What are some of the methods to determine my aerobic/anaerobic heart rate threshold.
The classic DIY method is the Conconi test which requires you to be able to measure your power output and your heart rate, slowly increasing your power over time. E.g. starting at a very low level, you increase your output by a set amount every minute until you can no longer do it. At each stage you take your average heart rate. Then when you have the data, plot them on a graph, time along the bottom, heart rate on the y.
For this you'd need to be in a relatively sterile environment - it's not something you could easily or accurately do on the road. A turbo trainer is perfect, incrementing your output in watts or speed.
What you should see is that your curve will slowly grow with a reasonably consistent gradient, but there'll be a point where it takes over and climbs much more steeply. That's your anaerobic threshold.
It will be quite vague, but it'll be accurate to within a few beats - certainly enough to be able to set your next training outing a few beats below it for your threshold session.
For more specific results, you'll need to do some lactic acid testing ...
There's a lot of confusion over the definitions of aerobic threshold, anaerobic threshold, lactate threshold and determining power levels or heart rates for each can be tricky. Some advocate working them out from a ramp test to exhaustion but that's stressful and probably unnecessary.
Joe Friel determines "lactate threshold heart rate" by taking the average HR of a decently long ride (~1 hour) giving it all you've got. Strictly speaking LTHR is when lactate concentration reaches a certain level but as you probably don't have a blood analysis machine to hand this'll have to do. You should end up working at just the edge of your aerobic capacity, on average, as you can't sustain anaerobic workloads for this duration. The average power produced during this workout would be around about your Functional Threshold Power (FTP), another handy number to know (though obviously you need a power meter to find it out).
LTHR/FTP is a good base to work out levels for other workouts. For instance, riding at VO2max can be trained by riding at 110-120% of FTP, or an intensity a bit greater than your LTHR (1 hour average HR). True anaerobic threshold work is at an even higher intensity.
If you're training by HR alone Joe Friel's book is well worth reading.