For a bit of scale on what we know the human leg can handle without breaking: the best drug tested, sleeves-only squat in the world is 490 kg (Ray Williams IPF Worlds 2019). Drop the drug testing and add multi-ply squat suits and the record is 590 kg (Nathan Baptist, UPA Utah Kick Off Meet 2021). Granted: these are two-footed squats and you run with one leg at a time.
Alternatively, look at Olympic weightlifting. While the weights used in the clean and jerk and snatch are less that used in the squat in powerlifting, the instantaneous forces are much greater. I don't think 1300 lbs is anywhere near enough to break a human femur if we're talking compressive forces, lateral force is a different story.
Olympic-style lifts are among the most powerful things a human can do. Elite athletes can push beyond 5kW at the peak of exertion. This is why technique is so important. The forces involved are insane once you go beyond 200lbs or so. The snatch can be extremely troublesome if you do it wrong. Clean and jerk is more tolerant to bad form.
oooh yeah the speed is definitely something to consider for them. Hmm. Kinda wanna grab some hookgrip slow-mo edits and do JV science with them. Kinda don't because I have shareholder value to create.
Not to down play the "what's possible", but it's important to note that bone strength depends on stimulus and nutrition just as much as muscular and connective tissue strength. Those athletes bones are likely far stronger than the average human of the same size without training.
Oh yeah, in fact Gene Rychlak (first lifter to bench over 1000lb) said he could feel his bones bending during the lift. Training is getting your body adapted to the movement, and that for sure includes bone density. I'm guessing our 100m runners are also pretty dense.
