How do I calculate my MHR?

Yes I know there's loads of info on this site how to do it, but I have a garmin 305, I am 36 yrs old and I know the old calculation of 220-age but don't think that works for me (as during my run yesterday my HR got up to 190 at one point and I wasn't running flat out at all!, I was running comfortably for the whole of my 5.5m run, average was 173)

I have read that to find your MHR, you should run flat out for 4-10 mins and read the highest from there, but I can't sprint for that length of time!, any other options?

I just used that and it gave me exactly the same as 220- my age....

And on a bike I've had 11 over that and running 13 over that......

I will no doubt be contradicted, but I am not at all sure that focussing on heart rate is the right thing to do.  I believe your perceived level of effort is a much better indicator: As you say yourself, at some point you were running comfortably and not flat out, and if you believe your heart rate monitor and the maximum calculated, you should have been dying.

If I were you, I would forget the heart rate monitor, and just use the old rules of thumb (can hold a conversation, short sentences, etc.) to estimate your level of effort.

Laurent D wrote (see)

As you say yourself, at some point you were running comfortably and not flat out, and if you believe your heart rate monitor and the maximum calculated, you should have been dying.

Karvonen shouldn't give the same as 220 - age. Are you looking at the upper and lower % training zones to the figure?

Karvonen calculator Then scroll down to see the % training zones.

That Karvonen calculator is calculating MHR as 220-age  

 Target Heart Rate Zone Limits (Old Method) ... i.e. basic "% max heart rate"

Karvonen Formula (Heart Rate Reserve Method - The Gold Standard) ... this is the "% working heart rate" (i.e. ala the Parker book).

Both rely on an accurate Max Heart Rate to obtain meaningful zones ... but the calculator uses "220-Age" which is not accurate for many people (though it's pretty close for me).

When you are at 'unable to speak' pace you are as good as damn it running to you MHR.

I agree with many others who say, do not rely on your heart rate monitor readings, they are prone to 'spikes' and therefore unreliable!

All in all I agree with Larent D

read what JJ put above.  That is the best way.  For wobbly legs you could read throwing up! 

It's not a pretty way of finding your MHR, but it works....

Thanks guys for all your replies, I did look at the Karvonen method and it calculated my MHR at 184 (220-age) and sllightly less than what my HR spiked up at on my steady run last week! It's the HR monitor with my Garmin 305 that I'm using.

 I will try the steep hill method, I guess I just want to try to train in the correct zones but without knowing my MHR this is difficult I guess, I suppose I could just go off perceived effort which I find easy anyway (and it might not scare me as much!)