How to determine if you need more fatigue resistance?

Anyone have an idea how to tell if you need to work more on this or what should I be looking at to determine im getting better?

It’s really difficult to have “enough” fatigue resistance. The wider the base of your pyramid, the more you can build on top of it. This is why even the pros spend so many hours doing those slow easy miles.

The metrics you can review are typically pretty straightforward.

  1. Heart rate - cardiac drift/aerobic decoupling is a telltale sign of insufficient aerobic base. Secondarily, where in your HR zone are you when performing endurance work? With more endurance work, you will find your heart rate decreases for the same effort. This means that you have greater mitochondrial density and more fatigue-resistant type 1 muscle fibers. A LOT of riders overlook this. They ride around with FTP in-hand and assume that zone 2 is zone 2 but really, they are operating above LT1. HR can be a good leading indicator of this.
  2. Power. How high into your zone 2 range can you sustain and for how long? This is a good use case for levels in TR. It’s pretty obvious that sustaining 55% of FTP and 75% are going to tax the body differently. Ideally, you want to work toward a higher achievement within zone 2 at a low RPE. This will allow you to push up lactate threshold from the bottom and execution all the way through your FTP. Most people cannot hold their FTP for an hour, despite what the common “one-hour-power” parlance would indicate. Approaching that benchmark relies very heavily on having the base of fatigue-resistant muscle fibers at the ready. A lot of people can turn themselves inside-out for a test, clinging to that number like a life-raft off the Titanic. Doesn’t mean it’s functional. After all, it is called functional threshold power.

Great post above on metrics. As a very basic answer: you need to understand the demands of your goal event. For example if you need to smash it at the end of a long road race (likely if in contention for a place), then you will probably need to be able to perform ‘efforts’ after e.g. 2,500kj. It really depends on what you think you need it for.

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WKO+ tracks this as FRC (functional reserve capacity). 35Kj’s for men and 25Kj’s for women is about the most you can expect to expend above ftp (if set correctly). So obviously it’s easy to tell if you are gaining or losing Kj’s. Without WKO IDK but, I don’t know how obsessed I’d be with it either. AFAIK everything we do from setting the foundation with LSD rides to intervals of 10-90 seconds improve the amount of work we can tolerate above ftp…

w/o consulting a program like WKO5 I would say that it’s more or less evaluating how you feel when you attempt some efforts at the end of a long ride. You really just have to go out and experiment.

There are a couple things you could do:

  1. Monitor your heart-rate decoupling, but I believe you need to keep power consistent in order to get an idea. Don’t ride at 200w, then smash a 2-min effort, then ride at 200w, then do a 30s sprint, etc. That will throw everything off. Go out and do a super strict ride at a set wattage and stay as close to it as possible, then see when (and how much) cardiac drift starts.

  2. Efforts after x-KJs. I like to do these after 2,000 KJ to get an idea.

  3. Just set a plan and work on it. Say you want to be able to do extended work @ FTP late in a ride. Go ride tempo for 90-min and then do 3x10 FTP work in the last hour of the ride. You could replace FTP with VO2, sprints, etc.

So many ways to work on this.

Here’s a ride where my goal was 4 hours between 190-210w (really close to my LT1). I made it about 2 hr 45 min before I started experiencing decoupling.

Here’s a ride where I rode endurance for the first 90-min and then I started throwing in efforts based on some climbs that came mid to late in the ride. This was to work on FTP+ efforts late in a ride, or to simulate race-specific efforts. I cramped around hour 2.5 in my last race after some really hard efforts so I knew I needed to work on this.


You recently completed training and finished Unbound 200, right? Have you looked at any metrics beyond FTP? What analytics are you using?

This is an interesting YouTube video:

Building Fatigue Resistance Strategy Into Training - YouTube

The basic strategy for increasing fatigue resistance is to go long. When I trained for a double century that involved hour of power workouts and centuries at upper tempo. Personally I’ve not seen much use for aerobic decoupling (power:HR) after 6-8 weeks of base, but I’ve seen posts from people that struggle with decoupling because they haven’t done a lot of longer rides.

WKO has interesting fatigue resistance chart and stamina metric.

FRC is not fatigue resistance. Like you already explain, FRC defines your power curve above FTP. For example your 5 minute power can be computed from FTP and FRC. Fatigue resistance is about what you still can do after you’ve done a couple of taxing efforts, and then recovered a bit below FTP. A higher FRC means your 5 minute power is higher. Higher fatigue resistance means you can repeat some amount of power more times, after recovering below FTP. Take a typical VO2Max workout, and keep adding intervals to it. At some point you can’t do the interval anymore, even though the amount of kJ in it above FTP are below your FRC.


I dont use a HR strap. My unbound data kinda sucks since I blew up so hard. I have a ton of data on 3-6 hour rides. This past weekend I made it an effort to not sit at the back of a group ride the final 30 miles and made sure I pulled.

Could just looking at NP by the hour work?

