched line indicates the time of peak rebound of the TTD, $=impact of hoof and head of TTD with track surface, "]'=hoof lift.
limbs. Therefore, the timing of the track rebound with the limb cycle may be one of the factors that influences racingassociated lamenesses. The dynamic properties of a track designed to minimize the effects of the soil on the locomotor stresses should have a relatively high energy return and low impact resistance. 11,21 These factors are influenced by the basic structure of the track, composition of the soil and moisture content. 11,~2,2e-25 The maximum rebound energy measured in this study indicated that only 3.5% of the energy applied to the track could be returned to the hooves under the conditions of the tests. The amount of energy returned after impact had a moderate relationship with moisture content. The lowest amount of rebound energy occurred at approximately 8% water content. The highest amounts of rebound energy occurred at low and high moisture contents of the track. Impact resistance also showed a moderate relationship with water content of the track. Lower impact resistance was associated with moderate water contents of 7-9%, and a higher impact resistance with water contents of 10-14%. These moisture levels were similar to those identified for changes in energy return, which reflected the close interaction between energy return and impact resistance with respect to moisture level. Previous studies also JOURNAL OF EQUINE VETERINARY SCIENCE
reported an increase in impact resistance and energy return with decreasing moisture contents.It,22 The coincidence of peaks in energy return and impact resistance at approximately the same moisture content suggests that the dynamic responses of the track were not ideally balanced to minimize the stresses imparted to the limbs of horses working on this track. From the results obtained, it is not possible to determine the relative contributions of the basic structure of the track and the soil composition on the observed differences in these dynamic properties. An earlier study, 12 which examined the effects of the base and cushion on the physical properties of several racetracks, found relatively no differences in the contributions of these components to the overall dynamic properties of the track surface. As expected from previous reports,10,15,26 horse velocity and moisture content of the track had an effect upon the forces exerted by the horses. Horses galloping at the higher speeds (Group II) exerted the greatest locomotor forces. For this group of horses, forces decreased at track moisture contents of 12%. Horses traveling at the slower velocities (Group I) exerted the lowest forces, which occurred at 8% moisture content. At this moisture content, the impact resistance and energy return of the track was low, which suggests that the dynamic properties of the track were best suited for horses galloping at the lower velocities. As expected from the strong correlation between energy return and impact resistance, similar relationships between locomotor forces, energy return and impact resistance were observed. At the lower speeds, the total forces exerted by the horses decreased as energy return and impact resistance decreased. Conversely, when the horses galloped at the higher velocities, locomotor forces decreased as energy return and impact resistance increased. This suggests that the influences of track recoil and hardness on locomotion may be dependent upon the velocity of the horses. As velocity increases, the support times of the individual limbs decreases. 2~ This decreased hoof contact time would reduce the time for the interaction Qfthe hoof with the ground, which may account for the lower effects of the energy return and impact resistance of the track on the horses when galloping at the faster velocities. This suggests that the dynamic properties of the track may be suitable for horses traveling at relatively narrow ranges of velocity and that when horses gallop at speeds outside of this range, pronounced changes in locomotor forces will occur. The variations in the dynamic response of the track from one site to another were probably due to the variability of the compaction and composition of the track. In order to reduce these differences due to compaction, the track cushion was extensively harrowed between trials. This had minimal effects on the deeper layers of the track with the exception of possible small increases in the compaction of these layers from the weight of the maintenance equipVolume 17, Number 1, 1997
ment. The daily variations in the physical properties of the track were apparently affected by climatic conditions and the track maintenance procedures used in the intervening week between each test session. During this time, no precipitation occurred and the ambient temperatures ranged from daily lows of 37~ to highs of 94~ The relative humidity during this period ranged from 24% to 91%. The maintenance procedures consisted of daily harrowing of the track with moderate amounts of water added to the cushion. Since these procedures would result in differences in the compaction of the deeper layers of the track, it is probable that the variation observed between the test periods were due to the dynamic responses of the base of the track. The data obtained from the TTD closely corresponded with that presented by Cheney, et a1.12and Henwood.21 The only problem encountered with the TTD was an occasional binding of the impact head on the load cell which resulted in incomplete force measurements. This did not affect the results of this study since the accelerometer functioned perfectly, which provided the necessary data. The total forces recorded from the instrumented shoes were less than the body weights of the horses. This was expected since forces exerted on the 3 transducers represented only a small proportion of the forces exerted on the entire hoof. A study comparing the forces exerted on the 3 transducers in the instrumented shoes and the total force exerted by the hoof on a force plate showed very strong correlations between vertical forces recorded from the instrumented shoes and the force plate, la The relationship between force and moisture content was the strongest one seen in this study. Relationships between force and energy returned and between force and impact resistance were less well defined, suggesting that the interactions between energy return and impact resistance and the forces exerted by horses are complex and warrant further study.
