Heart rate based / endurance training - am I doing it right?

[thenortherner]

I completed an Ironman 70.3 last month. It was my first triathlon and I managed it in just over 6 hours. My training was a bit hit and miss. I did get a lot of help with following a specific program which was based on heart rate. At the very start of the year I paid for some tests on the static bike to measure my heart rate zones, lactic threshold, Vo2 max etc. Although things have changed since then in that I'm much fitter, the results are as below:

Zone 1 - 110 - 128
Zone 2 - 128 - 148
Zone 3 - 148 - 160
Zone 4 - 160 - 173
Zone 5 - 173 - max

No doubt these are slightly improved now given how long ago it was and the training I've done all year. My Garmin has recorded my max heart rate at 192 rather than the 182 during the test.

I didn't stick to the heart rate based training as strictly as I could have and now want to start again. I reckon over training has been leaving me feeling knackered and has lead to a sore back, which has caused me to take a few weeks break recently.

Anyhow, I've started up again and this time without any specific guidance or help from anyone, using the rule that endurance based training should be 180 BPM - age (30). So exercise should be carried out with an HR of 150 or less for the next 16-20 weeks to see the benefit.

The idea being that over time as my fitness increases, I'll be able to go faster for longer at the same heart rate as I started the training at.

After only a short time I think I'm possibly seeing the benefits already - please see the picture below. What do you reckon? I started up again after a few weeks off which might be why the first runs are so poor.

Also, am I doing it right? Is it OK to experience some very high heart rates, as I have with some of the bike rides, so long as I'm averaging 150 or below for the duration of the ride?

Thanks,