Understanding Energy Systems: ATP-PC, Glycolytic and Oxidative – Oh My

Energy Systems in the Body

The human body uses different types of energy to perform various tasks. These include:

ATP-PC (Adenosine Triphosphate Phosphocreatine) – The main source of energy for all bodily functions including heart beat, muscles contraction, brain function and other vital processes such as breathing.

Glycolysis – The breakdown of glucose into pyruvate, which then is used for energy.

Oxygen Consumption System (OCS) – A type of metabolic pathway that utilizes oxygen to produce carbon dioxide and water. Oxygen consumption is necessary during normal activities like breathing or when working hard. It helps the body maintain its internal temperature and keeps cells alive.

Carbon Dioxide Removal (CDR) – This is a mechanism that removes excess carbon dioxide from the blood stream. It is used during exercise to increase performance and recovery time.

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Fatty Acid Oxidation (FAO) – Fatty acids are molecules made up of three fatty acids joined together with one carbon atom. They have no double bonds between their atoms; they are long chains of carbon atoms linked together by hydrogen bonds. They are an important source of fuel for the body and a large part of lipids or fats.

Understanding Energy Systems

The human body has a limited amount of energy available to it when performing physical exercise. This can be seen when you exercise at high intensities for long periods of time (long distance running, cycling or swimming). These activities rely mainly on the different energy systems within the body.

Energy systems can be defined as a group of enzymes and intermediates that produce energy for muscle contraction.

In the human body there are three main energy systems:

Aerobic Energy System – Also known as the Oxygen Consumption System, it is the process of burning fat and glucose for energy using oxygen. This system is slow to develop but can last for long periods of time (40-90 minutes). It is most efficient at between 65% and 85% of your VO2max.

Anaerobic Alactic Energy System – Also known as the ATP-PC System, it is the breakdown of adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and inorganic phosphate (Pi). It is only used in short bursts of activity lasting 10-seconds or less.

Anaerobic Lactic Energy System – Also known as the Glycolytic System, it is the breakdown of glucose into pyruvate and is faster than the previous two energy systems. The build up of lactic acid is a common side effect, hence why this system has its own dedicated removal system.

While all these three energy systems work at the same time they also develop in order, from fastest to slowest. The faster energy systems are used for short intense periods of time, while the slower ones take over when required. During a 10km run, the anaerobic lactic energy system starts you off, then the aerobic system takes over as you continue jogging and the ATP-PC System is used for activities under 10 seconds.

In Training

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To improve your running performance you need to develop your muscles by working them in different ways. This can be done through interval training. Interval training is a type of training involving periods of high intensity exercise followed by a period of lower intensity exercise.

The length of each session and the ratio between high and low intensity varies for each person.

Alongside good nutrition, rest and recovery intervals are an essential part of any running routine. They allow your muscles to recover from strenuous activity allowing you to train harder, for longer. They also boost your metabolism, allowing you to burn more calories and fat even when resting and help to prevent burnout.

Planning Ahead

Having a long-term plan is the best way to approach endurance training. It allows you to taper off in the latter stages of your training program and helps prevent burn out. As well as this a training plan allows you to break your race up into manageable chunks; this can be helpful in the later stages as the finish line approaches.

Your training plan should take into consideration your weekly activities; a full-time worker would have less time to train than a student for example. It is also important to take any other physical activities you participate in, such as cross-training, into consideration.

Make sure you leave a one to two days recovery period after hard training sessions; your body needs time to rest and recover after strenuous activity. A typical training week may look something like this:

Monday – Recovery. Light walk or jog, light stretch.

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Tuesday – Easy Run. 10-15mins light jogging, 10mins steady running.

Wednesday – Rest

Thursday – Tempo Run. 15mins easy running, 15mins steady running, 10mins easy running.

Friday – Rest

Saturday – Long Slow Run. 45mins easy jogging, 30mins steady running, 20mins easy jogging.

