Athletics: Energy systems and how they fit together

The body uses three energy systems to produce energy in the form of ATP (Adenosine triphosphate). The body decides what energy system will best serve its needs depending on for example; the exercise intensity or the duration. We’ll try and keep this as simple as possible so that everyone can understand this.

Energy systems:

• ATP-Pcr System (Phosphagen System)
• Glycolysis (Lactic Acid System)
• Oxidative System

ATP-PCr:

This energy system is used for the first 10sec of any activity regardless of intensity. It is primarily used in sports requiring short, explosive bouts of activity lasting less than 10sec e.g. 100m, 110m hurdles and all field events.

This energy system makes use of stored up ATP to provide the body with energy as well as stored phosphocreatin to replenish the ATP stores. There is a limited amount of phosphocreatine in the body and thus does not last very long.

ATP = ADP + P + Energy     

ATP is broken down into ADP, a phosphate molecule and energy that powers the body. Because the breakdown of ATP releases more energy than the breakdown of ADP the body always tries to replenish the ATP stores. Phosphocreatine (PCr) accomplishes this by donating its phosphate molecule to ADP to form ATP.

ADP + PCr   <  ^{Creatine kinase} >  ATP + creatine = ATP

Glycolysis (Lactic Acid System)

Glycolysis is the breakdown of carbohydrates in order to restore the body’s ATP. This is an anaerobic reaction and does not require oxygen.  This energy system takes over when the body is active for more than 10sec up to about 3min e.g. 400m, 800m

 Glucose either stored in the muscles as glycogen or from the blood is used to synthesize ATP. This process involves several complicated reactions. The end result in the presence of oxygen is pyruvate which is used in the oxidative system as fuel source. Pyruvate in the absence of oxygen is converted to lactate and an H⁺ (hydrogen ion). Lactate is often been said to be a waste product or the cause of fatigue or cramp. This is not entirely true as lactate, when transported to the liver, can be used to synthesize glucose thus acting as a fuel source to the body. Fatigue and muscle cramps are theorised to originate from the build up of H⁺ associated with the formation of lactate in the absence of oxygen from pyruvate. The H⁺ causes the muscle to become acidic and this decreases the muscle’s ability to function properly.

Oxidative System

The oxidative system makes use of four processes to produce ATP:

• Slow glycolysis (aerobic glycolysis)
• Krebs cycle (citric acid cycle or tricarboxylic acid cycle)
• Electron transport chain
• Beta oxidation

We’ll just cover the basics here:

The oxidative system is a slow energy yielding system that uses oxygen to produce energy. It becomes active after about 3min when an activity is slow and continuous and the body reaches a steady state of activity e.g. 1200m and greater distances

Pyruvate is converted to Acetyl-CoA and enters the Krebs cycle where many enzymes act on this substance causing several reactions yielding ATP. Glucose can also be used to sustain the Kreb’s cycle directly.  The metabolism of fat, carbohydrates or protein follows the same path into the Kerbs cycle; these substrates can enter either as pyruvate or glucose, the main difference here is that pyruvate is converted to Acetyl-CoA and glucose enters directly into the Krebs cycle without having to be converted first.

Many processes and reactions take place here and the detail is super complicated, but the bottom line is ATP, H₂O, CO₂ and H⁺ are the end products of the oxidative system.

Here is a table showing the predominant energy systems being used in different events:

Figure 1.1: energy demands in athletics

To achieve the best performance in your specific event, you need to train specific to your event’s energy demands. The body adapts to the needs of your sports in order to increase your efficiency there in e.g. a sprinter’s body stores more ATP and PCr which means his body can produce ATP during the ATP-PCr system more rapidly and for a few seconds longer. This gives him the ability to compete at a higher intensity for a bit longer.

If anyone out there has a question on the energy systems or on athletics, please feel free to send me your questions and I will make sure to get back to you as soon as possible.

References:

Jack H. Wilmore, David L. Costill. (2004). Physiology of Sport and Exercise (Third ed.). Champaign, IL: Human Kinetics.

William D. McArdle, Frank I. Katch, Victor L. Katch. (2010). Exercise Physiology (Nutrition, Energy and Human Performances (Seventh ed.). Philadelphia, PA: Lippincott William & Wilkins.

      Energy demands of athletics table 1.1. coutesy of AdrianSports.com 

Armant Goldswain
Bachelor of Sports Science

A beautiful game, if you've got the energy for it.

