Today I did a 42 minute short interval heart rate workout on the treadmill with an average heart rate of 148 bpm. But that average is a bit misleading because from the 30 minute mark to the end my heart rate never dropped below 150 bpm and for the last seven minutes (35 - 42 minutes) I kept my heart rate at or above 160 bpm (between 160 -165 bpm). This is by far the longest I have been able to maintain my heart rate above 160 bpm. This tells me that I have raised my threshold heart rate up to or even slightly above 160 bpm.  For the last seven minutes I was running 6 minute mile pace with a 5 degree incline (I kept a 5 degree incline for the entire workout) which is equivalent to a 4:45 mile pace effort on a track.