Getting the interval workout recovery right

I’ve previously written about getting the warm-up right and getting the cool-down right. Getting these components of training right is a relatively minor component of the design of an overall training program.

Still, if you’re planning on having a long running career (or if you’re a coach working with a team), you’re going to be doing a lot of warm-ups, cool-downs, and recovery intervals. So, it’s worth spending a bit of time to make sure you’re getting them right.

When it comes to the recovery during interval workouts, you’ve got three variables to optimize:

• How much recovery to take
• How you measure your recovery (i.e. as time vs. as distance)
• What to do during the recovery interval (e.g. stand, walk, jog, or run—and how fast)

Like in my cool-down article, I think it is useful to frame these questions in terms of who is doing the workout, what kind of workout they are doing, and what your training goals are, both for that workout and for the training cycle overall.

Interval workout structure: repeats and recovery

Since we’re going to be talking about detailed aspects of interval workouts, let’s make sure we’re on the same page when it comes to terminology.

Technically, the “interval” in “interval workout” refers to the recovery interval between the bouts of fast running, since traditionally that recovery was a specific duration of time—i.e an interval—that separated the individual running bouts at a specified pace. Those repeats, which I sometimes call “reps” for short, are also occasionally referred to as “tests.”

In casual conversation, though, coaches and athletes often use the word “intervals” to refer to the running part of the workout (i.e. the reps), and just call the recovery “the recovery” or “rest.”

I will stick with the traditional terminology in this article: “repeats” or “reps” for the running-fast part, and “recovery interval” for whatever separates the reps.

Interval workout recovery: distance, length, and duration

When designing a workout, there are three ways to structure the recovery: as a set duration (e.g. 10 x 500m with 30 sec walk recovery) as a set distance (e.g. 16 x 200m with 200m jog recovery), or using swimming-style “rolling” recovery times (e.g. 10 x 400m starting every two minutes).

Recovery intervals with a set duration

Recovery intervals over a set duration are probably the most common and are definitely the most flexible way to structure recovery intervals. You can stand, walk, jog, or run, and don’t have to worry about how long it will take you to cover a set distance.

You can also fine-tune the recovery interval as precisely as you like—in some workouts I’ll experiment with as little as five second increments in rest (e.g. 12 x 500m with 25 seconds versus 30 seconds walk rest). This level of precision isn’t quite as easy with distance-based recovery intervals.

It’s totally fine in some cases to give yourself a range of time for the recovery intervals. For the above 12 x 500m session, for example, if I’m uncertain about an athlete’s recovery capabilities, I might prescribed the workout as having 30–45 seconds rest, with the idea that we’ll start with 30 seconds, see how that goes, and bump it up to 40 or 45 seconds if it’s starting to feel too tough.

Recovery intervals over a set distance

Classic old-school workouts almost always use distance-based recovery intervals.

Quenton Cassidy’s infamous and (possibly?) fictional interval session in John L. Parker Jr.’s Once a Runner (3 sets of 20 x 440 yd) had 110 yd and 440 yd recovery between reps and between sets, respectively (though to be clear, I am in no way endorsing such an absurd session).^[1]

Recovery intervals over a set distance are useful in large groups, especially when you can’t count on everyone having a watch. When I was a middle school coach, for example, I used this style of recovery almost exclusively.

Set-distance recovery intervals are also useful if you want to be able to self-regulate the rest more naturally. Fast 200s are a good example—using a 200m jog as your recovery interval, instead of, say, 60 seconds jog, lets you naturally regulate how much rest you take.

If the workout is getting too tough, you can jog the recovery 200 slower, which might allow you to maintain good form more effectively in the following rep.

Of course, this perk also carries the risk of allowing you (or your athletes) to “sandbag” the recovery. If you want to ensure a specific physiological effect, or a specific difficulty level, it’s better to control the rest with duration-based recovery instead.

Set distance recovery is most useful for situations where you are trying to do your recovery interval fast—so-called float recoveries or on/off sessions, like the famous Oregon 30/40 workout^[2] or Renato Canova’s alternating kilometer sessions. 