It’s been referred to as the beautiful game and the greatest show on earth but what does it take to be on the world stage - a footballer competing at the highest level? Hopefully by analyzing and reviewing studies done on football professionals it will help you better understand how the demands of the game can guide your development and possibly guide any future ambitions you might have. 

The sport of football has always been popular worldwide and has been more so in the last few years after hosting the recent 2010 FIFA World Cup. Football is enjoyed the world over and this is evident by the vast number of players playing from a very young age. It’s a great sport for developing fitness, skills, sportsmanship and teamwork. Besides minor differences to pitch sizes and playing times, the game remains the same.

This blog is aimed at students and scholars wanting to compete at a top level or just wanting to 'up your game' so your aim in training would be to focus on your development (skills and fitness) and train at an intensity that would replicate a match situation.

But what are these energy demands that are required of you to perform at the top level?

The body's energy source in its most basic form is adenosine triphosphate or simply known as ATP (just like the tennis association =D)

The body utilizes 3 energy systems to provide ATP to working muscles. The best way to differentiate between them is to identify the timeframes in which these systems come into play:

ATP-PCr systemè provides energy for powerful movements over a short duration lasting up to 15 seconds. Think Usain Bolt and his 100m sprint and the movements required. Now think how many times during a football game you’re required to break into a sprint. It will be much less than 100m but the supply of energy needed is the same system.

Research has shown that professional footballers sprint 15m every 90 seconds [1].

Glycolytic systemè provides energy for activity lasting up to 2 minutes. Think a 400m sprinter. Now think how many times in a football game your team might lose the ball in attack and you have to track back quickly to defend. But just as you get back your team begins a counter attack and you have to get to the other end of the pitch. The tempo of the game would dictate this but at an elite level this is normally quite high with intermediate bursts of energy.

Oxidative systemè provides energy over a long period of activity of low to moderate intensity. Think a 10km run. Now think how many times in a match you’re covering a great distance across the entire pitch for the duration of the whole match. 

The ATP-PCr and Glycolytic system are known as the anaerobic pathways (without oxygen) and the Oxidative system is known as the aerobic pathway (with oxygen). All 3 energy systems do not work independently of one another. All three make a contribution, however one or two will predominate. [2] Have a look at the following table which indicates what percentage of each system is used during a typical game.

While the average distance covered by an elite football player during a 90-minute match is over 10km, at an average speed of over 7km per hour, these figures do not accurately represent the full demands placed on a player [2]. In addition to running, a player must jump, change direction, tackle, accelerate and decelerate, etc., and each of these individual tasks requires an energy input over and above that required simply to cover a similar distance at a constant speed. 

Scientific investigation has shown that the true demands on an elite male player can be approximated at roughly 70%VO₂max. VO₂max has been defined as the highest rate of oxygen consumption attainable during maximal or exhaustive exercise [3]. It is generally considered the best indicator of cardiorespiratory endurance and aerobic fitness.

Research has also shown that VO2 max has a high correlation to the number of sprints attempted during a football game which makes aerobic fitness an important component to footballers [4]. These values suggest that the total energy cost of a game for a typical male player weighing about 75 kg would be about 1600 kcal [2]. This is based on evidence of heart rate, sweat loss, increase in body temperature, and depletion of carbohydrate stores within the muscles. 

Carbohydrate is the main fuel for exercise, especially for prolonged or high-intensity exercise when rates of body fluid loss are high due to the sweating needed to dissipate body heat produced. Low carbohydrate stores in the body and just a small degree of dehydration (2% body mass loss, or 1-2 kg) lead to fatigue and impaired performance [5].

So training in football should focus on all three systems, with more attention on the oxidative system (aerobic) and ATP-PCr system (anaerobic).

In future blogs we will look at what the physical demands are on specific playing positions in the game, different training methods to target the energy systems and go into more detail about energy intake. 

1) Reilly, T., & Thomas, V. (1976). "A motion analysis of work rate in different positional roles in pro football match-play." Journal of Human Movement Studies, 2, 87-97

2) Mohr, M. et al (2006) Physical and metabolic demands of training and match play in the elite player. Journal of Sports Science 24(7): 665-74

3) Wilmore JH and Costill DL. (2005) Physiology of Sport and Exercise: 3rd Edition. Champaign, IL: Human Kinetics

4) Smaros, G. (1980). "Energy usage during a football match." In Proceeding 1st International Congress on Sports Medicine Applied to Football, Vol. II (ed L. Vecchiet), D. Guanello, Rome

5) Thomas, B.B. (1994) Carbohydrate, fluid, and electrolyte requirements of the soccer player: A Review. International Journal of Sport Nutrition 4: 221-236