top of page

Testing Energetic Capacity: What, Why & What has it got to do with my Nutrition?

Why do you perform the way you during exercise?

Setting aside psychology and acute fuelling, your performance potential is largely determined by how well your physiology is adapted to the exercise you undertake.

This comprises your energetic capacity (the ability to produce the energy needed to get the work done), force generating capacity (the ability of your muscles to contract and relax as needed to get the work done), and your neurological system (the ability to coordinate the contraction of the necessary muscles at the necessary time).

By understanding our capacity we can identify our strengths and weaknesses and adapt our training and nutrition to improve our physiology for our sport.

In this blog we are going to focus on how we can test energetic capacity, and what this might mean for training and nutrition.

What is energetic capacity?

Your energetic capacity is your ability to produce energy to do work, e.g. exercise. The energy systems of the body can be classified into:

Aerobic: oxygen dependent, and the dominant source of energy for moderate sub-maximal exercise intensities lasting beyond 2-3 mins.

Anaerobic: produce energy independent of oxygen, and the dominant source of energy for maximal exercise intensities, typically under 3 minutes (continuous work).

To read more about the energy systems of the body, follow this link to a blog on the subject.

VO2max represents the maximum volume of oxygen the body can consume per minute. The bigger your VO2max (or VO2peak for exercise involving small muscle groups), the greater potential you have to deliver oxygen to your muscles to power aerobic energy production, and the greater your aerobic capacity. Anaerobic Threshold represents the exercise intensity where anaerobic energy production begins to dominate. This occurs when your body needs to produce energy more rapidly than it can do via aerobic energy production, i.e. at higher exercise intensities. Pushing above the Anaerobic Threshold for time is when we will start to 'feel the burn' that may limit the duration and intensity we can exercise at. The higher your Anaerobic Threshold, the higher intensity the exercise you can typically maintain for time. Aerobic exercise can be fuelled by fat or carbohydrates. Fats require more oxygen and take more time to liberate all the energy they contain, compared to carbohydrates. As a result, fats are the dominant energy supply at rest and lower exercise intensities, whereas as exercise intensity increases and energy must be produced more rapidly and conserving oxygen in order to maintain performance carbohydrates dominate.

Anaerobic (glycolytic) exercise is fuelled only by carbohydrates. Therefore at the highest exercise intensities, where the anaerobic system is dominant, carbohydrates are necessarily the primary fuel!

How can we test energetic capacity?

By measuring the gases in your breath (like in the picture) in a graded exercise test. This is where you exercise at a steadily increasing speed or resistance until you cannot physically increase your power output anymore or your perceived exertion is so great you voluntarily stop the exercise (fun!!). For example, on a treadmill, stationary bike or rower. From this, we can determine the maximum amount of oxygen you utilise (VO2max or VO2peak) and your anaerobic threshold (the point we see a rapid rise in the volume of carbon dioxide exhaled).

We can also estimate the dominant substrate (fats or carbs) your body is using at the increasing exercise intensities by the ratio of oxygen consumed and carbon dioxide produced. Although there are other factors that impact the amount of carbon dioxide in your exhaled breath, particularly as exercise intensity increases, and this can impact the estimate. However, at this point we can predict the dominance of carbohydrate usage.

As a standalone, VO2max and the anaerobic threshold won’t determine your performance. They describe your potential to produce energy for an extended period of time. Your performance depends on how you are able to transform this energy production into work, i.e. appropriate muscle contraction. This is dependent on factors both within your muscle (how much energy is lost between being produced and making it to the contractile proteins to power work) and also your whole body movement pattern (is your movement streamlined or do you look like an octopus on acid!). It is your ‘mechanical efficiency’. We can get some insight into how our mechanical efficiency changes as exercise intensity increases for the specific mode of exercise (bike / run etc) undertaken during the test, by measuring the ratio between calories burned and power output and how this changes as power output (intensity) increases.

