average heart rate for my runs is 80%

Your max HR may be higher than you think, but it's very difficult to get your actual max HR.  I'm 6'3" 215, and I'll turn 40 this year, my avg HR for easy runs is around 80%, and for faster runs it's closer to 90%.  It is what it is, I use the HR monitor as a gauge of the workout intensity, but it's not the whole story, and I don't really belive the percentages are overly accurate.  I rarely look at the percentages (had to use a calculator to figure it out to post this).  For all I know my actuall max HR is 199, not the 187 I figure it as, but either way, you're body should be telling you how you feel.  My HR does go up quite a bit when it's starts to get hot out, the same effort in the fall or early spring will be about 10bpm lower.  As an example, I did an 'easy' run last night.  It was 85 out, and I ran at a pedestrian pace, but my HR was still in the mid 150's, and up to the mid 160's when I hit the hills. 

How have you come to know your max HR? 

I'm 49 - turn 50 next month. My typical running heart rate is in the 130s and 140s on the bike, but I had open heart surgery last year and am on a calcium channel blocker that suppresses my heart rate. When I was off the stuff, my heart rates were about 10 beats higher in each split. So, if you go with the 220-age = max heart rate, then, yes, I am in the 75 - 90% of max heart rate most of the time.

220-age is a bad myth that keeps getting perpetuated. It was based on a quickie one off study that had about 10 people in it. Even the docs in the study are surprised at how it took hold. I would bet that your max HR is higher than you think.

John

This.  That's why I wanted to find out how the OP was coming to know his "max" HR.  

Agree the 220-age rule is completely useless at best and could be hurtful to some.  Max heart rate is pretty much determined by genetics.  I am 52 and my max HR would be 168 by this rule.  I know for a fact I can hit 190-191 running or biking.  So, the 220-age rule is low by 22-23 bpm.  That is not a small error that would dramatically affect the results of heart rate zone calculations for training.  In my case, I simply wouldn't have been working out as hard as I thought I was and it wouldn't have been 'unsafe', just inaccurate for training.  Others could find completely different results.

Read this BT article.  (also here in this thread with 21 pages of discussion)

Remember any "study" has a standard deviation to it, who knows where you are, better to do the LT tests as stated in the article.  At 44 I would be seriously under training if I used the 220-age "guidelines"

Okay, some good stuff here.  Thank you all for your input.  I've always used the 220-age rule as that was what I was taught by my coaches and even a personal trainer I hang with.

Now that I realize my max HR is probably way higher then it is, are there any accurate studies out there for determining these numbers?

I've usually gone by the "if it feels good do it" way of life.  My training is no different.  When I'm training hard,  I train around how I feel rather then a digital number on my wrist.  I was going over my past averages and noted how high my numbers were.   That is what prompted me to ask the question in the first place. 

Oh well, guess I'll go back to the simple days before all these electronic gizmo's were around and just use the toys as a very rough guideline.

HR training is what it is, a method and not perfect because environmental factors can have a big affect on your HR. This time of year in FL I barely use the HRM as the heat & humidity will elevate the HR as the body is trying its best for cooling.  I use the HRM mostly in the winter months when conditions are "ideal" for running to make sure I have the proper feel to my runs.  It may allow better correlation to RPE, but you've been training for awhile and this is usually more of an issue with beginners that will often underestimate their RPE. I guess you want to know Max HR to get "proper" training zones, do the LT test on a day when you have a hard run scheduled.

Oh, an accurate study for the MHR is probably a dreadmill test.  Look up 'cusetri' profile, he has a video of himself doing a treadmill test.

You do have to get your HR tested to know your max.  That being said, I run at about 80% myself.