Presented at NACOB 98: North American Congress on Biomechanics Canadian Society for Biomechanics - American Society of Biomechanics University of Waterloo Waterloo, Ontario, Canada August 14-18, 1998

---

EVALUATION OF SHOCK ATTENUATION IN THE FORELIMB OF HORSES
WEARING BOOTS AND WRAPS

L.M. Luhmann ¹ , D.F. Hoyt ² , C.N. Kobluk ² , S.J. Wickler ^2
1 Exercise and Nutritional Science, San Diego State University, San Diego, CA 92182
² Equine Research Center, California State Polytechnic University, Pomona, CA 91768

INTRODUCTION

The forelimbs of horses are subjected to greater concussion at hoof impact than the hindlimbs during locomotion. It has been shown that the combination of rapid impulsive loading and high frequency oscillatory movement occurring at impact contributes to injuries such as osteoarthritis in rabbits (Radin et al., 1973). Methods to reduce impact shock have included different types of shoes and track surfaces. Supportive boots have also been developed to reduce hyperextension in the fetlock joint and provide shock absorption. This study used accelerometers to evaluate the shock attenuation in the forelimbs of horses wearing boots and wraps.

REVIEW AND THEORY

Previous studies have evaluated the effect of bandages on gait, strain in the sesamoidian ligaments, and energy absorption capacity. Kobluk et al. (1988) found that cohesive elastic bandages reduced fetlock hyperextension in some horses. Keegan et al. (1992) found that support bandages did not alter mean strain in the sesamoidian ligaments while the horses were standing or walking.

Crawford et al. (1989) developed a model using cadaver limbs mounted on a servohydraulic testing machine to investigate the energy absorption capacity of bandages. In subsequent studies, Crawford et al. (1990a) found that different bandage techniques significantly increased energy absorption capacity compared to an unbandaged leg, and that bandages applied at full stretch tension had significantly greater energy absorption capacity than those at half-stretch tension. In addition, different bandage materials provided varying amounts of energy absorption (Crawford et al., 1990b). Kobluk et al. (submitted) used Crawford's model to investigate energy absorption capacity in several different types of neoprene-based boots, elastic bandages, and polo wraps. Significant differences between treatments and control were found.

Shock absorption implies the damping of energy and attenuation of high frequency vibrations due to impact. Research using in vitro models demonstrated that support boots are energy absorbing, but did not investigate their effect during impulsive loading. In addition, the limbs were loaded at rates slower than in normal locomotion, possibly introducing rate effects and negating the elastic behavior of tendons in live horses (Kingsbury et al., 1978). Thus, the cadaver model may not take into account the initial shock absorbing nature of the tissues themselves. The purpose of this study was to investigate, using accelerometers, the shock attenuation in the forelimbs of horses wearing boots and wraps at the trot and canter.

PROCEDURES

Three horses were tested on a high-speed treadmill at the trot (3.5 m/s) and canter (6.0 m/s). Accelerometers were mounted on the hoof and on the cannon bone above the boot. The accelerometers were hard-wired to a data acquisition system, and the signals were sampled at 2000 Hz.

Each horse was tested under four treatment conditions: control, wearing neoprene-based nitrile-lined boots (boot 1), wearing neoprene-based nitrile-lined boots with tendon rolls (boot 2), and wearing polo wraps. Data was collected in three consecutive 15-second sets for each condition at both the trot and canter. Boots and wraps had been preconditioned for 10 hours, and were applied to the horses by the same person throughout testing.

Three dependent variables were analyzed at both the hoof and cannon bone. Peak axial deceleration (F) was measured in g's. Total power (energy transmitted in the leg, P_t) during impact was calculated by integrating over the power density spectrum of the signal. Finally, power was plotted versus frequency, resulting in an asymptotic curve. The frequency above which contributions to power were negligible (frequency at which the curve became asymptotic, f_asym) was found. Five strides from each set were analyzed. Variables at the trot and canter were evaluated separately. Reliability tests showed no significant differences on all variables at the hoof. Thus, differences between treatments were evaluated at the cannon bone for each variable at the trot and canter.

RESULTS

Results of six one-way repeated measures ANOVAs indicated no significant differences between treatment conditions on any variable at the trot or canter (p=0.160 to 0.306). Means and standard deviations are shown in Table 1.

Var.	Control	Boot 1	Boot 2	Wraps
F, g's Trot	26.39 (9.55)	29.55 (9.82)	33.16 (3.20)	30.22 (9.92)
Pt, V 2 rms Trot	0.0319 (.0191)	0.0513 (.0285)	0.0297 (.0173)	0.0383 (.0267)
fasym Hz trot	164.89 (32.12)	187.23 (14.93)	201.94 (28.07)	208.59 (21.58)
F, g's Canter	51.75 (9.46)	52.83 (10.19)	54.85 (4.05)	48.85 (9.67)
Pt, V 2 rms Canter	0.0880 (.0272)	0.1819 (.0369)	0.1525 (.0829)	0.1577 (.0220)
fasym, Hz canter	269.41 (83.91)	291.93 (70.92)	282.07 (24.94)	297.71 (64.09)

Table 1: Means and standard deviations.

DISCUSSION

Shock absorption is indicated by reduction in magnitude, damping of energy transmitted to the leg, and attenuation of high frequency components of vibrations resulting from initial, impulsive impact. Results did not indicate that use of boots or wraps provide significantly greater shock absorption compared to the control condition.

Cadaver model studies using hysteresis have reported increased energy absorption, measured as an increase in the force necessary to deflect the joint a given distance, using boots. However, they do not evaluate the effects of initial impact. While the results of this study were not significant, the damaging effects of shock due to impact warrants continued investigation with a larger number of horses. Further studies should also investigate the long-term effects of boots and wraps on the incidence of traumatic and chronic injuries.

REFERENCES

Crawford W.H. et al. Vet. Comp. Ortho. Traum., 4, 177-182, 1989.

Crawford W.H. et al. Vet. Comp. Ortho. Traum., 1, 2-9, 1990a.

Crawford W.H. et al. Vet. Comp. Ortho. Traum., 1, 10-17, 1990b.

Keegan K.G. et al. Am. J. Vet. Res., 53, 1203-1208, 1992.

Kingsbury H.B. et al. Am. J. Vet. Res., 39, 365-369, 1978.

Kobluk C.N. et al. Proc. 34th Ann. Conv. Am. Soc. Equine Prac., 135-148, 1988.

Kobluk C.N. et al. J. Equine Vet. Sci., submitted.

Radin E.L. et al. J. Biomechanics, 6, 51-57, 1973.

ACKNOWLEDGMENTS

This study was supported by National Institute of Health Grant No. 1S06GM/53933-01A1.