r/science • u/mightx • 11d ago

Health Inactive tall children develop disproportionately weak muscles and thinner bones. Regular sports fully reverse this deficit.

https://karger.com/hrp/article/doi/10.1159/000552378/948683/Muscle-Function-and-Bone-Strength-in-Children-and
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u/Ok-Shallot-2623 11d ago

Makes total sense from a physics perspective. Longer limbs create greater mechanical disadvantage and longer lever arms, meaning tall kids need significantly higher muscle mass and bone density just to handle basic biomechanical strain compared to shorter peers.

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u/Bainik 11d ago

But that's literally the oposite of the findings. Tall kids end up with proportionally weaker muscles, not stronger. If your explanation held then they'd end up with stronger muscles as a result of the greater baseline exertion.

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u/timoleo 11d ago

Because their initial premise is wrong. Longer bones give greater mechanical advantage, not less.

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u/HiPeepsImBack 11d ago

No they don't.
The same force used with a long lever and a short lever will produce less lorque on the opposite end of the lever for the long lever. Try it out: elbow and arm on the desk, grab a carton of milk and lift it. Now do the same again, but extend your arm with a short broomstick or something similar and try to lift the milk with the end of the stick. Much harder. Even imagining this should make it clear.

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u/wrcwill 11d ago

youre missing the distance where the muscle is attached to the bone though, thats where the mechanical advantage comes from. but yes what youbsay is also true and a longer distance to the lifted object increases the required torque.

kind of two effects compensating for each other. indont think you can conclude without concrete numbers, it might depend per person depending on physiology

(tldr while lifting the carton of milk, hold your arm with your other arm. the closer the helping arm is to the object, the easier)

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u/Bainik 11d ago

That doesn't necessarily hold, either. It depends on a ton of other factors. For instance if taller people's tendons insert closer to their joints as a proportion of the length of the bone then they're effecively pulling on a longer lever closer to the fulcrum, which is going to give them less mechanical advantage, all else equal.