Recovery/Load Ratio (“RLR”) and the anaerobic threshold

What I want to discuss here is how the load/recovery ratio of an exercise (sequence) relates to the anaerobic threshold and the VO2max.

Firstly I owe an apology – so far I have always used the load/recovery ratio (“LRR”), ie the ratio between the time under load, and the rest time. I will change this now to the recovery/load ratio (“RLR”) which does not roll as easily of the tongue, but which is easier to handle numerically: if exercising, load times are never zero, but recovery times might be, in particular in typical (“chronic”) cardio activities such as running a marathon. So whilst the RLR will start from 0 and might go about to say 5 within a typical exercise routing (ie recovery 5x longer than load), the equivalent LRR would start from 0.20 (1:5) and go all the way to infinity (1:0). Whilst mathematically tractable, dealing with those big numbers and infinity is cumbersome and confusing, hence the switch-over.

Before we continue I need to state a very important assumption: all exercises are executed at a level that is maximal for the athlete, ie there is little room to run faster / add more weight / do more reps within the alloted time frame. Obviously if there is no real need for recovery the concept of an optimal recovery/load ratio becomes meaningless.

There is another consideration that I will glide over in this post, and that I might develop more in a post further down the line: there are fundamentally two reasons why an athlete might hit a wall in a certain workout: (1) his cardio-vascular system can no longer keep up with the demands put on it by the routine and therefore the muscles can no longer be adequately supplied at the requested levels of activity, or (2) the muscles can no absorb the fuel they need to operate, and whilst there is still capacity to do work in general, the specific exercise in question has to be stopped. An prime example for the former would be a superset of exercises designed to ensure that muscles are given time to recover whilst the cardio respirator system is under constant demands, whilst an example for the latter would be something biceps curls which on most individuals would not lead to cardio-respiratory exhaustion.

Interpreting the RLR

Let’s start with a zero RLR, ie no recovery. Keeping in mind that the athlete is operating at maximal capacity this implies that this is a training which permanently stays at the anaerobic threshold, which will be the VO2max if the constraint is the athletes cardio-vascular system, or otherwise the maximum rate at which the muscles in question can absorb the necessary fuels. I would also argue that a if the recovery time is smaller than say 1/4th of the time under load than this is not much different from a continuous aerobic effort. Therefore defines the “aerobic (threshold) zone” as having an RLR from 0-0.25.

On the other hand is an extremely large RLR. To put some numbers to it, let’s assume that this will be an RLR of 50 or more. This is what Pavel calls greasing-the-groove (“GTG”): for example, every time an athlete passes the pull-up bar (let’s say every 1-2 hours) she does pull-ups for one minute. There is full recovery between sets, so there is no metabolic spillover from one set to the other, and hence the main focus is on maximum strength.

At least from a metabolic point of view this “full recovery zone” is rather big. It is not practical to put hard numbers onto it, but I would suggest that everything bigger than about 5 qualifies (depending on the exercise and individual this value might be slightly lower, say about 3, but I will ignore this in the following to not complicate things). So an athlete is operating in a RLR regime of 5 or higher than the constituent exercises are metabolically separated, something that you might be desirable for example for a 5×5 lifting protocol, or sprint training, where there should not be a spill-over from one set to the other.

Everything what is left is what  I want to call the “intermediate zone“, reaching from RLR’s of about 0.25 to about 5. This is where things get interesting – and complicated – as in this zone, the different sets are no longer metabolically separated, hence the later exercises are influenced by the incomplete recovery of the previous one’s.

The Intermedia Zone

Within intermediate zone, the following table from the CrossFit Journal where Coach Glassmann put together an overview of the various energy systems in the body (see also here), and how to train them, is rather enlightening

Sprint Mid-Distance Distance
Primary Energy System Phosphagen Glycolytic Oxidative
Duration of work 10 – 30s 30 – 120s 120 – 300s
Duration of recovery 30 – 90s 60 – 240s 120 – 300s
Load:Recovery ratio (“LRR”) 1:3 1:2 1:1
RLR 3 2 1
Repetitions 25 – 30 10 – 20 3 – 5

This table suggests that for RLR’s < 1 the oxidative system dominates. There might be small excursions into the anaerobic (glycolytic & phosphagen) systems, but they will be mainly depleted with very little chance of recovery. Having said this, it needs to be pointed out that the Tabata protocol operates on a RLR of 0.5 (20s on / 10s off) and this is markedly different from a pure cardio effort, therefore the information in the above table needs to be carefully interpreted – the duration of the effort is arguably as important variable as the RLR as it is this one indicates whether or not the fuel of a certain metabolic pathway has been exhausted or not.

When the RLR gets bigger, say in the region of around 2, then the glycolytic system can contribute more as it will have a chance to recover, and if it gets even bigger, towards three, then also the Phosphagen system can contribute.

Using the RLR for programming

The recreational athlete who is looking for all around fitness does not have to get too scientific about all of this. For her it is merely important to ensure that across the different HIIT sessions al metabolic pathways are covered. How this is done there is a lot of flexibility. One could for example go for a simple one-level approach. For the Phosphagen system for example this would be a workout of 25 all-out hill sprints, 15sec each, with 30sec recovery in between, and for the oxidative system something like laps of 600-800m each with a 1:1 recovery.

More interesting however is probably the multi-level approach where pauses are added between groups of exercises. The CrossFit Tabata This workout is a good example. It consists of 5 distinct sections with a one minute break in-between. Each of the sections is a Tabata, ie 8 rounds of exercises that last 20sec and have 10sec recovery. Within each of the sections, the RLR is 0.5, but the additional pauses bring the overall RLR to almost 1.0. Note that the above table is too simplistic to cover the intricacies of this kind of training though, as the key to the Tabata This protocol is the partial depletion an replenishment of the various different energy systems.

Without getting too much in details, I would suggest that for the recreational athlete it is important to vary the RLR’s and duration across the different HIIT’s. In my view this is particularly important at the highest level. For example, it might be useful to incorporate something like a hill-sprint (or kettlebell swing) Tabata This where the break is sometimes 1min (overall RLR of ~1 – oxidative system), and 3min (RLR ~2 – glycolytic system). To train the phosphagen system it might be better to break up the constituent Tabatas into say 2 rounds with appropriate break to achieve and RLR of ~3, ie 20on/10off/20on/110off.

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