I don't think it's bad for the knees; in fact, after I had knee reconstruction surgery, several of my physical therapy exercises involved lunges. But it can definitely be hard on the knee. A good rule of thumb in general is that if it's painful, don't do it. Make sure to keep the knee in a direct line above the toes while going down into your lunge.

Try not to let your knee extend out over your toes or veer off to either side. If it keeps wanting to extend beyond your toes, then take a bigger step, so your feet are further apart, before going into the lunge.

you can also try doing lunges in those ballet / dance practice rooms with mirrors along one wall and waist-high bars along the other ... lightly rest your hand on the bar while looking in the mirror to gauge how far down you're going ... if you lose control, the bar helps keep you from falling to the side / falling down ... even just resting your hand on a bar helps with your balance since the simple act of paying more attention to your balance makes you more careful / better balanced

be careful and have someone spot you if you need it ... at least they can make wisecracks about your posture ^_^

Yes, just be sure to use proper form. I used bad form this spring and i tweaked my knee and couldn't run or hike for months.

when doing lunges ,should your weight be on the front leg or the rear leg?

steamheather, the weight should be slightly more on the front leg, because that is the one you are training, but evenly divided. You want the back leg firm to stabilize.

In addition to making sure your front knee does not extend beyond your big toe, you should also make sure that your back knee NEVER TOUCHES THE FLOOR. You want to get as close to the floor as you can without touching it. This will ensure that your front leg gets the proper training and that your back knee remains uninjured.

You will definitely want to use mirrors to ensure proper form until you’re very comfortable with lunges.

¼ lunges are recommended if you have any knee problems. This is recommended because it puts less stress on the knee joint and you will still gain muscle if you are doing full lunges e.g. knee close to the ground. You can try using less weight or no weight at all for your lunges if you go through the full range of motion. Try what you are comfortable with is the main thing. If something is bothering you, switch it up or modify it like with what I suggested, the ¼ lunges