b'Dipl. ACVSMR, FRCVS, of Sport HorseThe two horizontal (longitudinal and Science, in Mason, Michigan, describedtransverse) GRFs are generated as a re- Stimulation Therapy GRFs and how they change with move- sult of friction between the hoof and theHelps Minimize ment patterns and lameness. ground, she said. Thats what stabilizes Ground reaction forces act in variousthe hoof and allows the leg to developMuscle Atrophydirections and can be affected by theforces that push the horse forward, back- Many owners use stimulation horses weight, gait, speed, shoeing, andward, or sideways. (therapy) when their horses are injured footing, said Clayton. Researchers studyAt the moment of ground contact, theand placed on stall rest, during which the vertical, longitudinal, and transversehorses hoof first decelerates in a down- horses can develop atrophy (muscle GRF components to understand how theyward direction; hard surfaces cause rapidwasting), said Ashley Greene, a affect movement and performance.deceleration and high concussion, whilegraduate student at Mississippi State Vertical GRFs represent weight-bearingsofter surfaces allow the opposite, sheUniversity, in Starkville. In a recent study forces; the heavier the horse, the highersaid. The hoof then slows in a forwardGreene looked at the effects of this type the vertical GRF. They increase to projectdirection due to the friction.of therapy on horses muscle thickness. the horses body into the air, such as whenIdeally, said Clayton, there should beWhile several therapeutic platforms jumping over obstacles. enough friction to slow forward motion exist, Greene used TheraPlate, which Longitudinal GRFs are responsible forgradually. On sand surfaces, the foot sinksis marketed to increase bone strength speed and acceleration. They intensifya little, then plows forward through theand density, increase circulation within when horses change speed, such as whensand for a short distance, slowing gradu- the hoof capsule, and improve or main-accelerating out of a starting gate. Theally. Hard surfaces such as blacktop oftentain muscle mass. TheraPlate is unique hind limbs are the horses motor, provid- have low friction and allow uncontrolledin that it uses vortex wave circulation (VWC) to deliver stimulating pulses to ing most of the propulsion, while the fore- sliding. Grippy surfaces, including manyall four limbs simultaneously, she said. limbs control speed and direction, saidsynthetic footings, create high friction andAt the beginning of her study, Clayton. Their orientation indicates themight stop the hoof too quickly, increas- Greene placed eight mature stock-type of forces they are generating. For ex- ing concussion. One of the challenges intype horses in a 45-day moderate ample, if a horse needs to stop abruptly, hefinding good footing is having enough,exercise program, then stalled them braces his forelimbs in front of his body sobut not too much, friction, she said. continuously for eight weeks to mimic the GRF acts in a backward direction. Clayton went on to explain how GRFsperformance horses going on stall rest, Transverse GRFs act from side to sidechange during circling. When trotting onshe said.to turn the horse. The forelimbs area circle, the fore- and hind limbs on theFour horses remained on stall largely responsible for this motion. Theoutside carry more weight than those onrest throughout the study (the control simplest way for horses to turn, saidthe inside. On small circles and/or at fastgroup), while four also received VWC Clayton, is to lean to the inside, makingspeeds, this asymmetry gives the appear- twice a day, five days a week. The it easier for the legs to push outward toance of lameness in the inside limbs. researchers provided all horses with generate a turning force. Her researchIts important for vets to be aware2% of their body weight in hay per day. has shown that, on average, horses leanof this when conducting a lameness orOn Days 0, 14, 28, 42, and 56, Greene in by 15 degrees on a 6-meter circle.prepurchase exam that includes trottingused ultrasound to measure thickness on a circle, Clayton said. Otherwise, theyof seven muscles in the horses back, might wrongly diagnose the horse with arump, and upper limbs. She recorded GROUNDincreases in treatment horses muscle REACTIONbilateral (affecting both sides) lameness. thickness vs. the controls, notably:FORCES Vertical In summary, she said, horses use theirThe extensor carpi radialis in the Force muscles to alter GRF magnitude and direction to adjust the speed or directionforearm increased in thickness by 30% after eight weeks;at which theyre traveling. Each gait hasThe longissimus thoracis, which runs its own fore- and hind-limb GRF pattern,across the back, increased by 9%; and lame horses modify these patternsandto unload the painful limb, leading to theThe longissimus lumborum, a loin characteristic signs of lameness.muscle, increased by 8%.Both the longissimus thoracis and Using Recombinant Equine Gonado- longissimus lumborum muscles are tropins to Enhance Mare Fertility supporting muscles in the thoracic Mare pregnancy rates are only 60-80%and lumbar regions, which are greatly COURTESY DR. HILARY CLAYTONLongitudinal due to factors ranging from age to stressrelied upon by the equine athlete, said Force to poor uterine environments. As such,Greene. Therefore, VWC appears to be veterinarians have turned to a varietya viable option for minimizing, if not Transverse of advanced reproductive technologiesimproving, muscle loss in performance Force (ART) to enhance mare fertility. Janethorses on stall rest.F. Roser, PhD, professor emeritus in the TheHorse.com | The HorseOctober 201923'