A word of warning: to get your true VO2max or VO2peak and an accurate estimate of anaerobic threshold and endurance, you have to push yourself to the limit!! Not everyone can do this.

In addition your results may be impacted by the foods consumed in the hours (and potentially days) preceding the test, supplements you have taken, the environmental conditions and the type of exercise used and so number of muscle groups (i.e. oxygen consuming things!) utilised. So always record these parameters so that if you repeat the test you can make it comparable to see how you have improved or changed over time, or to understand why the results may not be comparable!

What can we do with this information?

Now have an estimate of our energetic capacity, what next?

We can identify training and nutrition strategies that may support the greatest improvements in performance!

We can also try and understand a little more about why our capacity is what it is and what is holding us back in order to refine these. For example …

VO2max is determined by respiratory capability, cardiovascular capability, and the ability of the muscle to use oxygen.

During the test, breathing frequency and tidal volume (how deep we are breathing) is measured. To be most efficient during exercise our tidal volume should first increase, i.e. we breathe deeper, followed by an increase in breathing frequency. An increase in breathing frequency without utilising an increase in tidal volume is inefficient, using energy and oxygen to contract and relax the breathing muscles that could otherwise be directed to the muscles in the working limbs. And may limit our VO2max compared to increasing tidal volume concomitantly with an increase in breathing frequency. In addition, this can risk hyperventilation, resulting in vasoconstriction of the blood vessels in the brain, reducing oxygen delivery to the brain and reduced cognition. This reduces our ability to think and react quickly, as well as coordination. This can impact performance, particularly at high speeds and intensities. If we observe such breathing dynamics, limitation specific respiratory training exercises concentrating on coordinating breathing volumes and breathing frequencies can be used to address this limitation in appropriate training sessions.

If breathing frequency, tidal volume and heart rate all increase ‘as expected’ during exercise and yet VO2max is low and the anaerobic threshold is a low percentage of the VO2max, this may indicate that either the blood is not able to carry a high amount of oxygen, or that the muscles are unable to utilise oxygen efficiently. There are several potential causes for each of these limitations, and further investigation will be necessary to determine what the limitation is and why. But, for example, it may be that the red blood cells have a low oxygen carrying capacity as a result of low iron levels that can be addressed by increasing the consumption of iron rich foods.

We can also think about the fuels used to power exercise of increasing intensity. From these measures we can understand how ‘fat adapted’ an individual is. Fat adaptation describes the ability to use fats as fuel at higher exercise intensities. This supports higher intensity and / or longer endurance performance as it indicates an individual will spare their use of carbohydrates; exhausting carbohydrate supplies during exercise results in that feeling of ‘hitting the wall’ and having to reduce exercise intensity or stop. If an individual is an endurance athlete but appears to be poorly fat adapted, strategic ‘train low’ strategies may be employed. This is where the individual trains in a carbohydrate depleted state so that their body is forced to use fats to produce energy, with the aim of inducing adaptations that make the individual more effective at using fats during exercise.

Other insights that can be obtained to inform nutrition include whether an individual appears to have a low aerobic capacity that may benefit from nitrate supplementation, or a low lactate threshold that may benefit from beta alanine supplementation, or an impaired capacity to utilise carbohydrates at high exercise intensity that may be addressed by altering fuelling in and around training sessions. In other words, quite a lot!

In each case, we would implement the relevant strategies for a period and then ideally test the individual again to determine if this has improved their capacity and what is now their limiting factor to be addressed through training and nutrition. And so on, and so on … !

In summary

In short, metabolic and physical fitness testing is the chance to look under the hood and work out why you perform the way you do. And knowledge us power! By understanding where your strengths are, and what is holding you back, you can adjust your nutrition and training to capitalise on those strengths and tackle those weaknesses … and be fitter, go faster, and for longer. But as with anything, there are limitations and caveats and often potential alternative explanations … but by being aware of these we can consider them in our interpretations.

48 views0 comments

Recent Posts

See All


bottom of page