I'm no speed demon at all, but I have been working on improving my speed for triathlons and for my military PT test. Being in the Navy however, we have less room to run on ships, so our PT test is only 1.5 miles! John, I guess you are in the Army based on your PT run. My brother is a Cav Scout out of Fort Riley, currently in Iraq at COB Speicher.
Here is a graph of my HR from last week's track workout (intervals). The intervals workout was
4x600m (200m recovery @ int)
4x400m (200m recovery @ int)
3x300m (100m recovery @ int)
6800m total (4.25mi)
This week's workout was a bit different, but no less taxing. Yeah, I was working at the end.
1x 1600m; 4x400m then 1x 1600m. Last HR reading was 183 at the end of the last interval!
These workouts have made a big difference in my overall speed (measured in seconds unfortunately). Also, I have improved my ability to perform a "brick" workout, riding my bike for 32 miles then running a 5k. I busted out a PR on my brick 3 miler the other day, running it in 21:43! Intervals do help out a lot I think.