REFERENCES 1. Rooney JR, Genovese RL: A survey and analysis of bowed tendon in Thoroughbred racehorses. J Eq Vet Sci 1981 ; 49-53. 2. Rooney JR, McCue MC: Further studies on breakdown in Thoroughbred racehorses. Eq Vet Data 1983;9:133. 3. Rooney JR: Track condition in relation to lameness in Thoroughbred racehorses. Eq Vet Data 1983;9:134-135. 4. Hill T, Carmichael D, Maylin G, Krook L: Track condition and racing injuries in Thoroughbred horses. Cornell Vet 1986; 76:361-379. 5. Mohammed H, Hill T, Lowe J: Risk factors associated with injuries in Thoroughbred horses. Equine VetJ 1991 ;23:445-448. 6. Clanton C, Kobluk C, Robinson RA, Gordon B: Monitoring surface conditions of a Thoroughbred racetrack, JAVMA 1991; 198:613-620. 7. Drevemo S, Hjerten G, Johnston C: Drop hammer tests of Scandinavian harness racetracks. Equ Vet J 1994;Supp117:3538. 8. Drevemo S, Hjerten G: Evaluation of a shock absorbing
41
woodchip tayer on a harness race-track. Proc Equ Exerc Physiol 3, Persson SGB, Lindholm A, Jeffcott LB (Eds.), Davis CA, ICEEP Publications, 1991 ;107-112. 9. Pratt GW: Analyzing track characteristics. Thoroughbred Record 1980; 211:771-776. 10. Pratt GW Jr: Racing surfaces--a survey of mechanical behavior. Proc 30th Ann Mtg Amer Assoc Equine Pract 1984;321331. 11. Zebarth B, Sheard R: Impact and shear resistance of turf grass racing surfaces for Thoroughbreds. Am J Vet Res 1985; 46:778-784. 12. Cheney JA, Shen CK, Wheat JD: Relationship of track surface to tameness in the Thoroughbred racehorse. Am J Vet Res 1973; 34:1285-1290. 13. Ueda Y: Safety as a science. Proc 19th Ann Symp on Racing, Race Track Industry Program, 1992; 277-278. 14. Barrey E, Landjerit B, Wolter R: Shock and vibration during the hoof impact on different track surfaces. Proc Equine Exerc Physiol 3, Persson SGB, Lindholm A, Jeffcott LB (Eds.), Davis, CA: ICEEP Publications, 1991 ;97-106. 15. Ratzlaff MH, Grant BD, Frame JM, Hyde ML: Locomotor forces of galloping horses. Equine Exercise Physiology 2, Gillespie J and Robinson N, (eds.), Davis, CA: ICEEP Publishers, 1986;574-586. 16. Ratzlaff MH: Quantitative methods for the analysis of equine locomotion and their applications to other species. Proc Morphol Symposium, Amer Society of Zool. Am Zool 1989;29:267-285. 17. Ratzlaff MH: Current methods for the analysis of locomotion and their potential clinical applications. Amer Assoc Equine Pract 1989;99-127. 18. Ratzlaff MH, Hyde ML, Grant BD, Balch OK, Wilson PD: Measurement of vertical forces and temporal components of the strides of horses using instrumented shoes. J Eq Vet Sci 1990; 10:23-35.
THERE IS STILL TIME TO JOIN THE ALASKA '97 CRUISE WITH R.M. MILLER
19. Ratzlaff MH, Wilson P, Hyde M, Balch O, Grant B: Relationships between locomotor forces, hoof position and joint motion during the support phase of the stride of galloping horses. Acta Anat 1993; 143:200-294. 20. Hellander J, Fredricson I, Hjerten G, Drevemo S, Dalin G: Galoppaktion I--Basala gangartsvariabler i relation till hastens hastighet. Svensk Vet 1983;35 suppl. 3:75-82. 21. Henwood K: A study of the dynamic response of soils under impulse loading. M.S. Thesis, University of California, Davis, CA. 1969. 22. Zebarth BJ, Lee D, Kay BD: Impact resistance of three soils under varying moisture and subzero temperature conditions. Can Geotech J 1984;21:449-455. 23. Miki G: The construction of new type sand track on the basis of soil engineering. Soil Found 1960;1:38--49. 24. itakura Y, Fujisawa A, Asano M: Research report on a survey into the properties of dirt courses. Horse Sci 1980; 17:269285. 25. Uren NC, Scott RV: Objective assessment ofhorseracing tracks. Report to the Victoria Racing Club. School of Agriculture, LaTrobe University. 1982;1-56. 26. Ratzlaff MH, Frame J, Miller L, Kimbrell J, Grant B: A new method of repetitive measurements of locomotor forces from galloping horses. Proc 9th Nutrition and Physiology Symposium, Michigan State University. 1985;260-265. 27. Leach D, Cymbaluk N: Relationships between stride length, stride frequency, velocity and morphometrics of foals. Am J Vet Res 1986;48:880-888. 28. Ratzlaff MH, Shindell RM, White KK: The interrelationships of stride lengths and stride times to velocities of galloping horses. J Eq Vet Sci 1985;5:279-283.
Join us for a Seminar at Sea with RM Miller, DVM s p e a k i n g on
/,
i All participants r e c e i v e a c o m p l e t e set of reprints of Dr. Miller's Behaviorofthe Horse series (as it a p p e a r e d in JEVS). T h e s e reprints are not a v a i l a b l e a n y w h e r e else.
