Originally Posted by ws46060
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.
You are about my age, about my size, and you have a similar maximum heart rate. What are you using to set your heart rate range.
By the carmichael system, I end up with an aerobic training range from about 80 BPM up to around 145 BPM. I would sometimes do some tempo rides at the high end of that range - say 149 BPM for 20-30 minutes - but that's a pretty hard workout. I will sometimes do a hard hillclimb around here (1350' in 2.5 miles) in the high 150s / low 160s, but that's about 25 minutes of real pain, and I couldn't do it for a full hour. It sounds to me like you are in a similar zone, since you can't keep up the HR for the whole hour.
I think you're in what's known as "no mans land". You're HR is higher than the HR that would give you the best aerobic benefit, and yet you're not riding hard enough to improve your anaerobic system.
You might want to pick up a copy of "the ultimate ride", and use it to set your ranges and understand what kind of training to use for each energy system.