This post is broken into 3 parts:
1 – Genesis
2 – Application
3 – Exercise Physiology
Part 1 – Genesis
What is a Work: Work interval?
Quite simply, it is the alternation between two (or more) specific intensities of work. The intensities may be different due to a planned change in pace or power output, as may be seen in running or rowing or biking.
For example:
5 Rounds:
500m Run @ Easy Pace (MiD)
500m Run @ ~5k Pace (SiD)
Or the intensities may be different due to a change of modality. For example, switching from rowing, to thrusters. Noting that the power output of the rower can be assessed, while the power output of the thruster can only be assumed. Meaning, there is a definite power output to a thruster of a specific load and pace, but it cannot be easily known. The monitor on a rowing machine tells you the power output. There is no such thing currently for a thruster, or for any of the non-cyclical movements.
For example:
5 Rounds:
3 Min [10 fast Thrusters @ 50% RM + Row @ Easy Pace (MiD) Remaining Time].
I often talk about how Work: Work intervals seem to be the least purposefully utilized designs when it comes to endurance training.
You are much more likely to see Work: Rest designs (EMOMs are common) than Work: Work designs (see above).
Now, anyone familiar with CrossFit will be familiar with going from one modality to the next when it comes to performing an event or a “Metcon“. But, you may not have thought of it this way before.
Who do I think really benefits from these types of designs?
We will get to that, but let’s do a quick history on how I came to think about this topic in this way.
They say a picture is worth a thousand words, well, let’s start with that. Below you will see a screenshot from a version of a handout from the OPT CCP Program Design Module, now known as OPEX CCP. I remember my brother, James, would be in his office for hours on end, while I would be in the gym shooting the shit and training (this was probably back in 2009-2010 time line). I believe he was working to develop the OPT CCP at the time.
Moving along, at the time I did the training my brother would design, the OPT Big Dawgs. I remember a session we did on the Rower one day that was quite different from the previous training we had ever done. I am not going to try to remember all the details of the session, but suffice to say it would fit the Work: Work design I’m talking about here. There were variations in paces throughout, and I believe it was mainly one long work bout or maybe a few long bouts of work with various paces interspersed with short times of rest. It was a memorable session, because I still remember having the rowing machine facing the back window at the old OPT location. This was 15 years ago!
At the time I was a pretty good rower. I weighed about 180 pounds and I could quite easily row a 2K in the 6:30s.
What made me remember the session design was how hard it felt to row at seemingly easy efforts. Meaning, when I did my normal faster paces (i.e 2k Pace) followed by easier pieces (like 2:00-2:10/500m) it felt way harder than what we would normally do. We would normally do faster paces (i.e. 2k Pace) work followed by rest periods. I didn’t know why it was harder but I could feel that it was. Meaning, I didn’t have the knowledge to explain what was happening, but I had the experience to know what it meant.
I can’t remember if I spoke to my brother about this or if it was part of the original OPT CCP manual but I do believe that design (and the above picture of the energy system chart) came from biathlon Canada training manual, developed by Nelson Ayotte. I do believe he was connected to Charles Poliquin and that’s how my brother would have connected with him. Ultimately, his system was adopted and that’s what you see in the OPT CCP screenshot above.
Okay, that was the first instance of how I came to use these designs.
A few years later, one of my friends and colleagues, Todd Nief, sent me an article to read regarding track workouts utilizing these types of Work: Work designs as well. This was probably in 2013 or 2014. I would have to go into my email archives and dig that out but suffice to say it definitely stuck with me.
The next and most influential reason was due to necessity.
“I’m too fit to go slow” (paraphrasing)
I first encountered this type of resistance to doing “easy” paces amongst CrossFitters probably 10 to 12 years ago.
I would ask them to do a specific time or distance at a easy effort or sometimes I would prescribe the effort or pace and they would reply that they didn’t go that slow because it was pointless or they didn’t see the point.
Now, two things with that. First, if they didn’t understand why I would want them to do that then that is partly my fault for sure. Second, they should be doing what I’m asking them to do. So how did I resolve this?
I found a way to give people easy work/ low intensity work (MiD) by tricking them into doing it.
So, instead of just writing 60 minutes AirDyne at easy pace or low intensity pace (or what was then called Zone 1), I would then alternate between work intervals of higher intensity (SiD/EiD) with work intervals of low intensity (MiD).
A classic design in the old-school terminology of “anaerobic alactic power” would be something like this:
10-15 Sets:
10 sec AirDyne ALL OUT
Rest 10-15 x Work Time
Instead of this design I would simply fill in the rest period here with low intensity. That was the starting point of me using Work: Work (I think).
