We’re suppose to lift with our legs, but whats makes our back not suitable for it. Silly question i know.
In: Biology
Mechanical advantage, aka leverage.
Your spine is a stack of interlocking bones with tide-pod-like discs inbetween, laced with muscles that can pull it straight.
When it’s nice and vertical, it can bear your weight easily. The force is evenly distributed on all the discs, and everyone’s happy.
But try a little experiment: try straight-arm lifting a heavy weight. Pick up two heavy bags of groceries and hold them close to your chest – it may be an effort, but it’s fairly manageable. Now try lifting them straight out to the side, in a T-pose. It’s *way* harder, and you’ll get fatigued in no time.
The forces involved are way higher, because your arms have all the leverage; they’re acting like a crowbar against the muscles of your shoulder. It’s like trying to close a door against the wind, but from the hinge side instead of the handle.
Now imagine doing that with the stack of jelly and bones that is your spine. Not only does the force required to pull it straight *vastly increase* the more it bends, but the forces on the bones themselves will pinch the fuck out of the squishy discs on the inside of the curve.
Your legs, on the other hand, have long strong bones with the muscles attached a significant way past the joints – a way better ‘gear ratio’, and the strain is taken by bone, not squishy cartilage.
Using your legs instead of your back is like lifting with a seesaw instead of a fishing rod.
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