I have to switch up my cardio routine or else I get extremely unmotivated to do it. I love to switch up inclines and speeds, sprint to walking lunges; it not only benefits you more but makes the time fly by! These Hight Intensity Interval Training workouts raise your fat burning potential because of the increase and decrease of work and cardio output, your body has to perform.
One routine I do on the treadmill is grabbing a mini band and putting it right above the knees, you can do below but I have really long femurs so it works for me:
1 Minute Right Side Squatting
1 Minute Left
1 Minute Walking Kickbacks
2-5 Minute Jump Rope or 1 Min Burpees, Jump Squats (Something explosive off the treadmill)
4 Minute Incline Walk
You should repeat 3 times to get a significant cardio workout but 2 times for beginners is really a job well done also!
Also, if you're not a fan of cardio machines, you can get an amazing workout doing plyometrics, (explosive movements).
Try to stretch for at least 5 minutes before hand and warm up... something like a 3-5 min jog in place. Try 20 seconds of each resting 10 seconds between each.
Repeat 3-5 times