Week 4 Day 4 - Legs – HIIT: Strengthen and sculpt your legs with this all-out cardio meltdown designed to burn massive amounts of calories and increase muscle definition in around 30 minutes—no weights required. LIIFT4 combines heavy lifting and intense cardio to transform your body in 4 days a week. And with 32 unique, real-time workouts, you’ll never get bored, because you’ll never do the same one twice.