Plus a dumbbell is the same weight the whole time while the bow is only the draw weight at full draw.

On the other hand as someone noted: you don't bring up a dumbbell by a thin string with 3 fingers. I think when trained and without holding like in the movies you could go a bit longer than you'd expect with dumbbels but goddamn your fingers must hurt after.

Why would it ever be impossible/unbelievable? The whole point is it was commonplace for this type of person.

It's just surprising that the number's that large.

Yeah but spend your whole life malnourished and march 20 miles THEN do the reps (as peasant archers probably had to do).

I think only trained professional archers could use a 170lb pull bow at all.

Agreed. I'm an amateur archer and I asked my archery instructor the highest poundage recurve bow he's ever seen someone fire, and he says that one time someone came to the range with a 100 pound draw bow, but he's only seen that once in 10 years.

Compound bows of course you can go higher because of mechanical advantage, but either way I don't think that people realize how difficult it is to draw a 100 pound bow. Typical professional recurve bow users would rarely want to exceed 50 pounds as I understand it.

There’s also a bit of a different optimization goal in modern archery - the goal is to put as many arrows precisely on a target. More draw weight helps up to a certain extent, but ranges are pre-set and limited and once your draw weight is high enough to comfortably propel the arrow that far, more weight will not improve things. Aiming gets harder at a higher weight. You could shoot a heavier arrow, but the benefits are somewhat limited - it punches a bigger hole which helps a bit, but you’re not trying to kill the target - so the added penetration is not interesting.

In a war setting, higher draw weights increase both distance and penetration, which are desirable.

My understanding is that English longbowmen trained from their teens on the weapon and you can see on the skeletons how it warped their bodies.

Yes but they weren’t starving them for their whole lives.

This is highly contextual based on time and place. While most people would have had access to fewer calories compared to the modern day, the average person wasn’t starving to death under normal circumstances. We’re talking a population that engaged in regular manual labour, so sufficient nutrition was necessary. I’d also guess the societies starving their populace were unlikely to call them up to war unless they were really desperate.