Mhr and intervals: how do i know?

[defurr]

I've been doing HIIT on the bike recently, with pretty good results. But being a data head, I'd like to know: Is there a way to know subjectively when you've topped 90%? I'm not interested in paying $200 to a local triathlon dominatrix to learn my official/scientific MHR, but what I've observed is the following...

The most aggressive MHR calculation (Heil, which factors weight) puts me at 185 BPM, which would say that 167 is my 90% threshold. And yet I feel as though I could do 168ish forever, no problem. My typical ride includes intervals at 2 x 3 minutes to warm up, followed by 2 x 10 minutes, and finishing with a single 7 minute interval with natural breaks (stop signs and other unavoidable slow-downs), wherein if I'm at 168ish, I'm able to cope just fine.

But around 175ish, that's when I start to think, "Wow, not sure I can hold out much longer..." In theory, that would be 95%. But if 175 is 90%, then my actual MHR would be 194, which seems outrageously high for a 46 year-old male, weighing 155.

So is holding 90% for 10 minutes really not that big of a deal? Or is my MHR higher than I think it is?

 

[RapDaddyo]

Your specific question seems to be, "What is my max HR?" I'll get to that below, but let me first comment on your plan to use your MHR to develop a ride plan. Using HR to manage intensity of effort is a bit haphazard to begin with, for three reasons:

1. Your heart rate measures only half of your heart's response to intensity of effort, the other half being stroke volume. So, if your heart rate (bpm) goes up by 5%, you are probably assuming that your intensity of effort has gone up by 5%, but this is a false assumption. We don't have a lot of evidence as to whether stroke volume increases in lock step with heart rate or if they respond independently, or if they respond in the same way all the time.
2. At the same intensity of effort, your heart rate will vary quite a bit (e.g., 10bpm) from one day to the next and even from one segment to another segment of the same ride.
3. As we become more fit, we typically experience a decrease in HR for the same intensity of effort as a percentage of our max sustainable effort for a given duration. For example, at 90% of my maximum 1-hour power, my heart rate will decrease as I become more fit as measured by increases in my maximum 1-hour power.

With that said, I think you're better off setting your intervals at about 90% of your maximum heart rate for a given duration. You're doing 10 minute intervals primarily, so it shouldn't take too many trials to find the heart rate at which you are basically exhausted after 10 minutes. A good target for your 10-minute intervals would be 90% of that HR. You could bump that up by a few bpm for your 7-minute intervals.

Finally, as to your MHR, benchmarks are only averages for large populations of adults, with large variances. I would never use such an approximation to develop a ride plan. But, it's not hard to find your own functional MHR. On one of your 10-minute intervals, after 5 minutes begin to gradually increase your intensity of effort every 15 seconds until you can't increase intensity any more. Hold that to exhaustion and check your HR.

 

[Shalem'sDad]

Thanks for the post, I never really gave it much thought..

 

[workingguy]

This is a screenshot of my latest FTP test on trainer road with a Stages power meter and Wahoo Kickr. This is about 20W below what I could do before the holidays (recorded by a Powertap). By a couple of different MHR formulas my MHR should be 172 or 176. But during long intervals at or near FTP it can drift upwards of 187. I only this week started using a HRM because my wife doesn't want me to get a heart attack while training. It's always been higher than most the population and only drops to 130-140 during the rest intervals. The Kickr feels much harder for the same power level. I haven't tried the stages with the rollers as I'm waiting on another cassette.

 

[RapDaddyo]

Given that you now have a power meter, not sure why you're fixated on your HR. From your workout data, I would guess that your FTP is somewhere in the 170-175 range. But, as far as setting training targets, it doesn't really matter. You can set your targets as a function of your maximum sustainable power for a specific duration. So, let's say that you want to do 20 min efforts on a regular basis. You can set your target as a percentage of your maximum 20 min effort. I use 90%, but you could be more aggressive and use something above 90% (e.g., 95%). From your data, I'm not certain if your max 20 min power is 179W or something higher. Were you exhausted after 20 mins at 179W? If so, that's your max 20 min power. If not, then your max 20 min power is somewhat higher.

To learn the pitfalls of setting your training targets by HR, try this: ride a 20 min effort on several consecutive days at 179W. See if your HR is the same on each day. I'm guessing not.

 

[workingguy]

That's what I was afraid of. I was hoping for FTP numbers in the 190-200 range because my 2005 powertap wheel reported 2x20 efforts of 202-204 last month. Maybe it was over reporting power. I use Stages and Kickr with the Power match feature. Stages reports the power to trainer road, which in turn controls the electronic brake in the Kickr. In theory that's how it's supposed to work. Training and racing is always a humbling experience.

I'm not fixed on my HR per se. I just wanted to make sure I wasn't near the limit of passing out. My wife did not notice any a-fib when I ran the stress test using the Bruce protocol (5 step ramp test on treadmill) a few years back.

 

[workingguy]

Retested ftp, this time with 2x8 minute efforts. I know it's highly inaccurate but trainer road recommends this for crit racers vs the 20-minute test for time trialists.

This time I used standard (level) mode instead of ERG mode and figured out before the test which level to use (level 2 worked out best). In the last test I used ERG and kept trying to raise the power target which didn't work out so well. Trainer road reported FTP as 189 vs 170 previously, much better numbers. No wonder my last few workouts seemed easy.

Still trying to figure out how to use Trainer Road with the Kickr.

 

[mtb_baz]

Hey there! Love hearing about your FTP test and all the changes you made. It's great that you experimented with different modes and found what works best for you. Those improved numbers must feel awesome! And yeah, sometimes those easy workouts can make you question your progress. Keep pushing yourself and keep us updated on your biking adventures! ‍