I'm going to give some background in the next three paragraphs and then my actual Q will come in the final paragraph. I'm a male in my twenties if that matters.
Five years ago I had been running great, setting PRs at multiple distances and then suddenly my performance started to decline. More noticeably, the way I felt was very different -- I had no spring in my stride, wasn't recovering well from workouts, etc. Eventually my legs started feeling a bit numb and became very tight. Stretching did not seem to loosen my legs up all the way and no matter what I did they'd be super tight again the next morning. It was a period of high psychological stress and I'm sure this played a factor.
Since this started happening I looked a lot of different places for the cause/solution. I saw numerous medical specialists but all their tests came back normal. So for most of the last 5 years I just went on with my life without running essentially (I would jog 2x per week and this was all my body would tolerate). During this time I assumed the cause was something deep that I had little control over.
But recently I started wondering if it was actually *just* tightness and the tightness was causing the numbness and weakness/lack of recovery. I started trying a combination of progressive muscle relaxation and stretching and this seems to be working to at least get my legs loose again. But they're far from full strength. I've felt a lot better in my 2 runs since starting to loosen my legs but the pace and my heart rate are the same.
So my question is as follows. Let's assume that my legs were ultra-tight for five years straight due to stress + inertia and that I have now loosened them. How would you advise I approach this comeback? Should I keep the mileage super low for a few weeks and just focus on rebuilding with hip/core strengthening and maybe some hill sprints? Should I try bumping the mileage just to see what happens? Is there any specific nutritional guidance I should follow? Open to any kind of idea here.