The Garmin FR235 has a ‘race predictor’ function. This tells you how fast it thinks you can run a 5k, 10k, half marathon and full marathon. It is based on your aerobic fitness, which is shown as a VO2 max estimate.
(Note the words ‘prediction’ and ‘estimate’).
VO2 max is the maximum amount of oxygen (in mm) that you can consume per minute per kilogram of body weight at your maximum performance.
(Note: ‘can’ consume (as opposed to ‘do’ consume), and ‘maximum performance’. Let’s add ‘per minute’ in there as well).
The Garmin blurb says ‘this projection also presumes you have completed the proper training for the race’. It doesn’t say what the proper training is, but I’m guess Couch to 5k and a month of consolidation with the odd smoothie probably doesn’t cut it.
(Note: ‘presumes’).
What all of this adds up to, for me, is a kind of Utopian ‘potential’. I think this little gadget is telling me that if I ate, slept and trained like a professional athlete, ie, had ice baths, a personal trainer and personal masseuse (be happy to try that one), dietician, cross-trained, stayed injury free, etc... I might just be able to run a 5k in 24’12”.
What it means right now, is that 62.5kg of me can run at that pace for 1 minute. Not 24 of them, though. And I am afraid that my training, if one could call it that, will always veer toward the improper side.
But if my body was in the right hands, people!!!
There is no way I could ever imagine running any of the times it helpfully predicts! It's a nice feeling to know my watch thinks so highly of my running potential however! Seriously though, (in my case anyway) maybe the algorithm doesn't take sufficient account of age. i.e. a good VO2 max is no good if paired with a decrepit set of pins etc? Good fun though! 
My VO2 max made me smile ! 
Playing in the zones on a slow 5k 😊
Signing up for a race?
See a straw, clutch it tight!
Me running a race in the mid 1980’s!! 
