More to explore:
Halloween Hill Cardio Workout
Do this workout 3-4 days a week for quick transformation.
HIIT the Hill Workout. A killer treadmill workout to increase fitness, endurance, and also challenge different leg muscles (they'll be POPPIN' in your summer shorts) ;)
May Strength Circuit and HIIT Cardio
The Real Secret to Melting Fat | Your Science Based Workout
Cardio and Strength Workout "13" for 2013...click for printable version with exercise instructions
Hot Mess HIIT Workout
Multiple workouts - Treadmill, elliptical and strength - to shake up your routine
No Equipment Needed Cardio Circuit - this one would be great while traveling, could do in hotel room
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Frost HIIT workout. Bodyweight only. Torch calories in only 20 minutes!
Musical Cardio Workout for bike or running
Five-mile treadmill hill workout