Swimming-style rolling recovery intervals

Swimmers do most of their interval work using a rolling recovery clock, where each repeat starts after a certain duration.

This is mostly for practical reasons—swim coaches need to manage dozens of athletes doing intervals on a daily basis, and swimmers hate wearing anything on their wrist (for the same reason most runners would hate wearing a tracking device that you had to strap to your ankle). So, they all use the same pace clock mounted pool-side.^[3]

A running equivalent might be 10 x 400m “on two minutes,” meaning you would start a new repeat every two minutes, with the clock running continuously during the rest and recovery (so a 70-second 400 would grant you 50 seconds of rest).

I find swimming-style rolling recovery intervals the least useful of the three styles, since they has some undesirable properties: over set distances, they penalizes slower runners, and they requires doing a bit of math or watch customization (especially if you are using a non-integer rest duration, e.g. starting on 2.5 minutes).

Admittedly that latter complaint is a bit prosaic, but hey, you’ve got to be practical.

The only time I tend to use rolling recovery is when the repeat is also a time-based repeat. Two examples:

Cut-down workouts with large groups. A classic summer or early-fall workout for a high school cross country team might be 8–12 x 2min, starting out at a moderate pace and cutting down the pace on each successive repeat.

Doing these workouts on rolling recovery lets the whole team run together, which is good for building camaraderie, team spirit, and having younger runners get to run with the older, faster athletes.

Then, you can just have the less-fit athletes do fewer repeats and have your top runners continue progressing the pace. It’s also a good excuse to use your coaching whistle.

Kenyan-style mid-run pickups. One replacement for traditional post-run strides can be a set of pickups on rolling recovery in the middle of a run. Two variants I often use are:

• 30 minutes of (30 sec fast starting every 2:30) during an otherwise-easy run
• 40 minutes of (1 min strong starting every 4 minutes) during an otherwise-easy run

In both cases, the recovery is still an easy run, not a jog or a walk. These are not real workouts; they are just some lighter bouts of faster running to touch on faster speeds and to get your legs feeling more fresh for the following day.

“Fast” on the 30 second repeats doesn’t mean mile pace—more like 5k-ish effort at the beginning, perhaps getting down to the optimistic side of 5k pace by the end.

Likewise, the one minute “strong” repeats can start on the slower side of 10k pace and work down to 8k-ish pace. In both cases, though, you shouldn’t be looking at the pace on your watch—it’s about effort, not pace.

Heart rate based recovery

There is one style of recovery interval that I never use, and that is heart-rate-based recovery intervals. These are troublesome for many reasons, but the most important is that there is no reason to believe that your heart rate recovery is a strong indicator of your clearance of metabolic byproducts in your muscles.

While it’s true that well-trained athletes show a more rapid decrease in heart rate than sedentary people following exercise, the mechanisms that regulate heart rate recovery are a complex mess of sympathetic and parasympathetic nervous system activity [1,2].

Your “metabolic” recovery—i.e. how long until your body is to do another repeat at the same speed—is moreso a function of your ability to regenerate your non-aerobic energy reserves, as well as your ability to clear out local metabolic byproducts like calcium ions from your muscles. That process follows a more well-defined exponential decay-type process described above.^[4]

If you really want a technical, scientific method of individualizing recovery intervals, the right way to do it is with a critical speed model: if you know your critical speed and your D’ (“D-prime”), or anaerobic energy reserve, you can calculate the recovery needed to regenerate a given proportion of your anaerobic energy. Doing so is admittedly not trivial, but at least it’s well-founded in science.

I don’t feel super strongly about this one, though, so if you have a good case to make for heart-rate-based recovery intervals, I’d love to hear it in the comments section.

Determining the right length of a recovery interval for workouts

Choosing the right recovery length is a massive topic. Instead of trying to cover every possible case, I’m going to outline the basic science behind what’s going on during a recovery interval so you can make smarter decisions with your workout.

Broadly, we can divide interval session into two categories:

1. Workouts that use repeats at intensities above your favorite measurement of maximum metabolic steady-state (SSmax), e.g. LT2, critical speed a.k.a "CV," or MLSS^[5]
2. Workouts that use repeats at intensities close to or slightly below SSmax

There’s no third category (intensities much lower than SSmax) because it usually does not make sense to take any recovery at all in such a situation—just run it straight through as a continuous run.

