a horse is a horse, of course, of course

So an average size horse has a 200 lb. man on its back. If the horse in this scenario were a man, and had weight on his back similar to what the man’s weight felt like to the horse, how much weight would that be?

That depends on the weight of the horse in your original example, obviously, which you don’t specify.

The weight of an adult horse varies widely, depending on breed, nutrition and other variables. You specify a man of 200lb (= 90 kg, or close enough). That’s a big lad, so let’s say he’s mounted on a well-built horse of 16 or 17 hands; a reasonable figure for the weight of such a horse, and one which makes the figures nice and round, is 540 kg.

So, the horse is carrying a man one-sixth of his own weight. If the 90kg man does likewise, he’s carrying 15 kg (or 33 lbs).

I think you probably have to adjust for normal posture here. A horse walks on all fours. Adult humans don’t generally walk on hands and feet - and when they do, their spine is not in its optimal load bearing position - so for a fair and level comparison, it might be better to compare against a human carrying a load in arms or a backpack, in a standing/walking position

There’s probably also some square-cube scaling matters to factor in too, if the objective is fair comparison.

I had no idea what horses weigh, that’s why I said “average size”. And I think that a simple weight comparison might not take into account that the horse has different posture, structure, muscles, etc., but I appreciate your reply! I did not think this would be easy or simple.

The question is what weight would it require for a man to FEEL the same load as a horse feels. Since there’s no way to tell what a horse feels, this isn’t really answerable. Using a proportional body weight ratio is probably not going to be even close to the right answer, since as mentioned a horse’s body mechanics are very different from a human’s. I would think a better answer might be obtained by measuring the horse’s increase in heart rate and respiration during, for example, a hill climb with and without a rider, and seeing what weight produces a similar increase in a human’s. But this may vary significantly depending on the overall fitness of the particular human (and the particular horse).

–Mark

My thought would be to dig up a figure for the maximum amount a horse is capable of carrying, and seeing what fraction of that maximum weight a typical rider is. Then, take the maximum weight a human is capable of carrying, and load the human down with the same fraction of that maximum.