Installment numero three-o in the common exercise fix series. To recap: 99% of the time it's not the exercise, it's the execution that's causing issues.
So, let's say you're doing a split squat, step back lunge, forward/walking lunge or some other lunging variation that I forgot to mention and, oh bugger, your knee hurts.
If you have pain in the front knee...
- Check your shin angle. If it's not perpendicular to the floor... then you probably are experiencing pain in the front of your knee.
Look at that shin!
- Check your variation. Some folks just can't do forward-moving lunges. Switch to a reverse lunge (above) or split squat variation, thus minimizing the sheer force on the knee (also, of course, maintaining that vertical shin).
- Still having problems? Check how you're applying force through your foot. (Sorry, that was an awkward sentence) Are you pushing through the ball of your foot to stand up or your heel? Pushing through your heel will put the stress of standing up on your glute (instead of the quad) and your glutes are a LOT better at producing hip extension than your quads. Matter of fact, think about pulling yourself upright through your heel as you stand up. (This applies to step-ups too.)
If you have pain in the back knee...
- Check your back leg's placement. Are you in line or is the back leg at a goofy angle? You want to stand about hip-width apart and make sure that your knee is going straight down (instead of in or out at an angle). How does one create such a delightfully descending back knee? Squeeze your butt. It should straighten out any wild knees.
- Check your variation. Maybe switch to a lunge exercise that doesn't require the back leg to work as hard, a Bulgarian split squat, might work as you're not supposed to use the back leg as much.
Note* this has an ISO hold at the beginning of the set.
- Still hurting the back knee? Perhaps try a different single leg exercise such as a bowler squat, a single leg squat progression or single leg RDL. Those will help train the posterior chain (which might be the source of your knee pain, weak glutes or hamstrings) as well as your hip stabilizers (adductors, glute medii, quadratus lumborum) as it might be an instability in your hips that are causing the knee pain.
If, after trying all these fixers, your knees still hurt, well, don't do lunges (you're in the percentage of folks that just need to stay away from them). There are plenty of other single-leg exercises out there that are just as awesome!