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Why Functional Threshold Power is Only Half of the Equation

Functional Threshold Power Test Bike

Before diving into another season of training on the bike, or jumping into serious training for the first time, it helps to know a few things about your current fitness as you get started…

  • Where is my fitness at right now? Identify a baseline from which you plan to improve.
  • What are the best ways to spend my training time? In order to maximize your improvement.
  • What effort levels should you be training at? Set your training zones.

These insights can be found through power testing on the bike. For many years, a rider’s Functional Threshold Power (FTP) has been the main determining metric of a rider’s fitness and used to set his/her training zones. Functional Threshold Power works well. It shines light on one area of fitness and can be re-tested again and again to check for improvement.

By definition, your Functional Threshold Power is the power you could sustain for one hour, full gas. I say could sustain because who’s going to go all-out for an hour to find this value?

So it’s become common place to go hard for 20 minutes and then subtract 5% from your average power. Pretty much the Gold Standard, and everybody accepts it.

Even going all-out for 20 minutes is pretty tough on your own, so more recent models are doing either one or two 8-minute intervals and subtracting 5-10% from those averages to estimate Functional Threshold Power

All said and done, these methods of Functional Threshold Power testing highlight one energy system (v02 max) and calculate the Functional Threshold Power from a “one size fits all” percent reduction from the test effort. From there, it doesn’t tell you much else. Does it work? Sure. However, if you’re like me, you would likely prefer more.

What if we said we can offer you another, possibly better, way to test on the bike to gain insight on your fitness, set zones, and track progress?

Functional Threshold Power Test Bike

Over the last 10 years of training and coaching with power in our trainer studio environment, and out on the roads and trails, we at Sessions:6 have found a different way to perform power testing that presents us with more insight on a rider’s fitness and sets more personalized training zones. 

Every endurance athletes is different. Each comes to the sport of cycling or triathlon from different backgrounds of sport, and a different set of physiological strengths and weaknesses.

To generalize, we can look at endurance athletes as two types:

  1. Strength/Power Based Athlete: strong, powerful, can crush it for a few seconds (sprint!) to a few minutes, but then power drops off rapidly and he/she slows down from there. These athletes typically come from power/speed sports like soccer, football, or wrestling, or were “sprinters” on the track or in the pool in their youth; often larger and more heavily muscled builds. 
  1. Aerobic Based Athlete: not particularly snappy, but can churn out the steady power and can go all day long with minimal drop in speed/power. These athletes often were the “slow” kid on their teams growing up, enjoyed hiking or longer distance running and swimming events, or as adults have only done long (slow) endurance training/events over the years; commonly a smaller and leaner build.

When you have each of these athletes perform an 8 to 20 minute power test you will be taxing them in very different ways.

The Power Athlete’s test will likely result in values that are a bit too high for anaerobic threshold and sub-threshold power, and a little low for top-end power; whereas the Aerobic Athlete’s test will likely result in power values on the top end being too high and on the low end being too low.

Functional Threshold Power Test Bike

This may be “splitting hairs” a bit, but what’s important to consider here is that for endurance athletes of all types, the primary goal is to be able to produce the most power possible over the duration required for the event. Put another way… maximize the power, while minimizing the decline in power as durations extend.

In general, those that typically win endurance events are the ones that SLOW DOWN the least!!

To keep tabs on aerobic endurance or “fatigue resistance,” we include an Aerobic Threshold (AeT) Test interval as part of our testing protocol as well.

As you can see, there are two parts to the training equation, Power vs. Endurance, so we should have two parts to the testing protocol.

Your Aerobic Threshold, the key to Fatigue Resistance!

As discussed in a previous post, Training With Power or Heart Rate?, I mentioned a few of the primary objectives of aerobic training: improvements in cardiovascular infrastructure (stronger heart, more blood vessels, more mitochondria, etc.), and improvements in energy metabolism by increasing the use of fat for fuel and sparing glycogen at higher and higher outputs. Big power numbers are flashy and cool, but in the endurance sport world fatigue resistance is king.

Aerobic fitness is essential in cultivating endurance, the ability to resist fatigue, and minimize one’s Fatigue Rate.

With a lower Fatigue Rate an athlete’s power drops more slowly over time and therefore they can keep pushing the pedals harder, creating more power, for longer. 

Functional Threshold Power Test Bike

Improving or maintaining that balance between power and endurance is crucial to your success. If you improve power but in the process sacrifice aerobic fitness, you may not have actually gotten any faster at your target race intensities. This is why you must always keep tabs on your power at Aerobic Threshold (AeT) to be sure you aren’t increasing your Fatigue Rate any more than necessary.

In training our goal is then two-fold: to improve both your top-end speed & power through strength and plyometric training in the gym, and through high-intensity intervals on the bike; AND to improve your aerobic fitness so you can utilize more of that power over longer periods of time by minimizing the decline that occurs as you fatigue.

To test an athletes Aerobic Threshold  power, we include an Aerobic Threshold test interval in our testing protocol. The test requires an athlete to focus entirely on riding at their identified Aerobic Threshold Heart Rate for an extended period of time. Then we look for the average power that was a result of the aerobic effort. The overall goal is to improve your aerobic power while at the same time keeping your Fatigue Rate as low as possible. Therein lays the tricky balance of training and maximizing performance!

Part 2, of our Testing Protocol Series will lay out our exact testing session procedure and provide some real world examples from some of our athletes.

 Functional Threshold Power Test Bike

This article was written by Cody Waite, professional endurance athlete, endurance sport coach and founder of Sessions:6 Sport Performance. Looking for help with your endurance sport training? Check out S:6’s Training PlansTeam Programs, and  Personal Coaching options created to fit your needs and budget.

Curious to give the Aerobic and Anaerobic Power Test at try? Schedule your testing at Sessions:6 HERE.  You can also purchase our 24-Week Off-Season Trainer Series from Training Peaks that includes our testing protocol as well as a complete build through each energy system to improve your top-end power and fatigue resistant endurance. Check it out HERE.  


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