Last December, I started doing HIIT routines on an elliptical machine three days per week. On Mondays I do a modified version of what Martin Gibala calls "The Norwegian". For me, it entails four 4-minute intervals with a target heart rate (HR) of 140 bpm and a 2:30 recovery period at ~106 bpm between each high-intensity intervals. I warmup for 3 minutes at ~106 bpm and after the last interval I do a 2-minute recovery period with no target HR. The whole routine lasts 28:30.
On May 8, I shortened the recovery period to the current 2:30. Since that time, not including today, the average of my average HRs is 128.2 bpm (s.d.=1.1 bpm), the average of my max HRs is 155.9 bpm (s.d.=3.9 bpm), and the average of my Training Effect is 2.9 (s.d.=0.1). Normally, my Garmin estimated Recovery Time is about 18-19 hours.
Today, I did The Norwegian as normal with an average HR of 128 bpm and a max HR of 159 bpm. What's strange is my estimated Recovery Time today was 13 hours and my Training Effect was 2.3. So what happened? Did I have a sudden improvement in my fitness level or something else?
Also, when you use an elliptical how is average run cadence calculated? I take the wristwatch off during my HIIT routine. Is there an accelerometer or something in the HR sensor? Thanks for your feedback.