Power Zones, Physical Adaptations and Purpose of Training

One of the things that I really enjoy about cycling has little to do with being on the bike.  No, it's not the stretchy pants and plastic hats!  I love trying to find optimal nutrition and training plans.  To find optimization, learning about mechanisms that occur is important.   One of the things I've really been learning about this week is the purpose, the intended physiological adaptations sought, from each workout.

Tom Danielson kicked it off with some feedback on Facebook and with this article where he discusses how chasing an increased FTP doesn't promote winning races.  Here's the article:  FTP is not Functional.

In a similar theme this week's episode of VeloNews' Fast-Talk Podcast the discussion revolved around dispelling training myths.  They did an excellent job, but in many ways muddied the waters more than cleared them.  Like nutrition, training protocol is highly variable.  I believe this is to the individual genetic responses, psychological responses, drive and desire and potential of individual athletes, but also how specific practices fit within the whole of a coach's plan.  You know, the old, many ways to skin a cat thing ...

The biggest take-away for me was that I should know the intended training adaptations to be brought from each workout I perform. How do I know if training has been successful if I don't know where I should see improvements?

What is the purpose of each training zone (most of my workouts are done in a specific training zone that is a percentage of my FTP).  I have a general idea, but with a few simple questions, my level of understanding is exposed as surface level and flimsy.  Coach Chad does an excellent job describing the purpose of each workout on its own and how it fits into the week's objectives (from the Trainer Road programs), but I've been a poor student.

A quick google search showed me how to calculate each zone and many websites give the purpose of each zone with a one word, well, essentially name, like Endurance or Tempo.  Here is the basic gist of the zone calculation, along with their names:

Zone 1 <55% (active recovery)

Zone 2 56-75% of FTP (endurance)Zone 3 76-90% of FTP (tempo)Zone 4 91-105% of FTP (lactate threshold)Zone 5 106-120% of FTP (VO2max)Zone 6 121-150% of FTP (anaerobic capacity)Zone 7 >150% of FTP (neuromuscular power)

Sweet Spot 88% - 92% of FTP


Training Peaks had a great article on the topic, like they often do.  However, while they do a great job describing how each zone should feel (which is important to helping you understand if you're really in that zone), they don't describe the purpose of each zone.  If you, like me, are trying to more accurately understand if you're targeting appropriate zones to reap the adaptations intended, then these descriptions are very important to know!  Yes, a powermeter will inform you, but the more ways you have to know if you're right, the better.  I'll summarize below:

Zone	How it Should Feel
1 – Active Recovery	This is an easy spin, minimal sensation of fatigue in the legs and no concentration required to maintain the effort.
2 – Endurance	Generally easy, but should feel like it could be maintained all day.  Minimal concentration is required during difficult portions of a route, like up a hill.  You should not be too aware of your breathing in zone 2.
3 – Tempo	Requires attention to maintain when riding alone with deeper and more rhythmic breathing than in zone 2.
4 – Lactate Threshold	Duration exacerbates these signals, but the level of breathing required should make continuous conversation difficult, however, you should be able to talk.  This is mentally taxing and intervals of 10 to 30 minutes should feel difficult.
5 – V02 Max	This should produce severe fatigue in the legs and you will not be able to carry on a conversation during these efforts.
6 – Anaerobic Capacity	These will last 30 seconds to 3 minutes and much like V02Max, you will not be able to talk and you will experience severe leg fatigue and pain.
7 – Neuromuscular Power	Very short and intense, max efforts like sprints.

Finding the purpose of each training zone is a little trickier.  I did find this page on WattBike, which was useful, but I wanted a bit more.  Below I'll summarize what I've come to understand.  Keep in mind, I do not have a background in exercise science, and these are the rough interpretations after my blunt tool of a mind has fumbled through the information.  Also, my understanding is evolving, but I hope you find this useful as a start.  Even if I were an expert in the field, there'd be plenty of people that disagree. All that aside, here you go:

Zone 1:  The purpose of zone one is to promote recovery from taxing efforts without inducing further damage.  Sometimes resting for a day is better, depending on the level of fatigue, but even after a short rest, zone 1 work is important because it helps "clear" the damage.  (Clear, I suspect, is a word that is misused here, but it's the word I see and hear often in this context.)