42
"Behavior and Misbehavior of the Horse" August 11,1997 for a 12-day Heartland of Alaska Cruisetour We sail from Vancouver BC, cruise the inside passage (3 ports-of-call) aboard the Crown Princess (The Love Boat), cruise Glacier Bay, visit Denali Park, (there is even an optional trail ride), and tour Fairbanks where the cruisetour ends. Fares begin at $2,379pp (cruisetour, inside cabin, lower deck) $1447pp (cruise only, inside cabin, lower deck). A $250 deposit wilt hold your berth until June 1, 1997.
Write, call, fax, or E-mail for a brochure or to reserve your space to: Alaska Cruise, P.O. Box 1209, Wildomar, CA 92595-1209. Phone 909-678-1889; FAX 909-678-1885; E-math vetdata@ inland.net JOURNAL OF EQUINE VETERINARY SCIENCE
INTERRELATIONSHIPS BETWEEN MOISTURE CONTENT OF THE TRACK, DYNAMIC PROPERTIES OF THE TRACK AND THE LOCOMOTOR FORCES EXERTED BY GALLOPING HORSES Marc H. Ratzlaff, DVM, PhDl; Martha L. Hyde, PhD3; David V. Hutton, PhD 2 Rhonda A. Rathgeber, DVM, PhD4; Olin K. Balch, DVM, PhD 5
SUMMARY
Three methods were used to examine the relationships between the dynamic properties of a track and the locomotor forces exerted by galloping horses. The impact resistance and the percentage of energy returned by the track were determined using a trailer mounted track testing device. Vertical forces were measured from instrumented horseshoes nailed to all four hooves and the velocities of each of the six horses galloping in a track straight-away were determined from slow-motion films. The moisture content of the track was altered by the addition of water. These data were analyzed to determine the relationships between changes in moisture content on the energy returned by the track, impact resistance of the track and locomotor forces exerted by the horses. There was a strong linear relationship between impact resistance and the percentage of energy returned by the track. Changes in moisture content of the track cushion Authors' addresses: 1Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology. 2Department of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164. 3Department of Biology, California State University, 9001 Stockdale Highway, Bakersfield, CA 93311.4Hagyard, Davidson and McGee Equine Medicine and Surgery, 42550 Ironworks Road, Lexington, KY 40511. 5Department of Anatomy, School of Veterinary Medicine, Tuskegee University,Tuskegee,AL 36088 Acknowledgements: This study was supported by the Grayson-Jockey Club Research Foundation, C.N. Ray Foundation and the Equine Research Program at Washington State University. The authors thank Dr. John E. Hamell, (Department of Plant and Soil Sciences, University of Idaho, Moscow, Idaho 83843) for his advice and assistance in the interpretation of the data and Kathryn Kunka, Sarah Christian, Cody Ames and Stuart Nelson for their assistance during these studies. The authors also thank Larry Miller, Mitch Almeida and David Tibbals for the design and construction of many of the electronic components in the instrumentation used in this study.
Volume 17, Number 1, 1997
resulted in similar changes in both the percentage of energ 2 returned and the impact resistance of the track. Energ 2 return and impact resistance decreased at 8% moisture ant progressively increased from 8.5 to 14% moisture. The horses were divided into two groups based upor their speed during each trial (Group I: 14.5 to 15.4 m/se~ and Group II: 15.5 to 16.5 rn/sec). Changes in the moistur~ content of the track cushion altered the forces exerted b 3 the horses. Forces were lowest at 8% moisture content fo~ Group 1 and at 12% moisture for Group II. Changes in th~ percentage of energy returned and the impact resistance ol the track also affected the forces exerted by the horses. FoJ the horses in Group I forces increased as energy return and impact resistance increased. Conversely, horses in Grour 11exhibited a decrease in force as energy return and impacl resistance increased. These results suggest that the dynamic properties of the track may be suitable for horses traveling at relatively narrow ranges of velocity and tha! when horses work at speeds outside of this range, pronounced changes in locomotor forces will occur.
INTRODUCTION
The relationship between track conditions and injuries in Thoroughbred racehorses has been addressed in a series of studies based upon track surveys. 1-3 In these reports, the condition of the track was based upon estimated moisture contents and each track was rated as fast, good, sloppy, or muddy. It was found that the incidence of lameness was higher on the "fast" and "sloppy" tracks. The definitions of track conditions in these studies were subjective and other factors such as soil composition, length of race, and individual variations between horses may have also contributed to the incidence of injuries. Another report 4 concluded 35
Figure 1. Trailer-mounted
track testing device. A. Recorder B. Amplifiers and power supply C. Battery D. Impact head.
