Polar Running Index

Yippe, a non-back dated post!

I'm going to get a bit technical now.  I run with the Polar RC3 GPS running watch.  When I finish my run and hit stop, it reports something called a Running Index.  This is supposed to estimate your level of fitness based on the pace and HR during the course of the run.  Over time, the number gradually increases as you get fitter, so I thought it would be interested to see how well it is able to judge running performance based on my training.  

For some basic info and a cheesy youtube video, you can find more about the Index at Polar's site.

Basically the Running Index is supposed to be able to predict your level of fitness and race times. From what I'm able to gather, it takes your max HR that you enter and uses your HR data and pace data from a run, figures out where on the sliding scale of your HR that you are at and then tries to extrapolate what pace you would be able to run at a percentage of your HR max that is indicative of various race distances.  Sounds good in theory.  The polar website I linked to has a table of estimated race times for a given Index.

So what Running Index am I at? Well that's hard to say.  See, the HR issue I occasional have really screws up the Running Index calculation since my regular maximum heart rate is probably around 187 I'm guessing which is what my watch uses to calculate the number.  The problem is when my HR spikes it sometimes gets to that number even when I'm running relatively slow and sometimes goes even higher than that.  For an example, the marathon I ran where I encountered the HR spiking issue for almost half the race, calculated an index of  46 which according to the above table means I should have run the marathon in 4:24, but the run that was used to calculate that number was actually a marathon itself that I did in 3:25. So runs with the HR spiking can't be used.

Also, relatively short runs also don't estimate the Running Index accurately. For example, the 5k race I did back in September where I ran 3.18 miles in 20:46 gave me an Index of 54 (even though my HR didn't spike) which means I should have run the distance in 23:20, again not correct.  This I can kinda forgive though.  From what I understand, the watch doesn't start analyzing your data until the 12 minute mark of the run. I guess it's to allow a warm up so the watch only had about 8-9 minutes of data to work with. It doesn't know that I already ran 12 minutes at a faster pace so it assumes that since I'm at or near my max and that I only ran at that pace for 8-9 minutes that I couldn't sustain that for another 10 so it underestimates my performance.

On the other hand, slow recovery runs tend to overestimate the Index. The highest index I saw this training cycle was 66 which was obtained on a 5.1 mile recovery run two days before the marathon where I averaged 8:52 min/mile pace.  On a longer run back in September, I was able to get a 65 on an 11 mile run where I averaged 9:00 min/mile. These predict a 3:05 marathon. Yeah, not happening.

So the best combination is to find a moderately long run at a slightly fastish pace and see what Index was calculated from that.  Marathon pace long runs would have been perfect for that, but all of my marathon pace runs suffered from HR spiking issues (foreshadowing of race day, I suppose) and so the Index predicted from those is fairly low. The best run I could find that fit the bill was an LT run that was done as part of a 14 miler. This was done back on August 20th where I averaged 7:57 min/mile pace for the whole run with 7 miles done at 7 min/mile pace. This resulted in an index of 60 which predicted a marathon time of 3:20.  Now considering that this was done two months before race day, it's probably about right as I felt I could have done at least 3:20 if not for the HR issues on race day and of course I was aiming for 3:15 which I think was doable.

My runs lately have me at a running index of  55 which is probably due to the fact that I donated blood a few weeks ago, have put on a few pounds and am doing low mileage.  I think I'm going to try tracking this a bit more closely going forward.  At least I'll now have a point of reference for future training.