There are no bad exercises that the human body can perform. Many coaches/trainers like to write articles or post videos on bad exercises and why you should not perform them. They are not inherently wrong in their teachings but there is more to it than just claiming the exercise is bad and not to do it. Now do not get me wrong there are some exercises that some people should not perform or should stay away from due to previous injuries or pain.
What makes an exercise bad is the position and posture of the body, and its structures; not the exercise,
Posture is a key element to how the body moves, it influences positions of muscles, bones, joints, vision, hearing you name it. When this becomes altered it changes how we pattern function and move. The human system is asymmetrical through and though and the brain will look for symmetry throughout life and favors it. We then get the perception that our two sides of the body are symmetrical, and we treat them the same way as we go through movement. But that is not the case, our asymmetries create and drive patterns that influence movement.
When the patterns created are used constantly in life, we develop the body position and posture around those patterns and tend to use the predominant pattern most of the time. This patterning leads to certain positions of joints, muscles and bones that still have a need to move and function properly.
What makes an exercise bad is the position of the joints, muscles, bones and systems that make them bad. When we put load on the human body it must adjust for the load, the pressure, the forces, and the movement that we want to accomplish. This is muscles/tendons pulling bones in directions to move the weight.
If the joint is in a poor position then the bone that is being pulled or moved can create impingement on that joint, this then can cause pain, wear and tear on tissues, inflammation or tightness. Doing this continuously over time can lead to chronic issues and poor patterning of lifting mechanics.
The human body is designed to compress and decompress, side to side, front and back, when we are lifting weights we are putting the body in a compressed state to be able to withstand the forces of the weight being lifted and to stay rigid and not collapse to the floor. That is the purpose of strength training to put a load on the system that will make it adapt. In order to get the desired outcome we want we have to make sure that the system is put in a proper posture or position to be able to handle the loads correctly.
If we are out of position then the compressive forces become greater on joints that are not meant to take a lot of compression or it compresses the joint incorrectly. This is where exercise becomes bad, and harmful.
The system is asymmetrical and if we do not address the underlying asymmetries then we tend to be in a position that might not be conducive to the exercise being performed. Lets take in consideration bilateral exercises first loading the system and performing movement on both sides of the body that is exactly the same.
We need to create a stacked position through the hips (pelvis) and ribcage (thorax) that allows for proper position of the abdominals on the ribcage and of the hips (pelvic floor) to function as a unit. If not the lower back can take the compressive forces, one hip, ilio-sacral joint can take forces, some part of the system will take the compressive forces if we cannot absorb it with the proper muscles.
Creating a balanced ribcage entails making sure the left ab wall (internal oblique) is engaged and is able to pull the ribcage back into a more “neutral” position. We also want to create stability in the hips by creating a small posterior tilt that will bring the hips under the cage above. Setting these two will help align legs and arms, the influence of the ribcage and pelvis will change the appendicular skeleton thus allowing appropriate movement.
So those exercises that are bad, they can be done, you just have to make sure that your axial skeleton (ribcage, hips) are in proper position, that will allow full range of motion at the joint.