If you are standing, the hip flexors lift your leg when you step up on a stool. If you are lying flat on your back, the hip flexors can either lift your leg or lift your torso into a sit-up. In yoga, Navasana (Boat Pose) is especially good at strengthening the iliopsoas because it demands that the muscle isometrically contract to hold up the weight of the legs and torso.
There is no simple orthosis for the management of isolated paralysis of the hip flexor muscles. While the hip guidance and reciprocating gait orthoses mechanically assist hip flexion (see p. 115), neither is prescribed solely for this purpose. Rather they are prescribed for patients with extensive bilateral lower limb paralysis who also require orthotic support around the knees and ankles.
When it comes to training, I prefer to stick with the basics. People think they need 10 different exercises to fashion a fine pair of cheeks, but that's not what it takes. When it comes to toning your glutes, you only need two things: drive and dedication—and I mean real dedication. You must train your glutes hard and diligently to get a great response. If you stop every time it gets difficult or whenever it burns, you're not going to get anywhere.