Veterinary guidelines state that riders should weigh less than 10 percent of the weight of their horse, but researchers from Duchy College in Cornwall found that just 5 percent of the riders passed the test, reports the Daily Mail.
The study assessed 152 horses and their adult riders. Researchers found that 32 percent of riders weighed more than 15 percent of the weight of their horse, high enough to lead to health risks and injury.
Hayley Randle, one of the scientists who conducted the research said guidelines should be put into place to protect horses from overweight riders.
"People tend to think horses are such big animals they must be okay, and not to take notice of the weight issue of riders. But the health impact on the horse can be quite extreme, quite quickly."
Keith Chandler, president of the British Equine Veterinary Association, said his members spent a large part of their time dealing with lameness and back problems, which is often be caused by "the wrong riders on the wrong horses."
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