I'm a very fit triathlete one month away from my first Ironman. I'm strictly following Don Fink's training plan, which includes "interval training" in HR zone 5, or 90%+ max HR. (Fink actually calls it "zone 4" for some reason.)

The workouts used to involve more traditional intervals: bring your HR up to 90% for a few minutes, then rest, then repeat. But at this point in his plan - at the peak of the "peak phase" - he's asking me to do 12 minutes straight in zone 5 on the run, and 30 minutes straight in zone 5 on the bike!

I'm having a great deal of trouble with this.

How long should I be able to stay in zone 5? Am I simply not pushing myself hard enough, or did I just fall behind at some point?

Edit: on Fink's zone definitions, he writes:

Zone 4: 90-95% of maximum heart rate (primarily anaerobic training)
Zone 3: 86-89% of maximum heart rate (middle zone)
Zone 2: 75-85% of maximum heart rate (higher-end aerobic training)
Zone 1: 65-74% of maximum heart rate (lower-end aerobic training)

His example puts a 35-year old at 166-175 bpm. The vast majority of his plan is in "zone 2."

  • 2
    you should be able to answer if you fell behind at some point, no? have you missed key workouts? Oct 21, 2011 at 3:17
  • that does seem a little extreme, but not by much. Oct 21, 2011 at 3:18
  • Ironman 70.3 or Ironman 140.6? Oct 21, 2011 at 3:21
  • Full Ironman. The only training I've failed to complete has been these recent zone 5 expectations.
    – ladenedge
    Oct 21, 2011 at 14:59

1 Answer 1


You should not be able to last more than a couple of minutes in Zone 5. Maybe the problem is that he is talking about Zone 4, and you are thinking he means Zone 5. What is Fink's definition of Zone 5? Here is a detailed decriptions of the zones http://www.3-fitness.com/tarticles/zones.htm

  • Nice link. I'll update my OP with a Fink quote.
    – ladenedge
    Oct 25, 2011 at 15:34

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