Zone 2:  Zone 2 promotes mitochondrial growth, which has two big upsides for cyclists.  (The slow twitch fibers have the highest mitochondrial density and is the muscle type used and developed here.) First, it promotes fat utilization for fuel during your efforts.  If your body is dependent on using glycogen for fuel at lower intensity levels when it could use fat, you will run out of fuel when the race gets harder and fat cannot be used.  In other words, working in zone 2 helps you save your Go-Juice for when it's really time to go!

The second upshot of developing the systems used in zone 2 is actually improved lactate clearance.  Lactate is created when the body uses glycogen for energy (at higher intensity levels).  By mechanisms beyond me, but sound fancy enough where I read them that they must be true, the slow twitch muscles are responsible for clearing the lactate.  (Read this page for the real expert's advice on zone 2.)

The purpose of zone 2 is two-fold.  It should make you more fat-dependent (fueling during easier efforts) and promote the capacity to better process lactate at higher efforts.

Zone 3:  I've heard zone 3 called "No Man's Land," implying that it has little purpose and should be avoided.  From what I've read it is a cross-over zone between where the body uses primarily fat to using primarily carbohydrate for fuel.  Perhaps in this zone the point at which your body switches from fat to carbohydrate will be delayed (fat is an essentially infinite fuel source, but we can only carry and process so much glycogen).  That said, Zone 3's purpose is building muscular endurance with the intent of limiting fatigue over time, like in a longer race. (Zone 3)

Zone 4:  In zone 4 the body will not be using fat as this is where the fast twitch muscles take over the work.  Now, there are two types of fast twitch muscles, and they fire sequentially depending on the workload.  In zone 4 the first type of fast twitch muscle fibers are firing.  The purpose of zone 4 is to improve their efficiency, the body's efficiency at using carbohydrate and flushing lactate.

All that aside, one way to think of the purpose of Zone 4 work is to raise the ceiling; the ceiling being the limiting factor to how much power you can sustain over an extended period of time.  The better adapted your body is to working in zone 4, the longer your body will be able to sustain high efforts.

Zone 5:  In Zone 5 you are working to increase your cardiovascular efficiency and the body's ability to flush waste products.  In zone 5 the body starts switching from using the first type of fast twitch fibers to the second type.  The later the onset of that switch occurs, the better off you'll be.  Zone 5 work seeks to delay this switch.

One way to think of the purpose of the work here is raising the roof.  If your roof is higher, your ceiling can be higher.  Again, the ceiling is your lactate threshold.

Zone 6:  The purpose of Zone 6 is to increase your maximum, short term power.  This is where you start exclusively working the second type of fast twitch fibers.   Training here helps you drop the hammer, bring the thunder ... create separation on race day.

Zone 7: The difference between zones 6 and 7 is that zone 7 has a greater element of neuromuscular control.  The purpose of training in zone 7 is to increase maximum, short term power, but is at the very limits of what you can do.

Sweet Spot:  Sweet spot is the upper portion of zone 3 and the lower part of zone 4, right where the body switches from slow to fast twitch muscle recruitment.  So, my simple mind has put together the idea that by increasing efficiency in sweet spot you delay the recruitment of fast twitch fibers, which only use glycogen for fuel, thus making you a more efficient rider.

Regardless of the exact mechanism, the purpose of sweet spot is to increase the amount of power you can maintain for extended periods of time.  Also, while sweet spot work hurts, the recovery time is significantly less than work done in Zone 4.  So, more training can be done.

I hope this has proven useful in shedding some light on why we do certain efforts in specific zones, what the results should be, and so on.

Now the next piece will be how much of what to do when and why!