Their purpose is to aid with the motion of the hips and allowing you to move your upper hands and down in front of you as you would when you are climbing upstairs or on walking with a lot of uphill areas.
Your hip kidnapper calves, abs, and muscles likewise help your hip flexors with these motions. The others will compensate and attempt if any of these muscles are weak.
The antagonistic muscles are the excess, and they concentrically speed up a hip extension and as you would envision they do the reverse of what the helping muscles do. In such a way, they produce a balance for all the various series of movement the body can achieve.
When your hip flexors are reduced, they can pull on your spinal column and trigger a disc to slip out, which can then strike a nerve triggering all kinds of issues.
You require extending them to neutralize the impacts of sitting for hours on end when you have reduced hip flexors.