Using heart rate in training

HIS morning, I did a really easy training session. I started warming up with a slow run, using a heart rate monitor as guide (no higher than 130 bpm) at approximately 6 kph. Next I ran 5 K on forest trails, alternatively 5 minutes at 140 bpm and 5 minutes at 130 bpm. The end time was 38 minutes (7,89 kph, 7:36/K). That was a very easy training session.

Now, I wonder, could I turn this into a training method? I mean, running a certain distance, say 5 K, at alternating heart rates. Obviously, 130 bpm is much too low, and 150 / 160 bpm would be more challenging, but still very possible for me. I guess I would be needing around 30 minutes for those 5 K. However, what if I could do it in less time, with the same heart rates, simply by doing it lots of times (on different days, of course)? Wouldn't that mean my fitness is improved, or, at least, that I could run faster at the same heart rate?

Interesting....