The field of medicine has certainly known about heart rate for centuries. Long ago it was commonly accepted that a human heart held only so many beats, and when you used them up, . . . oh, well! As recently as 60 years ago, it was believed that too much exercise led to an enlarged, weakened heart, which would eventually lead to, shall we say, a permanent early retirement. Doctors in Boston detected an enlarged heart in Clarence DeMar and warned him to stop running immediately. He eventually won Boston seven times, more than any runner in history.

Thanks to physiology and other disciplines, we now understand more about the heart and how it works. From its very inception, the sports medicine and exercise science fields have been studying the relationships between human performance, cardiac output, and how muscles react to exercise. In The Lore of Running, author Tim Noakes, M.D., cites research work from the British physiologists A. V. Hill and Hartley Lupton dating back as far as 1923. Scientists in human performance laboratories have known for years that the more efficiently the heart can supply blood (which contains vital oxygen and nutrient supplies), the better the athlete will perform. As we will discuss later, scientists know that runners rely on a series of fuel systems to provide the energy for continuous running. Many physiological events connected with burning those fuels can be predicted fairly accurately by observing the heart rate during exercise.

Armored with their heart rate monitors (HRM), runners can now take advantage of years of research and apply those principles to the healthy and self-fulfilling pursuit of personal records. A heart rate monitor, properly used, provides a link to exercise physiology and science in a way that no other tool can.

Training at scientifically determined heart rates is the simplest way to train smarter. Because heart rate-based training is highly individualized, the numbers you rely on have to be your numbers, not your training partner’s. The remainder of our discussion will help you determine your numbers and explain what they represent.

HOW’S YOUR ENGINE RUNNING?

Explaining the science behind the fuel systems of the body and the effect training has on them can be confusing, even for experienced coaches. Let’s look at the body in terms of an automobile’s engine and see if we can make it all a bit clearer.

Typically, an automobile is powered by a combustion engine fueled by gasoline and oxygen. When the oxygen comes into contact with gasoline, either by way of the carburetor or fuel injectors, and a spark is provided, the engine fires. The proper mix of fuel and oxygen is necessary for a car’s engine to operate efficiently.

If your car has a standard (stick shift) transmission, it’s likely that you have a tachometer. This gauge, more than any other on your dashboard, gives you a constant reading of how the engine is running. If there is any sign of trouble in the engine, the tachometer will be the first gauge to let you know. The tachometer readings may reflect significant changes in temperature, oil pressure, battery voltage, and fuel supply, all of which affect an engine’s efficiency.

A car’s tachometer does not measure velocity or speed. It reads how many revolutions per minute (RPMs) the drive shaft is spinning. Those RPMs are dependent upon all of the individual parts of the engine working together as efficiently as possible.

In each gear, there’s a limit to how many RPMs can be reached before they hit the “top end” and the engine “redlines,” at which point the engine reaches a range where it is working too fast and therefore loses efficiency. The various parts of the engine are no longer operating in a rhythm; in fact, they have begun to work against each other. If you keep driving with the tachometer in the redline, your engine will begin to damage itself and eventually self-destruct.

The tachometer is the gauge of the pros. In general, race cars do not have speedometers. While fans in the stands suck down another cold one and argue about how fast their hero is driving, a race car driver is more concerned with how he can get the most out of his engine at any given moment. Being able to accelerate when necessary is far more important to a driver than the relative speed at which he’s moving. With the help of their tachometers, the best drivers develop a keen sense of just when to shift gears to achieve the maximum torque and horsepower an engine can deliver and achieve the acceleration necessary to pass other cars. Knowing the velocity (speed) is a nice feature, but hardly relevant to the driver who wants to win.

Now let’s apply this basic engine and race car knowledge to the human body.

