Monday, August 16, 2021

DFA a1 HRVT and ramp slope

 Official study data - Ramp slope and HRV a1 thresholds - does it matter?

 

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).


Summary:

  • 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


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Sunday, August 8, 2021

To train hard or not, that's the question

 New - Update Review in Frontiers in Physiology

 

To train or not to train - that is the question (Shakespeare - if he was an athlete).

We ask ourselves this on a regular basis since if we are not sufficiently recovered from prior hard workouts (or are subclinically ill), we can make matters worse by doing high intensity training.  If we have not fully recovered, we should just take it easy and do a "recovery day" style of workout.  Many studies have pointed to resting HRV as a good indicator of "readiness" to train.  Abundant journal article, blog posts, phone apps and HRV experts have written and recommended this.  The advantage to waiting for proper HRV recovery is to get a superior training response and fitness outcome, which has been shown by several studies.  Even our gold standard HRV software, Kubios has a "readiness" app for Android.

However, for some folks, it is difficult to find the calm, restful time needed at the beginning of the day and do this on a consistent basis.  There are kids to take care of, dogs to feed and a job to get to....  In addition, this type of measurement needs to be done often enough to get trends based on previous values.

In lieu of resting HRV as a readiness score, can we leverage the DFA a1 relation to exercise intensity as a surrogate?  In the last post we discussed the utility of DFA a1 as a marker of endurance exercise fatigue in ultra-marathon runners - while they were still exercising.  If the a1 is suppressed immediately post ultramarathon, is it suppressed the day after?  Although we do not have published data on this, I would like to begin to share some personal observations on how I use a1 as a training guide in alerting me to a fatigued state.  This type of observational evaluation should be easy to incorporate into one's training regime.

What are we looking for?

In essence we want to see if the DFA a1 is not behaving normally during or past the warmup before embarking on the decided session intensity.  For instance if your HRVT (power/run speed or HR at which a1 passes 0.75) becomes altered, this is an indication that the autonomic nervous system is being affected by some perceived stressor.  In my case, I start a session with cycling at a warmup power of 155 watts (50w below usual HRVT of about 205 watts).  At the warmup power, DFA a1 is usually well above 1.25, and it will take a few minutes at the HRVT/AeT power (205w) to begin to see the a1 drift to about 0.75 (and stay there).  Here is an example:

  • What happens the day after 2+ hours of mixed HIT and polarized training?  
  • What about after a really poor nights sleep?  Let's find out.

 

The following graph consists of an overlay of the plot above (Fresh), another day of "No sleep" (NS) and a third session consisting of the day after the HIT interval sessions (Fatigue).  The heart rate monitor was the same in each case, same room temp and fan speed, time of day, nutritional status, artifact <1%, etc.  

Fresh - This consisted of a 2+ hour ride with 10 minutes at the HRVT/AeT (above graph), 10 minutes just above the MLSS, a 60 sec Wingate max and otherwise mainly zone 1.  Although this may seem trial to many of you, keep in mind that I'm not a superior athlete and am approaching 65 years old.  Also of note, the "fresh" day was preceded by 3 days of "easy" cycling of 60 to 90 minutes each day (all zone 1 of 3).

Fatigue - This was the day after the "Fresh" session described above.  After the usual warmup, I cycled at about 15 watts below the HRVT for 5 minutes to see what would happen (so in zone 1 throughout).  Since the DFA a1 dropped so low, I did not extend the interval for 10 minutes, even though I wasn't subjectively tired.

No sleep - With the "no sleep" session, I had not done any exercise for 2 days and normally would have had very "fresh" legs to hit it hard.  Unfortunately due to some events beyond my control, I only had about 2 hours sleep.  I was pretty tired and did not even bother doing anything above the warmup power since my realtime a1 app, (Fatmaxxer) was already indicating lowish values.

  • Black - Normal/Fresh
  • Red - day after HIT
  • Green - poor sleep

Observations:

  • Heart rates were very close in all conditions (even during the interval) and would not be particularly useful in separating out fresh vs the others.
  • Poor sleep (green) had marked DFA a1 suppression at warmup power - values were near 0.75 at a power 50 watts below the HRVT/AeT.
  • Fatigue (red) showed lower values during the warmup but plummeted quickly when power was raised to near HRVT (about 15w below).  In fact, values passed 0.5 and were approaching 0.25 while in zone 1 - these are usually seen at intensities above the LT2, VT2, MLSS, CP.  As mentioned, I felt a bit tired and could have gone on (but did not).


Practical lessons:

  • Extrapolating from our ultramarathon study, it appears that DFA a1 behavior is altered even 24 hours post HIT training (and the day after poor quality sleep).
  • Realtime observation of DFA a1 while warming up and over a short low intensity interval near the HRVT/AeT (still zone 1) shows potential as a marker of persistent fatigue.  
  • Incorporating this comparison into the warmup or a brief interval done near the HRVT can provide interesting insights that may translate to a "readiness" to train indicator. Suggested comparisons include DFA a1 observation during the warmup and a brief (5 min) interval near the HRVT/AeT power - looking for unusual a1 suppression.  As noted in my example, DFA a1 values below 0.5 occurred with a short interval in the upper bounds of zone 1 (or zone 2 of 5) indicating autonomic perturbation.
  • Further study is needed to determine if DFA a1 can be used as a metric early in the exercise session to optimize what type of workout is most appropriate that day.  


Heart rate variability during dynamic exercise


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