So now you get something like:
15 Rounds:
10 sec AirDyne ALL OUT
1:50 sec AirDyne @ Easy Pace/Easy Effort (typically I would try to prescribe an exact power output)
Once I figured out that I could get people to do this type of session, I basically just continued to manipulate the work ratios with an emphasis to try to get them to do more and more “easy“ work if I had thought they needed that.
So yes, I basically tricked people into doing it. And I’d like to take this time to apologize to absolutely nobody.
Part 2 – Application
There are numerous ways to design Work: Work intervals. I’m not gonna give you every available example.We will go through some scenarios in which I like to use these designs. Please note, you should not limit yourself to only these scenarios.
Scenario 1 – Time Restricted Individuals (Endurance Focused)
If you only have 45 minutes or so to work out each day, I would recommend trying to make most of that 45 minutes utilizing nonstop work (assuming building endurance is part of your intention).
It’s really easy designing these types of sessions once you understand how to design the intervals appropriately for each individual.
By and large, endurance is developed mainly through accumulating training volume.
So, if you designed a Work: Rest session for improving endurance in an individual like this then you would assume at most there will be 25-30 minutes of work in a 45 minute session.
Why not simply make this 45 minutes non-stop? Meaning, you are accumulating more work and in all likelihood making more progress towards your goal of increased endurance.
Example 1 – Work: Rest
15 Sets:
1:30 Min BikeErg @ 3-5 sec/1000m faster than 10k PR Pace (SiD)
1:30 Min Rest
Example 2 – Work: Work
45 Min BikeErg:
1:30 Min @ Easy Pace (MiD)
1 Min @ Moderate Effort/Kind Of Hard (HiD)
30 Sec @ 3-5 sec/1000m faster than 10k PR Pace (SiD)
If you calculate the total work spent in a “high intensity” then Example 1 would provide more exposure to that. However, “high intensity” is not how you accumulate work volume as an endurance athlete. You have to slow down to do that.
Scenario 2 – “Work Capacity” limited individuals and or “Recovery” limited individuals.
These individuals are not quite fit enough in terms of ability to maintain a high rate of work (relative) or they display an inability to recover quickly (necessary for their activity).
Now, sometimes these recovery inabilities are pacing problems, which is usually related, but is indeed a different issue (Software).
What we are really going after here is individuals who need to improve cardiac output/VO2 max, and overall sustainability (Hardware).
In my opinion, the first way to go about helping this issue would be the same thinking as helping the individual that has “limited time” to train, although there will be a different design due to the different intention.
Another point would be you would not necessarily start with a work: work design for these people, but you would definitely want to work up to it.
For Example:
Week 1 – Work: Rest
10 Sets:
1 Min Bike Erg @ High Effort/Repeatable Pace (SiD)
1 Min Rest
Week 5 – Work: Rest
10 Sets:
3 Min Bike Erg @ High Effort/Repeatable Pace (SiD)
3 Min Rest
Week 10 – Work: Work
60 Min BikeErg:
5 Min @ Easy Effort (MiD)
1 Min @ High Effort (SiD)
Week 15 – Work: Work
60 Min BikeErg:
4 Min @ Easy Effort (MiD)
2 Min @ High Effort (SiD)
Week 20 – Work: Work
60 Min BikeErg:
6 Min @ Easy Effort (MiD)
4 Min @ High Effort (SiD)
Scenario Number 3 – “Skill” progression
Skill is a loaded word and I’m not going to try to completely explain it right now. Frankly, I can’t completely explain it so let’s just move on.
Individuals wanting/trying to progress certain skills out beyond an isolated training environment with no/low fatigue can use this design with great success.
Work: Work intervals serve as a simple and elegant way to progress and challenge the specific skill an individual is developing.
For example, instead of doing chest to bar pull-ups as part of an EMOM and adding reps per minute over the weeks in an effort to bolster the chest to bar movement, at some point you may switch to alternating between chest to bar pull-ups and easy shuttle running or rowing or whatever.
The workout itself would take the exact same time, but instead of resting the individual would now be engaged in light activity.
Example scenario for Chest to Bar
Let’s say this individual has seen good progress and has also had great movement consistency from start to finish with the chest to bar movement in the following training progression:
Week 1
EMOM x 10:
8 Chest to Bar
Week 3
EMOM x 10:
10 Chest to Bar
Week 5
EMOM x 10:
12 Chest to Bar
Where do you go next? How much volume do you think this person needs to be able to tolerate? I could entertain an argument to just keep adding reps up to a point of the movement beginning to break down.
