In reply to Mr-Cowdrey:
HR training is a rough guide only and false-positives could relate to all manner of things; lack of sleep, slight cold, poor readings from equipment, dehydration etc. You'll see that, to take cycling as an example, where data matters people train with power readings as opposed to HR readings but even then it still comes down to how accurate the meters are.
Generally I'd take your HR zone training with a pinch of salt and use it coupled with other data, even if that is just how you are feeling on the day.
To take your example from the book, even those terms are very loose terms. Example, define 'Short sentences'.
Joe Friel talks a lot about HR and power training on his blog:
http://www.joefrielsblog.com/