DIAGNOSING, MANAGING, AND RESOLVING LAMENESS IN HORSES Velocity and Speed—In general, these two terms


can be used interchangeably for practical purposes. However, there are distinct differences between the two concepts: velocity is a vector quantity, and is the rate at which an object changes its position in a specific direction, while speed is a scaler quantity, and refers to how fast an object is moving regardless of direction. For example, an object’s velocity would be 3 mph East, while the speed of an object would be 3 mph. Acceleration—The change in velocity of an object


with respect to time. For example, the acceleration of your car is determined by how fast it can go from 0to60mph.


Momentum—Is the product of mass and velocity,


and it is the quantity of motion that a body pos- sesses. The greater the momentum of a moving object, the more pronounced an effect the momen- tum produces on other bodies in its path. It re- quires more force to change the direction of an object that possesses large momentum. Force—Is the product and mass and acceleration (gravity). It is what alters a body’s state of rest (i.e., inertia) or state of uniform motion. Internal forces are within the body and external forces are outside of the body. In addition, structures in ad- jacent regions of a body will slide (see Shear Forces) relative to one another while under load. Torsion, Shear, Bending, and Compression—Fig-


ure 1 shows the differences between these loading patterns. Bending is the combination of tension and compression, and in the example of bone load- ing, is often superimposed on axial compression. Torsion is twisting, and it produces shearing forces within the body. Rotation—Also called angular motion. Move-


ment along a circular path about some line in space. This line can be within the body or external to the body.


3. The Biomechanics of Sports Injury


Injury occurs when stress (amount of force/area ap- plied) and/or strain (degree of deformation in re- sponse to stress) is higher than the tissue can withstand. In addition, the direction the force is applied is related to injury. For example, a limb bone can handle a higher level of force when it is applied during compression, than when that same force is applied during torsion. To reduce injury, the forces need to be managed in a variety of ways to reduce breakdown. Breakdown can occur as a traumatic injury, such as what happens when a horse falls or is kicked, or injury can occur over time as a chronic injury. The focus of this paper will be on the biomechanics of injury and rehabilitation techniques for chronic injuries. Recently, the understanding of the events leading


to sports injury have greatly improved due to the ease of obtaining high-speed video showing the oc- currence of the actual injury. Matching the post- injury diagnostics with video data of the injury in a


274 2019  Vol. 65  AAEP PROCEEDINGS


Fig. 1. Forces and the direction of action. Courtesy of Dr. James Funk, PhD, PE; and Biodynamic Research Corporation.


real-world situation has helped to refine the knowl- edge of how injury occurs.1 In addition, research has shown that data from previous cadaver studies are not reproducible as good predictors of injury.2 Some muscles seem to be more prone to injury


than others and eccentric (lengthening) muscle ac- tion is frequently the cause of injury.3 In humans, the hamstrings are a common site of muscular inju- ries with the m. biceps femoris being the most fre- quently injured. In one study, the m. biceps femoris was injured in 83% of 154 hamstring inju- ries.4 It has been proposed that this high injury rate, in part, could be due to the biarticular function of the muscle (the long head), whereby its length is determined by the coaction of both the hip and knee joints.5 For example, with the combination of hip flexion and knee extension, the hamstrings are placed in amaximally lengthened state predisposing them to injury.6 In addition, the role of the ham- strings to decelerate the limb prior to ground contact may make the m. biceps femoris more prone to in- jury.6 The high incidence of injury to the m. biceps femoris in comparison to the mm. semitendinosus and semimembranosus led researchers to discover, through the use of functional magnetic resonance imaging (MRI), a synergistic muscle recruitment


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