Factors Affecting the Human Tachometer

Your body relies as heavily on the oxygen/fuel ratio as your car does. Much like your car’s engine, your body uses oxygen and various fuels (carbohydrates, fats, and proteins) to yield muscle energy. When this ratio is not in balance in the body, a series of physiological events occur that can be gauged with your body’s tachometer—your heart rate (HR). And much like the automobile engine, the true efficiency of the body’s engine is dependent upon a multitude of parts working efficiently together. Your heart rate will indicate if there is any sign of trouble in your body’s engine. Here are a few of the factors that will directly affect your heart rate in much the same way that outside factors can affect your car’s engine:

• Body temperature: If you become too hot or too cold, your body senses a thermal stress load. Blood is sent to your skin to enhance heat dissipation to cool you or to increase blood flow to warm you. Apparent temperatures (which account for humidity or wind chill) above 70 degrees (F) and below 35 degrees (F) will increase your heart rate at least 2 to 4 beats per minute. Over 90 percent humidity can equal as much as a 10-beat increase in heart rate.
• Terrain: Run uphill, and your HR increases. Run downhill, and your HR decreases.
• Wind: Running with the wind at your back is easy, so your HR decreases. Running into the wind is more difficult, so your HR increases.
• Dehydration: As you become increasingly dehydrated during a run, your blood thickens and waste products build up in the bloodstream. Your heart will work harder to maintain constant cardiac output. A fluid loss of three percent of body weight increases pulse rate because of a decrease in circulating blood volume.
• Diminishing glycogen stores: Glycogen is your muscles’ primary fuel source. As the fuel depletes, your HR increases to maintain the same pace.
• Insufficient nutrition or sleep: Your HR increases.
• Insufficient recovery after a long run, race, or hard workout: Your HR increases.
• Recent illness, or, a signal of impending illness: You guessed it! Your HR increases.
• Medication: Depending upon the medication, one’s heart rate can either decrease or increase. Be certain to ask your physician about any medication you are taking and its effects on your exercise heart rate.
• Emotions and anxiety: These, too, can raise your heart rate! Unlike an automobile that is purely mechanical, we are not solely governed by working parts. Some days you can “feel” your way to a higher HR.

Just as your car’s tachometer does not measure velocity or speed, neither does your heart rate monitor. It will tell you how efficiently your heart is working, but it won’t tell you what pace you’re running. (Okay, there are some models that tell you both. For the sake of explanation, let’s concentrate on a model that does not have a built-in stopwatch feature.) In the human body, the car’s RPMs become beats per minute (BPMs). BPMs among various runners can differ about as widely as a new Ferrari differs from an old Pinto station wagon. (More later on estimating your individual BPMs.)

“Redlining” in your car can cost you a new engine. “Redlining” with your HRM can cost you your lunch. When you hit the “top end” of your BPMs, you’ve lost efficiency. Various parts of your body will feel heavy, and your running stride will no longer appear to have any rhythm. Push yourself too long, and you’ll be recovering for a few days afterwards.

You don’t have to be a pro to own a heart rate monitor, but you can drive your body like a pro with one. As you learn to read your personal tachometer more, you’ll rely less and less on your old stopwatch/speedometer. The increase in running pace you’ll experience will be a mere byproduct of the increase in your running efficiency. Instead of watching race cars, your friends will be sucking down a cold one and arguing about how fast you’re going while you glide along monitoring your personal tachometer. To further explain how a heart rate monitor can help you prepare for your next marathon, let’s look at a specific example.

CHRIS’S SATURDAY WORKOUT

Chris is a 44-year-old woman with a resting heart rate (RHR) of 50. She wants to run sub-3:30 for her next marathon. Her training has been going rather well, and she’s five weeks away from the big day. Her scheduled Saturday morning training run looks like this:

• Warm-up 15 minutes with an easy jog
• Run 8 miles at marathon goal pace (8:00 per mile)
• Cool down with 10 to 15 minutes of easy jogging afterwards

Chris chooses a simple out and back course, one of her favorites, because it rises uphill for the first half, and there’s usually a nice tailwind on the way back. She starts conservatively with an 8:05 first mile. Recording splits at miles 2, 3, and 4 of 16:05, 24:05, and 32:05 respectively, Chris is convinced she’s got the workout nailed as she hits the turnaround only 5 seconds behind pace.

She hits mile 5 in 40:10 and thinks, Oh, I must have fallen asleep. I gotta concentrate more. I still feel good. Confident that the downhill grade and breeze at her back will help her get those seconds back, she pushes the pace. At mile 6 Chris is incredulous when her watch reads 48:18. What’s wrong with me today? she mutters to herself. How could I have slowed down on that mile?

Chris decides she needs to focus on her form, her arm swing, and her leg turnover during the next mile. She tells herself to think positively and relax.

Fifty-five minutes into the run Chris finds it difficult to concentrate. Her legs are starting to get heavy, and she begins wishing the workout were over.

