Threshold Power

Also used as an acronym TP in Xert and sometimes described using the more colloquial term FTP, Threshold Power is a Fitness Signature parameter that represents the highest power that can be sustained without accumulating short-term fatigue.  Threshold Power can generally be sustained for just under an hour by most athletes, assuming that the discomfort generated is tolerable by the athlete over the entire period.

Worthy of note is that Threshold Power is affected by work performed, with work performed at higher intensities having greater affect.  This must be true otherwise it could be sustainable at any time, even after an hour of high intensity effort.