Strava Power and HR Zones

timmyotool Posts: 172
edited September 2018 in Training, fitness and health

I've recently added premium, and had a nosy at my time spent in HR and Power zones on a ride.
I've noticed I have quite a difference time spent in my HR zone vs Power. On a steady 50k outdoors of what I would call a "zone 2" ride:

Looking at HR I spent 35% in Z1 and 63% in Z2

Based on power I spent 31% of time in Z1, 15% in Z2 and 11% in Z3 and 35% above that.

Appreciate power is more responsive then HR so I should expect some variance, and time spent going downhill/stopping for traffic lights, will increase the power Z1 value, but I was surprised at the variance.

Question 1 - should I be expecting a Z2 HR ride to also be a Z2 Power ride?
2 - Is this variance common for a lot of people?
3 - If it is, should I be targeting a Z2 power ride or Z2 HR ride for all these "zone 2" benefits?



  • Putting aside how the power data is calculated (i.e. from an actual power meter vs estimated from your ride data, the latter of course may be a confounding factor), power and heart rate data provide significantly different filters for measurement of intensity distribution.

    e.g. the very same interval session may appear to have a polarised intensity distribution when viewed through the lens of one measurement device and pyramidal distribution with another.

    Interpreting such intensity distributions requires quite a deal of care and understanding. They can easily confound, mislead and lead one to think the sort of training they are doing is something other than what it is. So be careful when looking at such data.
  • As to training benefits and "zones", the impact of training intensity is on a continuum. "Zones" are mostly just an artificial construct for communication convenience and as a way to understand which aspects of development are emphasised when training at certain levels. but it's just an emphasis, not exclusiveness.

    IOW Zone 2 "benefits" also occur from training at other intensity levels.

    Whether the intensity of a given ride is appropriate can really only be considered in the context of *all* of your training.

    But for lower level endurance work, whether you choose to use power or HR or perceived exertion to guide you is probably neither here nor there, provided the work doesn't involved all that much high intensity effort.
  • Some pro’s actually have been known to put bits of tape over the power figure display box on their computers screens, in the days before Garmins, and the like, with their fancy customisable displays, when racing, rather than training. They often prefer using HR readings, especially on climbs.
  • Thank you for taking the time to reply - really interesting and they make a lot of sense.

    I think as you said to focus on training with an emphasis on "low level endurance work" is the key, and what I should work on rather than trying to stick religiously to zones.
  • That assumes of course doing low level endurance work is the right thing for *you* to be doing. But that's a different conversation.
  • this is an interesting question of whether power and HR zones line up. As you discovered often they do not. To put is simply HR is a measure of sustained effort. Power is a measure of energy output. Usually there is a correlation but not an exact one. For example try sprinting from a standing start, fresh, HR can be in zone 3 and power in zone 6. Over a longer ride there will be a correlation but there is no guarantee that your cut points are correctly set. For example is 50% of your HR max and power max correct in strava? In general the two metric will deviate when:

    1. the ride is short
    2. the calibration is out
    3. the zones have not been personalized
    4. outside conditions vary a lot
    5. illness / fitness variation

    If your training stimulus varies a lot (eg hills) then your power is going to be difficult to control perfectly but providing power deviations are small and short lived HR should still be "in zone".