Chris completely misses the huge oak tree that marks her 7-mile split. Discouraged, Chris cuts back the pace, finishing the 8 miles in 65:20. Later, she records the run in her training log as a “miserable” 8:10-pace workout.

During her cooldown, Chris’s mind clouds over with doubts about her fitness, her marathon goal, and her very existence as a person. She mentally reviews the last few weeks of training: I followed everything I was supposed to do. I even backed off the last three days. I can’t believe the workout was that hard! I’m just a flake.

Could This Have Been You?

Now some analysis. Let’s assume that Chris was indeed rested and ready to run this particular workout. What happened? If we make the same mistake Chris made and look solely at her mile splits, we’ll make the conclusion that she started out fine, but slowed down. . . Oh, well, a bad day.

But there’s more to this workout than that. Why was it her favorite course? Recall the uphill out, downhill back, and the wind factor. It’s highly possible that while Chris’s splits appeared slower over the last four miles, she was working harder than she imagined just to recover from the first four miles. She was certainly working very hard to maintain an 8:00-pace up those hills, into the wind! Chart 1 below shows Chris’s splits and what could easily have been her heart rate “split” at each mile for this workout, based on what she was feeling during the second half. To make sense of Chris’s “HR splits,” let’s do a little heart rate math.

As we noted earlier, Chris is 44 years old with a morning RHR of 50. We can estimate Chris’s maximum heart rate (MaxHR) by using the formula that has gained wide acceptance among coaches working with adult athletes: 205 − 1/2 × (age) = MaxHR. (See “Modified Karvonen Formula” on page 51.)

CHART 1

Mile	Split	Course Description	Heart Rate
1	8:05	Very gradual uphill; breeze in face	157
2	8:00/16:05	Significant increase in grade; breeze in face	168
3	8:00/24:05	Slight increase in grade; breeze in face	170
4	8:00/32:05	Minimal increase in grade; breeze in face	170
5	8:05/40:10	Minimal decrease; breeze at back	170
6	8:08/48:18	Slight decrease in grade	163
7	8:22/56:40	Significant decrease in grade; wind at back	160
8	8:40/65:20	Slight decrease in grade	150

For Chris, 205 − 22 = 183, so her MaxHR is 183 beats per minute. From that number, we subtract Chris’s morning RHR of 50 to receive her heart rate range, which is the total number of beats available between complete rest and maximum heart rate: [183 − 50 = 133]. We can then take percentages of Chris’s heart rate range (133) and add back in her morning RHR (50) to determine what her BPMs should be at different percentages of effort.

Modified Karvonen Formula (More accurate for the “Chronically Fit”)
Example: 44 year old runner, morning resting HR of 50 BPM
		Start with 205
1.	Subtract 1/2 your age	−22
2.	Result = Approx MaxHR	183
3.	Subtract Resting HR	−50
4.	Result = Total number of beats in Heart Rate Range	133
HR Range × .65 + (Resting HR) =		136
HR Range × .70 + (Resting HR) =		143
HR Range × .75 + (Resting HR) =		150
HR Range × .80 + (Resting HR) =		156
HR Range × .85 + (Resting HR) =		163
HR Range × .90 + (Resting HR) =		170
HR Range × .95 + (Resting HR) =		176
HR Range × 1.00 + (Resting HR) =		183

For most aerobically-fit runners, marathon pace is going to be about 78 to 80 percent of maximum heart rate. For Chris, that would be 154 to 156 BPM. Look back at the heart rate “splits” for Chris’s workout in Chart 1 and compare them to Chris’s data in the Modified Karvonen Formula box above. For mile 1, even though Chris was sure she was backing off, her 8:05 pace put her over 80 percent of her MaxHR with seven more miles to go. And, she was going uphill into the wind! So on an effort-based scale, Chris’s first 5 miles, even though they were only 10 seconds slower than her goal pace, were actually run at 90 percent of MaxHR (170). That is a running intensity equivalent to a 10K race pace! Chris’s stopwatch lied to her! She hit the 5-mile mark convinced that she needed to pick up the pace and effort when, in fact, she was already working way too hard to achieve the goals of this particular workout.

Chris fell into the trap of trusting her speedometer (her stopwatch) when she should have been monitoring her tachometer (her BPMs). If Chris had been a race car driver, she would have redlined, probably blown a piston, and been out of the race.

