Garmin, VO2 Max and hot weather

So I’m ngl it does feel kind of good when Garmin tells me my fitness age is 20 or whatever but I understand that one of the primary parameters used in Garmin’s (or the company that Garmin hired) estimation of VO2 max is HR.

So naturally, when training in the heat and HR is higher because body is spending energy to cool itself, reprinted VO2 max and ‘fitness’ as reported by Garmin also decreases.

Whilst Garmin can record don’t temperature I don’t believe this factored into its algorithm for determining VO2 max.

So anyway all this got me thinking, despite the obvious contribution that heat has to HR, will VO2 max actually be lower in higher, uncomfortable temperatures (like 31c upward). Anyone know anything about this topic?

Looked up something similar recently. I wasn’t able to find an exact answer but that Garmin factors temp in.

What Is Heat and Altitude Performance Acclimation? | Garmin Customer Support.

Hope this helps start the search

It should be incorporated, given that they also have their heat acclimatization measurement.

Ive not found mine to change with temperature (and the UK sees lots of changes in temperature); where it does seem to change is on the type of ride. It’ll fall with group rides where I’m not making a constant effort for a rise in HR (particularly a tough chaingang (paceline). Whereas on a TT or training session, it’ll rise.

This study suggests there is a link between temperature and VO2. However, I believe it may be distinguishable from the concept of VO2 Max, which is a similar/related but distinct measure. While VO2 may vary based on several factors (including temperature), VO2 Max is the highest rate at which oxygen can be taken up and utilized by the body during intense exercise.

Heat acclimation increases plasma volume and cardiac output.

Thereby increasing vo2max.


I was just thinking about something similar but about altitudes effect on VO2 max.

I live at 1200m/4000 feet, and when I was at sea level recently I was getting higher VO2 max readings off of Garmin. Which makes sense in the same way FTP is lower at altitude, but not sure if there is an altitude correction for VO2 max published.

Obviously the maximum amount of O2 processed when measured at altitude is going to be less than that measured at sea level.

I’ll definitely think about this when training in the heat as a bit of extra motivation.

Garmin always raises my VO2 in the summer heat

Link doesn’t want to work on my phone but interesting that temp is factored in. I always assume that wasn’t the case because on sporadic hot days all my stats go bonkers

Would you agree that prior to becoming heat acclimated, high temperatures adversely impact VO2 during an activity without either decreasing or increasing VO2 max?

This is a good question and maybe I should have added that this mainly when not acclimated to heat.

Anyone in the U.K. right now I’m sure can relate :smirk:


FWIW: Garmin relies on weather data (Garmin weather), rather than its internal temperature sensor (which is skewed by the heat generated by the device itself), in determining heat acclimation status, and I believe it is based on the weather at the start of the ride. Hence, if you start the ride in the early morning (when it is cool) and are out when it gets hot, those hours in the heat would not be included in Garmin’s heat acclimation status. In addition, if the weather station is far from your location, then the device would potentially use inaccurate weather information.

1 Like

All I know is that performance goes down! And then it doesn’t… In the last month+ I’ve been starting intervals in 90+F / 32C heat, and Monday the temps dropped to 79F / 26F and I did my best 3-min power of the year! Yeah for max aerobic power! That second interval I thought my chest was going to cave in :rofl:


^^^ what Cog said!

1 Like

Metabolic rate will be somewhat higher during exercise in the heat, but that is primarily due to a shift towards greater carbohydrate oxidation (so more energy produced per O2 consumed) than any increase in submaximal VO2.

In honor of Bill Finks’ rapidly approaching 90th birthday, here is what I believe to be his only first-author paper (out of >100).


Heat stress leads to increased use of glycogen. After heat acclimation there is glycogen sparing, correct? But is that sparing only relative to heat-untrained? How does glycogen utilization of heat-acclimated compare to a baseline during the months with cooler weather. In other words, am I always burning more glycogen at say 85-90F versus 55-60F?