The Assessment - Aerobic Endurance

The aerobic endurance test assesses the strength of your aerobic endurance for a given duration. Aerobic endurance is the ability to ride at a low-moderate intensity for a long time. The test answers this question – can you efficiently deliver oxygen to your muscles?

If you can, you can perform well. If you can’t, it needs to be improved.

The aerobic endurance test is simple in theory but complex in execution. Here’s the protocol:

After a brief warm-up, increase your effort to the top of zone 3, usually called ‘tempo’ by heart rate or power. If you don’t know what that is, you’re riding hard enough that you could converse but wouldn’t want a complex conversation. Hold that intensity for the entirety of the prescribed duration.

That’s it. Perform three to four of these tests in the early base period of your training year and compare the results to track the progression of your aerobic endurance.  Once you no longer aerobically decouple, it’s time for your training intensity to progress. 


How to Analyze the test

1. In TrainingPeaks, from open up the workout > highlight the steady Z2/Z3 effort.
2. On the right-hand explore, you’ll see the statistics for your effort.
3. In the post-activity comments, write down the duration, kjs, avg power, hr, and pw/hr decoupling (>5% decoupling is a sign that you did decouple, or your heart rate went up for the same input).

The key metrics to look at here are: aerobic decoupling and efficiency factor. Let’s go over each of them:

Aerobic decoupling (Power/heart rate)

Aerobic decoupling measures the normalized power to heart rate of the first half of the ride versus the power to heart rate of the second half of the ride divided by the power to the heart rate of the first half of the ride. 

That’s a mouthful, but the metric determines whether the athlete’s heart rate had to increase to maintain the same power output for the duration of the effort. Setting aside the math, this is a beautiful way to quantify aerobic fitness. If you’re aerobically fit, your heart doesn’t have to work much harder to maintain the same power output. If you’re not, your heart will have to increase to maintain the same power output.

Iif your normalized power to heart rate is less than 5% for the selected duration, you’re aerobically fit for that duration. If decoupling for the duration is greater than 5%, more base work is needed to improve the athlete’s aerobic fitness.

Efficiency Factor

Efficiency Factor divides normalized power from heart rate which produces a fraction that the athlete or coach can compare for aerobic efforts workout to workout* to measure progression. The higher the EF, the more power the athlete gets out of every heartbeat and the more aerobically fit they are.

Note here that EF in and of itself doesn’t tell you anything – there aren’t absolute EF values comparable to other athletes. EF values are valuable data to examine across tests – if EF increases test to test, your aerobic endurance has improved.

How to not mess up the test

Earlier I mentioned that the aerobic endurance test is simple in theory but complex in execution. To succeed in this workout, you need to prepare. Fueling, hydration, pacing, route selection, and duration make all the difference in its implementation


Let’s start with fueling. Look, to succeed in this workout, you’re going to need to eat a lot of carbohydrates, and you’re going to need to eat early and often before you’re hungry. Holding zone 3 doesn’t feel exhausting at first, but where it bites is that it quickly burns through your glycogen stores. It’s easy to bonk in the aerobic assessment, so it’s critical to start eating 30 minutes into the test. It’s helpful to adopt the mindset that you need to stay ahead of your hunger. If you get behind on fueling and start to feel hungry, it’s over – you will unravel. 

I’ve told athletes this for years, and it usually takes a few attempts for them to get this right simply because they underestimate just how much fuel they need to ingest to fuel this effort. 


Hydration also plays an essential role in execution. Even though the base period for cyclists often coincides with winter and less time spent riding outside, whether a cyclist is performing this outdoors or on their trainer, they’re generating a lot of heat because they’re working so hard. Humans dissipate heat through sweat. Our sweat capacity is mediated by the rate at which we delay the drop in plasma volume in our blood. 

To mitigate that drop, it’s essential to know your sweat rate and take on a sodium solution that replaces the sodium you’re losing in sweat.


The next thing you need to consider in your execution is pacing. Everyone goes hard when they feel good, but I want to reiterate that this effort is long, up to five hours in some cases, so how you think in the first hour says almost nothing about how you’ll feel in the last. Use the bottom of your zone 3 power or heart rate as a guide (pick one) and then hold it steady. The fatigue will find you eventually – don’t pick an unrealistic heart rate or power and expect it to go well.


To nail the aerobic assessment, pedal continuously. Pick a route that doesn’t feature many stops, and once you’re on it, don’t stop. Yes, that means no twenty-minute coffee stops, no stopping for calls, texts, or snaps for the ‘Gram. Why? Think of a traditional interval workout with shorter efforts like three minutes on, 3 minutes off. Do you think it would be good training to stop in the middle of the three-minute interval to take a photo? No? Why Not?

Because that’s extra rest, the aerobic endurance test is one long interval. Suppose you stop for a prolonged period during the effort that provides extra rest and skews the results. For best results, stay on the pedals and keep stops as brief as possible.

Notice the goal of not stopping much is so that you pedal continuously. With that, it’s also crucial that you pick a route that minimizes.


The final consideration is determining how long the test should be. It should be roughly as long as the longest competition in which the athlete competes. For example, if your longest gravel race takes about five hours, then you’ll want to perform an aerobic endurance test that’s five hours long and strive to get fit enough that you don’t decouple.

Some race durations are so long – like Unbound Gravel 200 – that it’s not realistic to perform an aerobic endurance test of that length. Pick a shorter duration – minimally five hours – and use that as an aerobic endurance benchmark.

Final thoughts

Tracking your aerobic endurance over the years of structured training showcases the power of consistent, structured training. I’ve coached many athletes who had improved their aerobic system so much that the power they can maintain for three hours equals or exceeds what they were initially able to produce for their 20-minute functional threshold test when they began coaching.

What should that tell you? Your potential to improve your aerobic endurance is probably huge. The catch is that it requires consistent work over extended time frames.

*EF is only valid for steady-state efforts, not efforts with lots of variation in power output. When power output is variable, the contribution of anaerobically sourced energy skews the results.