Movement always requires some form of resistance. Even if you’re not using external load like weights, you’re using gravity and the weight of your body.
Each form of resistance requires a different strategy from your body, depending on the load and the force vector.
When you move your body without using any weights or external load, it only takes a little effort and your body doesn’t need to give it much thought.
But if you do the same exercise with weights, your body is going to need a different strategy. It will engage different groups of muscles throughout your body to help you stabilize.
If you add more weight to that same exact lift, your body won’t just contract that muscle harder. It will make you change your force vector by shortening the axis of movement and help you stabilize.
If you add even more weight, you may not be able to lift it up at all unless you give your body some form of support like a bench for example.
There are different types of resistance that affect force vectors, you can manipulate the way your body interprets the movement and even add vectors by using two forms of resistance simultaneously.
Featuring Andrea Dusel-Foil's photo