Because of the terrain and the breeze, Chris probably could have run splits closer to 8:10 to 8:12 on the way out, not maxed her HR for the entire eight miles, and still run under 64:00 as she had planned. In fact, her splits could have looked something like this (see Chart 2):

CHART 2

Mile	Split	Course Description	Heart Rate
1	8:08	Very gradual uphill; breeze in face	155
2	8:10/16:18	Significant increase in grade; breeze in face	158
3	8:12/24:30	Slight increase in grade; breeze in face	155
4	8:07/32:37	Minimal increase in grade; breeze in face	154
5	7:53/40:30	Minimal decrease; breeze at back	156
6	7:50/48:20	Slight decrease in grade	155
7	7:46/56:06	Significant decrease in grade; wind at back	153
8	7:54/64:00	Slight decrease in grade	158

As the chart shows, Chris could have run her goal time and not recorded a single 8:00 split! Also notice that she would have topped 80 percent of max only twice, during the mile that climbed the most and at the end when she “pushed it home.” Even though Chris was 30 seconds “behind” at the halfway point, by keeping her HR under control, she could have been able to take advantage of the downhill and the breeze on the way back in.

Remember what happened to Chris at minute 55? Instead of falling into the depths of anaerobic debt—her legs unable to clear out the increasing levels of lactate—had Chris used an effort-based approach, she potentially could have run her fastest mile with the least amount of effort due to the significant downhill and breeze during that mile.

Chris’s experience is all too common. As a runner, and sadly, too, as a coach, from time to time I’ve fallen prey to the lure of the stopwatch—the spell of the speedometer. You look down and see those splits and ignore the signals your body’s tachometer is sending you. Anyone who runs for time secretly hopes that “this is the day I destroy my PR,” or “this is going to be the workout of my life,” when she has absolutely no basis for that hope. Too often, we are left shaking our heads, like Chris, wondering what happened at the 55:00 marks of our own races or workouts.

You could argue that scientific, effort-based training (EBT) takes away those magic, unexplained running moments when “everything clicked, but I don’t know why.” But wouldn’t you like to explain with some certainty at least some of those “miserable” workouts and “blown” marathons?

FINDING YOUR HEART RATE RANGE

Calibrating your heart rate monitor to work to your personal specifications involves determining your morning resting heart rate, your maximum heart rate, and some handy work with a calculator.

To determine your resting heart rate, do the following:

1. Before getting out of bed and before you give even a single thought to the pressures of the day, put on your heart rate monitor or find the pulse in the carotid artery in your neck.
2. Lie on your back quietly for 2 minutes.
3. If you’re using your HRM, look at the receiver and record your heart rate. If you’re counting your pulse, take a count for 15 seconds and multiply it by 4. This gives your beats per minute.
4. Repeat this procedure for five days in a row and average the readings.

MaxHR varies from individual to individual and decreases with age. For years, the standard formula for determining MaxHR has been to subtract one’s age from 220. However, science has determined that “chronically fit” individuals—the term bestowed upon creatures over the age of 30 who have remained fit most of their lives—do not lose an entire beat per year. For these individuals, the formula that we used for Chris earlier in the article works much better.

However, human beings don’t always fit into the same mold, and the standard charts don’t always hold true for everyone. It is no different here. Some people have physically larger hearts that beat slower than the results of the formula [205 − 1/2 × (age)], and others have physically smaller hearts that beat at faster rates.

The size of the heart matters little. They are both capable of being trained to the same levels. If it helps, think in terms of car engines: There are efficient three-cylinder engines, and there are efficient eight-cylinder engines. Both can move a car down the road at the same speed and RPMs, but the smaller engine works at a higher rate.

To get an accurate reading of your MaxHR, you have to do something that will take you to it. Being tested in a lab by an exercise scientist or physiologist should yield the most accurate numbers for you. Unfortunately, not everyone has access to a human performance lab and an exercise scientist-buddy. Contrary to popular belief, it is possible to determine your MaxHR without puking

on your shoes. Of the many, many whiz-bang formulas out there, I offer two options that seem saner than most. The first comes via John L. Parker, author of Heart Rate Training for the Compleat Idiot.

