Heart Zones

Are “heart rate training zones” for real?

Running coaches like Roy Benson, Phil Maffetone, and John L. Parker, Jr. tell us to keep our heart rate at 65, 70, 75, 80, 85, 90, or 95 percent of max depending on our goal: easy recovery, endurance, “fitness improvement,” speed-endurance, speed/turnover, etc.

Inquiring minds want to know: Why these figures? And why are they multiples of 5?

Why should we hold our heart rate under 65% during the warmup, for example? Why not 67% or 69%?

John L. Parker, Jr. urges readers of his book, Heart Monitor Training for the Compleat Idiot, to do most runs at 70% of MHR calculated by the “Karvonen Formula”: (maximum heart rate, minus resting heart rate) divided by 2 (plus resting heart rate).

Years ago, I asked Parker if the 70% figure was supported by research. His answer wasn’t clear and left me mildly frustrated. But now I believe Parker is right.

That’s because my body tells me so. I know there’s something to these heart-rate zones – or at least two of them.

I was recovering from bronchitis and went to the track to jog. After 20 minutes, I inserted a 30-second fast burst on each lap. These sprints raised my heart rate above 90%.

After each fast segment, I walked a bit, then bent over and watched the heart monitor as my pulse fell. (Research shows that standing still and bending over is the quickest way to reduce heart rate after hard running.)

I noticed an interesting thing: While my heart rate was still above 80%, I felt a bit nervy and pressured, as if my body were in “performance mode.” But the moment my HR fell below 80%, I felt more relaxed and “comfortably within myself.” My Karvonen 70% heart rate is about 78% of maximum.

In fact, this confirmed a phenomenon that I’d experienced for years. When I first read Parker’s book, I worked up to training 2 to 2½ hours three times a week at the 70% pace. These runs were wonderful – I felt that they were building my fitness, and the pace felt “just right.” But if I went faster than 80%, I paid a price — I couldn’t run as far.

Also, there was a different feeling when my HR climbed above 80% – it felt forced, as if my body was no longer building fitness, but was using its resources in a kind of “slow race.” It felt like I was no longer training for general fitness and endurance, but other qualities — Speed? Speed-endurance? It wasn’t clear.

I no longer cared if Parker’s 70% figure was “undocumented,” “unscientific,” etc. – all that mattered was that it worked.

I realized that Parker had tuned into his body’s wisdom – not surprising, given that he’d been a high-level runner for many years, and a teammate of Frank Shorter, Jack Bacheler, and Jeff Galloway at the Florida Track Club in the early 1970s.

Science can tell us many things about the body that we couldn’t know by prodding our own chests and legs. But there are some things the body can tell us directly, and the 80-percent ceiling on “fitness and endurance improvement” running is one of them. The 80% figure appears to be the hardest pace we can run safely, day after day, without overtraining. (There are countless ways to overtrain – increasing mileage too quickly, running long when we’re tired, etc.)

There seem to be as many training zone zones as there are coaches. Phil Maffetone suggest doing all running at a very slow pace in the early season. This “MAF (maximum aerobic function) pace” is determined by subtracting your age from 180 and adjusting the result by 5-15 beats depending on age and experience. After several months of base building, Maffetone has his runners do hard speedwork for 6-8 weeks leading to a target race. It’s how Mark Allen trained to win the Hawaiian Ironman Triathlon six times. It enabled Allen to train extremely hard – Timothy Noakes, MD observes in Lore of Running that Allen’s training during the speedwork segment may have been the hardest training that has ever been done. It’s also how Priscilla Welch set the women’s over-40 marathon record — 2:26:51 at age 41 in 1987, the year in which she also placed second at the New York City Marathon.

Which system is best? I simply don’t know.

For me, it’s almost a matter of taste. I did Maffetone-style endurance training for six months and experienced no improvement whatever. My “MAF pace” didn’t increase as predicted, and my fitness stagnated, contrary to the experience of hundreds of runners who’ve thrived with Maffetone. My body seems to need a sharper stimulus to improve. I feel much better training at 70% Karvonen, as Parker recommends.

Some runners can probably break the “80% rule.” World-class runners can run at very high heart rates aerobically.

Which system is best? A more practical question may be “What system is best for us?” Our bodies can tell us how fast and far to run. The heart monitor can give us a starting point. It can tell when our feelings, impulses, and emotional desires are wrong.

On long runs or recovery runs, we can watch for signs of “pressured running” that indicate we aren’t building fitness, but using existing resources. (We’re “slow racing.”)

Suppose we start running and anything faster than 65% or 70% feels labored, joyless, and “wrong.” That’s a clear sign that something is wrong – we’re not recovered, or we’re fighting a virus, over-stressed, need more sleep, etc.

