Here are a few of the interval workout that I do.  There are some people who can just run at one speed for 30 minutes and be completely content, but I get SO bored with that.  I enjoy switching it up, as well as really pushing myself when I do cardio and the interval bursts are great to raise your heart rate and break a good sweat. :)

This is one of my personal favorite runs to do.  The incline at the beginning and the end make the speed walking more intense and the speed in the middle really gets you going.

This is my go to run when I can’t think of anything else to do.  It’s such a good run and the minute intervals in the middle are much tougher than they seem in a chart.  This is a real sweaty run! :)