lumbar curve
My lower back does not curve completely when doing sit ups. I'm a US Soldier and required to do sit ups regularly so this is getting pretty annoying. Rather than curve nicely so that I can roll from the up to down position, my lower back stays straight when lowering down to the ground so that my upper back hits the ground with a thud. I completely lose the momentum needed to sit up again and continue with the exercise. Are there any stretches or exercises I can do to help my lower back curve more? Thanks!