If I wanted to know, I would have to google it. But I don't have a need to know.
The last time I needed to ride a horse for any distance, my knees were in agony from wrapping around the horse's barrel. For most of the day, I just walked and led the horse. It was less painful. Come to think of it, that horse probably thought I was a great "rider". No weight to carry.
After a week or two you'd get used to it.....but that first week would feel like you've been run over by a truck, after being drug behind it for a mile.
Your body can get used to being in unnatural positions, if it's contorted long enough.....I suppose there would be a few around here ,that could relate to that statement.
I prefer big horses for long distance, they're like riding an easy chair after awhile.....and are able to handle my size better.
They've an easy going attitude, don't spook under pressure, and have better feet ,just to support their own weight.
If they have some Draft genetics, they've been bred to have the gentle nature.....and because they outweigh a bear, don't bolt when you run into one.....which tends to happen to me on a regular basis.
Half of their kind are ok with gun shots....which is another thing that tends to happen.
I also high line them at night, and being calmer, are more likely to still be there in the morning....even though they are more than capable of breaking that high line, with their strength.