Aerobic Threshold Summary

I’ve been training for ironman distance triathlons seriously over the last four years. In this time, I’ve noticed that the many intensity guidelines for endurance training always seemed a little “too fast” for me. As a coach, I’ve often found that my athletes tended to simply dial-up a heart rate and then switch their minds off. Over the last six months, two of my coaching mentors (John Hellemans and Scott Molina) have worked with me explaining the concept of aerobic threshold (AeT).

How do we determine AeT?
My preferred evaluation method is to apply subjective perception. Start training at an easy pace and slowly increase the intensity of exercise. AeT is determined by noting the heart rate where you feel the first deepening of your breath. This deepening is caused by the body increasing its demand for oxygen to metabolize an increase in blood lactate.

Many coaches and athletes prefer a more scientific approach to AeT determination. My view is that this takes away from one of the key benefits of AeT training, that being, having our athletes to dial into their bodies. A flexible approach to determination is useful because AeT will often move 5-10 bpm based on an athlete’s daily recovery situation.

To guide my athletes, I will tell them that AeT typically lies near the top of Friel Heart Rate Zone 1 (“Friel Zn 1”). I’ve found that in nearly all triathletes, their AeT will be below this point. Indeed, for triathletes, their “weak sport” AeT will normally lie 10 bpm or more below the top of Friel Zn 1. This is important because, as coaches, we often specify Friel Zn 2 as the appropriate intensity zone for endurance training. In doing this we could inadvertently be giving our athletes tempo training in their endurance sessions.

For my athletes that have access to power, I have found that AeT will typically lie in a zone that’s 60-65% of their best average power for a 30 minute TT (60-65% of CP30). Again, this is merely a guideline as highly trained endurance athletes can have an AeT that is up to 75% of CP30.

Finally, AeT can be determined by lactate step testing. John Hellemans provides a clear explanation of this method in his book, The Training Intensity Handbook.

How do we determine AeT -- Part Two
When athletes start with AeT training, my MOP/BOP athletes will tend to locate AeT at 40+ bpm below LT -- especially riding on the flats. After several months of training, they often find the need to move more towards 30 bpm below LT.

Athletes with weak AeT endurance will often find that AeT is located well below Friel Zn 1. Especially when cycling alone on the flats.

This point rarely applies to highly motivated male AGers. More typically athletes (30+ yrs, 13+ hrs IM).

I see it with my ladies -- they experience muscular fatigue on the flats well before aerobic fatigue. Also seen with lanky males that come from a running background -- good aerobics relative to strength.

How to use AeT?
I have four main intensity zones that I use with my athletes.

Easy Pace – defined as less than AeT. There are “degrees of easy”. Well under AeT is recovery pace and also used for early season base building. I’ve found that slightly under AeT is a good pace for my novice and weaker athletes to build endurance. It’s also a suitable intensity for my stronger athletes to do long over-distance workouts.

Steady Pace – defined as AeT to AeT+10 bpm. My prime endurance objective is to maximize tolerance of (and pace for) steady state training. With my weaker athletes, I use upper steady (AeT+5 bpm to AeT+10 bpm) for their sport specific strength work. With my stronger athletes, we use upper steady for intensive aerobic training (done in low steady for my novices and weaker athletes).

Mod-Hard Pace – known by many as Tempo Pace (Friel Zn 3). Defined as AeT+10bpm to AeT+20 bpm. This zone is typically marked by labored, rhythmic breathing and a novice can mistake this sensation for the AeT subjective marker. With my weaker and novice athletes, I use very little of this zone. While there are physiological benefits to this intensity zone, I’ve found that the time lost due to recovery and illness ends up making its use counterproductive. My stronger athletes use this zone for sport specific strength work and muscular endurance training.

Threshold Pace – also known as Hard Pace. I don’t like to use the word “hard” with my athletes as I find their economy suffers when they try to “go hard”. So I prefer to use Threshold and/or Fast Pace. With my endurance athletes, this zone is used for intervals and, therefore, heart rates are less indicative of work being done. For running and swimming, we use 10K and 1000-meter best average pace, respectively. For cycling, we use CP30 wattage figures. I’m very cautious with this zone as it has the potential to result in extended recovery periods and deep fatigue.

AeT Physiological Markers
Don't over think this. You don't need to be sitting on an exact wattage or heart rate to benefit from your endurance training. The key thing is to be out there each day.

• Max Steady State -- the highest aerobic pace that you can back up every day
• MSS -- ride 90-150 mins outward at a comfortable aerobic pace -- aim to even split on the way home -- if RPE rises dramatically then slow down on the outward leg next time
• MSS -- run 40-60 mins outward at a comfortable aerobic pace -- aim to even split on the way home -- if RPE rises dramatically then slow down on the outward leg next time
• AeT -- typically close to top of Friel Zn 1 // less fit then lower, more fit then high
• AeT -- typically about 60-65% of CP30 for most AG athletes.
• AeT -- deepening of breath, see Endurance Essentials
• AeT -- first material up tick in lactate during a lactate step test
• AeT -- typically 25-40 bpm below LT // the more fit the closer to LT
• AeT -- a conversational pace that requires some focus to stay there for extended periods of time, no lactate burning in the legs, no rhythmic breathing (that's tempo/mod-hard).
• AeT -- ironman race pace for a well-trained, age group athlete
• Don't over think it.

Build endurance, aerobic power and strength.
Don't over think it.

AeT Q&A
Question: Will AeT shift over time? Specifically, as an athlete gets more experienced and efficient, will AeT lower. Obviously, fatigue will depress HR (which I am familiar with) but that's not what I'm experiencing. I have been using 130 as my bike AeT, and used to be able to rack up a lot of hours in the range of Aet -5 to AeT +10. It's worked well for me the past couple of years. I'm finding now that my previously defined "steady" takes a lot of work to get to. Only "odd" thing is that I had to take a bit of a forced layoff off the bike for about 8 weeks (mid Aug thru mid October). Since then, I've been putting in a lot of time in the saddle the last several weeks, and my bike fitness is at an all time high, but fatigue is not an issue, as my morning resting HR isn't too elevated, in the 50-52 bpm range. What do you think? —Sam

Answer: I think that it's pretty stable for most. Some things that can change... your RPE at AeT -- can go up or down -- haven't noticed specific co-relations like you said, it can take a lot of effort to get it up -- run-background athletes riding on the flats, strength/force-limited athletes riding on the flats having trouble elevating your HR -- can be a leading indicator of fatigue -- especially when accompanied with a reduce power/pace at higher intensity levels.

One thing that clearly changes is our tolerance for steady and mod-hard efforts within our Basic Week. I can handle far more of this that previously -- and I need it -- my IM race contains much more of this than, say, your IM. This is a function of my race being materially shorter as well as our relative fitness positions.

Most of us over-estimate our tolerance for steady/mod-hard as well as the true quantity of steady work that we are inserting in our programs. This is where bike & run main sets are quite useful.

I'd encourage you to use -5 to +5 for your endurance training -- when you want to step up a gear then build to +10 to +15. That's more effective (my view) than seeking to build a tolerance for sitting +5 to +10. Both Scott and Dave advised me to avoid +5 to +10 -- it's been a good tip from them.

Remember that overall what you are seeking to achieve is improved power/pace at appropriate race intensity -- this is where a powermeter is quite useful for your bike training.

If your main set power is increasing or stable with a lower HR then that is usually a sign of improved fitness. I say usually as you can see reduced HR in an overtrained athlete -- so you need to look at the whole package.

There are also periods where being over-reached can be a reasonable training strategy. Getting tired is the point of training -- knowing how tired to get is the tough part!

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