I ride a stationary bike for 60 minutes. I keep my heart rate between 150-160 bpm by pedaling a constant 90 rpms and adjusting resistance. The last 15 minutes of my workout I have to decrease the resistance a little every few minutes or my heart rate will stay over 170 (close to my max).
What is happening the last 15 minutes? Am I running out of glucose? How can I train to keep my heart rate in the desired range for the whole 60 minutes without decreasing the resistance?
I'm 47 yrs old. Male. 170 lbs. Until the weather turned cold I rode outdoors about 80 miles a week averaging 18-19 mph on mostly flat roads. Average heart rate on a 25 mile ride is 140-145.