Recovery length for workouts above SSmax

When you’re running faster than SSmax, your body is in an unstable metabolic state. The indicators of fatigue are spiraling out of control: VO2 is rising towards VO2max, heart rate is rising towards HRmax, blood lactate is steadily increasing, and so on.

During these workouts, the role of the recovery interval is to bring these markers back down so that you can do another repeat (and another, and another) without hitting the limits of fatigue.

Even if you don’t base your workouts off critical speed, the critical speed model is a useful conceptual tool here: it states that running above SSmax draws from a finite reserve of “anaerobic” energy.^[6] Once that energy reserve is gone, you will be too fatigued to continue.

Take the example of running 5000m at 5k pace: per the model, you steadily draw down your finite energy reserve, starting from 100% and reaching 0% after five kilometers. Such a session requires an all-out maximal effort.

Now, if you split that same amount of running into 5 x 1000m with a recovery interval of N seconds, the difficulty of the workout depends entirely on what duration you use for N.

Here’s the most useful thing to know about recovery interval length: The recovery process is not linear—it is an exponential decay-like process with a half-life. You recover faster initially, then slower.

Moreover, the more you deplete your anaerobic energy stores, the faster this initial recovery happens.

The graph below shows intramuscular phosphocreatine levels (PCr)—an excellent indicator of reliance on anaerobic energy, since phosphocreatine is split into phosphate and creatine to regenerate ATP when the demands of exercise outstrip your aerobic system’s power output.

For now let’s focus on the black dots. Notice how initial recovery is much faster than late recovery. That process is modeled quite well by an exponential-decay function.

Research in cyclists suggests that the recovery half-life is about four to five minutes.^[7] What’s important here, though, is not the absolute duration of the recovery half-life. It’s more the general intuition that recovery happens quickly early on in a recovery interval, and more slowly later.^[8]

The recovery half-life increases when you do your recovery interval at a faster speed; this is totally intuitive: faster paces leave less aerobic energy “left over” to mop up metabolic byproducts. If your recovery speed is faster than SSmax, you don’t recover at all. We will circle back to this effect when considering interval workout recovery speed.

So, if you only need to regenerate a modest amount of anaerobic energy, you can get away with very short recovery intervals relative to the length of the repeat (e.g. while doing 8k/10k pace work). However, workloads that deplete a lot of your anaerobic energy, or that require a near-total restoration of energy, can require very lengthy recovery intervals. One example of the latter might be 3 x 500m at goal 800m race pace—that session could easily require 8–10 minutes of recovery.

Unsurprisingly, though, this rate of recovery varies significantly from person to person—some athletes (probably the aerobically fit ones!) can recover quicker than others, even from the same relative workload!

Again, this should not be surprising to the experienced coach: If a 3200m runner and an 800m runner have the same mile PR, and are both doing 600m repeats at mile pace, the 3200m runner will recover faster during a given recovery interval.

Workouts at or below maximum metabolic steady-state (SSmax)

If you are doing workouts in the high-end aerobic domain (e.g. cruise intervals, half marathon pace, or marathon pace), you generally have one of two goals during the recovery interval: mop up any lingering metabolic byproducts in case you went a touch too fast; or put pressure on your body to oxidize lactate for fuel.

These are pretty different goals and as a result they have pretty different strategies for recovery interval length.

Staying in control during high-end aerobic workouts

If you’re doing a classic Daniels-style cruise interval workout (e.g. 10 x 3 min at predicted LT2) there’s always some chance that you’ve briefly exceeded SSmax during a repeat. A short rest helps you mop up any metabolic byproducts and bring your whole-body metabolic state back below SSmax.

In this situation, because of the half-life dynamics of recovery, you can use almost comically short rest—even 60 seconds will feel luxurious for a reasonably fit runner doing the above LT2 workout. Stronger runners can bring this down to 45 or even 30 seconds without too much trouble. Even relatively long bouts close to SSmax, like 3 x 10 minutes at predicted LT2, typically only require 2–3 minutes of recovery.

