You don't say what cadence/gear combo you are using. If you try to push too big a gear your legs will fatigue long before your HR gets high enough. HR is a cardiovascular measure. You need to use an easy gear and spin it fast to get your HR up. If you are used to pushing big gears slowly, the gear you should be in will feel ridiculously low and wimpy, but that is the point. It SHOULD be easy for your legs so they can do it for a long time. Spinning lower gears faster produces more power for the effort expended. Going the same speed, say 17-18 in a big gear may feel hard, but it is just your legs feeling it; you may not even be breathing too hard. Doing the same speed in an easy gear at 90-100 will get the heart and lungs involved. You will be breathing harder, but your legs will last longer.
OK, all fine and good, Rainman, but what gear are we talking here? Obviously it depends on your particular fitness level, but I will try to give you some benchmarks. When I first started working on cadence, the most I could consistently pedal 90 was about 39/21 (54 inch gear). Now I've gotten a little stronger, and 39/17 (62 inch gear)feels like 39/21 used to. If you have a triple, 42/19 (60 inches) is close to 39/17. You may be much stronger than I. To calculate gear inches:
Teeth on chainring divided by teeth on cog times wheel diameter in inches (for 700c use 27 inches).
Regardless of what specific gears are involved, gear inches is a consistent measure of effort, ie 62 inches feels the same whether you are using 39/17 or 48/21.
Regards,
Raymond
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