After warming up and beginning to push, my heart rate climbs to 85% of max and I breathe hard. It's uncomfortable and I'm hurting. In about 15 minutes, my heart rate climbs even higher to 90% of max --but I'm not breathing as hard and the effort is more comfortable. What's going on? 

The last time I did intervals, my heart rate was about 15 beats per minute higher than usual -- it peaked at 184, a new high for me -- and the workout was a huge effort. Does this indicate overtraining? I hope not because a week off to recover would be a real setback in my training goals. 

 I'm 32 and been riding for 16 years, but I've just begun using a heart monitor. Last winter, when I was training only three or four times per week, I checked my max HR on a hill and it was 189 bpm. My average for a time-trial effort was 170-175 bpm.  Now, after several months of increased training, my maximum is down to 175 and my TT average has fallen to 165.   When I go past 165-170, I often flag and my legs sting, although last winter I could ride through this. I had a virus that hung on in the spring. Do you think that's what's causing this? 

I do a lot of long-distance rides, including double centuries and brevets. During the first few hours, I can raise my heart rate to 160 or 170 bpm for several minutes at a time with few ramifications.  However, as the ride goes on, particularly after the first 100 miles, it's impossible to get my heart above 150 bpm. My legs don't burn, but I feel like I just can't get enough air. This seems to happen even if I stay below 160 bpm early in the ride. What's making my max heart rate decline? 

I have read with great interest the discussion regarding stress tests for heart health. I'm 59 and just bought my first road bike in over 30 years. I'm addicted! I use a heart rate monitor and my maximum heart rate should be 161 beats per minute, but when climbing or riding hard I easily reach 155-160. Is it harmful to be so close to my maximum?

I calculate training zones by percent of max heart rate. I've started a new program, and I'm not sure how much longer I can endure the daily pain.  For instance, I'm doing 20-minute intervals at 90-93% of max heart rate. That's higher than I time trial in competition. So I'm wondering if my training zones are calculated incorrectly. Help! 

I'm 55, have been off the bike for five years and gained significant weight. I also had two angioplasty procedures. Now I'm riding again, but my cardiologist recommends a max heart rate of 145. It's hard to keep it so low. I want to train normally. How can I convince my doctor to allow me to do that?