that track conditions did not influence the occurrence of racing injuries in Thoroughbred horses in New York. However, a more recent study 5 reported that breakdowns on the New York Racing Association tracks were related to the specific track and track composition, as well as season of the year and inherent factors within the horses. The dynamic properties of the track surface vary with its moisture content, composition and compaction. The moisture content of the base of the track remains relatively constant, however, the water content of the track cushion may fluctuate widely. 6 Several studies have shown that the composition of the track surface alters the dynamic responses of the soil 7,8 and that the compaction of the track surface may vary widely over different areas of the same track. 6-1~A study 11 on the impact and shear resistance of turf racing surfaces, using two mechanical devices, found that turf roots were responsible for increased impact resistance (hardness) and resistance to shear. Additionally, these investigators reported that changes in soil moisture altered the soil properties and that soil composition affected the resistance to shear. The dynamic responses of the surfaces of five racetracks were measured with an impact testing machine and these results were compared with the incidences of lameness in horses working on these tracks. 12 These investigators concluded that the dynamic responses of the soil were related to the water content and depth of cushion and that the incidences of lameness on these tracks could have been related to the hardness of each track. Studies 1~ using accelerometers attached to the hooves of horses have demonstrated that both the compaction and composition of the track surface dramatically affect hoof impact deceleration. Lower compaction and higher percentages of organic matter result in lower impact forces. Another study 15using instrumented horseshoes, showed that as moisture content of the track surface increased, the variation in the magnitude of vertical forces between successive strides decreased. This study was undertaken to determine the effects of 36
Figure 2 . Track testing device in the transport position. A. Linear variable differential transformer B. Accelerometer C. Load cell D, Impact head.
changes in moisture content of the track cushion on the dynamic responses of the track surface, the locomotor forces exerted by galloping horses and the interrelationships of the locomotor forces and the physical properties of the track. Two procedures were performed concurrently; a trailer mounted device was used to measure the physical properties of the track and instrumented horseshoes were used to record the vertical forces exerted by the hooves as horses galloped through a track straightaway.
MATERIALS AND METHODS
A trailer-mounted track testing device (TTD), modified after the drop-hammer device used by Cheney, et al.12 was used to measure the dynamic response of the track surface to impact loading. This machine, designed to simulate the vertical force exerted by a galloping horse, consisted of an 80 pound (36.4 kg) weight dropped in free fall from a height of 5.0 inches (12.7 cm) and is shown in Figures 1 and 2. The weight consisted of a stainless steel disc, 5 inches (12.7 cm) in diameter, bolted to a steel ram. The instrumentation for the TTD consisted of a load cell, a accelerometer, b linear variable differential transformer, c amplifiers, d power supply, d and recorder, e The force, displacement and acceleration of the weight at impact with the track surface were recorded from 10 sites for each trial. A typical recording of these parameters is shown in Figure 3. The impact force, impact resistance (deceleration at impact) and the rebound energy, expressed as a percentage of the initial impact energy, were determined. The rebound energy was determined from the rebound height which was calculated using the formula: aModel 9011, Kistler InstrumentCorporation, Amherst, NY bModel EGAXT-*-25, Entran Devices, Inc., Fairfield, NJ CModel0246-000, Trans-Tek, Inc., Ellington, CT dElectronics Division, College of Veterinary Medicine,Washington State University, Pullman,WA eTEAC R-61 Cassette Data Recorder, B.J. Wolfe Enterprises, North Hollywood, CA JOURNAL OF EQUINE VETERINARY SCIENCE
Displacement
/\
I
Accel.iltion
,.2_. ai'--lt _
]!<, i!~ !iil .
.
.
.
.
.
.
.
.
.
-
-
-
LJ
...........
i I
i~
o.2o~ .
~1
Figure 3. Force, acceleration and displacement traces
Figure 4 . Instrumented horseshoe with piezoelectric transducers located at the toe (A) and both sides of the heel (B). The leads (C) from the transducers exit the lateral side of the shoe.
recorded from the track testing device. 1 G = 9.8 m/sac 2
1) Where:
H = 1/2 gt 2 H = rebound height g = acceleration of gravity t = one-half of the time the weight was in the air between the initial impact and the rebound impact
The percentage of rebound energy returned was determined by the formula:
2) Where:
U=mH x 100 mP U = % energy returned m = mass of the weight H = rebound height P = total drop height of the weight
Since force is directly proportional to acceleration (F = m-a), and the mass remained constant, impact resistance (deceleration at impact) and the percentage of energy returned by the soil were used to characterize the dynamic responses of the track surface to impact loading. A straightaway of a track f was harrowed to a depth of two and one-half inches. On each day, tests were conducted sequentially under four conditions:
soil samples were weighed, dried in an oven at 100~ for 24 hours and reweighed to determine the percentage of water in each sample. The textural classification of the track cushion was loamy sand and the soil composition is presented in Table 1. Six conditioned Thoroughbred horses, two mares and four geldings, were used to determine the effects of changes in moisture content of the track cushion on the locomotor forces exerted by these horses as they galloped through a track straightaway. The hooves of each horse were shod with instrumented shoes containing piezoelectric transducers located at the toe and both sides of the heel (Figure 4). 16-19The leads from the transducers in each shoe were connected to preamplifiers dtaped to the lateral aspect of the distal end of the metacarpus/metatarsus of each limb. The cables from the preamplifiers were taped to each leg and connected to a multichannel recorderg carried in a backpack by the rider. The vertical forces exerted on each transducer were recorded from six consecutive strides for each trial as each horse galloped through the straightaway. The forces exerted on each of the 12 transducers were stored digitally in the recording unit. These data were transferred to a Table
1. Soil composition of the
track*
1: track harrowed, no water added; 2: track harrowed, water added; 3: additional water added, track harrowed; and 4: additional water added, track harrowed. The physical properties of the track surface were recorded from 10 sites using the TTD and the moisture contents of the soil were determined on a dry matter basis from samples collected immediately after each trial. The
Very coarse sand 15.2 Coarse sand 23.1 Medium sand 19.3 Fine sand 13.7 Very fine sand 5.8 Silt 15.8 Clay 7.1 Organic matter 1.1 *Soils laboratory, College of Agriculture, University of Idaho, Moscow, Idaho. U.S. Departmentof Agricultureclassification.
