@SoliD - Yeah after these years doing this to ourselves it sometimes still makes no utter sense what so ever. It's quite frustrating but equally what keeps a certain mystery as you say. If we all knew how to get 100% out of ourselves at any given time it would be rather boring. The chase of form is a great thing.
Was talking to my mate about it last week. In the midst of big base block I done last year I could jump on the bike feeling fresh, ready for a big structured session, and end up bailing it after 1 effort..... then other days I could have done 3 hour rides both days before and jump on the bike for another 4 hours feeling like utter rubbish. Barely even the motivation to get on the saddle then 4 hours later come home having averaged 34kmh and going like buggery. NO SENSE! I've almost given up and just put way less thought process or effort into understanding aspects of training/myself now. Take it as it comes.
incredible numbers and some I would love to be able to achieve some day! 
