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The warmup readiness check is displayed 12 minutes (on the 920XT) into an exercise. Usually you will still be warming up then. The readiness check will display a message something like “Fair”, “Good”, “Excellent” indicating how the watch thinks your readiness for the session might be.
FIRSTBEAT write this recovery algorithm. They use Excess Post-Exercise Oxygen Consumption (EPOC) and TRAINING EFFECT (TE) to calculate Training Load (TL).
VO2max estimates are used in these calculations.
I haven’t seen the full calculation. HRV measurement is used to work out the number of breaths. (Different from resting/waking HRV measurements). The CURRENT session’s Training Load and EPOC is used to work out the current VO2max and then compared to your last session’s VO2max. The closeness of the two indicates your READINESS.
Other factors are brought in, such as the amount of time remaining from your previous session’s estimated recovery time.
The algorithm calculates a value; let’s say 568 and then that numeric value is set against a scale to give you the FAIR or EXCELLENT readiness.
Cool! Certainly very clever Mr Firstbeat.
You can probably see many possible flaws such as: if your previous session was a bike session then power data is required by the 920XT to calculate VO2max. And such as; what if your last session was a swim session? (A: no HR data at all). Maybe other factors too.
However I’m sure it is easy to criticise many measures. This is a simple to interpret measure that IS potentially useful. I think we can take it that FIRSTBEAT do base it on sound science.
Don’t treat the brevity of the information provided with this check on your watch with disdain or scorn. It’s useful !! There is science behind it !
Combine this useful information with a waking/resting HRV reading and you have a very good steer on your readiness for the session ahead.