Split squats are a great exercise to build your legs without over stressing your low back. If you do have low back tightness you can use a lower step or bench for your back leg. Check out my older post on Bulgarian split squats to learn the proper form. http://h4training.blogspot.com/2010/03/eom-bulgarian-split-squat.html
Split squats- 5 sets of reps at 12, 10, 8, 6, 4
** Rest 90 seconds between sets
** Each set you will increase the weight as you decrease the reps. Start with about 60% of your 1 rep max for 12 reps and each set after that I would add 5-10 lbs. So if your max is 200lbs you would use 120lbs for the 12 reps.
Split squat- 1 set at 15 reps
**After you have done all the work above you will burn out the legs with one set of high reps. Focus on speed and drive up as fast as possible. Use about 30% of your 1 rep max. So if your max was 200lbs use 60lbs here.