Many use their hip flexors to do core work. Instead, use your
core to do core work. To test, cross your legs and attempt a
roll-up. This takes your hip flexors out of the equation.
• Lie on your back with arms out-stretched or crossed
• Do not use arms for momentum
• Keeping your legs on the mat, slowly roll up
• Legs long is more challenging, bent legs easier
• Legs crossed is the most challenging, as it removes the ability to use your hip flexors