Increasing muscle oxidation of lactate

A more advanced technique for half marathon and especially marathon runners is to use interval workouts with fast recovery to put your body in a physiological situation where lactate is available as a fuel for aerobic energy. Doing so requires two ingredients:

1. Elevated levels of lactate production in fast-twitch fibers
2. High rates of carbohydrate oxidation in slow-twitch muscles

The way to achieve this is to alternate doing repeats at a fast but fully aerobic pace (e.g. marathon or half marathon pace) with “recovery” intervals that are still fairly fast—perhaps only 10–15% slower than the repeat itself. This fast recovery is necessary to create that second ingredient: a high rate of carb oxidation.

The problem with jogging or walking during your recovery is that your metabolic rate in your muscles will drop, and their fuel preference will switch to fats.

So, to encourage the development of your body’s lactate shuttling mechanisms, you want to use recovery intervals that are fast enough to burn a lot of lactate during the interval itself, but still slow enough that some recovery will actually happen—when you go faster than SSmax, you don’t recover at all.

One interesting outcome from cycling research is that the half-life of lactate clearance can be several times slower than the half-life for regenerating anaerobic energy. That fact, combined with the fact that your rate of recovery will necessarily be slower during fast intervals (since you have less surplus oxygen to do the recovering with), means that recovery intervals should generally be three or four minutes long (or an equivalent-ish distance) for workouts with a lactate clearance goal, as compared with doing the same session for purely high-end aerobic fitness benefits.

That’s the reason why you see top marathoners and half-marathoners using “alternator” workouts like 10 x 1k at 105% MP / 1k at 90% MP. For a pro, that workout would be a cake-walk even with a 30 second jog recovery. But doing that full kilometer of fast recovery lets them spend more time in a state of high lactate shuttling and oxidation, getting a greater training stimulus for those capabilities. 

What to do during your recovery interval: stand, walk, jog, or run?

On the topic of fast recovery intervals, let’s return to the other main question when it comes to recovery: what do you do during it? On paper, you have four options: standing, walking, jogging, or running at speeds ranging from easy run pace up to a fairly fast recovery intensity.

At a high level, the main thing to know on this front is that recovery is faster when running (or walking) intensity is lower. You can manipulate this to your advantage during workouts to get the benefits you want.

One way to think about recovery intensity is that it’s a function of how much “extra” oxygen is available to your muscles. This heuristic helps understand that (a) faster recovery intervals mean less recovery, and (b) athletes who are more fit will recover faster due to their superior oxygen delivery capabilities.^[9]

Standing recovery

I basically never recommend a true standstill—the difference in metabolic cost between standing and slow walking is not very big, and the benefits of continued blood flow from the “muscle pump action” is a benefit that walking offers that standing does not.

In large groups, a bit of standing around is fine, but I don’t think it is wise to literally stand completely still for more than thirty seconds or so.

Walking recovery

Walking recovery is best used when you want to recover as fast as possible, and aren’t trying to squeeze in any extra aerobic benefit—or when you’re trying to keep the mileage of a session to an absolute minimum (e.g. with an injury-prone athlete, or during an already high-mileage day as is the case when doing double threshold).

Here are two use-cases to illustrate these principles at work:

Example workout: 12 x 500m at 10k–8k pace with 25 seconds walk recovery

Explanation: This session is an afternoon session that’s in the vein of Ingebrigtsen-style double threshold days.^[10]

You want to keep the recovery as short as possible to maintain a quasi-stable blood lactate level and heart rate, but also want to squeeze as much recovery as possible out of the brief time period. Also, given that you’re already sitting on a lot of mileage for the day, you want to avoid racking up extra running volume. So, you walk the recovery.

For this session you want to keep the fitness of the athlete in mind. For high school middle distance runners, I would bump the recovery up to 30–40 seconds. For a high-mileage 5k/10k type, you could probably get away with as little as 20 seconds.

Example workout:  6 x 300m at 105% 800m pace w/ 4 min walk recovery

Explanation: This is a “specific speed” session for 800m runners. The fast pace and long rep length will rapidly draw down the anaerobic energy reserve. You might finish the very first rep with half of your anaerobic energy gone.

