When i try to engage my l quad muscle, wont engage. been problem for a while. r weakly engages. hamstrings do engage though. why is this?

Engage ?: Do you mean contract the quads ? This is an unusual complaint... If your quads is not contracting normally because of a recent injury or no injury see your physician for evaluation . If it is not" engaging" because you haven't worked your quads in a while start doing some straight leg raises, ex. Bike or leg press to get it' going'. Good luck!