TOGWT said:
...On a different days do, squats, leg lifts and crunches and cardio on separate day.
Update on that bit of conventional wisdom (which *does* seem intuitively obvious at first blush):
Studies done at the Karolisnka Institute in Sweden (see the March '12 Medicine & Science in Sports & Science) and at McMaster U. in Canada (see 5 April issue of the Journal of Applied Physiology) both refuted the idea that doing both resistance and cardio on the same day can compromise results in either category.
So it turns out there's no need to separate "Leg Day" and cardio, and I've been doing both on the same day (HIIT cardio in the morning, resistance work for legs, and then abs, later in the day) for decades with great results. When I did try separating them, it did *NOT* improve upon my results in either category, which really surprised me since I work my legs awfully hard during my cardio session (which goes way anaerobic).
Regarding the crunches/etc., I find that my Cardio + Leg day is also the best time for *me* to do my ab work. Actually, I do abs (and usually my grip work too) most every day that I do cardio (but I do the cardio first). It seems that all the work I do before abs is the perfect "primer"/warmup for my abdominal exercises.
YMMV and all that, but I found it interesting that the study confirmed what I'd determined through trial-and-error, works best for me.