I'm a soon to be 59 year old woman. I try to do 40 sit ups (20 AM and 20 PM) and walk a mile every day weather permitting. I thought over time my muscles would get used to this routine, but every day I seem to get sorer and sorer and the lower back and shoulder pain is sometimes excruciating. Now I though muscles adjusted to activity - why aren't my muscles getting any better?
I've been doing it about 3 months now, since I retired from work and don't have much to do in the way of physical activity. I had a bone density scan a few years ago which showed osteopenia in the lower vertebrae, so my doctor put me on calcium. It seems shortly after I started taking the calcium is when I started having a lot of back pain. I went to my primary care doctor last month and told her about my back and asked for another scan. She refused to order it saying I didn't need one. Last week I went out to bundle some twigs to put out for garbage pick-up and when I came in the muscle in my arms were twitching involuntarily. I was like a person with Parkinsons. It too about an hour for it to stop. It just got me wondering.
Do one thing. Try adding a magnesium supplement, up to half the dose of your calcium supplement, but no more than 500 mg. Your muscles need calcium and magnesium in balance to work properly, and it MAY be you have too much calcium in your blood and not enough magnesium to balance it out.
I agree with the other poster, add magnesium to balance the calcium.
As to your sore legs after your walks, how much walking were you doing before this routine? You may be progressing too fast. Your body needs to be challenged, but even more it needs a rest period in which to repair strained muscles and to grow new ones. If you are challenging the same muscles every day, without a rest you are breaking them down without allowing them to be built up again. The older you are, the longer the rest period should be. Try doing these long walks every 3rd day. An intense work out is just a beneficial as a long one, try to find a route that has some hills even if it is not as far. Many trainers no longer recommend sit ups. It is too easy to hurt yourself. Try doing crunches instead and again, not every day. One last suggestion. Muscles need to be in balance, those days you are not doing sit ups try doing some upper back exercises. Talk to your doctor first. If you have back issues already, you want exercises that help, not ones that may make things worse. Lower back pain is something I occasionally suffer from too. I am the same age as you and gentle, gentle stretches can help. I find it is best it I try stretches I can do lying down, even in bed before getting up in the morning.
I hope this helps.