September 10, 2005

On Being a Statistical Outlier

Before she went off-line Sua Sponte posted about her heart rate jumping into the 170's during her workout, and how this was evidence that she was posing as a Californian, never truly one of us.

This prompted me, a fifth-generation Californian, to finally post about yet another wonderful thing I've learned from my heart rate monitor (great birthday present E! Thanks!). Sua, you too can belong here in the sunny land of awesome produce. Your skyrocketing heart rate doesn't even have the right to exclude you.


The standard logic about heart rate training zones is all derived from statistical means for groupings by age, sex, resting heart rate, weight, BMI, etc. The experts fight about the importance of many things, but, most of them agree on one thing: what really counts is that you train at the proper percentage of YOUR max heart rate. So, if your heart rate jumps to 170 during workouts that you perceive to be of medium intensity and you are otherwise healthy, then your max heart rate is probably just an outlier on the high side.

The best measure of your max heart rate is to actually max it out. That is, take a stress test in a lab, or buy a heart rate monitor and wear it whenever you exercise (eventually, you'll notice where you typically max out and some day, you'll do something stupid like go too far uphill in the heat or something and see a number that is probably right around your max).

After exercising with my HRM for the last couple of months, it looks like my max is around 200-205. What this means is that I regularly hit the low 170's (85% of my max) during most workouts, but it's nothing to be alarmed about. Before I got the HRM, I ignored the predicted heart rate max calculations (which all take averages for my age, sex, etc. into account) because I couldn't get a good workout if I followed them. Depending on which formula I use, my heart should max out somewhere between 176-196. Given that I hit 199 on my last 10.5 miler and easily lived to talk about it, this is clearly not the case.

Basically, if you are an oddball like me, you need to do all of your own personal calculations based on my measured (not predicted) HRmax.

But, say you don't want to go the HRM route, and don't want to get a professional max stress test, so you aren't going to have a "measured HRMax" regardless of how sloppy the measurement is. What then? Well, according to those in the know, the next best thing is to take one of the Sub Max Tests. I haven't taken either of them (perhaps I will in a follow up post), but I believe that if I were to walk a mile as fast as I could, my heart rate would level out somewhere around the mid 120's. This would put me at a calculated max of 185. So, anecdotally guessing (could this be any less scientific?), the mile walk test could provide a low prediction if you're a high-heart-rate outlier.

****Training Zones:
The general rules about targeting zones haven't changed in the last 30 years (50% warmup, 60% easy/fat burning, 70% aerobic fitness, 80% anaerobic fitness, 90% VO2max). But the old [(220-age) * Zone Percentage] formula isn't preferred anymore. Today, the Karvonen formula is the favorite. It multiplies the zone percentages against your Heart Rate Reserve (HRMax - HRResting) and then adds the percentage of your HRReserve to your resting heart rate to give you the target for the zone. So, if you have a high resting heart rate, you'll have higher Zone calculations under the modern formula, whereas in days past, your resting heart rate was not given a moment's thought.

For those of you still reading, you can try the Karvonen formula here.

Finally, if you'd like to read some reassuring writing about variance in max heart rates from someone who didn't just read a pile of running books and take a few exercise physiology courses in college, I recommend this article.

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