You’re trying to turn a multivariate analysis into a univariate one. There is no way of using power only to indicate fatigue resistance, full stop. You truly need a measurement of strain to understand what is happening. Heart rate is indicating how much blood needs to be supplied to the working muscles. A higher heart rate (for the individual) indicates that the body is starting to rely on fresh type 2 muscle fiber recruitment to maintain aerobic level work. This requires more blood and increased heart rate. Yes, you can make a partial analysis of RPE against execution hour over hour, but you run into the limitations of working memory as well as quantification of those values. RPE can be driven up by a number of factors that don’t speak to general fatigue resistance. If you really want to understand fatigue resistance, I recommend some sort of heart rate monitor to evaluate strain.

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Sounds like we need to start there, ill get a HR strap ordered.

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get a Polar. You can then use it with a mobile HRV app to really get some neat info.

Will that tie into my garmin 830?

I have never worn a watch so some of this stuff new to me.

Guess im showing my age

While I agree with Sarah about wearing a heart rate monitor, its been my experience (and confirmed by my coach) that fatigue resistance benchmarking is really best understood by looking at your power curve after XXXX kJ like Anthony mentioned earlier. Which has nothing to do with HR.

Here is one chart in WKO that is helpful, it can be modified to show after 1500kJ or 2000kJ or 2500Kj or …

My decoupling stabilizes early during base, and then I see almost zero decoupling on 2-4 hour zone2 rides, 40-70 minute threshold efforts, etc. For example here is 133 minutes of lower tempo in 85-90F heat, after 8 weeks of base:

Aerobic decoupling is 0.25% (Pw:Hr) which is nothing, and like I said it was a hot day where you might expect more decoupling.

With all the long rides you’ve done I’d be surprised if you find much useful information with respect to fatigue resistance from looking at Pwr:HR / aerobic decoupling.

Yes if it supports ANT+/Bluetooth. I’m happy with my Garmin dual HRM.

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I don’t discount that these charts have value, but as a standalone, they aren’t as predictive as we would want them to be. Depending on how advanced one is in their training, this chart can be limited by the “central regulator” theory. The chart can’t in a vacuum draw the distinction between muscular damage, body temperature, glycogen depletion etc. (nor can heart rate for that matter, but it can add some insights) and psychological potential/limitations.
Seeing a measurement of strain, especially during longer sustained efforts, can demonstrate to an athlete whether they are breaking down physiologically or psychologically. The fatigue resistance curve will tell you where you are based on past execution, but determining how one bridges the delta between current state and theoretical future state involves a more holistic view of training.
For the vast majority of athletes, WKO+ charts can be confounding if not overkill. That is not to say they are without value, for the athlete who is looking to compete at a high level and is approaching their genetic potential, they can be abundantly helpful. But to address the original question, “how do you know,” that is going to come from combining benchmarks with strain.
But, to my original point, this is almost the wrong question, your curve may indicate whether or not your established fatigue resistance meets the demands of your event in a strictly one dimensional sense, but thinking of fatigue resistance as almost a pass/fail is leaving a lot on the table.

Predictive? Sorry you seem to be talking in circles. Decoupling is NOT predictive. The fact that I can hold my FTP for 1 hour, and have virtually zero decoupling is NOT predictive. The fact that I can go out and ride 3-5 hours of tempo with low to zero decoupling is NOT predictive. My power duration curve has some predictive value on max efforts, until improving fitness results in setting a new best.

Fatigue sets in after cycling for a period of time. It is seen as a loss of power relative to cycling in a fresh state. Another interesting article, from the WKO product lead:

You don’t need WKO to test… One simple way to test it, for someone like the original poster (Unbound 200), is to go out and ride z2/tempo for 3-5 hours and then do a 20-minute max effort. Compare that to a fresh 20-minute max effort. Its really that simple. Do that once a month and see if you can improve. For example if you can do 20-minutes at 300W while fresh, and 260W after 2500kJ, work on improving by getting to 270W or 280W or 290W. Notice that when we talk about pivotal moments late in a race, its about ability to produce XXX watts of power.

And that doesn’t require any benchmarks with strain (HR).


another good article on fatigue resistance:

from the article:

showing pros vs U23 and ability to deliver more power after long efforts

I stand corrected. Thank you. I was trying (poorly) to conflate frc with what @bbarrera posted below regarding power after 1000kjs and 1500kjs into a ride.

edit: meaning, when I experience a higher FRC Kj my % drop in power after 1000 and 1500Kj’s is usually less. I’m not sure if there is a relationship. I’m not necessarily trying to make one. Just an observation…

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WKO does has a fatigue resistance metric, Stamina

I do not have much experience with it though as I do not use WKO.

For Xert, they have their lower threshold power(LTP) which is another way of trying to quantify fatigue resistance. The higher you can get that number the longer you can ride at a given subthreshold power IME

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If you can’t understand the point, it doesn’t mean I am “talking in circles” you can take it down a notch with the chest-pounding, no one is impressed. Decoupling IS predictive. If you observe decoupling it is an indication that your fatigue resistant muscle fibers are not sufficient to meet a particular output and will not be until trained appropriately. Power curves include what you have executed and does not always reflect capability. But, we are done here. I don’t waste my time with rude, bad faith commentary.