BUT, the challenge with a sport like CrossFit though sometimes it is just that specific movement, but sometimes it is what has occurred before and what will be required after the movement in question.
If the person in question has indeed successfully completed the above mentioned 5 week progression, they may further take the skill to a new level with a progression like this:
Week 1
10 Rounds:
1 Min Row @ Easy Pace (MiD)
10 Chest to Bar
Week 3
7 Rounds:
2 Min Row @ Easy Pace (MiD)
15 Chest to Bar
Week 5
5 Rounds:
3 Min Row @ Easy Pace (MiD)
20 Chest to Bar
In this progression, the work volume on the chest to bar is not increasing week to week, but the challenge is. And almost by definition, the adaptation surely will be too, though never guaranteed.
Part 3 – Exercise Physiology
About 15 years ago, I had read a paper about how blood lactate recovers more quickly after a bout of high intensity work if active recovery (doing something) was employed versus passive recovery (doing nothing). At the time I was influenced, like many other people, about the perceived detriment of blood lactate and endurance performance. I did not know how to account for this very well. I did not truly understand it. Like many things, I understood the topic just enough for it to be a problem. Meaning, I had an inadequate working knowledge of the subject, and therefore I’d let myself astray. Let me explain.
The quote below is from a different paper, but it is indeed similar enough in scope to get the point across with regards to passive versus active recovery in blood lactate clearance.
From the authors, “This study shows that active recovery is superior to passive recovery for clearing accumulated blood lactate after short bouts of maximal, all-out exercise that substantially raise blood [La] (>10mM), and that lactate clearance depends on the intensity of the active recovery to the point where it peaks at an active recovery intensity of 80% of lactate threshold. This is in line with previous results indicating intensity-dependence of lactate clearance during active recovery after a bout of exercise that raised blood [La] to ~4 mM. Thus, lactate clearance during active recovery is intensity-dependent after both low and high accumulation of lactate. The finding that active recovery is preferable to passive recovery is not new, but the intensity-dependent dose-response relationship of the active recovery is only now becoming apparent. As such, this informs strategies to facilitate recovery after both aerobic sub VO2 max and anaerobic supra VO2 max exercise bouts. This may therefore improve the outcome of exercise training programs or even exercise performance.” (1)
Here is a visual of this effect from a different paper (2). As you can see blood lactate does indeed go down faster with active versus passive recovery.
Why is that? Why would active recovery clear blood lactate faster than simply resting and doing nothing? Because working at a low intensity allows the muscle to utilize lactate to create energy via oxidative phosphorylation (ie. in the mitochondria) versus passive recovery in which the lactate would not be used directly as a fuel source and therefore would take longer to clear.
To quote from one of my favourite articles, “We know that during physical exercise lactate disposal is accomplished mainly by oxidation (75-80%) in working muscle”. (3)
This is great information to know. However, unless you put it in the right context, it can really mess you up.
As a coach, you need to be able to differentiate the signal from the noise. You must be able to discern what really matters, what will really effects the outcome (Signal) versus what is potentially clouding your judgement, information that may be leading you astray (Noise).
The previous discussion has shown that active recovery below lactate threshold (ie Moderate Intensity Domain) will clear lactate from the blood more quickly than passive recovery (ie Rest) in an intensity dependent manner (up to ~80% LT1).
Let us now turn our attention to the “signal“ – ie. performance. This next paper is a simple examination of active versus passive recovery and power output on short term sprint cycling.
Individuals had to sprint all out for 4 seconds, followed by 21 seconds of recovery for 6 sets. One group followed a passive recovery design (ie Rest) and the other group had an active recovery design (cycling at 60 Watts – which would be assumed to be well below lactate threshold for all of these individuals). (4)
The results may be viewed below. From the article, “The major finding in this study was a significantly lower peak power output for the last sprint and a significantly greater power decrement in the active compared with the passive recovery condition, despite no difference in relative or absolute total work. A second major finding was that the active recovery resulted in a significantl higher (P = 0.048) [MLa ] and a strong trend (P =0.06; effect size = 1.2) for lower [PCr] immediately following the repeated-sprint test, compared with the passive recovery condition. This suggests a potential suboptimal effect of active recovery in terms of [MLa-], [PCr], and ability to maintain sprint performance.”(4)
Why would an active recovery reduce power output in this scenario?
