[Zulu451]

I would be that once your HR gets that high the accuracy of the instrument goes down. It is hard for medical EKG's to capture a HR that high.

I have and wear a Polar F6 as well. At my gym my wife and I did VO2 max testing and it was quite interesting. For about 5 years I have been running about 15-20 miles a week at a level pace 160-170 BPM. The science shows that at this range you are mostly burning carbohydrates. I found that after running at this pace for so long, my HR goes up that high b/c I have conditioned the motor to run at that speed, almost regardless of how hard I am running.

I put myself on a interval running / eliptical machine plan:
Day 1: 129-139 x 4 139-154 x2 for 50 minutes
Day 2: 129-139 x4 139-154 x4 154-170 x2
Day 3 154-170
Day 4 139-154 x4 154-170 x4

I was pretty skeptical and it was torture to reign in the workout. After doing this for a couple of months, I have seen a difference in that it takes me much longer to reach the 160's than before. The whole premise is that at the lower HR levels you burn a greater percentage of fat, and this is analyzed by the CO2 emission levels when you exhale. CO2 is a by product of aerobic metabolism. Some may argue that fat or carbohydrate metabolism just doesn't matter, your body has a total pool of energy reserves from which it draws.

As I considered this what made sense to me is that constant stimulation of carbohydrate receptors in the myocardium (heart) and in muscles increases the total number of receptors and therefore I condition my heart to work more efficiently at higher HR's. What I want to do is increase the lipid metabolism of the heart and muscles, so training at levels where the body can use fat, lower HR's (it makes sense, but trust me you don't want to read about it).

And, the most important reason why I use a HR monitor is that it give the ADHD part of my brain something to do when I am running.