Combine the large anaerobic power requirements with the fact that 800m runners typically have a low SSmax and you can easily see the need to maximize recovery rates. Even jogging the rest in this workout might not allow you to hit the required pace for the final few repeats, especially if you are in poor aerobic shape.

Jogging recovery

Jogging recovery is usually my go-to default. For young runners, it lets you sneak in some extra aerobic running during the recovery, and for older, more fit runners, usually your fitness is high enough that jogging is not a real burden on your ability to recover.

Example workout:  8–12 x 300m at “XC effort” with 100m jog recovery

Explanation: This is an easy catch-all workout you can use with a mob of 50+ middle school kids and expect almost everyone to get a reasonably good benefit.

For slower runners, the rep may not be much faster than the recovery, but that’s ok—it’s really just a run with the first part at a faster pace (until they get tired and have to slow down). At the very least, you can be sure they’re not sneaking off to play Frisbee.

For faster but inexperienced runners you are hitting a higher intensity on the reps that will produce some solid benefits, without the rep being so long that poor pacing will really sink you.

Lastly, for faster runners who are more experienced, this session becomes more about improving running economy at close to race pace, but because the rest will only take them ~30 seconds, you’re still able to get a decent metabolic challenge, while also preventing things from getting off the rails.

Running recovery: easy, moderate, and fast

To understand the effects of intensity during the recovery interval, let’s return to the plot from above. Now, let’s look at both the black circles and the white circles.^[11]

Black circles are true rest (sitting on the bike; this is from cycling). White circles are continuing to ride, but at an intensity lower than SSmax. Notice how (1) recovery is slower, and (2) recovery stabilizes at a level lower than baseline.

The picture doesn’t show it, but how much slower you recover, and what that new, lower baseline is, are both a function of intensity: the faster your running recovery, the slower you recover, and the less total anaerobic capacity you regenerate.

Like walking recovery, you want to use these to your advantage to achieve workout outcomes that you want. With running recovery I find it more useful to think about when it would be a bad idea.

First, you definitely do not want to use running recovery when you need to recover very quickly.

Second, you also do not want to use it with high-speed sprint work, or long intervals at 5k pace or faster—in these cases, you want to regenerate a lot of your anaerobic energy reserve so you can continue the workout.

So, when to use running recovery at easy, moderate, and fast speeds?

Recovery intervals at easy or moderate run pace

I use these often for inserting very low-key fartlek-style pickups into an otherwise normal easy run. These can help freshen your legs up for a workout the next day, or shake out a bit of fatigue a few days after a really big workout.

Example: 60 minutes easy with 30 minutes of (30 sec fast, circa 5k-ish effort, starting every 2:30) in the middle

We actually saw this session above when talking about rolling recovery. We still want to get the benefits of an easy run, and it’s not like 30 seconds at ~5k pace is delving deep into your anaerobic energy reserves.

Easy run pace recovery is also a good precursor to faster recovery. Here’s a good late-summer/early-fall session for a higher-mileage high school cross country runner, or a marathon/HM runner early on when building general fitness: 

Example: 6mi easy + 3 sets of: 1.5mi at 88-90% 5k pace with 0.5mi easy to moderate recovery

Doing the back end straight through (as 4.5mi at 90% of 5k pace) would likely be too tough. However, 1.5mi a touch backed off from SSmax is barely taxing your anaerobic energy reserves at all. The easy to moderate recovery prevents the 1.5 mi reps from getting too fast, and maintains the long-run-like benefit of the run as a whole.

For a HM/M runner, this session also serves as a nice precursor to more structured sessions with fast recovery. It also has many avenues for progression: either more volume (4 x 1.5mi), more extension (3 x 2mi), or faster recovery (0.5mi at 80% 5k).

Recovery intervals at a fast pace

We’ve finally arrived at the fun workouts. Doing a recovery interval fast—as in, significantly faster than your easy to moderate run pace—is an advanced technique, but can be extremely useful for pushing beyond the fitness plateaus that arrive after a few years of traditional interval work.

