No power in right leg while doing leg extensions

[MBeach]

I am 42 yrs old. Several yrs ago (~7) I hurt my knee playing wiffle ball. My foot and body went in one direction and my knee bent inwards toward the other knee and it hurt like crazy. Since I was through playing competitive sports I just hobbled around until it got 'better.' Now I have started a work out routine at the Y and when they were doing my assesment and I came to the leg extensions I could only do 30lbs twice with my right leg and my knee was in excruciating pain. I did 100 lbs 10 times with my left leg. It really doesn't bother me in my everyday life but I tried doing a lunge on that side last night and almost couldn't raise back up when using my right knee. What does that sound like?

[Heidi]

Where is the pain in your knee? From what you have said about the injury and how it happened, I suspect there was some damage to a medial structure, such as the MCL or medial meniscus.
http://www.sportsinjuryclinic.net/cybertherapist/front/knee/medialligament.htm
http://www.sportsinjuryclinic.net/cybertherapist/front/knee/medialmeniscus.htm

It is surprising that you haven't had any problems day-to-day and then all of 2 light leg presses causes so much pain. If it was a case of doing a full set and then it hurt or it hurt later then I would suspect that you just need to strengthen the muscles surrounding the knee.
I think I would get it checked out by a professioanl to try to establish what the initial injury was and what is causing the current pain!