Peak and fade intervals are a key component in the training regimens of elite athletes. These Peak and Fade Intervals start at a very high intensity and gradually decrease, offering a unique approach to training. This article not only delves into the science behind Peak and Fade Intervals but also covers pre-loaded intervals, another effective training method. Learn how these intervals can help you sustain a lactate concentration of 10 mmol/l for 20 minutes without fatigue.

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The most extreme example of a peak and fade interval is probably a true peak (all-out sprint) that slowly and automatically fades, like a 30-second Wingate test.

Although maybe not exactly the same, let’s consider pre loaded intervals as peak and fade intervals too. Pre loaded intervals start with a high intensity and then step back to a steady intensity. 

Threshold ladders for instance start at an intensity above threshold and then slowly drop to threshold intensity or slightly below. In fact, one single over-under interval could also be considered as a peak and fade or pre loaded interval. 

Example Over-Under interval workout: 2 sets of 4x2min. at 105% AT, 4x1min. at 95% AT. 5 minutes recovery in between intervals.
Example Over-Under interval workout: 2 sets of 4x2min. at 105% AT, 4x1min. at 95% AT. 5 minutes recovery in between intervals.

Before diving into the science behind peak and fade intervals, let’s first explore an example workout designed to improve athletic performance.

When designing a peak and fade workout, it’s crucial to decide on the peak intensity and the lowest fade intensity. Here’s an example of a pre loaded interval workout that can help you improve your lactate concentration and athletic performance:

  1. Warm-up
  2. Intervals: 3 intervals of 8 minutes
    • Peak: first 20 seconds near all-out effort
    • Fade: rest of the interval at threshold intensity
  3. Recovery: 5 minutes between each interval, at an intensity of 50% of threshold
  4. Cool-down

This workout would take roughly 35 minutes (ex warm-up and cool down).

Example of pre loaded peak and fade intervals: 3 sets of 20s near all-out, 8min at 100% AT. 5 minutes recovery in between intervals.
Example of pre loaded peak and fade intervals: 3 sets of 20s near all-out, 8min at 100% AT. 5 minutes recovery in between intervals.

Continue reading if you want to know why elite athletes call pre loaded intervals their secret training, and how they create the most effective peak and fades.

Here’s how the best athletes do pre loaded intervals, without blowing up.

INSCYD lactate recovery (grey) & accumulation (purple) graph
INSCYD lactate recovery (grey) & accumulation (purple) graph, depending on the exercise intensity (x-axis). Example from a cyclist with an anaerobic threshold of 295 watts.

This graph shows how fast lactate accumulates (purple line) above threshold. We can use this data to create a pre loaded interval that increases lactate concentration. For example: 5 minutes at 350 watts will increase lactate concentration by 6.5 mmol/l (5 min. * 1.3 mmol/l/min = 6.5 mmol/l).

If you have a specific lactate concentration in mind that you want to target, you can also use the INSCYD Training Zone Builder (TZB). We asked the TZB to create two training zones. One that results in a lactate concentration of 7.1 mmol/l, after 20 seconds. Another one that results in the exact same lactate concentration, after 120 seconds. 

The INSCYD Training Zone Builder now calculates the corresponding intensities.

Two pre loading intensities, both leading to a lactate concentration of 7.1 mmol/l. The first training intensity (660W) will reach the desired concentration in 20 seconds. The second intensity (386W) will reach this concentration in 120 seconds.
Two pre loading intensities, both leading to a lactate concentration of 7.1 mmol/l. The first training intensity (660W) will reach the desired concentration in 20 seconds. The second intensity (386W) will reach this concentration in 120 seconds.

Now that we have 2 options to increase lactate concentration, we can pick one and add the “fade” part of the interval. For instance: 10 minutes at threshold intensity, at which no lactate is accumulated nor cleared.

As a result, our example athlete will maintain a high lactate concentration of 7 mmol/l over the course of a 10 minute interval, without blowing up. This is quite unique, and only possible if you know your lactate recovery and accumulation rates, depending on the exercise intensity.

Interested in how lactic acid affects your performance? Hear from pro cyclist Thomas Skujins in this short video.

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High intensity peak and fades, similar to a 30-second Wingate, are likely to improve your tolerance for high lactate concentrations. If not physically, then mentally.

If you keep the HIIT interval duration short and the recovery between intervals long, you rely heavily on your anaerobic system. This can have a positive (increase) effect on your VLamax.

If increasing VLamax is your goal, you should keep the peak and fade interval short. That is because once lactate accumulation results in high lactate concentrations, the anaerobic energy system will be hampered. This will also hamper your VLamax adaptation. In other words, don’t allow for a long “fade”.

The duration and intensity of the recovery between intervals is also essential. Use the INSCYD lactate accumulation graph shown previously, to calculate the lactate concentration at the end of the “peak”. Let’s take 10 mmol/l as an example.

Now use the graph to find out at which intensity you clear lactate fastest. The previous graph shows that our example athlete recovers fastest at 200 watts. At this intensity lactate is cleared at a rate of 0.7 mmol/l per minute. As a result, to recover back to 2 mmol/l, it takes 11 minutes and 25 seconds (8 mmol/l ÷ 0.7 mmol/l/min). Just to give you an idea of the length of recovery.

If you don’t implement such a long recovery in between, the anaerobic energy system will be hampered during the next interval. This will again hamper your VLamax adaptation.

Ready to dive deeper into the science of interval training for runners? Our webinar will teach you how to create individualized training programs based on metabolic profiles, optimize recovery periods, and much more. Don’t miss this chance to elevate your coaching skills and athlete performance.

When comparing these types of peak and fade workouts with longer pre loaded intervals, you can expect a different training effect. Long pre loaded intervals allow you to ride at a high lactate concentration for a long time. This lactate is a fuel for the aerobic energy system. If you “improve what you train”, you’d expect an improvement of the aerobic energy to use (burn/clear) high amounts of lactate. These benefits are more like the over-under interval benefits.

The beauty is, that you don’t have to wait for scientific publications on HIIT training methods to know what the exact training effect is. Instead of learning about the training adaptations of others in literature, you can easily test it on yourself.

Simply implement a training method in your training program and perform an “at home metabolic performance test” before and after the training program. With “at home” we mean you can easily do such a metabolic test remotely without entering a lab. You only need a power meter (cycling) or GPS watch (running), to get lab-level accurate data. Of course you can also do the test using lactate samples, or even add a metabolic cart if you’re in the lab.

The pre- and post test will tell you exactly how you adapt to a HIIT training stimulus, like peak and fades.

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Are you a coach or lab looking to take athlete performance to the next level? INSCYD’s metabolic performance software offers unparalleled insights into lactate accumulation, recovery rates, and individualized training zones.

As you’ve seen in this article, INSCYD enables you to create highly effective peak and fade intervals, optimize recovery, and much more—all backed by lab-level accurate data. Don’t miss this opportunity to revolutionize your coaching or testing services.

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Athletes why train with generic plans when you can have a program tailored to your unique physiology? INSCYD is the key to unlocking your full potential. Find your dedicated INSCYD coach or lab here. 

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LOEK VOSSEN

Human Movement Scientist | Content Marketing and Education

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