Marching bridges should work mostly the glutes, so if you are feeling it in the lower back or quads, you may need to adjust your form.
It is easy for the quads to take over this exercise, putting unnecessary strain on the lower back. Avoid arching your back — press your heels into the floor to effectively target the glutes. Do not bring your knee in past the hip, toward your chest, or the hip flexors will take over.

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