Tuesday, August 23, 2011

A Crash Course in Heart Rate Monitors...


So, I'm currently working on a post about tempo runs and how fascinating it was to do one the other day with the monitor. In fact, the first post about heart rate training last week originally started out as the tempo run post, but the more I wrote, the more I kept being like, "Okay, wait--back up. Wait a minute--back up again. Okay, back up some more." Finally I decided that the heart rate monitor stuff probably deserved its own post.

Before I finish up the tempo run post, though, I thought it might be useful to go into how an average, non-elite runner (ie, moi, and potentially vous) can use a heart rate monitor to get the most out of it with a minimal amount of time and effort. I'm not an expert or anything, but this is what I've learned about heart rate and running, and how I've used my monitor in my own training.

First, in order for the numbers on your monitor to really mean much to you, you'll need to get a reasonably good idea of what your maximum heart rate (MHR) is. Your MHR is the fastest that your heart is physically capable of beating. MHR is mostly genetically determined; while losing fitness can cause it to drop a little, you can't increase your MHR through training once you're in reasonably good shape, and higher MHRs are apparently not correlated with better fitness or performance (ie, take two equally fit athletes of comparable ability; one may have a MHR of 170 and one may have an MHR of 230).

There are lots of formulas you can use to estimate your MHR based on your age, but they are notoriously unreliable. For example, the most familiar formula is probably 220 − age; at age 30, this would predict an MHR of 190 for me, when in fact mine is actually more like 225. People have come up with any number of more complex formulas over the years that are supposedly more accurate, but because MHR varies so dramatically from person to person, none of them are really all that reliable. From what I've read, the least objectionable one thus far is MHR = 205.8 − (0.685 × age), but again, that would predict an MHR of ~185 for me, which is an even worse estimate than 220 − age.

If you have your MHR tested in a lab, a doctor or technician will hook you up to a heart rate monitor or EKG machine and have you run on a treadmill progressively faster and faster, causing your heart rate to increase. At a certain point (essentially an all-out sprint), no matter how hard you run, your heart rate won't increase (and will probably start to decrease pretty rapidly, because you won't be able to sustain that peak effort for very long). That's your MHR.

The trouble with lab tests is that they cost money, and are deeply unpleasant, and many technicians report that they aren't even able to find MHR for a lot of people because they're just not mentally capable of pushing their bodies and handling the pain and discomfort long enough to reach peak effort. (Less relevant for runners who are in good shape, but sometimes a physician won't even do an MHR test for a person if they are out of shape or have heart issues because an all-out physical effort could be dangerous.)

If you have a heart rate monitor and do any kind of speed work or hard racing, though, you can approximate your MHR on your own reasonable well. One way to do it is to head out to a track wearing your monitor, warm up with a mile or two of jogging, then run a lap at a harder effort, then push yourself through one more lap at close to an all-out effort and do your best to sprint the last 50 or 100 yards as hard you can. You'll probably finish gasping for breath and kind of wobbly-legged, but if you're able to push yourself to that point, the highest number recorded by your monitor will probably be pretty close to your MHR. All but the most bare-bones monitors should have a way for you to see the highest number recorded (see the summary screen from my 305 above), and most fancy-schmancy ones, like Garmins, record your heart rate along with pace and elevation data and come with computer software that will let you see exactly what your heart was doing over the course of your workout, like so:

(Click to embiggen)

(This is a screen shot from the Training Center application that comes with most Garmins, which will store maps, time, distance, pace, elevation, and heart rate data for all of your runs.)

Another way to estimate your MHR is to wear your monitor the next time you run a hard race, particularly if you're able to sprint towards the end, and look for the highest number. For the most accurate results, you'll probably want to give it several tries over a few weeks. Eventually, you should get a pretty good idea of about where your MHR lies.

(If you have a Garmin, it's also somewhat possible to reverse-engineer your MHR. In order to get accurate calorie burning information, you need to calibrate it by entering your weight, age, and MHR. When I first got mine, I didn't have the first clue what my MHR was, so I just used 220 − age and entered 192. The first clue I had that this might not be accurate was my Garmin telling me that I'd burned something like 1300 calories on a 5 mile run. After wearing it for a while during speed work and races and occasionally seeing numbers in the low 220s, I changed the number in my Garmin to something more in line with that, after which it gave me much more reasonable calorie readings. So that's one way to tell how close or far off you are.)

Once you have a pretty good idea of what your MHR is, you can use your monitor to help you stick to the right intensity levels during different types of runs. Different experts seem to give slightly different numbers, but for the most part they seems to stay in the same range. Here are the guidelines that Jack Daniels gives in Daniels' Running Formula:

  • Easy runs -- 65-80% MHR
  • Marathon pace runs -- 80-90% MHR
  • Tempo runs -- ~90% MHR
  • Speed work -- 98-100% MHR

This is definitely what I've found to be most useful about running with a monitor.

Be prepared for your heart rate to fluctuate somewhat, both during your runs as well as from day to day, week to week, etc. I think this is why Daniels gives such a wide range for easy runs. So many things can affect our heart rates in subtle ways (sleep, nutrition, hydration, medication, stress, weather, etc.) that on one day you might find that an easy effort gives you numbers in the 65-70% range, and another day the same level of effort gives you numbers closer to 80%. I also find that my monitor can be unreliable for the first mile or so, for whatever reason, but it settles down pretty quickly after that.

Another fun thing to measure with your monitor is your resting heart rate (RHR). Unlike MHR, RHR is something that can change as you get fitter -- as you become more fit, your RHR will drop due to your cardiac muscle becoming stronger and able to move a greater volume of blood with one beat. The best way to accurately measure your resting heart is to keep your monitor on your nightstand and check it first thing in the morning while you're still lying in bed, as still and relaxed as possible without losing consciousness. It's cool to do this maybe once every couple of weeks and note any changes (again, data nerd...). For average people, RHR is usually somewhere between 60 and 80 bpm, but for athletes in good shape, it may be lower. Less relevant for recreational runners (like me), but one symptom of over-training that elite athletes sometimes look for is an abnormally high RHR.

Knowing your RHR also lets you make sense of another term that pops up occasionally, heart rate reserve (HRR). HRR is the difference between your resting & max heart rates -- essentially, how far your heart rate has to go from complete rest to peak effort. Sometimes instead of describing an effort level as a percentage of MHR, you'll see it described as a percentage of HRR. Because heart rate reserve takes resting heart rate into account (which changes with fitness), this can sometimes be a more accurate description than something that just relies on MHR (which does not change as much with fitness). For example, if I wanted to calculate 75% of my heart rate reserve, I would calculate: (MHR − RHR) × .75 + RHR, or (225 − 55) × .75 + 55 = 182.5 bpm.

It's also interesting to watch how quickly your heart rate falls once you stop running. For an average person, heart rate will drop by about 20 bpm per minute; as you become fitter, you should see your heart rate fall faster and faster during those first minutes of rest.

So yeah -- that's more or less how I use my monitor, for anyone who is curious. :) Any day now, I'll finish up the tempo run post & get that up...Until then, anyone else have any hot heart rate monitor tips?

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