As you know, using your heart rate to monitor your effort levels is a great tool. However, using your HR is only effective if your numbers are accurately determined. The traditional online calculators are often far enough off that you would be training outside your optimal effort level… so much so that you might be better off sitting on the couch!
Have you been making these mistakes?
Here's what's going on...
For example: If I use the popular 220 minus age to determine a maximum heart rate for a 40 year old, it would give her 180 beats per minute. So her 75% aerobic threshold would be 135, meaning she should try to stay below that number on easy runs. This is reasonable for most people. But, since about 20% of all people are “outliers” with a heart rate significantly higher or lower than the average person, her 75% threshold may be way off. Suppose her “true” maximum heart rate was just 10 beats slower than her calculated number, say 170 instead of 180. This now makes her 75% aerobic threshold only 127 (7 bpm less!). Why is this important?
Training even just a few beats-per-minute above your 75% aerobic threshold will cause your body to make a dramatic shift into the ANaerobic zone. That’s when your body begins to rapidly increase demand for glycogen for fuel. Since the body can only sustain a run above this zone for about 2 hours, anything longer will force a runner to dramatically slow down, also known as “hitting the wall”.
How can she fix it?
If she trains below the 75% aerobic threshold most of the time, she will be conditioning her body to rely almost exclusively on fat-stores for energy… her body adapts. As she continues to train in this zone over a few weeks or months, it will get easier and easier. She will actually be able to run faster at the same effort level and still remain under her 75% aerobic threshold. So yes, her overall speed will improve as a result, even at faster ANaerobic running speeds.
As an example: If you’re running at say a 13:00 pace to stay below 135 bpm for 3-4 weeks, you’ll discover it gets easier and easier because you’ll be building your cardiovascular engine. You’ll also be conditioning your body (adapting) to burn 99% fat for fuel. By the end of 3-4 weeks, you’ll be running at a quicker 12:00 pace at that same effort (135 bpm). In another 3-4 weeks you’ll be running at 11:00 pace at that same effort (135 bpm). This is an exaggeration of course, but you get the idea.
Now here’s the bonus! By running truly below her aerobic threshold (<135 bpm in this example), it’s a genuine easy day so she can be fully recovered the next day. That makes the quality of her next run (hard day) much better so she can stay in her target zone easier and finish the run well! She can crush her paces for full benefit.
Again, the trouble with running even a little bit too fast is you end up conditioning your body's fueling system (adapting) to rely more on glycogen AND you begin to accumulate effects of fatigue (musculoskeletal microtears). You simply don’t get the recovery you need to build strength and stamina. Most runners complain that they “hit a plateau” and gain weight.
Improving fitness is a delicate balance between breaking the body down and rebuilding. About 83% of all runners fail to follow this principal resulting in too much accumulated fatigue…and injury. So how can YOU get it right?
First of all, you must accurately determine your 75% aerobic threshold by finding your TRUE maximum heart rate AND resting heart rate. Remember, using the traditional calculation is not reliable enough for any serious runner, so you must first find your maximum heart rate another way. As you might have guessed, that will require you to perform an all-out maximum effort - high intensity run to achieve your true maximum heart rate. A physicians “treadmill stress test” might get you there but since they are often overly cautious, they may stop the test short of your true maximum. After all, they’re usually working with cardiac patients. Another option is to find a lab that performs what’s known as a treadmill ramp test, or “V02 Max Test”, usually costing about $150. Or, if you wore a heart-rate-monitor on a recent 5K race where you sprinted the last half mile to the finish, that would certainly do it. Finally, the best way, and the least expensive (free) is to deliberately run a test on yourself at the track.
To perform a maximum heart rate test all you need to do is a 20 minute warm-up followed by a high intensity run. But wait, the run part has to be incrementally harder and harder, and the toughest part is that you must hold that last, and most painful super high intensity effort for another 60 seconds. Now THAT will be your true maximum heart rate.
Try this: Put on a heart-rate-monitor and run an easy 20 minute warm-up, then start the test: Run one lap around the track at about 80% effort followed by a 60 second jogging rest. Run a second lap at 90% effort followed by a 30 second jogging rest. Finally, run one last lap at 100% effort but instead of stopping, continue for another 60 seconds at your all-out maximum effort. Now walk off the track and puke, you’re done. You now have your maximum heart rate number.
Get a professional assessment to be sure!
Finding your resting heart rate is a lot easier. Simply set a special alarm to wake you gently a few minutes before you actually need to get up. Your heart rate may spike in the first minute so I suggest sitting up for a few minutes while quietly and motionlessly checking for your lowest heart rate. Since your resting HR can be a few beats faster than normal due to stress, lack of sleep, illness or fatigue, it’s important to do this for several days in a row to find your lowest number.
Now that you have your TRUE maximum HR and your true resting rate, you can accurately determine your 75% aerobic threshold using what’s called the Karvonen Method. Here’s how to do the calculation. Simply subtract your resting HR from your max HR, then multiply by .75, then add back the resting HR to get your 75%.
Enter Max HR ____________________
Subtract Resting HR - ____________________
TOTAL = ____________________
Multiply x .75 X ____________________
TOTAL = ____________________
Add back Resting HR+ ____________________
Your 75% AThreshold= ____________________
This is your new 75% aerobic threshold that you should stay below on about 3/4 of all your miles. Remember, going even a little bit above this number will condition your body to rely more on glycogen and less on fat-stores for fuel. Staying below this number will also allow for more complete recovery between your speed work days. Yes, it’s okay to go above that number on fast days, you just don’t want to do it all the time…which is what most runners do, even if it’s just a little bit.
But wait! There's more!
A final word about your 75% aerobic threshold. That number is somewhat arbitrary too. Ask yourself, "Is my exact aerobic threshold really at 75%, or is mine actually 69%, 72%, 76%, or even 79%?" Now that you have your calculations and you can hold a pace based on an accurate heart rate, you’ll want to “fine-tune” your effort level by confirming your threshold. To do this, simply check yourself occasionally using your sense of feel. The best self-test is the “conversational pace” where you decide honestly if you can easily carry on a conversation (without chopping up sentences). That moment where it gets harder to finish sentences is your breaking point. You’ll soon discover that you can sense your body shifting over the aerobic threshold and into the anaerobic zone… and you’ll know what heart rate that happens at regardless of what percentage it is.
Well, that’s it. There are other variables that I didn’t cover here but I’ll save those for another time.
Good luck and enjoy!