Sunday – Rest

Nutrition and Hydration

The benefits of good nutrition and adequate hydration are essential to your training. Without the correct nutrients your body won’t work as efficiently as it could, meaning you won’t burn as many calories during training. This in turn means you won’t get the results you want, so its important to fuel your body correctly.

When training for a 5k or 10k, it is important to remember that long distance running takes its toll on your body. While regular exercise will improve your strength and stamina, you also need to make sure that you get enough rest in order to recover from your exercise. This is extremely important when training for a race as it allows your muscles to repair and grow stronger.

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You should aim for at least eight hours sleep every night when training.

In order to perform at your peak, it is important to fuel your body with good quality food. Carbohydrates are a particularly important energy source for runners; foods such as pasta, rice, bread and fruit are all good sources of carbohydrates and should form the basis of your diet. Proteins are also essential; found in foods such as meat, fish, beans and lentils, make sure you eat some form of protein every time you eat.

Calories are a measure of energy in food and can be used to indicate how much energy your body can expect to get from the food you eat. Most running guides will provide an approximate amount of calories you’ll use during running, so it can be useful to keep a calorie counter book around when training.

Alongside nutrition it is also important to stay hydrated during training. Staying hydrated not only helps your performance, but can also help prevent injuries and muscle cramps. Runners are typically advised to drink 500ml – 1 litre of water or sports drinks per day.

You should also keep a water bladder in your training bag to make it easier to stay hydrated during longer runs.

You can find more information about nutrition and hydration at:

Training Plans

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Once you’ve selected a race and prepared yourself through diet and training, it’s time to put everything into practice with a proper training plan. There are a wide range of training plans available through books and the internet, each one tailored to a different level of runner and a different race.

There are several factors to take into consideration when choosing a training plan; your current fitness level, the distance of the race you’re training for and your busy schedule are just three. The most popular type of training plan for first-time runners is the ‘Frequency Model’, which splits your running into three types of sessions; a long slow distance run (LSD), a medium pace run and a short fast run, with days of rest in between each one.

The McMillan Running Calculator is an excellent online resource that will generate individual training plans based on information you enter about yourself.

The following sites also provide a range of different training plans:

Training Plans – Running USA

Marathon Training Guide – Runner’s World

Beginner’s Marathon Training Schedule – Cool Running

Whatever plan you choose and however you train, you should make sure you enjoy the process. ‘Cross training’ such as swimming and cycling can help build up your fitness before you start running, and don’t forget to vary your routine to prevent your body from getting bored. Aim to run alongside a friend or join a running club in your area; not only is it more fun, but you’re more likely to complete your training routine.

Good luck and most importantly of all, have fun on race day!

Sources & references used in this article:

Estimation of the Contribution of the Various Energy Systems During by O Serresse, G Lortie, C Bouchard – Int. J. Sports Med, 1988 – researchgate.net

Study of heart mitochondria and glycolytic metabolism in experimentally induced cardiac failure by A Schwartz, KS Lee – Circulation research, 1962 – Am Heart Assoc

Tune Up Your Conditioning: A Primer on ATP by OR from Exercise, MUA Patterns – Clinical Decisions in Therapeutic …, 2006 – Prentice Hall

Specificity of aerobic and anaerobic work capacities and powers by C Marker – breakingmuscle.com

Lactate metabolism during exercise: analysis by an integrative systems model by MR Boulay, G Lortie, JA Simoneau… – … Journal of Sports …, 1985 – researchgate.net

Hypothetical Approach to the Location of Genotypes (ACE & ACTN3) Associated with Energy Systems for the Athletic Performance by ME Cabrera, GM Saidel… – American Journal of …, 1999 – journals.physiology.org

Potassium contracture and utilization of high-energy phosphates in rabbit heart by M Cerit – Spor Bilimleri Araştırmaları Dergisi, 2018 – dergipark.org.tr

Contribution of anaerobic energy expenditure to whole body thermogenesis by TL Rich, AJ Brady – American Journal of Physiology …, 1974 – journals.physiology.org