Heart rate question - am i doing it wrong?

HI all - i think im confused about heart rates. First a little history of my training.

I have done two sprints last year and plan to do a few more this year. In terms of training, i have been a weekend/casual runner for almost 4 years participating in 10ks and 1/2 marathons. my aim this year is to break my leisurely 10 min/mile. I have been swimming most of my life - and am quite comfortable swimming 1mile 1-2x week. Altho i was always a casual mountain bike rider, i recently purchased a new (well acutally its 2nd hand but new to me Trek 1000 to bring me up to speed on a road bike.

I've been reading alot about heart rate training and wanted to start getting the most out of my training sessions rather than just adding volume. I am 40yrs old and when i use the various methods i come up with the following information:

Method: Lower zone higher zone
180-40 140 150
220-40=180 *70% = 126 *80% = 153

See these numbers feel very low to me. Usually when im running i reach 150 at a conversational pace (nice and easy) and when i start to work hard I hit about 170-180. I am most comfortable at 163. FYI - i measure by just counting my pulse for 10 sec and multiplying by 6.

What does this mean? I cant believe it means im working to hard...cause if i try to maintain a 150 only i'll never break the 10m/mile. I may as well be walking. It feels like im working at an aerobic state because i can go for a while....are the numbers for a 40 yr old that hasnt been in shape?? If thats true how can i get a true "base" for my heart rate monitoring.


Any advice is welcomed. thank you