First, welcome to the show. You'll get tons of advice and opinions here, and some of it may actually be useful.

I don't know if you've calculated your target rates incorrectly, but I suspect that either (a) you did a calculation on paper rather than through a road test, or (b) you calculated your max heart rate on a run and are trying to use that for cycling? I've found that my heart rate targets are 10-12 bpm lower on the bike vs. running.

Google around a bit for lactate threshold field tests. One I've used is:
- 15 minute warm up
- Do a 30 minute timetrial. The intention is to maintain a steady level of effort through the full 30 minutes, and end knowing you've got nothing left in the tank.
- At 10 minutes into the test, hit the 'Lap' button on your heart rate monitor, and calculate your average heart rate over the last 20 minutes.
- The average for the final 20 minutes is an approximation of your lactate threshold.

You can do the same test for your run. I bet you'll find a difference between the two.

I know this didn't answer your question directly. for me, 70-75% effort feels like I'm working, but I could hold that work level for quite a while

I use perceived effort instead of HR, because I had a lot of trouble following HR based training. All I can comment on is that a 75% effort should feel hard but sustainable. For example if you are doing a short work out, Say 40 minutes. Your legs will feel tired, but you can easily recover from the session. At least that's how I think of it.

Yes it does. At least for me it does. I go by HR feel. When I first started training I was setting off alarms on my HR monitor all the time. And yet, I used my HR zone calculations based on my age correctly. I got frustrated so I stopped using my HR monitor. Although I never actually tried doing the calculations based on a road trial, maybe that would have been better. But now, is also based on my muscular endurance. ie. how easily my muscles fatigue. I don't find that my HR is a limiting factor in biking unless I am biking on a really hilly route with steep hills. My muscles always give out before I reach my max heart rate. I don't know if that makes sense.

Really depends on how you calculated your max HR to begin with. You have different max HR's for each sport. My guess is that the max HR you are using is for the run perhaps as your calc. Max HR I come up with is 175ish. (174.66 to be exact). In order to find you max bike HR do a 20 minute warm-up on the bike and then do 3-4 maximum effort rides at 5 minutes each. Do this 2-3 times and you come up with a avg. max HR on the bike.

Since you are new to cycling your max HR on the bike will change as you body grows into cycling. You'll have to re-measure again in 6 months. Another way to track training effort is perceived exertion like hamelt said. I use 5 intervals as follows: sprint pace, Oly pace, HIM pace, IM pace, and easy spinning. Until you do a few races at each of the distances it will be hard to figure out what these paces should be though.

With enough experiernce under your belt you'll stop using the HR rate and move to a race pace range instead for all three sports.

Nothing really for me to add to the above except "Welcome to Trifuel!"
And yes...you need tougher legs but that takes time! ;)

[quote=hamlet_cat]I don't find that my HR is a limiting factor in biking unless I am biking on a really hilly route with steep hills. My muscles always give out before I reach my max heart rate. I don't know if that makes sense. [/quote]

That makes perfect sense to me. My cruising HR is in the low 120s, I can hold around 130 for long stretches, and can get my heart rate up to 170s if I turn myself inside out on a steep hill. But assuming that I'm not killing hills, Once I'm at the tail end of a long ride at moderate-hard effort, my legs just stop producing power with a heart rate in the 130s.
Not sure what that means ham_cat. either we're both normal, or we both have the same weakness to work on.

[quote=dkhartung][quote=hamlet_cat]I don't find that my HR is a limiting factor in biking unless I am biking on a really hilly route with steep hills. My muscles always give out before I reach my max heart rate. I don't know if that makes sense. [/quote]

That makes perfect sense to me. My cruising HR is in the low 120s, I can hold around 130 for long stretches, and can get my heart rate up to 170s if I turn myself inside out on a steep hill. But assuming that I'm not killing hills, Once I'm at the tail end of a long ride at moderate-hard effort, my legs just stop producing power with a heart rate in the 130s.
Not sure what that means ham_cat. either we're both normal, or we both have the same weakness to work on.[/quote]
I have no idea. I can easily get my HR up in running and swimming. But cycling it isn't the same.

This is a great question. Yesterday my brother asked me the same thing about running.

With all the good input from this thread, maybe the answer is easy to find. However, why not find a plan that you already know how to execute? When I had a marathon plan it used 4 paces. Race pace, 30% slower than race pace, 10% slower than race pace, and tempo pace (forget how tempo pace was calculated, but I could find out). Needless to say, I understood the plan from day one. Instead of adapting my training the fit the plan, it already fit.

As a side note... I need power, and a plan that incorporates it.

[quote=JulieVK] . . . 131 beats per minute . . really tough to stay there . . . but it's torture . . . for my legs.[/quote]

Then you don't have your cyclin' legs yet. Your cardiovascular system may be able to handle 131bpm, but if your legs are giving out, I'd suggest it is because they aren't built up enough. And by "built up", I mean after months/seasons/years of cycling. You could get to a point where you can hold 131 for hours then run right afterwards. It just takes time. If I had to put a number on it, I'd say you probably need 1,000 miles on the bike in one season (just a guess/opinion) before you start feeling comfortable at 130-140 for an hour or more.

How totally unscientific of you Sooner... and probably a pretty good guesstimate!