You need pretty good pacing skills to do these kinds of workouts correctly, and if you overshoot in the wrong way—either doing the reps too fast or the recovery too fast—you can dig yourself into a hole that’s very hard to get out of.

Above, we already discussed the main rationale for fast recovery intervals: it creates a metabolic situation in your muscles that is highly conducive to oxidizing lactate for energy.

Running a long-ish interval at or slightly below SSmax, such as doing 1km at predicted LT2 pace (as in “cruise intervals”) or 2–3 km at marathon pace, creates an elevated level of ambient lactate in the blood and muscles.

Then, if the intensity during the recovery interval continues to be high, you’ll encourage your body to shuttle this lactate around and oxidize it for energy.

Here are two sessions that are paragons of this technique:

Example workout: 6 x 1200m at predicted LT2 pace (“T” pace) with 400m recovery at 90% LT2 pace

If you’ve done Daniels-style cruise intervals at “T pace” before, this workout is a logical progression. Instead of the traditional one minute jog, you do 400 meters fast, then launch right into the next repeat. Strictly, it isn’t optimal from a lactate oxidation perspective because the recovery is only going to last ~1.5–2 minutes, but it’s a good stepping stone away from “vanilla” cruise intervals.

This workout is amenable to progression in three directions:

• More volume (7 x 1200m / 400m)
• More extension (5 x 1600m / 400m)
• Faster recovery (6 x 1200m / 400m at 95% LT2)

I think of this session as having more of a 5k/10k flavor, because it emphasizes aerobic intensity and modestly de-emphasizes total workout volume and lactate oxidation. I would only use this with a fairly experienced distance runner—not with high schoolers (in most cases).

Example workout: 8 sets of (1 km at 105% marathon pace (MP), 1 km at 90% MP)

This is a classic Renato Canova workout seen many of his training schedules. Emile Cairess did three variants of this kind of “alternating kilometer” session in his build-up before his 2:06 marathon at the 2024 London marathon.

Applying what we’ve seen above, we can see why this workout creates a highly favorable situation for oxidizing lactate: it combines speeds close to SSmax with a recovery interval of a few minutes in length that is still quite fast.

This session is also amenable to progression in three directions:

• More volume (10 x 1k / 1k)
• More extension (5 x 2k / 1k)
• Faster recovery (8 x 1k at 105% MP / 1k at 95% MP)

That final means of progression is perhaps the most advanced technique at all–I basically only use it with sub-2:40 marathoners whose fitness is quite strong already. However, I’ve found that the ability to recover while running very close to marathon pace is a hallmark of excellent marathon-specific fitness. It is possible to progress this kind of session (8–10 x 1k / 1k) to the point where you can do the recovery as fast as 96–97% MP and feel good while doing so. If you can get to this point you can be certain your marathon fitness is extremely strong.

Conversely, if you try this session and find it much too hard, even at 90% MP for the recovery, you can back it off to 85% or even 80%. Then, in your subsequent workouts or your subsequent training sessions, you can increase the recovery speed. You can also try introducing intervals with easy to moderate recovery first (e.g. the 3 x 1.5 / 0.5mi workout above)

Recap

In most cases, using duration-based recovery is the best option. Distance-based recovery is useful in large groups, or if you want to give yourself more leeway to adjust recovery by feel.

During the recovery interval after a repeat at faster than maximum metabolic steady-state (SSmax), your goal is typically to regenerate some portion of the anaerobic energy you burned through in the repeat.

Recovery intervals following repeats at SSmax or slower have one of two goals: either to safeguard against going a bit too fast on the repeat, or to encourage your body to transport and oxidize lactate. In the former case, a short jog is best. In the latter case, you should use longer (~three to four minutes) of running at a speed that is fast, but still around 5–15% slower than SSmax

Recovery is an exponential decay process with a half-life, so you recover very quickly at first, then more slowly later as the recovery interval continues. Short repeats at moderate intensities require barely any recovery at all, while very fast sprinting or very long repeats can require five, eight, or ten minutes of recovery.

The rate at which you recover is a function of your aerobic fitness, so stronger and more experienced runners require less recovery, even for the same relative workout (e.g. 6 x 1 km at 5k pace), as compared with less-experienced, less-fit runners.

