I think I may have found a solution, that will probably seem improbable, but it seems to work for some reason. You might flame me, but it is based in some science.
So, I started having problems in 1999. Running track and pretty fit. Once I got to a very anaerobic state in the race, my leg would lose strength and begin the flopping feeling that we all dread. WTF? It was intermittent at first, but became almost daily, even during easy runs. I would take time off, and it would get a little better, but never 100%.
Fast forward 9 years. I basically have quit running, save for 15-20 miles a week. I'm a jogger, but I still want to run. In the past few years, I have tried many supplements to see if they could help, but nothing really did. One of the supplements, CLA (conjugated linoleic acid) really made this condition WAY worse. (google CLA, it is typically used for weight loss, but has a muscle preserving aspect about it as well). What does this tell me? That there is something more than just an impinged nerve that is causing the problem. I also noticed that other supplements would make it worse, such as caffeine.
But, even if I stayed away from those, still a problem. Sometimes. It came and went, but seemed to come when I wanted it the least.
I have read this entire thread, and another one similar. I've tried some of the exercises, ran around the track backwards, etc. Better, but not healed. I have a background in biomedical engineering, with a focus on orthopedic products. I know that if a nerve is impinged, you will have many other sensations than just loss in strength.
So, I asked myself, why would a muscle just quit? I researched some reasons, but this area really is not well studied. For some reason, I got into the acid/base relationship in the body. I personally believed this was some pseudo science, but I like to make that decision after reading about it. Sounded a little hokey, but could make some sense. I also read about a study using a buffering agent that was successful in building bone in women over a six month period. (not calcium). It is potassium citrate. They hypothesized that it was creating a more basic blood chemistry, thus not breaking down bone as much.
So, I went to the local GNC to find it. Nothing. Went online. Found a few that carried it. It turns out, potassium citrate is also being used to treat kidney stones, among a couple of other diseases that are known caused by an acid environment. I bought some online here:
http://www.vitaminshoppe.com/store/en/browse/sku_detail.jsp?id=VS-1081
No, I don't work for them, it is a cheap ($11) vitamin. I tried taking one or two capsules a day. Not much change. Then, on a whim, I took 4 before a run. My run was awesome. My leg was fine the whole time, and seemed to get better as I went. It could have been just a fluke, as that happens some time. It's been two weeks, and I can't be happier. Back to normal, as far as I can tell. The 20 pounds I have added don't help, but I feel strong.
So, am I saying this is the cure? No, maybe not. But, maybe it is. I've been thinking that the reason the muscle may quit is that it became so overworked, that the biochemistry inside the localized muscle tissue may have caused it to fail. Kind of like a safety response. Or a glitch, whatever you call it. But, change the biochemistry, and back to normal. I remember one of the doctors I had study me (nerve specialist) said that I may have just overworked the muscle, and it might be damaged. Well, I think it might be damaged in a temporary way.
Do your research and give it a try. Check the internet, peer reviewed journals, etc. It might only cost you $10.
I'll report back with more findings as they come