Join Date: Dec 2010
Location: southern Arizona
I think the 20% rule is utterly groundless.
There was one study done on horses who were deliberately made to be out of riding shape. The horses were not ridden for 4 months. Then they were ridden 45 minutes every two weeks. Based on the blood markers, those out of shape horses could carry 25% of their body weight without a problem. Based on people giving horse massages, the people believed the horses carrying 25% had a little more soreness than those carrying 20%, so they recommended 20% as the limit. The possibility that a fit horse might carry much more, or that the massagers had a bias affecting their results (since the blood work was clean) wasn't considered.
It was a poor study, and it conflicts with what I see every time I ride - which is always at above 20%, and is normally right around 25%. It conflicts with what I saw a couple of weeks ago, when 850 lb Trooper carried a 6'6" guy who had never ridden before for 2.5 hours in the desert.
If you want a horse to max perform, then the lightest weight possible works. But lots of cow horses carry big guys for long hours working hard, and do so successfully.
I also agree with gottatrot. The weight limit is defined by more than just "will the horse be sore". When I put 200 lbs of me & saddle on 700 lb Cowboy (29%), Cowboy doesn't get sore. But he also has less reserve strength to call upon when going up a steep hill, or descending an uneven & rocky path, etc. Turning quickly at speed, my height (5'8") versus his height (13.0 hands) pulls him more off balance that a smaller rider would, or even a heavier saddle might. It is simply harder for him.
That doesn't mean I cannot ride Cowboy, but it does mean I need to be aware of what I'm asking of him. He can handle me fine for most of the trails near me. There are a couple of spots where I need to dismount. Not because he couldn't carry me there, but because any slip or stumble would over-task him in a way a larger horse would not be.
Riders ask "How?" Horsemen ask "Why?"