fHitchcock EquineResearchTrack, WashingtonStateUniversity,Pullman, WA
gData Logger,Scientech,Inc. Pullman,WA
V o l u m e 17, N u m b e r 1, 1997
37
138
3.5
136
3
I~. t-
u.I
132
2.5
2
9
9
99149
q)
128
=.
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126
9
1,5 124 122 4
6
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%
10
12
14
' ' = 9 ' ' ' . . . . . . . . . . . . 6 8 10 12
4
computer h and analyzed i to determine the maximum vertical force exerted on each transducer and the sum of the peak forces exerted on the transducers in each shoe during the support period of the limbs. This sum was expressed as a percentage of body weight. A high-speed 16mm cameraJ was used to photograph each horse as it galloped through the straightaway. Each trial was filmed at 300 frames per second using black and white film. k The running line was marked with lime and 2 reference stakes, 5 meters apart, were positioned behind the running line. The rails and posts were removed from the inner railing of the track to provide an unobstructed view of the horses as they traversed the course. The films were analyzed to determine the velocities of each horse during each trial. The physical properties of the track, moisture content, forces exerted by the horses and films of the horses were obtained for each trial. These data were analyzed ~ and polynomial equations fitted to determine relationships between changes in moisture content on the energy returned by the track, impact resistance of the track and locomotor forces exerted by the horses.
RESULTS The relationships between changes in the moisture content of the track cushion and the physical properties of the track are presented in Figures 5-7. Changes in moisture content resulted in changes in the percentage of energy returned following impact of the head of the TTD on the track surface (Figure 5). Energy return decreased at 8% moisture and progressively increased from 8.5 to 14% moisture. This relationship between moisture content and hDeskpro286, Compac Computer Corp., Houston,TX iASYT version 3.0, Asyst SoftwareTechnologies,Inc., Rochester,NY JModel 1PL, InstrumentationMarketing, Inc., Burbank, CA kTri-X 7278, Eastman Kodak Co., Rochester,NY ISigma-PIot,version 3.10, Jandel Scientific,Corte Madera, CA
16
. . , , 18
% Water
Water
Figure 5 . R e l a t i o n s h i p b e t w e e n t h e p e r c e n t a g e of energy returned and the moisture content of the track cushion. r=0.64, y=3,622-0,399x +0.027x 2.
38
..... 2
16
Figure 6. Relationship between the impact resistance and the moisture content of the track cushion, r=0.58, y=138.362-2.405x+0.161x 2.
3.5
E
3 2.5
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2 1.5
.
122
,
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.
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,
124
I
126
,
J
.
128
.
.
z
.
.
130
Deceleration
132
134
136
138
140
( r ~ s e c 2)
Figure 7. Relationship between the impact resistance and the percentage of energy returned from the track, r=0.92, y=-I 6.270 + O.143x 2.
energy return was not strong (r=0.64). The relative change in soil recoil approximated a two-fold increase; however, the actual increase in the energy returned was low, averaging less than 2.5% of the initial energy applied to the track. Changes in the moisture content of the cushion had a similar effect on the impact resistance of the soil (Figure 6). Impact resistance decreased at 8% moisture and gradually increased from 8.5 to 14% moisture. This relationship was low, r=0.58. A strong direct linear relationship (r=0.92) occurred between changes in impact resistance and percentage of energy returned by the track (Figure 7). The horses were divided into two groups based upon their speed during each trial. Horses in Group I were traveling at a moderate gallop at speeds between 14.5 and 15.4 m/sec and horses in Group II were running at a fast gallop at speeds between 15,5 and 16.5 m/sec, a~ The effects of changes in moisture content of the track cushion on the vertical forces exerted by all four limbs of the horses are presented in Figures 8 and 9. These relationships were relatively strong (r=0.81). Horses galloping at JOURNAL OF EQUINE VETERINARY SCIENCE
80
95 9o
75
70 9
9
2
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|
'
'
9
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=
9
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=
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.
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.
9
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% Energy Retum
Figure 8. Relationships between the forces exerted by the horses galloping at velocities of 14.5-15.4 m/s (Group I) and the moisture content of the track cushion. Forces were recorded from transducers in the instrumented shoes nailed to each hoof. r 0.81 y=97.620-8.367x + 0.515x 2.
Figure 1 1. Relationships between the forces exerted by the horses galloping at velocities of 15.5-16.5 m/s (Group II) and the percentage of energy returned from the track. r=0.74, y= 131.557-34.276x +4.944x 2.
