totally un-scientific on my part.

Have a 10+ year old blackburn mag trainer. collected dust for about 8 years. So still in good shape. Since I've been back on my bike for the last year and sporadic two years ago, it still does the job, TO WEAR ME OUT.

I can set the thing to different level of resistance and I can also shift around in my gears. In other words, I have lot of freedom on how hard my workout is going to be. It doesn't matter which gear you are in. It's how much power you are generating at the cadence you are spinning. I can make it like I'm climbing a 20% grade by setting the mag unit to max and "riding" at 52x11 gearing. or be lazy and set the mag unit to zero resistance and spin at 39x23 gearing.

So if you are getting crushed by the trainer, think about dropping to a smaller chain ring instead of the large one and maybe even go with bigger (teeth count) cog. Don't think of it like if you are riding on the flat or on a climb. Don't compare your gearing out on the road and on the trainer. Trainer has nothing really to do with the terrain you ride. You can set it to mimic "epic" climb or leisurly climb or coasting on the flat. It's just a matter of setting it up for the kind of training you want to do.

As for your HR, everyone has their natural range. Need to start thinking in terms of your resting HR and max. As you get fitter the max/resting ratio will get bigger because your resting rate will drop but your max will stay constant.

my max hasn't changed in years and I'm pretty old. Max is around 203-210 depending on amount of sleep I had the night before, how fresh I feel in the morning and amount of booze I drank the night before. my resting HR is still in the low 50s. That's what my doctor said just last week. What I am trying to say here is that don't compare your HR to others. compare your HR to your base line both at rest and your max HR. Everyone has a different set of numbers.

Another point having a low HR is not necessarily a good thing. I tend to get light headed fairly often and near fainting spell several times a week, thus my visit to the doctor last week.

Hope this helps with your trainer ride.