Altitude Training Physiology Question : AdvancedFitness

Tim Grover spoke about preparing Kobe Bryant against an opponent whos performance would start to drop off after about 6 minutes. Grover planned Kobes training so that he would peak at 6 minutes.

One of the methods he mentioned to achieve this was to have Kobe wear a training mask then take it off after a certain time period and as Grover described

“you can maximise a person’s O2 capacity so you can deprive O2 to a certain point. During the time where you need it most take the snorkel (mask) off, more O2, more RBC are recruited and now all of a sudden you have that burst of energy. You cant always train at altitude but there’s way of creating the same effect “

Can someone please explain the desired physiological effect of taking the mask off after a certain time interval during training and how this can make Kobe “peak” at around at a desired time?

I always thought that that lack of oxygen can increase RBC production and other things and that’s how we can increase performance? So how does taking the mask off give the desired effect?