95
80
9O
75
80
LL 6O
70 65
7
8
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128
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=
136
Deceleration (m/sec2)
Figure 9. Relationships between the forces exerted by the horses galloping at velocities of 15.5-16.5 m/s (Group II) and the moisture content of the track cushion. Forces were recorded from transducers in the instrumented shoes nailed to each hoof. r=0.81, y=152.606-13.216x 0.550x 2.
Figure 12. Relationships between the forces exerted by the horses galloping at velocities of 14.5-15.4 m/s (Group I) and the impact resistance of the track, r=0.79, y=3565.337+55.106x-0209x 2. 95
80
90
75 85
m 0C. 0
70 80 65
7s
LL 60
70
55 1.5
2
2.5
3
3.5
% Energy Return
Figure 10. Relationships between the forces exerted by the horses galloping at velocities of 14.5-15.4 m/s (Group I) and the percentage of energy returned from the track. r=0.60, y=24.739 + 33,168x-5.878x ~. Volume 17, Number 1, 1997
65 124
B
126
128
130
132
134
136
138
Deceleration (m/sec 2)
Figure 13. Relationships between the forces exerted by the horses galloping at velocities of 15.5-16.5 m/s (Group II) and the impact resistance of the track, r=0.66, y=-1062.584 + 18.981 x - 0,078x 2. 39
40
speeds between 14.5 and 15.4 m/sec (Group I) exerted an average force of 72% of body weight at 4% moisture content; this decreased to 64% of body weight at 8% moisture and gradually increased to 68% of body weight at 11% moisture (Figure 8). Horses running at speeds between 15.5 and 16.5 m/sec (Group II) exerted average forces of 85% of body weight at 7.5% moisture which decreased to 73% of body weight at 12% moisture and increased slightly at 13.5% moisture (Figure 9). Relationships between the total forces exerted by the two groups of horses and the percentage of energy returned following impact of the head of the track testing device with the track surface are shown in Figures 10 and 11. For the horses traveling at 14.5 to 15.4 m/sec, total force increased as the percentage of soil recoil increased (r=0.60). Conversely, horses galloping at speeds between 15.5 and 16.5 m/sec exhibited a decrease in force as soil rebound increased (r--0.74). Similar relationships between the total forces exerted by the limbs and the impact resistance of the track were observed (Figures 12 and 13). Forces exerted by the horses in Group I (Figure 12) increased as impact resistance increased and plateaued at the higher resistances (r=0.79) Forces decreased as impact resistance increased (r=0.66) for the horses traveling at the higher speeds (Figure 13).
DISCUSSION
A study on racing surfaces suggested two important properties of the dynamics of hoof/substrate interaction: loading of the hoof while in contact with the track and the rotation of the toe of the hoof into the substrate in preparation for push-off. 11 The track surface presents compressive and frictional forces against the hoof during the support phase of the limb. The measurement of the impact resistance (hardness) of the track surface is a measurement of these forces. When compressive forces alone are considered, the difference between deformation of the track surface under load and when the load is removed represents rebound energy of the track. Since elasticity of the track surface may return energy to the hoof immediately before toe lift-off, the rebound energy occurring immediately after impact of the head of the TDD with the surface of the track may represent some of the energy that can be returned to the hoof if this energy is returned at the end of the support phase. The energy returned to the TTD occurred within 0.06 seconds following the initial impact. This energy, if returned to the hoof at this time, would be applied immediately after peak vertical force occurred on the hoof (Figure 14), while the hoof is in contact with the ground and the metacarpophalangealjoint is still maximally extended.~9 Rebound energy occurring at this time would not assist in elevating the foot from the ground and may, in fact, represent additional force which must be dissipated by the 40
I 4
-
3
-
m gO
9
'3"
O U. 2
E 8 r
\t 1
(/)
10
t
I 0
l
-1
-2 0
011
!
I
02
0,3
Seconds
Figure 14. The relationship between the time of the peak rebound of the head of the TTD from the track surface as recorded from the linear variable differential transformer and the sum of the forces recorded from the three transducers in the instrumented shoe nailed to the hoof of the lead foreleg of Horse 4 galloping at 15.9 m/s. The hatched line indicates the time of peak rebound of the TTD, $=impact of hoof and head of TTD with track surface, "]'=hoof lift.
