I started going to the gym about 3 months ago, and have been pleased with my progress. I'm a little more slim than I'd like, and am getting some nice muscles.

On the machine that uses the same muscles as used when you do squats, I was doing about 80 pounds with no trouble. I reasoned that, since I weighed 104, I should be able to use that amount, since that's about what my legs lift naturally. I upped it to 100 lbs, and did fine. After about 2 weeks, I went to 105 lbs. and the next day, I had a pain in my right knee. I skipped my next lower body workout, and the pain eased quite a bit. When I started back again, I lowered the weight to 90 lbs. The pain came back, just not as badly as before.

I really don't know whether to quit doing this exercise for a while, of if I should do it using a lower weight. Would it be better to rest the knee, or try to strengthen it? (Actually, the pain is slightly to the left of the knee cap - don't know if that's knee, ligament or tendon.)

First, go see a doctor or physical therapist so you can understand what is going on. Then, have them suggest the exercises and best course of action. Without a proper examination, any suggestions from this forum are just guesses and could cause more harm then good.

General rule of thumb though is if something hurts, stop doing whatever it was that made it hurt. You do not want to wreck your knees. Also, remember to ice your knees after a workout if they hurt.

Doctor first.

If he clears you for lifting get someone who knows the proper squat form (and i mean make sure they know what their talking about) to show you how to lift. Its one of the best and safest and easiest on knees when done right.

I've tweaked my knees on machines lots of times in my life but never while squating (even when maxing out).

Is this machine a Smith machine? If so, it could be contributing your knee pain, since it forces you into unnatural motions.

I was afraid the question of what the machine was called might come up. I won't be back at the gym until tomorrow. I go to Planet Fitness, and there is one where you're slightly reclining, with your feet on a platform in front of you, and you push yourself away from the platform - it's the same position I see when someone is lifting the heavy barbells in the Olympics, except they aren't squating when they do it. I think it's machine #1 - will have to check the name. I'm always very careful about form, and work slowly rather than any jerky movements.