I've had knee surgery in the past, and am missing patches of cartilidge in both. I'm able to perform squats without too much pain, but not the full distance of the exercise as described. I have a great deal of difficulty with lunges and split squats, even without weights. I plan on keeping the squats, but do I substitute step ups for both, which don't hurt me, or are there other options?
Also, when doing the break in and fat loss programs, should I add a protein suppliment drink after the workouts, or is this unecessary calories that I should skip?
I also have torn cartilage in my knees, and have to be careful when doing leg exercises. I’ve found that going to just above parallel for squats works the muscles adequately. Slow and steady with concentration on form is the key. Obviously, you know your body better than anyone else, so just listen to it when it's telling you something ain't right and you should be fine. If step-ups don’t give you pain, I personally would recommend trading them for lunges. You could also try “sitting” against a wall with knees bent at 90 degrees. Hold that for 30-60 seconds before going right into your step-ups, and your legs will be getting a good knee-friendly workout.
I also recommend icing the knees for 15 minutes after every workout involving squats, lunges, step-ups, etc. Personally, I put an ice pack on top of and behind the knee, as this does wonders for keeping tightness and pain at bay.
As for post-workout nutrition, you should definitely NOT skip it. I’d recommend (at minimum) a shake with 0.25g of protein per pound of IDEAL bodyweight (i.e. the bodyweight you are trying to achieve), and 0.25g of carbs per pound of ideal bodyweight. For me, this is 1 scoop protein powder, ¼ cup Quaker oats, and 4 tbsp of Ovaltine (Malt flavor)….stick it in a blender with 10 oz water and a little ice, puree on high, and then slam it right after your workout. Your body needs that nutrition right after lifting…if you need to cut calories, find somewhere else to do it in your diet.