Heart Rate vs Power for Measuring VO2Max and HIIT Workouts

There is lot of talk about power in watts vs heart rate as standard measurement for HIITs and VO2max workouts. I get that if you want to be better cyclist and win races then power is what matters at the end and should be primary measurement.

But what if you are just concerned with improving your cardiovascular health, conditioning and VO2Max? Shouldnt you in that case go just by heart rate and use power only as secondary measurement?

In my experience during HIITs and VO2max workout I can in later intervals easily reach and stay over 95% of my HR max while decreasing power output significantly. So if my goal is to improve my cardio and vo2max instead of power output, then it shouldnt matter that power is much weaker, right? Only thing it does, as far as my feeling goes, is that it demands more recovery and exhausts my muscles rather than cardio.
At the end of intervals I can keep my power output higher but my HR stays the same as if I were to lower my power output by 20%. Hence my conjecture is that if goal of this workouts is improved VO2max and conditioning I should rather focus on my HR and spare my muscles and CNS recovery for other types of workouts.

Some forum posters continue to claim that VO2max intervals should be at a maximum. I think that is poor judgment as, just as you point out, it induces unnecessary fatigue and stress on the body delaying recovery.

According to various research the heart rate should exceed 90% but not necessarily 95% for optimal adaption. In my opinion it is better to extend the intervals and TIZ then keep pushing the heart rate. Reducing power to keep the heart rate in the 90%-95% bracket is a excellent idea and lines up nicely with the concept of hard start intervals.


I would say both; focus on power for most workouts but for some people a VO2max power target doesn’t put you into the correct oxygen based zone and you need to push by the target and into the true maximum oxygen based zone in that case HR for me is a better guide. For me thats pushing my HR to 90-95% max; I find that greater than 95%max just takes too much recovery. There’s some good podcasts on the subject, I like this one:

Vo2Max has two elements

Oxygen Delivery via cardio vascular
Oxygen extraction by muscles

You need to improve both to improve your vo2max. It’s no good being able to deliver huge amounts of oxygen if your muscles aren’t able to utilise it.

I’ve also read that you don’t want to be pushing heart rates over 95% as it blunts the adaptive response …


Interesting. That is helpful to know. But I would assume that if my muscles are not able to keep high power output and my HR keeps increasing despite power output decreasing I might be still be getting both benefits since muscles are more fatigued already and hence at the point where adaptation is occurring?

Also if I have to keep my HR under 95% then I definitely have to keep lowering my power output throughout the intervals.

Thanks for this resource! I will check it out.

Thank you for your input on this! That were my thoughts, even based ony my subjective feeling where I can feel that I breath as hard I as possibly can and am uptaking as much oxygen as I could but still feel like I could push for more power but that would just require more recovery for muscles and did not do much for VO2max or cardio.

When it comes to getting lots of time in the zone I find it very easy to get lots of TIZ at 90-95% max HR while decreasing power. I can sustain longer efforts and do more intervals without taxing my muscles and CNS too much and hence decrease my performance and recovery for other sessions like strength training etc.

So I think that no single measurement is perfect alone but focusing mainly on HR is probably most sustainable and beneficial if you are not focused on winning races.

Tom Bell covers this nicely.

Yay! Glad I created those 8 minute VO2 Max Hard Start custom workouts :sunglasses:

Does it resemble anything like described in this article?
My take looks looks like this:

I included a slight taper to make it easier to mentally manage the 8 min threshold part; I’m terrible at threshold work…HR stays in the 90-95% zone though.

Funny enough, my workouts for VO2max look almost exactly something like this. What I do is following: 30s hard 30s mid effort and keep repeating for 10mins or sometimes for as long as possible if I dont want to do another set. First couple of hard 30s is about twice as much power as last hard ones. But my HR is higher in those last sets despite them being half of the power. This continues even in another set, or if I continue for longer I can even drop to my zone 2 power for 1-2 min and still stay at 90%+ HR. I can later easily resume higher powers for 20s bursts to get my HR to its max. But I found that for stable HR and extending time in that zone my power has to vary widely. If I try to keep my power constant then I will fatigue too quickly.

Mine’s pretty straightforward: 2 minutes at 120% followed by 6 minutes at 110%. The idea being that the 120% is a “hard” target where the power must be held on target and I wouldn’t really look at heart rate, and the 110% is a “soft” target where I’ll seek to maintain target power as far as possible as long as heart rate is in the right zone.

Three of those with 6 minutes of recovery. I’ll progress them by adding an interval and/or reducing the recovery slightly.

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