An insight in to the development of the aerobic system.

Pacing is a huge part of a well-developed aerobic system, and at the start of an aerobic capacity development phase, the ability to pace in a cyclical modality (rowing, running, cycling etc) is incredibly important in terms of volume acquisition and the development of a large aerobic base.

Why? Well let’s use a sample workout I designed for an individual athlete who has just started a phase of aerobic development.


@85% consistent effort

Row 2km

Rest 1 min

X 4

As you may have noticed during aerobic workouts (aerobic meaning sustainable), going out too hard can often leave you in deep oxygen debt. Anaerobic respiration produces an oxygen debt. This is the amount of oxygen needed to oxidise lactate to carbon dioxide and water. The existence of an oxygen debt explains why we continue to breathe deeply and quickly for a while after exercise. This also leaves us unable to replenish the energy you have expended in the first effort. This then sets off a cycle in a place we all know too well “THE PAIN CAVE!” This is one of the many reasons why the ability to maintain sustainable aerobic work rates during workouts is so important.

With a distance like 2km, the ability to hit a good time is potentially a tough, high lactic capacity type of workout. (Please don’t get confused with lactic acid *a term to be used loosely* as that is not the problem during high powered work). This is why staying in an aerobic state is hugely important – your aerobic system is designed to put out max output for little effort (relative effort that is). This also allows you to re-synthesise ATP at a constant rate (for those that are unsure, ATP is needed for the production of muscular contraction, and stands for Adenosine Triphosphate).

So, if you hit a hard 2km row and are unable to recover in time for the next workout you leave yourself unable to hit the next 2km efforts at a high, constant pace. This subsequently leaves you unable to accumulate the volume you need to optimally develop your aerobic system. In terms of competition this will ultimately leave you doing less work resulting in a worse score.This is not to say that the work you have just done hasn’t contributed to your development, it has, but your overall work output is now lower as a result of the eagerness to smash yourself at the start. This can be a common misconception to high intensity work amongst CrossFitters.

Once an athlete or group of athletes has got the hang of pacing in a cyclical modality, we can concentrate on transferring that into a mixed modal setting, where different movements will have their own energy cost. You will need to learn how to pace through different combinations of exercises at this next stage. This you may recognise in the classes as the ten minute amraps where the aim is to be consistent all the way through the workouts. An example might look like this;

10 min AMRAP

Row 300m

15 Kettlebell swings

15 burpees

rest 5 min

x 3

The aim during this type of simply programmed WOD would be to get the same score in each individual AMRAP. This would train your ability to pace through mixed modalities and consistently move for an extended period of time. This lower relative rate of work is a key component to developing a strong, broad and large aerobic base, whilst also accumulating the volume required to to have a high level of fitness. This volume is important for competitive athletes when you may be competing at several workouts / events over a short period of time. It is highly recommended that you do not exceed a heart rate above your aerobic threshold. “The aerobic threshold is the level of effort at which anaerobic energy pathways start to be a significant part of energy production. Athletes should strive to increase their aerobic threshold because this will enable them to pace at a higher rate for longer before they tip into anaerobic metabolism which cannot be sustained for as long” The use of heart rate and heart rate variability monitors before, during and post workouts can be a good tool to help you monitor your work rate, for those at CrossFit Cambridgeshire this is something we are going to be experimenting with in the future.

This type of workout then sharpens down into the 60 seconds of work to 60 seconds of rest type workouts where you are hitting close to your aerobic threshold and trying to maintain that work rate for an extended period of time. We tend to see this close to testing phases or competition. It is also extremely useful when we want to improve your ability to hit high consistent powerful efforts in movements like burpees and pull ups. Movements that are extremely tiring and on a competitive level appear time and time again (ie the CrossFit Open). This type of work rest ratio helps you develop the ability to express the capacity you have gained through the lower relative effort during the longer aerobic workouts.

As we know, CrossFit’s model for fitness is to be generally physically prepared. This is also conducive to life, as we never know what combination of physical tasks or movements may challenge us next. That being said, we can utilise the time spent in the gym more effectively than just throwing up random workouts on the whiteboard. This isn’t what CrossFit is about, but I have seen this done way too many times. There needs to be an overall structure as CrossFit training isn’t random. So as a gym, we periodise training to suit the average needs of the member base to help our athletes develop to a higher rate over time.

In terms of competing and going hard, we need balance! Balance is one of the key fundamental aspects of fitness and you will often hear me refer to it as pacing. It’s not an exact replacement for the word, but it is closely related as a concept. Your ability to pace at a rate higher than everyone else in mixed settings, whether in everyday life or competition, is the key to being successful in fitness.

I hope this gives you an insight into your aerobic development.


By Coach Lee


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