Repeat Speed Intervals: Why Going Really Hard Needs to Be Trained Too

Good conditioning isn’t built by living in one intensity. If you want the adaptations that come from aerobic work, threshold work, and high-output anaerobic efforts, you have to train all of them. That’s why our conditioning doesn’t look the same every day. We use longer aerobic pieces to build the engine, PPM to teach pacing and control across different intensities, and Repeat Speed Intervals to train the ability to go very hard, recover, and do it again.

Think about a miler running hard 400-meter repeats. They aren’t doing those intervals because a mile race is simply four separate 400-meter sprints. They’re doing them because those faster efforts expose the body to speeds, energy demands, and levels of metabolic stress that an easy run or longer threshold session cannot reproduce. Repeat Speed Intervals serve a similar purpose for functional fitness athletes by giving us a controlled way to spend meaningful time at very high intensity.

What Are Repeat Speed Intervals?

A Repeat Speed session is built around relatively short, aggressive efforts with enough recovery to allow you to produce another high-quality effort. Here’s an example from one of our recent Training Day sessions:

6 Sets

• 8/7 Calorie SkiErg
• 8 Dual Dumbbell Shoulder-to-Overhead
• 6 Dual Dumbbell Hang Squat Cleans
• 4 Dual Dumbbell Thrusters

All Dual Dumbbell: 50/35 lb
Rest 2:00 between sets
Target: 55–75 seconds per set

The intention isn’t to pace this like a 20-minute AMRAP. You should be working hard from the start, but not so hard that Set 1 destroys the next five. The goal is to get up near the high end quickly, then see how well you can reproduce that output after a short recovery.

That distinction matters because intensity determines adaptation. A 60-second hard effort creates a very different demand than a 20-minute piece, even if both workouts leave you breathing hard when they’re over.

These Are Heavily Anaerobic Efforts

At lower intensities, the aerobic system can supply most of the ATP needed to keep you moving. As intensity rises, energy demand increases faster than aerobic metabolism alone can meet it, so the anaerobic systems contribute much more heavily.

During a short, explosive effort, the phosphagen system provides immediate energy through stored ATP and phosphocreatine. As the effort continues, anaerobic glycolysis contributes more heavily. In a workout like the one above, you’re hitting the SkiErg aggressively, moving directly into loaded pressing, and then carrying that fatigue into squat cleans and thrusters. There isn’t enough time to settle into a comfortable aerobic rhythm.

Phosphocreatine stores drop quickly, glycolytic energy production rises, and the internal environment of the muscle becomes progressively less favorable for force production. The challenge is to keep producing power and maintaining movement quality anyway.

That is one of the biggest reasons we use this type of work. You simply do not get the same stimulus by only training at moderate intensities. If you want to become better at producing high power, you have to spend some time actually producing high power.

Lactate Isn’t the Enemy

Lactate gets blamed for almost everything that feels bad during hard conditioning, but that is an oversimplification. Lactate itself is not simply a waste product, and it can be transported and reused as fuel. What matters more is the broader metabolic disturbance that occurs alongside rapid glycolysis.

As intensity rises, lactate production and turnover increase significantly. At the same time, other changes are occurring inside the muscle that make maintaining force more difficult. Hard interval training exposes athletes to that environment repeatedly and teaches the body to function better inside it.

Over time, that can mean improvements in lactate transport and utilization, buffering capacity, and the ability to maintain output while metabolic stress accumulates. In practical terms, you become better at continuing to perform when the workout gets uncomfortable instead of immediately losing pace as soon as your legs, shoulders, or lungs start burning.

The Rest Period Is Part of the Workout

The two-minute recovery is not dead time. It is one of the most important parts of the session.

After a 55–75 second effort, your aerobic system immediately begins helping restore homeostasis. Phosphocreatine starts replenishing, oxygen consumption stays elevated, breathing and heart rate begin coming down, and metabolites are transported and used throughout the body. The goal is not full recovery. The goal is enough recovery to give you another legitimate shot at high output.

Two minutes later, you go again, and that is where the real value of the session shows up. Repeat Speed isn’t just asking how hard you can go once. It is asking how much of that high output you can access again after partial recovery. In functional fitness, that quality matters constantly because workouts rarely give you perfect rest between demanding efforts.

Your Aerobic System Still Matters

Calling Repeat Speed “anaerobic” does not mean the aerobic system switches off. It contributes during the interval itself and becomes especially important during the recovery period.

A strong aerobic system helps restore phosphocreatine more quickly, supports recovery between bouts, and allows an athlete to reproduce a higher percentage of their previous effort. This is why two athletes can look almost identical on the first set and completely different by the fifth.

One athlete might still be within a few seconds of their original pace, while the other has lost a large percentage of their output. The difference is not just who can sprint harder. It is also who can recover fast enough to sprint hard again.