Finding Your Actual Max

1. Find a fairly steep hill 200 to 300 yards long.
2. Do the warm up you’d do before an interval workout or a race, with a few very easy miles, followed by light stretching and some striders to get your muscles loose and your heart rate up.
3. Do a series of five repeats up the hill, gradually increasing intensity on each one, using only the jog down for recovery. Check your monitor, and take note of your HR at the top of each repeat.
4. On the last repeat, increase intensity until you’re sprinting at least the last 100 yards at maximum speed.
5. Check your heart rate monitor as soon as you’ve finished and keep watching it for about 10 seconds. Often, your HR goes up several beats after you’ve finished an interval. Note the highest number you reach at any point during this workout.

You’ll probably reach your MaxHR on the last repeat, but it might come on an earlier one. At any rate, the highest number you see will probably be as close to your MaxHR as you’ll be able to get.

The second, an indoor option, comes from the esteemed exercise physiologist Owen Anderson, PhD. His method most closely resembles an actual lab protocol and is highly effective as long as you are used to treadmill running at a stressful level.

Figuring Out Your MaxHR Indoors

1. Warm up with a 10-minute easy jog on the treadmill.
2. Then start running at your marathon pace at a 0-percent incline. Every 45 seconds, add 2 percent elevation, keeping the same pace. Check your HR after each 45-second interval.
3. Continue until you can no longer maintain your effort.

Your MaxHR is the last number you’ll see on your heart rate monitor just before you decide to pack it in.

Now What Do You Do?

To determine what your numbers are for each of the percentages, plug your MaxHR and morning RHR into the appropriate spaces in the modified Karvonen Formula box below. Then grab your calculator and multiply your heart rate range by the various percentages. Fill in the numbers, and you’re on your way! Stay within the percentages of MaxHR given below for the following workouts:

• 60–75% for long endurance runs (start easy, HR will drift). Watch your heart rate during the second half of the run. Muscle fatigue, glycogen depletion, and fluid loss will increase your HR—especially if you are just beginning to increase your mileage. Don’t let your HR creep above 75 percent of max.
• 80–85% for tempo runs for anaerobic strength (stamina). When you go over 80 percent of MaxHR, your fat stores won’t be your body’s choice of energy. Carbohydrates and your glycogen stores take over more of the load. If you run out of glycogen, you’ll hit the “wall,” no matter how much fat you have left.
• 90–95% for intervals for speed development.
• 60–70% for easy days for recovery (HR can drift at end).
• 70% for ultra runs of 50 miles or 100K.
• 60% for all runs 3 hours or more; begin with 60%.

Modified Karvonen Formula
(More accurate for the “Chronically Fit”)

Subject: (your age) year old runner with a resting HR of (your RHR) BPM

	Start with	205
1. Subtract 1/2 your age	−	_____
2. Result = Approx Max HR
3. Subtract Your Resting HR	−	_____
4. Result = Heart Rate Range (total number of beats)
HR Range × .65 + (Resting HR) =
HR Range × .70 + (Resting HR) =
HR Range × .75 + (Resting HR) =
HR Range × .80 + (Resting HR) =
HR Range × .85 + (Resting HR) =
HR Range × .90 + (Resting HR) =
HR Range × .95 + (Resting HR) =
HR Range × 1.00 + (Resting HR) =

Closing Thoughts

Over the last five years, I have coached over 150 people using effort-based training, which uses a combination of objective heart rate monitoring and a subjective rating of perceived exertion as the primary guide for training load. We still use pace per mile as a guideline, but only as it relates to a scientifically-based and individualized goal.

If you stick to the range of percentages for the workout you intend to do on a particular day, you will see that your pace may vary, but you’ll accomplish what you set out to do for that workout. It is very true that your HR will drift a bit higher toward the end of most workouts due to glycogen depletion and early stages of fluid loss. Therefore, you need to start every workout at the beginning of the range listed above. If you start at the end of the range, you’ll finish that particular workout overtaxed. You may make it through the workout all right, but day after day of being at the edge eventually leads to overuse syndromes and injuries. Which, of course, can get in the way of training for and finishing a marathon.

I wish you the best and encourage you to be patient with your tachometer. If your personal calibration is correct—and that may take some fiddling—the number appearing on your HRM ain’t lyin’. It knows how hard you are working on most days, whether you want to admit it or not. Trust the tach and good luck!