Here’s a workout that I’ve tried a couple times. The first time, I couldn’t keep up with the 12 mph pace during the 2nd or 3rd set, so I turned it down to something more manageable, e.g., 8.0 mph.
Today I attempted it again. This time I set the treadmill to 9.0 during the working sets. I felt like it was bit easy to manage, so I raised the speed to 10 mph. It felt more strenuous when I attempted it that fast. Next time I’ll set it for 10 mph and report back.