Based on our previous discussion, you would assume the low intensity active recovery would reduce blood lactate as opposed to the passive recovery. Well, this is why… “Because PCr (Phosphocreatine) resynthesis depends on oxidative processes, a possible explanation for a reduction in PCr resynthesis during active recovery is competition for the limited oxygen supplies. This is supported by a reduction in muscle oxygenation recovery (i.e., oxyhemoglobin and oxymyoglobin changes measured via near-infrared spectroscopy), relative to preexercise level, during active compared with passive recovery.” (4) (Note – I will provide an example using near infrared spectroscopy, but keep this paragraph in mind).
What matters is actually recovering between bouts of intense work. What doesn’t matter is how to speed blood lactate clearance in the context of repeated bouts of unsustainable work.
Now, anyone familiar with endurance training will know that more endurance training will lead to lower blood lactate levels during a specific workload and likely faster clearance of lactate post workload. Note, that is a separate issue from what we’re talking about here.
As well, doing an active recovery post training session may indeed help performance in a subsequent training session hours later or a day later. That is also not what we are talking about here.
Here is another example of passive versus active rest and performance outcomes on a time to exhaustion scenario utilizing a 15 sec work: 15 sec recovery design.
“The purpose of this study was to compare the effects of active vs. passive recovery on the TTE (time to exhaustion) for short intermittent runs (15-s) at supramaximal velocity (120% of MAS). It was hypothesized that the TTE would be longer with active recovery than with passive recovery. However, the results show that this hypothesis can be rejected, as the TTE was significantly longer for IR-PR1 (passive recovery group) than for IR-AR. (active recovery group). This difference in TTE may be in part explained by a higher energy requirement for IR-AR than for IR-PR.” (5)
As you can plainly see from the graph below there is a major difference in terms of oxygen intake between the two graphs. You can see O2 intake remains generally high, near maximum, in the active recovery group. Whereas in the passive recovery group, you can see significant reductions in O2 intake during the rest periods. Actual recovery is occurring. And, because actual recovery is occurring performance is significantly improved.
The final paper we will use is an absolutely classic paper that I would recommend anyone interested in Work: Work designs needs to read. It is fundamental to this understanding.
This paper utilized a design of 60 seconds of unsustainable (Severe) work followed by 30 seconds of recovery on a cycle ergometer. The recovery power output varied in each condition as you can see from the graph below.
You should mainly concern yourselves with the bottom to graphs in this picture below. The one on the bottom left is S – M and the one on the bottom right is S– L. What you are looking at is the black dots that look like a line. As you can see similar to our previous example with regards to oxygen intake, which these graphs are plotting, the group working at the lowest intensity, effectively resting, the fastest recovery in oxygen intake between bouts of unsustainable work.
Results in terms of performance are in the exact opposite of the listing above. Meaning that the group designated as S – L (Severe – Lite Intensity) performed the best because the recovery power output was the lowest, being 20 Watts, which is effectively barely moving.
The next group up the list would be S – M (Severe – Moderate Intensity). The reason I chose this paper is because this group group S – M is working at exactly the same intensity that would theoretically clear blood lactate from the system faster than any other condition in this study (see references 1 and 2). Because, this group is working below lactate the threshold, but at the highest intensity relative to the lactate threshold.
The last example I will use here to finish off this post will be my own training. It comes from using a bikerg. I placed one Moxy device (NIRS) on my right Rectus Femoris.
Following an extensive warm-up to ensure SmO2 (muscle oxygenation) levels were sufficiently high (75%) I performed the following session:
5 rounds:
1 min bike @ 1:45/1000m
1 min bike @ 2:30/1000m
(Into…)
2 min Rest
(Into…)
5 rounds:
1 min bike @ 1:45/1000m
1 min rest
Note: 2:30/1000m would be slower than LT1 for me as confirmed via NIRS.
What were the results? See the chart and graph below. What I really wanted to measure here was recovery rate. So, I measured the rate of SmO2 recovery in absolute values in the first 30 seconds of the recovery period. Also important to note, I maintained the exact same posture and foot position during the recovery periods for all intervals, with my feet on the pedals.
| Work: Work | Interval # | Work: Rest |
| 36% Recovery | 1 | 40% Recovery |
| 33% Recovery | 2 | 36% Recovery |
| 28% Recovery | 3 | 38% Recovery |
| 35% Recovery | 4 | 42% Recovery |
| 30% Recovery | 5 | 38% Recovery |
Note: grey area is SmO2 measurement, brown line is THb (total hemoglobin – or alternatively a measure of blood flow).
I hope you enjoyed this post. Let me know what you think.
Michael
References:
(3) Poole et al. (2021). Anaerobic Threshold: 50+ Years of Controversy.
(5) Dupont et al. (2003). Performance for short intermittent runs: Active recovery vs. passive recovery.
