What does 90% feel like?

Bicycle nuts of all kinds (including those in the “Slow Bicycle” camp) have been sharing this story at the New York Times about the benefits of short, high intensity interval workouts to your health.

Researchers at McMaster University in Ontario have found that relatively short, twice weekly 20 minute workouts of high intensity have as much benefit as longer, daily low intensity exercise.

For the high intensity intervals, you push yourself for a minute at 90% of your maximum heart rate, then rest for a minute at low intensity. Repeat ten times for 20 minutes of intervals.

So how do you know when you’re at 90%?

Your Maximum Heart Rate

The gold standard for determining an individual’s maximum heart rate is through a treadmill test while you’re connected to an EKG. This can be a little pricey, so most people use an age formula for their maximum heart rate.

The rule of thumb for maximum heart rate is 220 minus your age. This was established in 1970; more recent research found HRmax = 206.9 − (0.67 × age) seems to work a little better.

For the average 40 year old reading this article, you get the same value either way — 180 bpm. Remember, also, that there’s wide variability determined by fitness level and genetics, and there’s evidence that women have higher maximum heart rates than men. Since you’re doing this for personal fitness benefit, the value you get from this formula is likely close enough for government work.

90% of maximum?

To get the fitness benefit found in the McMaster study, you need to push yourself at 90% for a minute, then slow for a minute, then 90% for a minute, rest a minute and so forth for 20 minutes. 20 minutes happens to be the time I spend on the completely grade separated Guadalupe River Trail on my bike commute. But how do I know when I’ve hit 90%?

Inexpensive heart rate monitors start at about $35 (avoid “strapless” monitors — you have to touch a finger to the watch to get your heart rate, which can be difficult when you’re pushing 90% on a bike). They also have a handy interval training feature, beeping to let you know when to start and stop your intervals.

What if you don’t care to own the technology? What if you’re a Slow Cyclist who just wants to try this out to see how it feels? Dr. Gunnar Borg at Stockholm University showed that perceived exertion is an accurate predictor of your actual exertion. In other words, if you think you’re at 90% of your maximum effort, you probably are. He created the 15 point Borg scale of “Rating Perceived Exertion” (RPE). You rate your effort on a scale of 6 to 20.

  • 6: No effort. Awake and breathing but completely relaxed.
  • 7-8: Very light effort, like reaching over for a bowl of chips or lubing your bike chain.
  • 9-10: Light effort – coasting to a stop on a bike path.
  • 11-12: Still light, but a little more — very relaxed “slow bicycle” speed on a level surface.
  • 13-14: Noticeable exertion. You’re breathing more deeply and maybe breaking a sweat, but you can still talk. The “brisk walk” the American Heart Association recommends as a daily fitness activity. Easy, conversational pace for roadies. Nose breathing still possible.
  • 15-16: More effort, about 70% of HRmax. The long distance endurance zone that road cyclists aim for. It takes an altered state of consciousnesses to remain at this level of exertion for hours at a time. You’re definitely sweating.
  • 17-18: Almost maximum effort. We’re at 90% right here. It hurts, you’re gasping for breath and you’re probably shaking a little at the end if you’re not used to it. If you’re doing intervals you’re counting down the seconds until the pain is over. You’re drenched with sweat when it’s all over.
  • 19-20: Up against the wall – everything you’ve got and more. Extreme tunnel vision, spots in front of your eyes, pain, and it takes extreme motivation and willpower to keep this up for more than a few seconds. Sprinters pushing a 1500 watts as they gun for the finish line at the end of a stage race are at this level.

The dedicated roadies are likely beyond the fitness level claimed as a benefit in the McMaster study. What about the rest of you — especially those of you with short commutes? Do you plan to give this a shot?


  1. Is that scale supposed to be mph (if not, why is it 6-20?)? It seems fairly close except the last few would be a bit faster for me. 8mph I’m barely pedaling – 0%. 15mph I could go all day – 40%. 17mph is a challenging pace for a century – 60%. 20mph is tough be possible for up to a few hours – 80%. 23-25mph is where my races are normally, I’d call that my “90%”. 35mph is an all out sprint that I can hold for just a few seconds – 100%.

  2. Am I the only one who doesn’t think trying this during a commute is a good idea?

    “17-18: Almost maximum effort. We’re at 90% right here. It hurts, you’re gasping for breath and you’re probably shaking a little at the end if you’re not used to it. If you’re doing intervals you’re counting down the seconds until the pain is over. You’re drenched with sweat when it’s all over.”

    This is not a description of someone who should be on the road dealing with traffic, IMHO. 

    Having said that I wonder how this compares to my “suburban commute.”   I’ve got 3-4 minutes of hard riding (80% exertion maybe?) followed by a stoplight induced rest.  This happens 3 or 4 times, depending on the lights.  

  3. It’s just a scale, no MPH. Dr Borg is Swedish so unlikely he’s thinking in miles. He had a 1-10 scale earlier, but discovered that his 6-20 scale works better in correlating perceived effort with actual effort. Weird, huh?

    And if you think about it a little more: 12 MPH is almost no effort for a fit cyclist, but can be considerable effort for somebody hopping on the bike for the first time in 20 years.

  4. That’s a good point, Chip.  Extreme effort takes away from our capability to focus on traffic. Reminds me of the time skier Bode Miller advocated for doping — he claimed EPO could enhance safety because more oxygen is available to the brain.

    And like you point out, intervals are kind of built in with traffic lights 🙂

  5. I’d hate to see someone apply Bode’s style to cycling. He either crashes spectacularly or wins by a good margin. Go big or go home!

  6. Did Bode Miller have any evidence for that?  It seems quite likely all that extra oxygen would still go to the muscles and not the brain.  Would athletes bother with it if it just meant more thoughts and not fewer seconds?  

  7. “…relatively short, twice weekly 20 minute workouts of high intensity have as much benefit as longer, daily low intensity exercise.”

    So, what you are saying is if we only commute once in a week, we have to ride so hard we’re ready to puke each way, but if we ride every day, we can ride the way most commuters ride. Do I get it right? So, what happens if we ride every day and pick one of those to pretend we’re really late. Does that mean we’re going to live beyond what we’ve saved up for retirement?

  8. Sir!  All my internet comments are thoroughly thought out.  That probably says something about the quality of my thinking. . . 

  9. I definitely ride my commutes as hard as a possibly can.  I also have the benefit of living near a trail that is a good chunk of my commute (though I do miss the Guadalupe River Trail!) and I generally go all out, highest gear, gasping for breath when I get to and from work. 

    However, when I’m riding in traffic, I’m much more concerned about safety and following the rules of the road!

  10. I was about to say that it will work better if you have a big hill on your commute, where 90% happens at fairly low and therefore safe speeds. But with a hill, of course, it’ll be difficult to rest between the intervals. I’ll have to play around with GPSies or mapmyride a bit to see if I could design a route that would work well.

  11. There’s another article popular in our part of the world that says that if you go 90% for 20 *seconds* and then off for 10… and do that for oh, I think,  five minutes, that you get the same benefits. (Tabata is its name.)
         I also don’t get that intense on a commute without provocation… and I just don’t like pain. I get all kinds of benefits from riding at a pleasant level of exertion — which I can sustain for a long time, because, you know, it’s pleasant. Then when I’m pitted in a competition, I ramp it up and suffer a little… but I’ve been extremely pleasantly surprised at what’s possible with, oh, hard breathing… but not “boogie ’til you puke.”
        Be it also known that I *much* prefer endorphins to adrenaline, and other folks don’t share that hormonal perspective.

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