What about the 65% ceiling that many coaches recommend as a ceiling pace for the warmup?

Physiologists have discovered a sudden shift in the way the heart functions when heart rate reaches 65%. I described this research in Fitness Intuition. Before you read the quote below, you need to understand the term “heart-rate variability,” or HRV. The heart changes speed continually, like a car on a curvy road. Heart-rate variability is a measure of how often these hear-rate changes occur within a given period – say, 5 seconds. When scientists plot HRV and observe a smooth, sine wave-like curve, indicating that the heart is changing speeds in a regular, harmonious rhythm, they know that I reflects calm, positive, harmonious feelings. But when the HRV curve is jagged and irregular, it indicates negative, disturbed, or depressed feelings.

Now then, regardless of whether we’re feeling positive or negative, there’s a sudden change in the HRV graph that occurs at about 65% of MHR. From Fitness Intuition:

Several high-end Polar heart monitors now use heart-rate variability data to help runners determine their best individual warmup pace. At the start of a run, the amplitude of heart-rate variability falls off rapidly until a runner’s heart rate reaches roughly 65% of maximum, whereupon the amplitude levels off and falls much more gradually as running speed increases. A reduction in amplitude means that, for example, instead of shifting from 65 beats per minute (bpm) to 70 bpm and back in a given time interval, the heart changes from 65 bpm to 67 bpm and back. The Polar monitors signal a runner when this shift occurs, at a heart rate around 65%. The Polar scientists feel this is a safer, more precise way to determine a sensible 65% warmup pace than testing maximum heart rate with a stressful all-out run, or by using the notoriously inaccurate age-based formulas and tables. You simply start running and let the monitor tell you when you reach 65% of your maximum.

I’ve noticed that holding my heart rate around 65% at the start of the warmup feels subtly “just right.” After perhaps 15-20 minutes at 64-67%, I’ll speed up tentatively and see how it feels. When my body is sufficiently warmed up, there’s a quiet feeling of “readiness,” and I’m able to slip effortlessly into a higher gear. There’s something about running at 65% that prepares the body to go faster.

What about the other zones, such as 70-75%? John Parker seems to feel they’re transitional. And I agree. During long runs, after the warmup, my body usually “wants” to linger briefly at 70-75%, but not for long. If I’m rested and healthy, my heart will often give the okay to step up to the 75-79% zone.

In Heart Monitor Training for the Compleat Idiot, Parker does a wonderful job of describing what happens as we become fit from regular speedwork. As our bodies become more efficient, it gets harder to raise our heart rate — we may need to run 6:40 pace to reach 90%, where formerly we could only run 7:15 pace at 90%.

Parker believes all kinds of speedwork develop the same level of fitness; Phil Maffetone says the same thing. But research shows that intervals and repeats raise VO2Max more efficiently than tempo runs. And very hard, very short intervals raise VO2Max most effectively of all. (I described this research here and here.) If you want to quickly improve your ability to process oxygen, you must train hard, at heart rates above 90%.

I’m not sure there are natural signals from the heart that tell us what’s “right” for the body at these higher speeds. But I do know that running fast is much easier when my heart’s feelings are harmonized. I describe many examples in Fitness Intuition.

I’m fascinated by the way the body talks to us. I’ve mentioned two physical markers that reflect how the body “likes” to train – the sudden leveling-off of amplitude in HRV at 65%, and the speed limit on fitness improvement pace at just under 80% – both of which are accompanied by inner feelings of “rightness.”

Fitness intuition has a higher dimension. Yesterday was a perfect spring day for runningg trails. Yet a clear inner feeling told me to go to the track. And not just any track, but the track at Foothill College.

Angell Field at Stanford was a lot closer, yet when I arrived there, it felt subtly wrong. I’ve learned to trust these feelings, so I drove an additional 10 miles to Foothill – and had a wonderful run. The Stanford track has a kind of high-powered, public feeling, possibly because so many world-class athletes have trained and raced there. The US men’s and women’s 10,000-meter records were set at Angell Field, and I feel a bit shy about running there, even though there are plenty of walkers and joggers. But I was recovering from illness, and I needed a quiet run in the heat, on a more downscale track where dad and kids were tossing a football, where hawks were soaring overhead, and world-class feet had seldom trod. Foothill was perfect.

But how did I know? By the subtle feeling of lightness that accompanied the thought of driving there, as I sat in the car and got quiet inside. I don’t want to rhapsodize about those feelings, because in fact they’re simply practical. Intuition is nothing but calm, impartial feeling. It can help us in whatever we do – whether we’re deciding how fast and where to run, or if we’re so inclined, listening for answers from a higher guidance.