When I first started this running malarkey ,one of the problems I noticed was how heavy my legs felt when I ran. This did get better as I got fitter. Then I noticed at night when i was resting,I was experiencing sharp random pains in my legs and joints. I could only get relief from this if I moved them. This continued for several weeks and I put it done to age and the usual wear and tear on aging limbs. However I googled my symptoms and found a suggestion that lack of vitamin B12, zinc and magnesium can cause these symptoms. So I bought some liquid supplements from ASDA and 1 week later I am pain free!