Firstbeat VO2 estimation - comparison to true gas exchange

bjrmd Thanks for your interest in the work that Firstbeat is doing and taking the time to write up your inquiry. I skimmed your blog, found it generally sound, and promise to have a closer look later. In the meantime, if you have any specific questions, feel free to shoot me an email ([email protected]) and I'll do what I can, within reason and ability, to fill in any blanks. Firstbeat recently underwent a sort of brand renewal project, and I can't count the number of times that our key players iterated and reiterated that being 'science-based' is a core value for the company. 

I don't recall seeing that Fenix 5X VO2max validation study you referenced before, so thanks for sharing it. I will say, however, that it can be frustrating to see studies like that published, purporting to test the validity of a device - and Firstbeat analytics by extension - while clearly documenting the fact that they didn't follow the basic instructions included with the device and basic guidance that is part of practically ever write up we've ever done. 

"Possible limitations of this study included wrist placement of the GF5 with each participant, self-perceived exertion level of each participant completing the Garmin outdoor run, and only conducting one outdoor run with the watch. The GF5 manual recommends watch placement above the styloid processes of the radius and ulna. During some testing, there was potential for the watch to slide down a participant’s wrist due to wrist diameter and size limitations of the watch strap. Garmin states that a runner can obtain their VO2max estimation with as little as one 10-minute run outdoors, and the measurements become more accurate the more one trains with the GF5. Due to only running once outdoors, the GF5 may not have recorded the most accurate VO2max estimation."

I'm glad you are willing to answer some questions and perhaps consider some suggestions.

An email is on the way but I just wanted a couple of things documented on the net if you don't mind.  Here goes:

Are you getting good agreement with the derived respiratory rate (with a valid ECG source) and benchmark values?  My personal experience with the resp rate matching a Hexoskin output is not great (although the pattern is partially matching).  Is this something that your algorithm will improve over time or just a limitation of the tech?

In regards to cycling, what is the ideal interval intensity and duration for optimal VO2 max estimation by your method. Since the 3 to 5 minute max constant interval power is generally related to VO2 max power, does your formula like to see some of that?  Or are you looking for 10-20 minute segments?  If the longer segments are needed, does that handicap an athlete doing primarily shorter high intensity segments?

Is any consideration being given for a "Maximal Aerobic Power" display in watts (in the Garmin metrics) for the cyclists out there?  As I'm sure you are aware, training at or near the VO2 max may be very useful.  Although knowing the VO2 max as a number is interesting as an index of fitness, it would be of some practical value to convert that to a power figure for training purposes.

Yes, that Fenix 5 study blew it.  However, a similar attempt with proper HR monitoring, accurate cycling/running power, would be nice to see.

Thank you in advance and nice hearing from you!

I wrote a followup review of the Firstbeat VO2 estimation under diverse ambient temperature conditions.  The consistency was quite good despite large variation in heart rates.  Also discussed is the effect of temperature on VO2 max in general, stroke volume and interesting data using beta blockade in exercise.

Hi bjrmd, thanks and appreciation for the first piece and the follow-up. Very interesting to read (well done).

I finally went through an official VO2 max gas exchange test - here is the comparison to the Firstbeat results as well as a discussion on test interpretation:

VO2 max by gas exchange Vs Garmin/Firstbeat - my data

Last post in the series:

Why is the Garmin Firstbeat VO2 max estimate inaccurate, can we do better? 

For those of you interested in the FTP vs MLSS equivalence, I have put together an interesting review:

• Does the FTP relate to the MLSS - Yes, No, Maybe? 

A look at the usage of smart trainers for cycling metric, ramps and training:

Smart trainer usage in physiologic testing and interval training 

A review on a recently published case report using non linear HRV (DFA a1) as a method of zone 1 demarcation (I'm the author):

A just published article on DFA a1 and Zone 1 demarcation