May 12, 2016 cburnham

More On Levels and Zones

An example of a power duration curve in WKO4

I had a few people ask for some explanation on my comment about training levels being more descriptive, not prescriptive in the last article “Not So Secret Sauce.”  I thought it would be helpful to explain and to expand a bit more on training levels, zones, and threshold to help athletes and coaches have a better understanding of these concepts.

Why zones and levels?  Seems redundant right?  Actually there is a fundamental difference in how we define these.  Levels are descriptive and used in post ride analysis.  They tend to be broader than training zones, and have some dependency on the workout as a whole. For example, an endurance training level may be anywhere from 200 – 265 watts, but we may want an athlete to be more at the lower end versus the higher end of that range depending on the goals of the workout.

Technically we really only have 3 levels: above Threshold (anaerobic), between aerobic and anaerobic (between threshold), and aerobic.  In other words, this is easy, moderate, or hard.  Of course there are transitional zones between these that can elicit different responses.  This is where training zones start to come in.  Zones are prescriptive and include how hard and for how long.  As technology evolved we started to have ways to provide more detail and specificity.  This detail allows us to hone in on specific aspects of fitness adaptation.  To achieve these definitions of zones we had to have an anchor that varied by fitness.  Thus threshold (however you want to define it) became the anchor as the alternative of anchoring at “max” wasn’t as accurate.  Whether you are using heart rate or power, anchoring your training zones at threshold will provide you a lot more accuracy in your training.

These are the traditional training levels created by Dr.Coggan

These are the traditional training levels created by Dr.Coggan anchored by threshold in level 4.

With power becoming more prevalent, we were able to test as often as we would like to set accurate functional threshold numbers.  You didn’t need to travel to a lab to find out where VO2, lactate threshold, or any other physiological number was at.  You could easily go out and do a test to figure out where your functional threshold is and set your training levels optimally.

One important note: functional threshold power is really a surrogate power for maximal metabolic steady state and does have its definition rooted in physiology, but is much more actionable and  predictive of success in sport than a lab derived number like VO2. 

As a definition, functional threshold is the max power or pace you can maintain for an hour.  Doing an hour-long effort can be technically challenging (where to do a steady state 1-hour effort, pacing, fueling) that we often use a 20-minute test done after an all-out 5-minute effort to exhaust anaerobic ability and then take ~95% of that 20-minute effort to determine threshold.  We could then use that functional threshold number to create individuality in our training levels as well as track changes in fitness over time.

Sea Otter CX

This works well for about 80% of the athletes out there.  In a typical bell curve application, the 10% of the athletes on either end need a bit more customization.  This is where using diagnostic tools can be very helpful in determining those outliers and creating a more individualized approach for those athletes that fall outside the bell curve.  Individualization is one of the core training principles and is the key to increasing training efficiency and effectiveness (I will write more on the other core training principles in the future).  It is defined as training that recognizes the unique physiology of the individual athlete.

One of the most powerful diagnostic tools we currently have is the power duration curve for cyclists using power.  This is essentially what is your maximal workload for any time frame.  While this is an extremely valuable and informative chart for cyclists with power, the core principle can be applied to all athletes even if not using power, heart rate, or any training metrics.  Essentially, your maximal intensity will decrease as time duration increases.  All athletes can produce a higher output for 5 minutes than they can for 10 minutes.  Most coaches have used this principle in prescribing workouts for shorter durations for quite some time.  In athletes using heart rate, we often wouldn’t even prescribe a specific heart rate for efforts less 5 minutes due to the limitations of how heart rate responds.  Instead, we would have athletes do close to maximal efforts for the prescribed duration.  There are some limitations to this, but it often works well for those athletes not using power.  In runners, I have also found that running pace on flat ground or normalized graded pace in the hills is a good proxy for power and while fundamentally a bit different, the same power duration curve principles apply.

An example of a power duration curve in WKO4

An example of a power duration curve in WKO4

Back to cyclists that have power, using the power duration curve allows us to customize power prescriptions for workouts based off their unique physiology and not off generalized percentages of threshold.  Don’t get me wrong, using percentages of threshold is pretty accurate for efforts up to and including threshold workouts but when we start working on those efforts that are higher than threshold percentages don’t give us a level of specificity that respects the individuality of the athlete.  For example, we may have two athletes at the same threshold power but one can produce 10% more power at 5 minutes than the other.  Prescribing a 5-minute effort based off a percentage of threshold for those two athletes would produce two different workouts and two different results from that workout.


Achieving this level of individualization was the goal of Dr.Coggan in using the concepts of the power duration curve to create iLevels.  This gives us 9 training zones based on the data from the power duration curve.  Before the release of the iLevels, we would often have to look at mean maximal powers for a variety of durations to set prescribed powers in workouts.  Now we have the very robust iLevel algorithm that does a lot of that work for us.  There is still some need to tailor the prescribed powers and durations for athletes, but the heavy lifting is done.



Using the power duration curve we are also able to phenotype athletes, or defining the specific type of an athlete.  Some cyclists are TT specialists while others are road sprinters and others are all-arounders.   Defining the type of the athlete is useful in guiding training and better preparing them for the demands of their goals. For athletes that are using heart rate, we tend to use performance results from races, group rides, and rider feedback to phenotype an athlete and get an idea of where their strengths and weaknesses lie.  While this is significantly less precise than what we are able to do with power it can still be a very powerful tool in individualizing training for an athlete.

Hope that explains a bit more the function, definition, and value of training zones as well as highlight the heightened specificity that results from using a power meter.  Training with heart rate or even perceived exertion can still be very effective, but it is hard to beat the added specificity and individuality that training with power can give us.

Happy Training!