Monday, August 16, 2021

DFA a1 HRVT and ramp slope

One topic we have not explored is the effect that ramp slope (rate of power/speed increase) could have on the HRVT (1 and 2).  Ramp slope does not appear to have a major effect on gas exchange parameters such as the VT1 or VO2 max, but it does affect corresponding cycling power (and muscle O2 desat).  The idea behind this issue is that there is a lag between what is going on in the muscle and the associated ventilatory metrics.  However, since HR is usually a linear function of VO2 (up to the VT2 at least), HR at the VT1 appears to be an accurate measure.  Does that apply to the HRVT as well?  On one hand there may be a lag in autonomic balance, causing a delay in a1 drop with a quick ramp.  In addition, we are looking at 2 minute window sampling in a1 computation, another potential area for lag in response.  However, it would be nice to have a shorter test to obtain readings for many reasons.  Therefore I decided to do a 30w/minute cycling ramp instead of my usual 5w/minute standard.  In addition, the end ramp power was planned to be well above the MLSS (but not to exhaustion) to make sure the a1 drop was sufficient.  As in previous tests, time of day, sleep,  nutrition, temp, fan, cycling gear were all similar.  The 5 w/min ramp was done from 130 to 230w (20min) and the 30w/min ramp from 100 to 340w (8min).

Standard 5w/min Ramp:

30w/min Ramp:

  • Both ramps have near linear HR rise (and hence VO2 increase).
  • The 5w/min ramp did not have the low nadir DFA a1 seen with the 30w/min ramp - as expected since the short ramp was done to MLSS+.
  • Despite the huge difference in ramp slope, both HRVT and HRVT2 were very close in each case.
  • The HRVT is usually what I see when fresh, without fatigue.  The HRVT2 HR is a bit on the low side (should have been about 156 bpm).  Recall from our study that the limits of agreement are wider at the HRVT2, but in line with those of other comparative methods of MLSS (muscle O2 desat and critical power).


  • Although this is N=1 early data, it may be possible to get an accurate measurement of the HRVT HR with shorter ramps.  For those of you comparing HRVT over ramp slopes, I would love to hear of your experiences.
  • HRVT power should not be inferred with steep slope ramps, instead use the 5w/min or even constant power intervals for that.

Heart rate variability during dynamic exercise


  1. Hi Bruce, were your ramps constantly rising or done in "block" steps?

  2. Incremental ramps done with Zwift. So very smooth resistance increase.

  3. If you are able to see this link, like this?

  4. OK I'm not sure what you mean by incremental. So, 130W for 1 min then jump to 135W for 1 min etc or are you increasing from 130 to 135 over the course of 1 minute?

  5. Incremental generally means a continuous even rise (changes every few secs). So 60 w rise in 1 minute would end up as a 1 Watt increase per second. Yes, Zwift can do that very well.

  6. Ah I see, I need to edit my workouts then

  7. i figured out, that if i drink something during a ride my dfa-a1 increased for a moment, so the value is falsified.
    Do you even noticed this effect during your tests?? And what do you recommened during a ramp-test, drink or not to drink?

    1. I don't think it's the drinking but that your cycling power temporarily drops. I wouldn't call it a false value. Ramp tests will be difficult to interpret if they are interrupted.