limbs. Therefore, the timing of the track rebound with the limb cycle may be one of the factors that influences racingassociated lamenesses. The dynamic properties of a track designed to minimize the effects of the soil on the locomotor stresses should have a relatively high energy return and low impact resistance. 11,21 These factors are influenced by the basic structure of the track, composition of the soil and moisture content. 11,~2,2e-25 The maximum rebound energy measured in this study indicated that only 3.5% of the energy applied to the track could be returned to the hooves under the conditions of the tests. The amount of energy returned after impact had a moderate relationship with moisture content. The lowest amount of rebound energy occurred at approximately 8% water content. The highest amounts of rebound energy occurred at low and high moisture contents of the track. Impact resistance also showed a moderate relationship with water content of the track. Lower impact resistance was associated with moderate water contents of 7-9%, and a higher impact resistance with water contents of 10-14%. These moisture levels were similar to those identified for changes in energy return, which reflected the close interaction between energy return and impact resistance with respect to moisture level. Previous studies also JOURNAL OF EQUINE VETERINARY SCIENCE
reported an increase in impact resistance and energy return with decreasing moisture contents.It,22 The coincidence of peaks in energy return and impact resistance at approximately the same moisture content suggests that the dynamic responses of the track were not ideally balanced to minimize the stresses imparted to the limbs of horses working on this track. From the results obtained, it is not possible to determine the relative contributions of the basic structure of the track and the soil composition on the observed differences in these dynamic properties. An earlier study, 12 which examined the effects of the base and cushion on the physical properties of several racetracks, found relatively no differences in the contributions of these components to the overall dynamic properties of the track surface. As expected from previous reports,10,15,26 horse velocity and moisture content of the track had an effect upon the forces exerted by the horses. Horses galloping at the higher speeds (Group II) exerted the greatest locomotor forces. For this group of horses, forces decreased at track moisture contents of 12%. Horses traveling at the slower velocities (Group I) exerted the lowest forces, which occurred at 8% moisture content. At this moisture content, the impact resistance and energy return of the track was low, which suggests that the dynamic properties of the track were best suited for horses galloping at the lower velocities. As expected from the strong correlation between energy return and impact resistance, similar relationships between locomotor forces, energy return and impact resistance were observed. At the lower speeds, the total forces exerted by the horses decreased as energy return and impact resistance decreased. Conversely, when the horses galloped at the higher velocities, locomotor forces decreased as energy return and impact resistance increased. This suggests that the influences of track recoil and hardness on locomotion may be dependent upon the velocity of the horses. As velocity increases, the support times of the individual limbs decreases. 2~ This decreased hoof contact time would reduce the time for the interaction Qfthe hoof with the ground, which may account for the lower effects of the energy return and impact resistance of the track on the horses when galloping at the faster velocities. This suggests that the dynamic properties of the track may be suitable for horses traveling at relatively narrow ranges of velocity and that when horses gallop at speeds outside of this range, pronounced changes in locomotor forces will occur. The variations in the dynamic response of the track from one site to another were probably due to the variability of the compaction and composition of the track. In order to reduce these differences due to compaction, the track cushion was extensively harrowed between trials. This had minimal effects on the deeper layers of the track with the exception of possible small increases in the compaction of these layers from the weight of the maintenance equipVolume 17, Number 1, 1997
ment. The daily variations in the physical properties of the track were apparently affected by climatic conditions and the track maintenance procedures used in the intervening week between each test session. During this time, no precipitation occurred and the ambient temperatures ranged from daily lows of 37~ to highs of 94~ The relative humidity during this period ranged from 24% to 91%. The maintenance procedures consisted of daily harrowing of the track with moderate amounts of water added to the cushion. Since these procedures would result in differences in the compaction of the deeper layers of the track, it is probable that the variation observed between the test periods were due to the dynamic responses of the base of the track. The data obtained from the TTD closely corresponded with that presented by Cheney, et a1.12and Henwood.21 The only problem encountered with the TTD was an occasional binding of the impact head on the load cell which resulted in incomplete force measurements. This did not affect the results of this study since the accelerometer functioned perfectly, which provided the necessary data. The total forces recorded from the instrumented shoes were less than the body weights of the horses. This was expected since forces exerted on the 3 transducers represented only a small proportion of the forces exerted on the entire hoof. A study comparing the forces exerted on the 3 transducers in the instrumented shoes and the total force exerted by the hoof on a force plate showed very strong correlations between vertical forces recorded from the instrumented shoes and the force plate, la The relationship between force and moisture content was the strongest one seen in this study. Relationships between force and energy returned and between force and impact resistance were less well defined, suggesting that the interactions between energy return and impact resistance and the forces exerted by horses are complex and warrant further study.
