Hi - I wonder if any of you might have any input on this?

I am a pretty unfit new cyclist - 3 months of cycling and just 600 miles so far as a base - got a heart rate monitor today and according to the formula by HR max is 180--

did 27 miles today and my HR is 150-160 throughout -- maybe 148 on the flat going 'easy' and 162 trying to get my unfit self over the motorway overpass--

according to all the stuff this is about 90% max HR I am doing the whole 27 mile ride on -- supposedly at anaerobic threshold which seems unlikely to me-- but even on the flat I am at like 85% of supposed max HR when I am supposedly taking it easier... even after a couple minute break for a drink it is still in the 120's--

are these numbers just a reflection of my unfitness and the supposed 'training zones' only apply when you are really fit or something?

i thought at anaerobic threshold it would be impossible to ride for 27 miles so I am mystified as to what to do with these numbers...

any ideas?
bat