When you need to recover as quickly as possible, or you are trying to minimize total workout mileage, use walking recovery. As a catch-all, jogging recovery is a reasonable default for most cases.

Running your recovery interval at an easy to moderate pace helps keep the overall benefit of a workout closer to an easy to moderate run, and can serve as a precursor to doing more structured fast recovery intervals.

Running your recovery interval at a fast pace below SSmax encourages your body to oxidize lactate for fuel. This is an especially useful ability for marathoners and half-marathoners, which is why repeats at MP and HMP with recovery intervals at only 5–15% slower than the repeat itself feature prominently in the training of top long-distance runners.

Finally, if you run your recovery interval faster than SSmax, you don’t recover at all!

Learn more about training

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Footnotes

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^[1] Once a Runner is a work of fiction, but I’ve heard that more of it is real than you might think.

^[2] The Oregon 30/40 drill involves alternating 200m in 30 seconds with 200m in 40 seconds. Steve Prefontaine famously held the record for the greatest number of sets in a row, until Galen Rupp broke it. I put this workout in the same category as “The Michigan”—famous, but also vastly overused for the same reason. I think “The Michigan” is silly and would never use it, but during my time as a high school coach, we would (on very rare occasions) employ 30/40s, adjusted to be mile pace / mile pace + 10 seconds per 200m, as a very tough but low-volume session for late-season 3200m runners who would be racing tactical championship-style races.

^[3]  The pace clock you see at every lap swimming pool was invented by swim coach and scientist “Doc” Counsilman at Indiana University, where I went to graduate school. During my PhD I would occasionally do deep-water running sessions in the swimming pool that housed the very first pace clock. A magazine advertisement for mail-order pace clocks, hand-made in Bloomington, Indiana, was framed on the wall. I took a biomechanics class in a classroom adjacent to the “dimly lighted” four-lane pool described in the linked article.

^[4] For distance running workouts, at least. The situation is different for true sprint workouts, e.g. fast 150s with full recovery. There, “nervous system” recovery matters as well as “metabolic” recovery

^[5] If “SSmax” makes your brain hurt, just replace it with “threshold.” I have a full blog post forthcoming about SSmax and why I’ve begun using that term, as opposed to LT2.

^[6]  Strictly speaking, it is not correct to talk about D’ being entirely “anaerobic” energy. Some of the energy production in the finite supply of energy in D’ is produced aerobically; evidence for this comes from the fact that D’ goes down at altitude and goes up when you breathe hyperoxygenated air. It’s just not sustainable aerobic energy production. However, outside of physiology circles nobody knows what you mean when you say “D-prime,” and everybody knows what you mean when you say “anaerobic energy reserve” so I’m going with that one even if it’s technically wrong.

^[7] It is possible to explicitly model this process mathematically, but the math gets very scary very quickly. The best way to do it would be with a clever app that abstracts away the math, which I may try to develop someday. In lieu of that, I may explore this process more in a deep-dive blog post in the future.

^[8] From the figure, it actually looks like the half-life for phosphocreatine recovery is shorter than the overall anaerobic energy reserve half-life for recovery, but this might just be an illustrative image from one person with a particularly short recovery half-life.

^[9] In a technical sense, recovery is proportional to the difference between your current running speed and your critical speed. So, slower-paced recovery intervals and superior aerobic fitness (as captured by critical speed) both increase your rate of recovery.

^[10] Yes, this pace is, strictly speaking, faster than “threshold,” i.e. LT2 or SSmax. One of my earliest blog posts here was about how you can mimic threshold using higher-intensity sessions with very short rest. Indeed, one of the examples I gave way back in 2011 (16 x 400m at 8k to 10k pace with 25–30 seconds recovery, copped from John Kellogg’s writings in the mid-2000s) is now seen as a classic double threshold session.

^[11] The white triangles are for recovery at a speed above critical power, i.e. faster than SSmax. They end after less than a minute because you literally cannot recover at all at that speed, so exercise terminates basically immediately—remember, the run-up to this was exercise to exhaustion!

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