I almost never get into strava’s z5. Even in CX races I’m 0-1% anerobic. For much more of the race I’m panting and I feel the painfull lactic accumulation but according to strava I’m still in threshold. Surely that is anaerobic?

question one: what the h£ll does z5 feel like if not that?

Question two: Do other cx racers expect to spend more time anaerobic? Am I not psuhing enough? I basically am in top end of z4 the entire race (between 175-180ish)

I know I need to do some proper testing to define my HR zones but as yet I haven’t so I use Max HR based on the max I’ve ever seen (187 in a few cx races), and then stravas algorthim for the other values.

Question 3: Is stravas zone calculation a bit funky? I guess my max hr might be higher, but this would mean I’m spending less time anaerobically.

Zones can be very subjective

I was taught that Z5 is the power/HR you can maintain in a functional threshold test. This means it’s a very narrow band that is hard to spend much time in because the moment you drop 1W or 1bpm you are in Z4 and the moment you exceed it by 1W or 1bpm you are in Z6.

The anaerobic component of riding doesn’t happen like a switch it ramps up. Threshold is merely the level of intensity you can manage for 20minutes(x0.95) or an hour ie the level of intensity you can clear lactate at the rate you produce it (I think)

also 177/187 is nearly 95% of max – you’re pushing!

Haha yeah, actually that makes sense, given that the race is an hour (give or take a couple of minutes), top end of threshold makes sense to be able to ride without blowing up.

Actually just re-looked at strava had a glitch, it had defaulted to a max hr of 189, put it down to 187, z5 goes from 184 to 181 and suddenly its 20% anaerobic, 80% threshold. Which seems a bit more realistic to me, but also shows how sensitive zone calculations are.

Its a good point about how fine all te z5/z6 zones are. I don’t really see the need to distiguish though, at lwast not for cx or xc

Is disappointed. Expected a transport for London thread 🙁

Question 3: Is stravas zone calculation a bit funky?

This.

Obviously you need to do a test to find out where your LTHR is.
I also have an MHR of 187, and my LTHR is at 172, so i’ve got z5 in strava set as 173+.
Basically I map the first 4 zones to Friels first 4 zones and condense his 5a-5c into strava’s z5

Q1: feels like you’re on borrowed time and about to blow up 🙂 (though it can still be quite a wide range) As for Z4, I’d say threshold is around the middle of Z4 and should be a proper hard effort (your 60 min absolute max.)

Q2: For CX race I’d expect it to average around threshold effort as races are about an hour… but they are much like over/under sessions which might skew that. Doing it off HR though, depends how quickly your HR tacks effort.

Q3: How does Strava do it? Looks like 5 zones based on percentages of max. Zones based on percentage of max HR are very rough estimates and a bit rubbish for this sort of analysis. Zones based on an estimate of LTHR are a bit better.

Edit… just looking at Training Peaks, it has about 20 different methodologies you can use to set up your HR zones based on one or more of max , LT and resting HR. And they all give different values for ranges.