Do you know about the yoga sun salute? If not, what you do is you eventually get to where you bend down trying to touch your toes (don't push it), then flat back, bringing your hands to your knees, then touch your toes again, then stoop down, then up to where you touch your toes again, stoop down again, touch your toes again, stoop part of the way down, flattening your back into a warrior pose with your arms at a diagonal forward, then touch toes again, then come up one vertebra at a time. Again, don't push yourself but you will see a stretch in your hamstrings in backs of your knees.