Do leg extensions kill anyone elses thighs? There's few lower body weight machines at the gym I go to, and I've only found two that are low impact on my knees (which is required for me), but man the leg extension machine makes my thighs buuurrrrnnnn. I've only been doing a 30 lbs weights, 4 sets of 12 reps. I keep telling myself the burn is a good thing, but I feel so silly compared to the built guys that use the machine doing 100lbs+ with ease. The only issue is, with all other machines I've been working so far for upper and middle body I'm starting to notice that I have to do higher weights to get the same workout, but not my legs... I really need a good leg strength workout.

Welcome to the bad knees club! Even though it doesn't involve impact, the leg extension machine can be really hard on bad knees because of all the shearing force. It puts a lot of stress on your knees and some physical therapists and doctors advise tell those of us with bad knees to avoid it.

You might want to check out this thread for some ideas for exercising with bad knees : My KNEES! I feel so old....