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 these terms.
When you're using free weights, it's all about how parallel your limb or the lever is to the ground. The more parallel the working limb is to the ground, the more magnification to that muscle.
Think about a bicep curl. The hardest part of a bicep curl is when your arm is halfway up. The active lever for your bicep is your forearm. When your forearm is parallel to the ground, the exercise is the hardest. This is because the moment arm is the longest. The exercise gets easier as you approach the top of the movement. If you were only doing top half curls, you could use a lot more weight because the lever is less "active" or less parallel to the ground. So just because you could lift more weight only doing top-half curls, it doesn't mean it's loading the bicep more.
This can be applied to any muscle group in any exercise, but it gets more confusing when we get to the legs.
Let's look at a common exercise, the squat. To load the quads, you have to use a lot of weight in a squat, which compresses the spine. However, there's another exercise that can load the quads MORE with just your body weight, called the sissy squat.
I calculated the load through the quads in squats vs. sissy squats in the two photos below.
You can see that in a squat, I'm holding 40lbs, and the work through each quad is about 577.5lbs.
In a sissy squat, all we did was change the lever, moving at the knee more than the hip. The tibia is now closer to parallel to the floor, creating a longer movement arm to the knee. I'm only using my body weight (i.e., not compressing the spine with additional weight), and the work through the quads is now 1,000lb PER leg.
This illustrates that I'm placing significantly more work through the targeted muscle even though I'm using less weight.
I'm not implying that everyone should do this exercise in full range right away. If you're struggling with knee pain, it might take some time to work up to full range of motion (Join Levo, and I'll guide you through this). But this is one of many examples of how physics is more important for results than the amount of weight you're using.
Side note: sissy squats do not shear the knees like we once believed they do. Check out this video for an explanation on this.
If you're interested in this and want to become a fitness teacher, I'm hosting a 200-hour Fitness Teacher training, starting April 3rd, 2021! Registration is now open. Click here for more details!
And if you want to exercise in ways that cause minimal damage to your joints but give you better strength and fitness results, click here to get started in Levo.