These basic Pilates exercises can help increase awareness and set the foundation for abdominal strength and body mechanics that balance ab and hip flexor use:
Knee Folds: In knee folds, we use the abdominal muscles to stabilize the pelvis so that we can feel the subtleties of the hip flexors at work. In knee folds we also try to keep our big muscles, like the quadriceps of the thigh, out of the exercise as much as possible.
Chest Lift: Chest lift engages all the abs but it feels more like an upper-ab exercise. In it, we stabilize the pelvis in a neutral position and move just the upper body in isolation. Your hips and legs should stay still and do not grip. If the hip flexors start to get over-involved, you might have a sense that your knees want to pull toward your chest, or tightness in the groin and thigh.
Supported Roll Back: This exercise invites a deep abdominal scoop. Right there you feel those abs. As you begin to roll back, You might sense a point where the hip flexors want to grab the movement. You can feel that at crease of your thigh. As you roll down, the hip flexors will have to do some stabilizing, but try to maintain a focus on rolling down and controlling with the abs. Thinking of getting some space between the top of the thigh and the lower abs can help.
The Hundred Modified: The full hundred calls for the legs to be extended. The hip flexors often see that as a call to over-action. Work with the hundred in a modified position with your knees bent and feet flat on the floor, or legs in table top. That way you can focus on using the abdominals.
As you work with increasing your awareness of the relationship between the abs and the hip flexors, you will discover that there is reciprocity in terms of one set of muscles doing the stabilizing of the trunk or pelvis while the other set moves. What we want to achieve is muscular balance, better functionality, and ultimately more choices about how we move.