That intersection between anaerobic power and aerobic recovery is one of the main reasons Repeat Speed training is so valuable.

Buffering and High-Intensity Tolerance

Another adaptation we are after is the ability to continue producing force while the internal environment becomes increasingly difficult.

Hard glycolytic work causes major changes in acid-base balance inside the muscle. The body has buffering systems that help resist those changes and delay the loss of performance associated with very intense work. Repeated high-intensity training challenges those systems and can improve the athlete’s ability to maintain output under conditions that previously would have forced them to slow down sooner.

This is one reason hard 400-meter intervals have been used for decades in middle-distance training. The athlete is not just practicing running fast. They are practicing running fast while dealing with a level of metabolic stress that cannot be recreated with easy mileage.

We are doing the same thing here, just with the movements and demands of functional fitness.

You Also Have to Learn How to Go Hard

There is another part of this that is harder to measure but still matters. Athletes need exposure to high intensity.

If most of your conditioning is performed at comfortable or moderately hard efforts, truly aggressive output can feel foreign. Your breathing spikes, heart rate climbs quickly, your legs and shoulders start burning, and your brain immediately starts looking for a reason to slow down.

Repeat Speed puts you into that environment often enough that it becomes familiar. There is a neuromuscular component to repeatedly practicing high force and movement speed while fatigue develops, but there is also a very practical skill being built: learning how to stay composed and continue moving well when the effort gets ugly.

You learn that a rapidly rising heart rate does not automatically mean the workout is getting away from you. You become better at maintaining technique while breathing hard, and you develop a better sense of the difference between discomfort and actual loss of performance. That matters in competition because high-intensity moments are rarely comfortable, and they should not feel unfamiliar either.

Repeat Speed vs. PPM

Repeat Speed Intervals are very different from PPM, even though both use repeated efforts.

Read our full breakdown of PPM here.

With PPM, the goal is progression. You might begin around 70% effort, then move toward 75%, 80%, and continue increasing the intensity as the session develops. The goal is not to match the same interval over and over. It is to improve each one.

That teaches pacing, restraint, and body awareness. Athletes learn what different effort levels actually feel like instead of treating every conditioning session as either easy or all-out. Because PPM intentionally moves through different levels of intensity, it also gives us a way to train multiple zones within the same session.

Repeat Speed has a different objective. We want you near the high end much earlier, and the recovery period is there specifically so you can keep returning to that high output.

PPM is about building the effort correctly. Repeat Speed is about producing a hard effort, recovering, and reproducing it. One develops pacing and awareness across intensities, while the other develops repeatable high-intensity performance. A complete athlete needs both.

Why Not Just Do Longer Metcons?

Because longer conditioning creates different adaptations.

Long aerobic work is excellent for developing mitochondrial density, capillary development, stroke volume, and the machinery needed to produce energy efficiently for a long time. That work is essential, but it does not create the same rate of ATP demand or the same metabolic environment as a 60-second effort near your high end.

You cannot expect one intensity to prepare you perfectly for every other intensity. This is exactly why a miler does not only run miles. They may use easy mileage to build aerobic capacity, threshold work to improve sustainable speed, race-pace work, and faster 200- or 400-meter repeats to develop qualities that slower running will not touch.

Functional fitness should be approached the same way. We need the aerobic engine, threshold capacity, pacing, strength, and the ability to produce serious power when the workout demands it.

Why This Creates Better Athletes

Look at what competition actually asks from you. Very rarely do you get to operate inside one clean energy system for an entire workout.

You might sprint a machine, pick up a moderately heavy barbell, perform gymnastics, transition to another station, get a short break, and then be expected to produce another hard effort. Your success depends on more than having a high VO2 max or being strong.

You need to produce power, tolerate the metabolic consequences of producing that power, recover quickly enough to access it again, and maintain coordination and movement quality while all of that is happening.

Repeat Speed trains that entire sequence. The first set tells us how fast you are. What happens in Sets 4, 5, and 6 tells us how well you can reproduce that speed when fatigue is already present, which is a much more useful measure of fitness for a functional athlete.

The Bigger Picture

The point of conditioning is not to become good at one type of workout. It is to create adaptations across the entire spectrum so the athlete has more tools available when the demands change.

Long aerobic work builds the foundation. Threshold work improves what you can sustain. PPM teaches you to understand your effort, pace correctly, and progressively move through different intensities. Repeat Speed takes you toward the other end of the spectrum by exposing you to high rates of energy production, significant glycolytic stress, incomplete recovery, and the requirement to repeatedly access power.

That is how you build a more complete athlete. Competition is not going to keep you inside one perfectly controlled zone, so your training should not either. Sometimes you need to pace, sometimes you need to endure, and sometimes you need to put your foot on the gas and go.

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