Strong Legs, Strong Back
It's true that strengthening your abdominal muscles can help prevent lower back pain. What's not as commonly known is the connection between lower back pain and the hamstrings (the muscles in the back of your thighs).
Tight, inflexible hamstrings are often at the root of low back pain. The good news: simply stretching those muscles regularly -- using yoga, pilates, or basic stretches -- can go far in keeping them supple and keeping back pain at bay.
The cardinal rules of stretching apply. Stretch muscles when they are warm, after warm-up activity or a workout. Stretch as far as you comfortably can. Hold each stretch for 20-30 seconds, and repeat 2 or 3 times.