Event Fuelling Part (1) – Our Body Energy Systems

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Alicia Edge

Event Fuelling Part (1) – Our Body Energy Systems

Now I was about to write a gem of an article on event fuelling, particularly with the Crossfit Open in full swing. However, I had a realisation as I started writing that without knowing the background to how our body’s energy systems, confidently fuelling a session is not going to be as effective or intuitive.

So here goes, an article written for everyone who exercises – no matter your age, training level or goals!

Firstly, what is energy sourced from?

Energy comes from a tiny molecule with a very big name – Adenosine Triphosphate (i.e. one adenosine molecule attached to 3 phosphate molecules) OR what we will call, ATP.

Energy releases when the bond between the phosphate molecules breaks. There is only enough ATP stored in your muscles for around 2-3 seconds of work – so that is where your energy systems replenishes the ATP stores.

Creatine Phosphate System

This system uses Creatine Phosphate as it’s fuel source.

It can provide the highest of power outputs with high rates of energy production, however is depleted within 10 seconds. For this reason, it is used for max intensity efforts of very short duration.

The muscle creatine phosphate levels decline so rapidly. Therefore passive recovery for at least 30 seconds and up towards 3-5 minutes is essential.

Creatine is the limiting factor. For this reason, increasing creatine stores in the muscle (through supplementation) can be beneficial to performance.

Creatine Phosphate
Anaerobic Glycolysis

Anaerobic glycolysis is the predominant energy system for efforts lasting 5-30 seconds. As well as repeated efforts with a short recovery time.

This source of energy breaks down carbohydrate stored in your muscle (glycogen) to pyruvate. Then to lactate (or lactic acid). This process produces 2 ATP molecules.

As lactate accumulates in the muscle, the pH falls and has a variety of effects. One of them being that all too familiar discomfort! This is where buffering supplements can come in handy, such as beta-alanine and bicarbonate. We specialise in implementing these, so contact us for more info on if they could be of benefit to you.

This energy system produces a high rate of ATP, but really needs an active recovery to get rid of the waste products.

Anaerobic Glycolysis
The Aerobic System

For efforts beyond 30-60 seconds, your body requires oxygen to create ATP. Pyruvate gets oxidised to carbon dioxide and water, instead of being broken down to lactate.

This is a much slower process, but generates a lot of energy that is really unlimited. It can use carbohydrate (glycogen in muscle and liver), fats (triglycerides in muscle and fat stores) and some proteins (amino acids). Consuming food/drink during exercise can replenish the aerobic system.

Oxidation of one molecule of glucose results in 38 molecules of ATP, while one molecule of triglyceride can result in over 100 molecules of ATP. The amount of protein you use is proportional to how much protein is in your daily intake.

Each athletes aerobic energy system generates different amounts of power. It is characterised by your VO2 max which is influenced by your training level, genetics, gender, age and body composition.

The Aerobic System
How this Translates in Energy Systems for Endurance Events

Although endurance events such as marathon, triathlon, road cycling, etc relies on the aerobic system, the anaerobic metabolism still makes a significant contribution. This energy system kicks in when there is a high energy demand such as hill climbs, intermediate sprints or finishing sprints. We are often bouncing between different energy systems.

So although it makes sense to be efficient in fat oxidation, for reaching top-end speeds and pushing the limits of performance, carbohydrate stores (muscle glycogen) are key to maximising power output.

This is why our advice focuses on driving adaptations to training. This can improve fuel use, while also balancing the need to hit those top-end speeds.

How this Translates in Energy for Team Sports of Events with Repeated Efforts

Team sports or any events with multiple efforts, the anaerobic system is essential. However, the aerobic energy system will still be important in recovery following each effort. During this recovery, the aerobic system replenishes the fall in ATP, increases the Creatine Phosphate stores and oxidises that lovely lactate build-up.

So What Next?

Understanding what energy system your body uses for your chosen exercise will then help you decide what kind of fuelling will be best pre- during- and post.

This is a summary of a very complex topic. But we hope you have gained some insight, and with it some ideas! Stay tuned for Part 2 coming up soon!

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