4. Take to the hills. Hike an uphill trail or climb stairs to add intensity and work muscles in a different way. Do the Side Squat up and down a hill, for example.

5. Play with plyometrics. String 1 minute each of the following moves together for a 6-minute calorie blaster, or add these to your regular cardio workout:

Jumping Jacks The gym-class classic: Stand with feet together, then jump, separating legs. Land with feet hip-width apart as you raise arms overhead. Jump feet back together and lower arms; repeat.
Jumping Rope Do a basic boxer's shuffle or two-footed jump. Stay on balls of feet, jumping close to the floor, keeping elbows by your sides.
Squat Jumps With feet hip-width apart, bend your knees, lowering hips to squat; jump into the air by pushing off and straightening your legs, lifting arms upward. Land softly and repeat.
Split Jumps Stand in split stance -- one foot ahead of you, one foot behind. Bend both knees and jump, switching legs to land; pump arms in opposition to legs as you continue to alternate legs with each jump.
High Jog in Place Lifting knees high up in front of you as you jog in place, swing arms naturally in opposition. Land softly, ball of foot to heel.
Side-to-Side Leaps Place any object, such as a broom, on the floor. Leading with the leg that's closest to the object, leap sideways over it, bringing both feet together to land, then repeat in the opposite direction.