leg gives way when sprinting. hamstring?

[dxVxb]

hi,
I have been in the weight room for the past year and have really not gotten any sports in, so decided it was time to start playing again. But iv noticed that when i started sprinting the other day (on real ground and not a treadmill which i have been using for way to long) that every now and then my leg will just give way, and I just lose control of that leg for a second or two. its not enough to make me fall or anything, but its very curious and strange. iv been playing sports all my life, since i was a kid and iv never had issues like this before. im wondering if something like this has happened to anyone else before? iv also had reoccuring knee aches (and elbow aches) for the past 2-3 years for no reason, and stretching or working out or resting really has no affect on the pain/ache. i heard once that sometimes if your hamstrings are much weaker than your quads it could lead to a "muscle imbalance" and may be the reason. I have really weak hamstring compared to quads (which is a mystrey as to why since i work them both out regularly. the imbalance is such that my quads are almost 4X stronger than hams. ). but this stumbling/loss of leg control is reallllyyy annoying. any help or advice? thanks and sorry for the long question.