This is a special exercise I use to teach the hips to fire while keeping the back arched. Many times over the years while showing people how to squat (and there have been hundreds) I run into a problem that technique will not fix. This is when you see the knees cave in very hard out of the bottom when you tell them to arch. You will think it is a technical problem but it stays regardless of the weight and what you say.
To test this I will have the athlete sit on their box squat box and ask them to get into their bottom position with their legs out. Next I ask them to round their backs (this is how they have been squatting). I also tell them to force there knees out as hards as they can. I will actually push my hands against their knees so they can push against it. Next I push their knees in as hards as I can. In this position I can't move them.
Next, I do the same thing but this time I ask them to arch their back. Now I will push their knees in again. Most of the time their knees will slam in with little effort. They have trained their body to fire their hips and glutes with the back rounded. When they arch the pattern gets all messed up.
This is a problem when they squat, BIG TIME. If will lead to the bar falling forward, back problems and knee problems.
To fix this I have them take a band around their knees and face a wall (or bar in a rack like pictured). They have to arch or they will hit the wall. The bands are their to train them to push out. So we have the wall and the bands forcing them to fire right.
This is a movement that needs to be done all the time, every session or every day. This is not about muscle weakness but firing patterns.
Bands
The past 5 years has seen a dynamic shift in the approach to strength and flexibility training. These bands are the reason! Do not get left behind..