I was handicapped and not able to walk much for 12 years until I found out that my hamstrings needed stretching. Doesn't matter how messed up the back is, it will not refer pain to back of knees or bottoms of feet or likely even to sciatica, if the hamstrings are super stretched. So now I dance! No more crutches and wheelchairs and pain meds! Yogis don't get strokes and high blood pressure and all this other nonsense, but then they also probably don't take in any partially hydrogenated oils (i.e. plastic sticking to arteries) or MSG (poison that makes you fat) or NutraSweet and sucralose (poisons) either..
One kind of hamstring stretch that should not harm the back is when you are on a curb outside and you hang off it from the front part of the foot, or when you lie on your back with a towel around your feet (these are lower back protective). I wake up and throw my leg on the back of the couch or a high bar stool or bathroom counter and begin stretching all kinds of ways from that position, but I have been doing it for a long time, and also stretch the inner thing that way. When I sit here at the desk, I throw one leg at a time up on the desk and reach for my feet, but people need to work up to what works for lower back support in each case. and YES yoga!!!
If we can merely stretch the back the six directions any way we can (rest always between the twist directions), then put some traction (I'm thinking of buying a swing to hang from the hips, but now I get traction from back of couch (breathing deeply) with palms on it after stretching, and if we go upside down regularly, even shoulder stand is enough, just think how many pains we will save ourselves! (One stretch is feet together, arms high and straight and hands touching like a steeple and a straight stretch to the side, hold for count of 10 (breathe). It's hard to do much stretching in the morning before movement has taken place or when it's very cold.
No artificial sweeteners (not even splenda) NO trans fats, and no MSG along with stretched hamstrings and lots of water, I doubt people would age badly or lose memory or get strokes, even doing the minimal amount of stretching. Yoga is enough even for osteoporosis, I heard. And it wouldn't hurt to question the calcium rule of thumb, as it appears Magnesium needs to be much higher. I can send the formula, if you like, though it's a matter of opinion. Stores now carry it both ways. I never did the huge calcium to half magnesium ration and my sisters got the arthritis by my age, not me, and I am not active enough, I admit. The extra calcium running around the body is a bad thing. This is something people can research for themselves.
Here's what I was told, 600 elemental magnesium, preferably, if possible, the citrate maleate, 450 elemental calcium citrate, and 400 units of D (not more D than this). Researching the occasional Vit. K once a week for bones might be good to do for oneself too. I take that, but one must research, as I think it thins the blood a little, but is supposed to help with osteoporosis.
One more..... memory is not lost if one does the shoulder stand to replenish the 180,000 miles or so of capillaries in the brain, nor does hair go grey. Some have had it grow back in brown or grow back period, and it's good for wrinkles, organ flushing (due to new positions of organs) and insomnia and constipation.