Spinal compression is a huge issue for humans - we are constantly under spinal load when we are upright because gravity is pulling us downward. Therefore, disc and spine degeneration is an extremely common issue as we age. So the less we can compress our spine throughout our lives, the better.
So the question is, how can we load the skeleton the LEAST, minimizing spinal compression, while loading the targeted muscle the MOST? It's not about how much weight you're holding; it's about changing the physics of exercises.
Effectively targeting a muscle is about the lever or the moment arm to the muscle. The longer the moment arm, the more magnification or work through the muscle.
Changing the physics will reduce or increase the magnification to the muscle or how much that muscle is loaded.
In every exercise, you have an axis, a moment arm, and a line of force. Check out this blog to read more about using physics to calculate force if you aren't yet familiar with...