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HR zones confusion


I'm a cyclist preparing to get into triathlon. The first step in this preparation is to read a lot about triathlon. For that reason I bought the "All new triathlete's training bible" from Joe Friel. I really liked the book, but there's something that got me confused.

In the book as well as in other books like the 80/20 triathlon and other sources,There's a lot of talk about the importance of zone 2 training (in a 5 zone system). The bulk of your training has to be in zone 2 (low intensity).

At the same time, and I suppose it has to be actually more or less the same thing, It is said that bulk of training has to be at or below the aerobic (or first ventilatory) threshold. It is also said that that threshold is about 20 to 40 bpm below your LTHR (or FTHR or second ventilatory threshold) Joe friel says to take 30 bpm as a guideline.

But... If you look at my FTHR f.e. of 168, this means an aerobic threshold of 138. If you look at the zones as used by Joe Friel (but also in 80/20 triathlon and others) however, the cap of zone 2 is at 89% or 150, while the cap of zone 1 is at 81% or 136. So the zone 1 cap seems a better approximation of aerobic threshold than the zone 2 cap. So 80% of my training should be in zone 1 and zone 2 is actually the so called "no go" zone (usually called zone 3)

My head is spinning. Confused :D.

Hope someone can help me out.

Thanks for reading!


  • HarryDHarryD Posts: 425

    Hi Glen,

    Zones are often poorly described and I can see where your thinking has gone awry.

    I reality you have two main ventilatory thresholds. The lower one is when your training starts to stress the body so you breathe a bit faster. This should also be your aerobic threshold and marks the lower limit of Zone 2 (Joe F has Z2 as 81 to 89% of FTHR & Matt F in 80/20 has Z2 as 81-90% of LTHR). This ties in with your 136 to 150 calculation.

    The second ventilatory threshold as you say is at LTHR or FTHR which ties in with your anaerobic threshold. So Z2 is above aerobic and below anaerobic thresholds. Not below aerobic as you say. Z1/recovery is below aerobic. The difference between the two is the estimated 20-40 or 30bpm. The anaerobic threshold is easy to calculate from self tests but the aerobic threshold which you also need isn't, hence the 20-40 or 30 estimation.

    Why the 20-40 or 30bpm is mentioned at all is beyond me. It adds confusion because to use it you need your LTHR/FTHR and if you have that number you can apply the % calculations that seem to be well proven.

    JF's Z3 relates to MF's Zone X (no-mans land), both of which I tend to avoid.

    JF's Z4 relates to MF's Z3 which is a great training zone in lower volumes.

    Hope this helps

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