The Point of Application of the Ground Reaction Force Moves in Circling Horses
Authors: Merritt JS, Starke SD, Clayton HM
Journal: Equine Veterinary Journal
Summary
# Editorial Summary: Ground Reaction Force Application in Circling Horses When horses work on circles, the distribution of forces through their limbs shifts dynamically—a biomechanical reality that Merritt, Starke and Clayton investigated by examining where the ground reaction force actually applies within the hoof during straight-line versus circular locomotion. Using motion capture technology and force plates, the researchers tracked eight horses at walk and trot both on the lunge (6 m circles, left and right) and in straight lines, analysing 2,018 strides to calculate the precise point of force application weighted by load magnitude. At trot, the point of force application shifted medially (towards the centre of the circle) by approximately 20 mm—a statistically significant change—whereas at walk no meaningful shift occurred regardless of circle direction or limb position. This medio-lateral redistribution of loading during trotting work has considerable implications for practitioners: the altered force application likely creates uneven loading through the distal joints and potentially compromises optimal load distribution through crucial structures like the collateral ligaments, cartilage surfaces and suspensory apparatus, which may contribute to asymmetrical wear patterns or injury risk during sustained circular work.
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Practical Takeaways
- •Lunging at trot creates unequal loading across the foot and lower limb compared to straight-line work—consider alternating circle direction frequently and incorporating straight-line trotting to balance structural stress
- •Walking on circles does not produce the same problematic loading shift as trotting, so walk work on circles is biomechanically safer for rehabilitation or conditioning
- •The inward shift of ground reaction force at trot on circles likely increases stress on the medial (inner) structures of the limb; this is relevant when managing or preventing overuse injuries in working horses
Key Findings
- •At trot, the point of force application shifted toward the center of the circle by 19.8 ± 10 mm (P<0.001), indicating altered medio-lateral limb loading during circular movement
- •The force application shift occurred equally in forelimbs and hind limbs at trot
- •Walking on circles produced no significant shift in force application point compared to straight-line walking
- •Altered force application during trotting circles suggests suboptimal loading patterns in distal joints and limb structures