This is with respect to cycling really but it's largely the same score with running, so here goes.
At my spin classes (which are more like group turbo sessions) we use Suunto heart rate monitors and their five-zone system which is calibrated by percentages of max heart rate.
I estimated my MaxHR a year or two ago by doing a sort of self-inflicted lactate threshold test, which gave me a LTHR of 165.
The Suunto zones put your LTHR at 85% of max, the border between zones 3 & 4. (Zone 4-5 border is 92%.)
So in order to set my zones I put my max at 194.
Now, I just did a class where I pushed v.hard and recorded an average HR of 178 (91% of estimated max) over 53 minutes.
Isolating the last 30 mins the average was higher, something like 181.
Now, I've got all sorts of Qns:
1. Does this mean I need to readjust my HR zones up? Accepted advice on how to estimate LTHR says knock about 5% off your 40-minute max effort HR - so that would put my LTHR at something more like 170-1. (So my max should be set somewhere around 200 on this system - even if that is not my actual max).
2. Other HR systems put your LTHR at more like 87-88% of max, and it varies between individuals, no? Could it just mean that my LTHR rather than being 85 per cent of my max, is actually 90% of my max? And is this a sign of fitness, i.e., do fitter people generally have a higher LTHR as percentage of max HR?
3. Does your LTHR change over time? Does it go up or down as you get fitter?
4. Could it just mean I was tired / had a bug and therefore had inflated HR? It was also hot in there: do the same efforts power-wise produce higher HRs in hotter conditions?
(5. Should I just save myself the bother and forget about bloody heart rates altogether?)
Phew. And thanks in advance.