VO2Max intervals and time in HR Z4/Z5

Hi all

Firstly let me say I appreciate that TR is a wattage/FTP centric product and I may be trying to compare apples with oranges, but…

Bird -1 is an anaerobic workout and therefore I would anticipate my heart spending a fair period of time in Z4 and Z5 during the 15 minutes of effort.

I have noted that I have spent 6 mins in Z3, 6 mins in Z4 and no time in Z5.

So the question is, will this workout be achieving the desired physiological effects or should I be swapping it out for something with longer efforts and/or shorter rest periods to make the cardiovascular system work harder?

Appreciate your comments.


The whole workout is .89 IF for an hour. Which combined with short intervals is unlikely to get your heart rate really high for very long.

Have a go at Spencer +2. If that doesn’t get your heart into the right zones, it’s probably time to re-assess your FTP…

1 Like

In addition, it looks like the workout is part of triathlon base, in which case you’re only in week 6. Be patient, they’re building you up slowly and the harder vo2 sessions will come in weeks 9-11.

1 Like

Important to note that intervals are 1 minute long and HR has a lag period to it as your body adjusts to the new workload.

Cheers guys

This is the second year I have used the Triathlon Full Distance plans but trying to think more about what I am trying to achieve from each session and subsequently evaluating whether i did or not.

Yes the body has a lag entering each interval but it also has a lag exiting it, thus circa 1 min of effort could be expected.

Have just come back off a two week training camp, so yes I may also need to reassess the FTP - Ramp Test is scheduled for next week.

Will most certainly have a look at Spencer though as I cant afford low return workouts.


You could also just be fatigued and overreached. HR depression is one of the early signs even if you can hit the power targets

Maybe there’s a bigger re-evaluation needed. You can’t expect every session to yield immediate measurable results, or fulfil an obvious need. And if every session hurts, you’ll soon burn out.

Base training plans are like they say - building a base of endurance on which to build. If you feel like you need to make gains more quickly, e.g. you have an event coming up, a Build plan might give you more of that “this is really doing something” feeling.

Hi all, almost a year later and I am noticing the exact same thing :smile:

Have just completed Ansel Adams -2 which is an anaerobic session, yet each interval pushed my heart rate to upper Z2 / lower Z3, with cardiac lag not of relevance as my total time above Z2 was 6 mins which fell into low Z3. Nothing in Z4 or Z5.

So in the knowledge that a polarised approach is considered appropriate, i’m curious as to whether I am getting the physiological adaptions desired from the anaerobic work as I am able to hit the goal wattage numbers, or should i discount the desired wattage numbers and push harder to hit the Z4/Z5 required of HIIT?

Appreciate your thoughts on this.



If you make your workouts public then people can look over them. Might improve the advice.

Is your FTP correct? 50secs on, 50secs off on an anaerobic workout would have me 90% to 95% MHR. If it is correct then it may be that the gap between your FTP and the VO2 max and anaerobic power zones is much higher than normal. Ansel Adams -2 has an IF of 0.95, that should have your heart close to bursting out of your chest Alien style.

Edit: alternatively, are your HR zones set correctly? What you are stating doesn’t really add up - basically a workout that is effectively 95% of the workload of that same duration as at FTP raises your HR to that expected for a Zone 2/endurance workout.

The general guidance, repeated extensively in the text of most workouts that go well above threshold, is that some experimentation is needed to find what is the right intensity for you, at this particular time. The workouts are built around a “decent guess” of what that power target might be, but that’s just a starting point. Adjust actively to find the power target that matches the workout goal (e.g., repeatable power for the given recovery duration vs. all-out effort with no thought about what comes after).

How are you establishing your HR zones?

I had a similar issue today. Did Taylor + 2 and didn’t peak but I’ve put it down to an increase in fitness? I compared with the last time I did Taylor (-2!) and my heart rate was significantly lower (-11bpm avg.) this time around.

Alternative theory: This is where the old adage “FTP doesn’t mean everything” comes in to play? As all these workouts are based off of FTP there could be discrepancies between VO2 Max and Sweetspot workouts in terms of how they hit your cardio systems. Not everyone will have the same curve.

What is your RPE in addition to the HR zones? Seiler recommends doing intervals self paced

Hi bobw

I assumes all post were public - cant see the point in a forum if no-one can see the posts :slight_smile:

My FTP is as per Ramp Test which is consistent with 20 min tests over the past few years. My heart rate zones are as close as anyone’s can be considering they are based on moving targets. My zones are based upon 81-89% of bFTHR taken from a 20 min test. These figures are very close to 75-80% MHR, where my cycling MHR is 162 (running MHR is 174) which places me in Z2 119 to 131 bpm.

Maybe the zones are out a tad - as everyones probably are - but probably not the difference between Z2 and Z5.



Cheers pkwell. I am thinking I probably need greater intensity to hit the goal of being anaerobic. Ill play with the interval length and rest periods and see what happens.


Hi stevepetts372. Sorry i got hijacked by work. I have added this info to another reply.



Hi jordonp. Yes sure. Its touch to make a one size fit all. Just curious as to whether i will be getting teh adaptions i need at this intensity or not. Im drawn towards not :slight_smile:


Hi redlude97. Thats a great point. Cardiovascularly probably a 5 at end of each interval, although muscularly probably a 9 by the end of each. I do tend to naturally grind a bigger gear and these intervals are circa 95rpm. Maybe i need to work at a higher cadence to tax the heart and lungs more.


On another thread there is a link to some recent videos by Stephen Seiler. In it, he reviews some prior studies on how HR, RPE, and VO2 evolve over the course of short-interval workouts of different structures. His takeaway is that equal work:recovery is generally not enough to get you above 90% of HRmax, but that 30/15 is. It depends on the work intensity, too, which tended to be around 120% of the 6-minute power. It was kind of interesting. Then I took a nap.

Side note: this weekend I learned that you can do all the fine-tuning of interval sessions you want, but you’ll still get your butt kicked if your bike handling skills aren’t there. Nothing makes you doubt your training like being passed by someone carrying an extra 30 pounds and wearing a parka.