The first key to remember is that you cannot do cardio the day before you train the legs with weights. Your leg muscles and glycogen stores need to be replenished. You can’t expect a good performance on the squat rack if you went all-out just 12-24 hours earlier. Give then a rest before pushing them to the limit.
Second, you must ramp down the cardio intensity and angles in those two days following leg day. After all, DOMS, or delayed onset muscle soreness, is at its worst in the 48 hours following a workout. So after you destroy your legs on leg day, the two following days will be slow, relaxed cardio, which gives the lungs a workout, yet works around the well-worn legs.
Finally, you should take advantage of the numbness you are feeling at the conclusion of your leg weight training session, and complete a very intense cardio session directly after completing your leg routine. Same day, same session. Climb off of the calf machine and get on the stair stepper. Your legs will already be torched, so you won’t feel much of the pain. You might as well get the most possible gains out of the day’s workout by torching them at this moment.
Day 1 – Rest (no cardio)
Day 2 – Full leg workout (quadriceps, hamstrings, and calves) followed by 30 minutes interval cardio on the stepper machine.
Day 3 – Full Chest/Triceps workout, followed by 30 minutes walking on treadmill
Day 4 – Full Back/Biceps workout, followed by 30 minutes elliptical machine at low intensity
Day 5 – 30 minutes medium- to high-intensity cardio
Day 6 – Full shoulder workout, followed by 30 minutes very intense cardio
Day 7 – Rest day (no cardio)
Source: www.BodybuildingToday.com