VO2max Discrepancy (Garmin vs Firstbeat)

subra said:

This means that if the body weight is reduced, the VO2max in a spiro lab test increases,

In a lab VO2max is measured in L/min. This is absolute VO2max and weight (body mass to be precise) has no bearing on the result.

subra said:

However, reducing weight alone does not change Garmin's VO2max, as weight is not included in the estimation formula.

To make it relative to other athletes and easier to understand,  the measured result from a lab test is usually re-calculated and presented as ml/min/kg. Every VO2max estimate (ie one not measured in a lab is presented as a relative result in ml/min/kg. That means a reduction in weight (one of the input variables) will have the effect of increasing the relative VO2max. 

Somewhere along the line, weight is an input variable for an estimated (ie not directly measured) result presented in ml/min/kg.

A little bit of thought, and a little more understanding of simple maths, and it's clear that since the units are volume (ml), time (min), and body mass (kg) these factors must be in the calculation somewhere either directly or indirectly.

True that weight is not measured, but it is a major factor. The less a person weighs, the less energy they will use at a given pace. I'm 30 lbs. over weight right now.

If I weighed 30 lbs. less right now, and did a run, my VO2max would probably measure in the high 30's instead of 30, because I would be able to move my body at a faster pace with less effort.

Just because it's not measured in a test, does not mean it's not a MAJOR factor.

I may be over weight right now, but I do exercise regularly (as is reflected in my RHR of 59 (which used to be in the high 80's)). I was a fitness instructor in the army (back in the 1980's), so I have a good basic understanding of fitness. People get too hung up on science and formulas and stuff, and forget other factors that come into play.

I mostly agree with what you are saying, but do not agree with what subra is saying.

 VO2max measured during a test is independent of pace or weight. It’s simply down to how hard a person can push themselves during a test, which is a measure of the maximum amount of oxygen (volume) that can be consumed for the duration of the test (time). Pace, distance, or body mass is immaterial for the test. The starting point for a test is such that a person will complete the test to failure within 12 to 14 minutes to reduce the chance of fatigue affecting the result. The pace or distance, speed or power attained is simply an outcome. A fitter person will get a better outcome whether they be overweight or underweight, fast or slow. Once the absolute measurement is obtained it’s made into a relative result using body mass as an input so that a meaningful comparison can be made between individuals. It’s actually a reasonably crude tool to use for fitness in isolation. And as already discussed, different tables give different categories for the results. 

Once a person’s VO2max has plateaued following sustained training, other aspects of fitness need to be used to meaningfully assess fitness. Pace at VO2max is a good one for example. While absolute VO2max will not change in a well-trained person as a result of weight loss, relative VO2 max will for the reasons already stated. And as recognised, if weight is lost, pace at VO2max is also likely to increase too. 

I get what you are saying, and understand that weight is not directly measured on the test. But IMO weight is still a major factor indirectly.

I would like to see the results of the same person taking the same VO2max test twice. Once as normal, and once with a 30 lb. weight vest on.

I exercise regularly, and try to get at least 30 minutes per day. I could probably do more high intensity workouts, but at least once a week I do a workout where I try to hit my max heart rate multiple times. I could probably do that one more to increase my VO2max, but I think losing weight would have the most impact. And based on this chart from Garmin, it agrees...

weight is still a major factor

Yes it is, of course. As others discussed here, the weight is not an input of the algorithm that the watches uses to estimate your absolute VO2 Max fo running. This algorithm mainly uses an estimate of your ventilation (VO2 using HR and HRV) during "on" efforts (ie non rest) and examines the relaltionship between your output (pace) and VO2 to estimate your VO2 Max (even with sub maximal efforts). The key manual input to that algo is your HR Max. Other factors are altitude and temperature.

If you put on a 30lb back pack and go running, you will get a lower performane condition and a lower VO2 Max estimate. You might not see the drop because the run-to-run VO2 Max changes are dampened.

A study of treadmill exercise at 75% of VO2 Max, varying additonal weight of 10,20 30kg has shown that each additional kilogram increases oxygen uptake by 33.5 ml/min and heart rate by 1.1 beats/min. Interestingly, this relationship doesn't vary much with the intensity of the exercise.

https://pubmed.ncbi.nlm.nih.gov/648506/#:~:text=In%20dynamic%20exercise%20oxygen%20uptake,of%20the%20dynamic%20work%20load.

However for the UI, the watch displays your relative VO2 max so that it can benchmark you against peers. The conversion uses the weight you input in the watch.

If you gain 30lb and you don't change the weight on the watch, your relative VO2 Max will be over estimated since you keep on dividing the absolute value by a number lower than the actual number. 

You don't need to update your weight for every couple of lb of variation though. If an athlete weighing 200lb enters 190lbs instead, his relative VO2 Max of 50 will change to 52 assuming the absolute value remains the same. These 2 points are within the average 5% error of the absolute VO2 Max estimate, and "run-to-run" contextual changes (health, environment) so the weight change might not impact the estimates that much.

I respect that you seem to know all the scientific details and formulas and such, but I like to keep things simple and basic.

IMO, if a person did a VO2max test, then fully recovered, then did the same VO2max test at the same lab wearing a 30 lb. weighted vest, he/she should get a lower VO2max score on the test with the additional 30 lbs.

Based on the chart I posted, Garmin seems to agree that lowering my BMI (losing weight) is the higher priority to improve my fitness age (increase my VO2max), so that is what i am going to try and focus on. Maybe if I lost this 30 lbs. I wouldn't have to beat the crap out of myself as much to get in a good workout, and would have enough energy to do more of them, which would improve my VO2max even more. 

And getting back to the original topic, I think a VO2max of 30 (for a 66 year old male) should be at least in the "fair" range for Garmin. Most of the charts I have found say it's average or above average.

IMO, if a person did a VO2max test, then fully recovered, then did the same VO2max test at the same lab wearing a 30 lb. weighted vest, he/she should get a lower VO2max score on the test with the additional 30 lbs.

Your opinion lines up with reality!

improve my fitness age (increase my VO2max

The fitness age formula from Garmin doesn't use Vo2 Max any longer, but you are still right, you will improve your fitness age and you will increase your VO2 Max, all other things being equal.

I wouldn't have to beat the crap out of myself as much to get in a good workout,

Although high internsity workouts have shown to increase VO2 max faster than low intensity ones, low intensity workouts will help increase your VO2 Max, compounding the increase due to the loss of weight.

I think a VO2max of 30 (for a 66 year old male) should be at least in the "fair" range for Garmin

No comment on that one :-)

Etupes25 said:

Although high internsity workouts have shown to increase VO2 max faster than low intensity ones, low intensity workouts will help increase your VO2 Max, compounding the increase due to the loss of weight.

Most of my workouts are lower intensity. Like right now I am going to walk 1 mile (low intensity), do 10 hill repeats (high intensity), then walk a mile (low intensity). I am going to record it as a run with a workout I created for the hill repeats. It's a mile to the hill, and a mile back, so I set them for the warm up and cool down in the workout.

a workout I created for the hill repeats.

Hill repeats are an excellent workout for any runner, and a staple for many 5k-10k training plan and up.

Alas, the watch doesn't give you full justice for your effort on hills and will under-estimate your anaerobic training effort (if any) and possibly your performance condition, aerobic training effect and your VO2 Max for that run. This is because pace is impacted by the slope. That shouldn't preclude you from doing the workout though as the benefits will still be there.

For a good VO2 Max estimate, the second most important input is the quality of your running data: your HR (use a chestrap) and your pace (run on flat terrain using the best GPS setting).

The first most important input is your HR Max though. How did you determine your HR Max?