Another variation for hill intervals on a treadmill is to increase the incline with each interval. The workout would go as follows:
- warm up for 10-15 minutes at an easy pace
- increase treadmill pace to somewhere around 30 seconds to a minute slower than your 10K pace and run for 2 minutes at 1% incline
- increase incline to 2% and run for 2 minutes, then decrease back to 1% for 2 minutes
- increase incline to 3% and run for 2 minutes, then decrease back to 1% for 2 minutes
Keep repeating this pattern of 2 minutes at an increased incline and then 2 minutes at 1%. By your last interval, you should feel like you are exercising at 95-100% effort. You can then finish up with 10-15 minutes at an easy pace.
When I do this, I usually do 6 intervals, starting at 2% grade and gradually increasing to 7% grade. It's quite a workout, and the constant change in incline adds some variety.