People train to develop and improve a physical ability through instruction from trainers and by practicing
Each exercise is designed to produce a result, to target specific muscle groups and to put those muscles to the test
Each exercise has a certain pattern, form, and technique that needs to be followed, or the exercise can become useless
Let’s take the squat as an example, as this is one of the exercises I have seen the most problems with. The primary muscle targets of the bodyweight squat are the quadriceps and gluteus maximus. The squat exercise is designed to improve leg strength and flexibility. In other words, the desired outcome of squatting is to be able to safely squat heavier weight and go deeper.
Proper form and technique is to pull yourself down into the squat while maintaining an upright torso; placing the weight on the quadriceps, the gluteus maximus is engaged to keep the pelvis upright, remove pressure from the spine and extend the hips. In the end phase of the squat, the hips should ultimately be past the knees when viewed side-on, the torso should be as upright as possible, the spine is neutral, the shoulders approximately aligned with the ankles, the knees in-line with the hips and feet. The up phase of the movement is powered by the quadriceps, hamstrings, and gluteus maximus.
Here is what I notice in many people. Without seeing themselves in a mirror and paying attention to the muscles they should be feeling, they end up in an end phase of the squat which looks like this:
The end result is a badly executed squat that puts more weight on the back muscles as opposed to the muscles targeted – the muscles that should have been worked in this exercise have almost totally been taken out of the equation.
In some cases people take a shortcut because they want to end up in the same position as the people next to them, or at least feel like they are, while they should be focusing on their own personal form and technique, building up strength and flexibility by only doing half the movement but keeping the muscles under as much load as possible. Each person needs to work at his/her own capacity in order to progress.
The point I’m making is not about the squat itself, but that one should understand the goals of an exercise, understand the form and technique required to execute the movement, understand the muscles targeted, understand the muscles powering the movement, understand the muscles assisting the movement, and ultimately understand the ‘WHY’ behind the exercise in order to progress to new levels of ability, which is why you are training, after all!
With that said, it should be noted that a lot of exercise movements can be powered using different muscle groups. This is not always a bad thing if it’s intentional, works towards your goals, makes sense and is technically safe and sound.