I’m 56. I run 7-miles/day (6 days a week); One hour Krav Maga workout 3-times/week; various strength training 5-days/week. Same thing happened to me about a year ago. It was like I wasn’t recovering from my runs and always sore. What fixed me was Magnesium (Taurate). Recommended by sports therapist. Took less than a week and I felt at least 10 years younger. As an added bonus, my 9-year battle with plantar faciitis was finally cured and hasn’t returned since. I think the minerals in our soil is so depleted that most people have a magnesium deficiency and don’t know it. Try it (make sure you get the right kind of high absorption magnesium) and you’ll feel like a new person. Always a good idea to check with your doctor first.