REFERENCES 1. Rooney JR, Genovese RL: A survey and analysis of bowed tendon in Thoroughbred racehorses. J Eq Vet Sci 1981 ; 49-53. 2. Rooney JR, McCue MC: Further studies on breakdown in Thoroughbred racehorses. Eq Vet Data 1983;9:133. 3. Rooney JR: Track condition in relation to lameness in Thoroughbred racehorses. Eq Vet Data 1983;9:134-135. 4. Hill T, Carmichael D, Maylin G, Krook L: Track condition and racing injuries in Thoroughbred horses. Cornell Vet 1986; 76:361-379. 5. Mohammed H, Hill T, Lowe J: Risk factors associated with injuries in Thoroughbred horses. Equine VetJ 1991 ;23:445-448. 6. Clanton C, Kobluk C, Robinson RA, Gordon B: Monitoring surface conditions of a Thoroughbred racetrack, JAVMA 1991; 198:613-620. 7. Drevemo S, Hjerten G, Johnston C: Drop hammer tests of Scandinavian harness racetracks. Equ Vet J 1994;Supp117:3538. 8. Drevemo S, Hjerten G: Evaluation of a shock absorbing
41
woodchip tayer on a harness race-track. Proc Equ Exerc Physiol 3, Persson SGB, Lindholm A, Jeffcott LB (Eds.), Davis CA, ICEEP Publications, 1991 ;107-112. 9. Pratt GW: Analyzing track characteristics. Thoroughbred Record 1980; 211:771-776. 10. Pratt GW Jr: Racing surfaces--a survey of mechanical behavior. Proc 30th Ann Mtg Amer Assoc Equine Pract 1984;321331. 11. Zebarth B, Sheard R: Impact and shear resistance of turf grass racing surfaces for Thoroughbreds. Am J Vet Res 1985; 46:778-784. 12. Cheney JA, Shen CK, Wheat JD: Relationship of track surface to tameness in the Thoroughbred racehorse. Am J Vet Res 1973; 34:1285-1290. 13. Ueda Y: Safety as a science. Proc 19th Ann Symp on Racing, Race Track Industry Program, 1992; 277-278. 14. Barrey E, Landjerit B, Wolter R: Shock and vibration during the hoof impact on different track surfaces. Proc Equine Exerc Physiol 3, Persson SGB, Lindholm A, Jeffcott LB (Eds.), Davis, CA: ICEEP Publications, 1991 ;97-106. 15. Ratzlaff MH, Grant BD, Frame JM, Hyde ML: Locomotor forces of galloping horses. Equine Exercise Physiology 2, Gillespie J and Robinson N, (eds.), Davis, CA: ICEEP Publishers, 1986;574-586. 16. Ratzlaff MH: Quantitative methods for the analysis of equine locomotion and their applications to other species. Proc Morphol Symposium, Amer Society of Zool. Am Zool 1989;29:267-285. 17. Ratzlaff MH: Current methods for the analysis of locomotion and their potential clinical applications. Amer Assoc Equine Pract 1989;99-127. 18. Ratzlaff MH, Hyde ML, Grant BD, Balch OK, Wilson PD: Measurement of vertical forces and temporal components of the strides of horses using instrumented shoes. J Eq Vet Sci 1990; 10:23-35.
THERE IS STILL TIME TO JOIN THE ALASKA '97 CRUISE WITH R.M. MILLER
19. Ratzlaff MH, Wilson P, Hyde M, Balch O, Grant B: Relationships between locomotor forces, hoof position and joint motion during the support phase of the stride of galloping horses. Acta Anat 1993; 143:200-294. 20. Hellander J, Fredricson I, Hjerten G, Drevemo S, Dalin G: Galoppaktion I--Basala gangartsvariabler i relation till hastens hastighet. Svensk Vet 1983;35 suppl. 3:75-82. 21. Henwood K: A study of the dynamic response of soils under impulse loading. M.S. Thesis, University of California, Davis, CA. 1969. 22. Zebarth BJ, Lee D, Kay BD: Impact resistance of three soils under varying moisture and subzero temperature conditions. Can Geotech J 1984;21:449-455. 23. Miki G: The construction of new type sand track on the basis of soil engineering. Soil Found 1960;1:38--49. 24. itakura Y, Fujisawa A, Asano M: Research report on a survey into the properties of dirt courses. Horse Sci 1980; 17:269285. 25. Uren NC, Scott RV: Objective assessment ofhorseracing tracks. Report to the Victoria Racing Club. School of Agriculture, LaTrobe University. 1982;1-56. 26. Ratzlaff MH, Frame J, Miller L, Kimbrell J, Grant B: A new method of repetitive measurements of locomotor forces from galloping horses. Proc 9th Nutrition and Physiology Symposium, Michigan State University. 1985;260-265. 27. Leach D, Cymbaluk N: Relationships between stride length, stride frequency, velocity and morphometrics of foals. Am J Vet Res 1986;48:880-888. 28. Ratzlaff MH, Shindell RM, White KK: The interrelationships of stride lengths and stride times to velocities of galloping horses. J Eq Vet Sci 1985;5:279-283.
Join us for a Seminar at Sea with RM Miller, DVM s p e a k i n g on
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i All participants r e c e i v e a c o m p l e t e set of reprints of Dr. Miller's Behaviorofthe Horse series (as it a p p e a r e d in JEVS). T h e s e reprints are not a v a i l a b l e a n y w h e r e else.
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"Behavior and Misbehavior of the Horse" August 11,1997 for a 12-day Heartland of Alaska Cruisetour We sail from Vancouver BC, cruise the inside passage (3 ports-of-call) aboard the Crown Princess (The Love Boat), cruise Glacier Bay, visit Denali Park, (there is even an optional trail ride), and tour Fairbanks where the cruisetour ends. Fares begin at $2,379pp (cruisetour, inside cabin, lower deck) $1447pp (cruise only, inside cabin, lower deck). A $250 deposit wilt hold your berth until June 1, 1997.
Write, call, fax, or E-mail for a brochure or to reserve your space to: Alaska Cruise, P.O. Box 1209, Wildomar, CA 92595-1209. Phone 909-678-1889; FAX 909-678-1885; E-math vetdata@ inland.net JOURNAL OF EQUINE VETERINARY SCIENCE