The Missionary Position
When you are in the missionary position on the bottom, you can support your low back by putting a rolled towel under it. This will place a slight arch in your low back, a position recommended by physical therapists to help alleviate symptoms. Your partner can straddle you while in a kneeling position. You will be in the passive position. Straddling can also be done while sitting in a chair.
Sitting and Kneeling
You can also sit on your partner's lap. This will give you some control over your back's position. Explore and be aware of the positions of your spine that make the pain worse, and better.
Another possibility is to kneel as you support your weight on your elbows. In this position, there is room for you to adjust your back to a place of comfort. Your partner can enter you from behind.
Lying on your stomach will automatically put your back in an arch. You can control the amount of arch from this position in several ways. To add more arch, start by placing a pillow under your chest. If that does not provide enough extension, prop yourself up on your elbows. To decrease the amount of arch in your back, place the pillow under your stomach. Find the right amount of arch for your back by trying these variations to identify for yourself which is the most comfortable. While lying on your stomach, your partner can enter from behind.
Hebert, Lauren, A., P.T. (2001). Sex and Back Pain. Greenville, ME: IMPACC USA.
White, A., III, M.D. (1990). Your Aching Back: A Doctor's Guide to Relief. New York, NY: Simon & Schuster/Fireside.
Kisner, C., & Colby, L.A. (2002). Therapeutic Exercise: Foundations and Techniques.Philadelphia: F.A. Davis Company.