The effects of a rider’s mass on ground reaction forces and fetlock kinematics at the trot.

This research study investigates how a rider impacts the ground reaction forces (GRFs) and movements of a horse’s fetlock joint while trotting. It finds that having a rider increases absolute peak GRFs, changes the time of peak GRF occurrence, and alters fetlock joint positioning, indicating that ridden and non-ridden horses should not be directly compared in studies normalizing for body weight.

Ground Reaction Forces and Fetlock Joint Kinematics

• The study’s primary focus is on ground reaction forces (GRFs), the forces exerted by the ground on a body in contact with it, and how they are affected by the presence of a rider on a trotting horse.
• The research also investigates fetlock joint kinematics, or the movement of the horse’s joints, most comparable to the human wrist or ankle, during trotting.

Study Methodology

• The researchers used five dressage-trained horses and three experienced dressage riders for the study.
• Both GRFs measurements and sagittal view (side-view) videotaping were collected while the horses trotted at the same speed, both with a rider and without (in-hand).
• The data were then normalised for the duration of each horse’s stance (the period when the horse’s hoof is grounded).

Findings

• The study found that all the horses displayed consistent changes when comparing ridden and in-hand conditions.
• When ridden, there was an increase in the absolute peak vertical GRFs for both the fore- (front) and hindlimbs (rear).
• Interestingly, the peak vertical GRFs, normalised for mass (either horse alone or horse with rider), were lower during ridden trotting.
• The time of peak occurrence shifted, happening later in the forelimbs and earlier in the hindlimbs in ridden conditions.

Fetlock Joint Observations

• The maximum angle of the fetlock joint and its time of occurrence were largely similar in both ridden and in-hand conditions.
• However, the fore fetlock joint was more extended during the later part of the stance phase when a horse was ridden.
• This suggests that a horse’s joint movement is affected by the presence of a rider but in a marginally different way than the GRFs, indicating complex limb coordination during horse riding.

Implications for Future Studies

• The evidence suggests that a horse with a rider is not simply equivalent to a proportionately larger horse, meaning that when comparing horses in different conditions and normalising for body mass, the presence of a rider should be accounted for.
• These findings underline the importance of considering the effects of a rider’s mass in assessing the biomechanical aspects of horse movement, especially in clinical and sport horse research.