What's a Progression Run?

I did a nice progression run on the treadmill today. What's a progression run, you ask? Take a look at this heart rate graph:

Get the idea? Start slow and incrementally progress to faster and faster paces. The key is to finish faster than you started. No dramatic changes, just a smooth progression from walking to jogging to running. I stopped around my lactate threshold (HR=170-172). My breathing never became labored. Some progression runs finish with sprinting, but I wasn't up for that today. You can see after almost reaching my lactate threshold, I took a recovery walk, then went for about 1/2 mile back at that top threshold pace (for me, today, it was 9 mph). That isn't a characteristic of most progression runs, but it felt right today! These runs are great fitness boosters and they should leave you refreshed, rather than fatigued.

PS: The zone labels on the left of the graph are my Arthur Lydiard/Roy Benson effort-based zones derived from my resting heart rate and maximum heart rate. Just a way to see how much time I spend in each zone per run, per week, or per training cycle. The key to progression runs is the steady progression in pace and heart rate--the actual zone is not crucial. Although, in my mind, this is a progression run THROUGH THE ZONES.