The robust stature of horses makes them appear strong and able to withstand even the most glaring mismatch of rider size and weight. However, a recent pilot study revealed that horses are sensitive to rider weight and balance in ways that affect their performance.

The study, headed up by Sue Dyson, MA, VetMB, PhD, DEO, FRCVS, head of Clinical Orthopedics at the Animal Health Trust Centre for Equine Studies in Newmarket, UK, was presented at the National Equine Forum in Great Britain. Dyson and colleagues looked into how the size of a rider affects a horse’s gait and behavior. Funding of the study was obtained through several welfare-minded organizations: World Horse Welfare, the British Equestrian Federation, the Saddle Research Trust, the British Horse Society, the Pony Club, Polocross, the Showing Council, the Showing Register, the Society of Master Saddlers, Riding for the Disabled, British Eventing, British Dressage, the British Horse Foundation, the Worshipful Company of Saddlers and Endurance Great Britain.

The objective was to evaluate a rider’s proportional weight on horse performance. Six horses used in the study weighed between 1,100 to 1,300 pounds. The four riders in the study were similar in equestrian ability, but their weights ranged from 134 to 313 pounds.

A comparison of the ratio of rider to horse’s body weight was made to determine effects on the horse:

a) A light designation indicated rider weight that is 10 to 12% of the horse—as, for example, a 110- to 132-pound rider on a 1,100-pound horse;

b) A moderate designation described a rider at 12 to15% of the horse’s body weight—as, for example a 132- to 165-pound rider on a 1,100-pound horse;

c) A heavy designation described a rider at 15 to 18% of the horse’s body weight— as, for example a 165- to 198-pound rider on a 1,100-pound horse; and

d) A very heavy designation described a rider with a body weight that exceeded 20% of the horse’s body weight, such as a 220-pound rider (or heavier) on a 1,100-pound horse.

The horses in the study were exercised wearing their normal tack at a trot and canter in specific, set patterns. A Master Saddle Fitter consultant checked tack during every part of the study to ensure correct fit for each horse. The researchers assessed horse response to back palpation, alterations of back dimension from exercise, heart and respiratory rates, gait under saddle and horse behavior. Stress responses were measured using saliva cortisol levels and the blink rate. A horse’s full and half blinks decrease significantly in response to stress.

Not too surprisingly, horses carrying the heavy and very heavy riders had significantly higher pain scores than those mounted by light or moderate riders.

In fact, the added weight factor by the heavy and very heavy riders elicited transient lameness significant enough that the riding exercises of these individuals were halted. Lameness issues became apparent 30 minutes into flat work with the heavy rider at 16.7% of the horse’s body weight.

It was noted that the saddle also did not fit this rider.

Only one moderate rider’s testing had to be stopped due to horse pain scores.

Dyson noted that horses with low-grade lameness when ridden by a lightweight rider tended to show more obvious lameness when mounted with a heavier rider.

The horses affected by the excess weight ratios returned to their original levels of soundness within 45 minutes of cessation of the set riding patterns.

While a high proportion of rider weight compared to horse weight resulted in temporary lameness in the study, there is a potential for lameness to become more permanent if a heavy or very heavy rider continues to ride the horse on a regular basis.

Variable factors affect how well a horse tolerates the body weights of different riders: Conformation, body condition score, and a horse’s strength and fitness were several relevant factors. A horse with soundness or health issues is likely to be more affected by a heavy rider. Saddle fit and rider skill and balance also factor in to how well a horse does under saddle.

In a previous study of 506 horses, 50% were ridden with poorly fitting saddles. That study helped to define what happened to horses carrying very heavy riders, particularly with ill-fitting saddles. Other significant factors from that study showed how well a horse did relative to rider weight and ability, including exercise demand, type and duration of exertion, footing, terrain difficulty and climatic variables.

Take-Home Message

The take-home message is that riders should be paired with horses that are in appropriate proportion to the rider’s weight. Also, saddle fit is critical to horse comfort, particularly with heavy riders who make more of an impact sitting on a horse’s back.

Because this study used a rider who could move with the horse rather than dead weight, it further identified that weight is not the full story, but rather, that distribution of the weight has consequences. For example, the height of a rider and/ or the fit of a saddle might affect a horse’s comfort through a rider’s position and weight distribution when mounted.

A tall rider or one bothered by saddle fit might find himself or herself sitting more to the back of the saddle near the cantle. In that case, rider balance becomes an issue with direct consequences on horse comfort, soundness and performance. The horse’s back length then becomes an additional factor in determining appropriate match of horse and rider.

Common sense is useful in determining fit of rider to horse. If a mounted rider visibly appears too big for a horse or is not able to achieve proper position in the saddle both in location and posture, then efforts should be taken to fix the horse-rider combination and/or saddle fit.

Ongoing studies are needed to provide exact ratios of the horse-and-rider combinations that work best and to project guidelines as to specific cut-off levels based on both horse and rider body weight. Increasing a horse’s body condition to overweight is not an answer for “fixing” the body weight ratio of horse and rider. Instead, the fit of rider to horse should be adjusted based on a healthy body condition score of the horse.

No matter the outcome of future evidence-based research, a good piece of advice is to pair bigger riders with bigger horses and to ensure saddles fit well for both horse and rider. The more comfortable the rider and the better his or her balance and weight distribution, the more comfortable the horse. And that comfort means that the horse can perform, also increasing the likelihood of a longer athletic career for that horse.