Your body is designed to make work easier. If there is a more efficient (easier) way to perform a movement, your body will gravitate toward it. Go to any gym and watch the people shifting side-to-side on the elliptical trainers. Their body has found that shifting body weight to use gravity is much easier than the much harder, and more effective, method of holding steady and just using the leg muscles to power the movement.
There are many common examples of this: from appearance goals like the inability to build the pecs of the chest because the shoulders take the stress, or the hamstrings doing the work that would otherwise build the glutes, to functional goals like hip pain due to stabilizing muscles not working or the spine taking the stress that should be on the midsection muscles.
All of these are examples of the body finding the easiest possible way, and how this is not in line with the goals that you may have for your body
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