Originally Posted by
mollusk
The effort level in the 5 minute part is crucial. It is designed to deplete the "high octane" muscle fuel. Sandbagging it will throw things off. Also some people have a lot more anaerobic capacity. 5 minutes might not burn it all off.
I'm not a fan of the "depleting your high energy stores" idea behind the 5min pre test interval.
Your PCr stores will be replenished during the recovery period (as shown by P nmr spectroscopy). If they weren't what is the point of the 0.95 factor? If your anareobic energy was truly used up the 20min would be at no more than cp.
However, I do think you need a solid and consistent warmup. A 5 min vo2 interval does that, but I don't think it should be an all out 5 min test, more like 105 - 110% of your last / expected ftp.