stretch wrote:Thanks Alex. But isn't it true that different people will go anaerobic at different %'s of max HR.
Well the question really doesn't make sense because HR response is far too slow when talking about anaerobic efforts.
If you mean perhaps when the Onset of Blood Lactate Accumulation (OBLA) occurs, then sure, that will occur at different relative HR to HR Max for different people but even then for an individual it will vary from day to day and upon the protocol of the ramp test used to assess it.
stretch wrote:Therefore, if you are training based on max HR you may be riding in an aerobic state when in fact you are attempting to train at an anaerobic intensity (and vice versa)?
Unlikely. If you were riding anaerobically, you would be forced to slow down significantly after only a very short time.
You can only sustain an anaerobic effort for a couple of minutes at most (and even then quite a lot of your energy is supplied by aerobic sources)*, so I think you are getting confused by what's anaerobic and what's aerobic.
Anaerobic efforts are very short and very hard. HR response is way too slow to be of any value for guiding such training. Even a maximal effort of 90-seconds duration is still dominantly powered by aerobic metabolism.
* how long, for instance, could you swim
hard while under water holding your breath?
Here's some data to help explain what I mean. It shows the relative total energy contributions from the three main energy production pathways during maximal efforts at various durations.

stretch wrote:I am going to conduct a LTHR test as described by Joe Friel to find a rough estimate. Basically it is the average heart rate in the last 20 mins of a 30 min TT.
Which is essentially the same thing I suggested in point 2. of my original post.
The exception being that Friel has a tendency to bastardise many terms (e.g. LT and Critical Power).