Left at 5:30 this morning and 15 minutes into the ride decided to ride controlled hard tempo up every hill with heart rate in mid 160s to low 170s. Since there was next to no flats on the ride, I spent about 40 minutes doing these intervals in the pre-dawn darkness and recovering on descents. It being dark, I had my light on, which completely fritzed my heart monitor, so I went by RPE, occasionally turning off the light to check the heart rate -- when the light was off the HRM magically resumed functioning. (Additional benefits of a helmet-mounted light: (1) the lamp is too far from bar-mounted electronic gadgetry to cause interference; (2) since the light "follows" the eyes it is easy to read HRM and computer displays with no need to use gadget backlights.) Thus, I became very well acquainted with my bar-mounted light's on/off switch.
Thought I'd try to ride these intervals in low gears. I am not much of an uphill spinner, so this was a new challenge: reaching the desired exercise level and staying in it for 3-12 minutes, depending on the length of the hill, while riding a smallish gear. It worked pretty well after a while. When I felt like I was bogging down, I concentrated on spinning smooth circles and breathing, which got me over the tough parts. A hard ride this was.