ENERGY SYSTEMSSo we all thought energy just came from food…

Energy systemsHuman body requires a continuous supply of energy both to meet the needs of its systems and organs AND to power muscular contractions for movement.

However, unlike a car that carries fuel around in its tank – the body’s energy is stored I chemical bonds that joins atoms and is released only as needed.

The transformation of food (chemical energy) to energy that the muscles can use (mechanical energy) is the role od the energy systems.

Food & energyEnergy provided by food is measured in kilojoules (kJ)

When food is digested, it breaks down to sugars, amino acids and fatty acids – substances that become available as a usable form of energy

From these, ATP or adenosine triphosphate is produced and represents the most important substance in energy production.

ATP can be likened to a spark plug in an engine as it enables the release of energy where all other functions are possible.

ATP CompoundThe ATP compound consists of a large molecule called adenosine (A) and three smaller molecules called phosphates (P). Each of the phosphates is held together by high energy bonds. The chemical structure of ATP is shown below

ATP CompoundWhen the last phosphate is detached, energy stored in bonds between the phosphates becomes available and this is transferred to the cells. The process is like flicking a switch. The light will not work until the current flows and provides energy to light the globe. In muscle cells, the energy from ATP allows the fibres to contract and make movement possible.

ATP CompoundHowever, ATP now has only two phosphates attached. In this state it is referred to as ADP (adenosine diphosphate) and is powerless to provide energy.

ATP CompoundUnlike food, used ATP does not become a waste product that is discharged from the body. Instead, it has the ability to quickly rebuild and or resynthesise, allowing us to continue to function on limited stores.

ATP needs to be continually rebuilt to enable energy flow. Under normal conditions such as sitting, lying, only sufficient amount is produced to enable basic function to be sustained. However, if intense physical demands such as cycling, swimming or running are placed on the body, the systems respond by producing much higher levels of ATP to ensure that our immediate energy needs are met.

ATP CompoundThree systems that make ATP available are:•The Alactacid System (commonly known as ATP-PC)•The Lactic Acid System (glycolytic system)•The Aerobic System (oxygen system)

These systems are commonly called energy pathways because they eachy supply ATP but use different processes to do so. Each system has their own way of resynthesising – how well the system resynthesises ATP determines its efficiency in energy production.

ALACTACID system (ATP/PC)• Supplies of ATP I the body are very limited.• We have sufficient supply for only ONE explosive

muscular contraction, for example, a standing long jump or sprint start.

• Lasting 1-2 seconds• An explosive movement causes ATP molecule to ‘split’

providing energy for muscular contraction.

ALACTACID system (ATP/PC)• Further muscular work relies on creatine

phosphate (CP) breaking down to creatine and phosphate, and releasing energy in the process. The energy is used to drive the ‘free’ phosphate back to ADP so it can once again become triple phosphate.

• Once reformed, ATP can break down again – and the process goes on.

• The problem is, however, is that CP supplies are exhausted with 10-12 minutes and then takes 2 minutes to be restored.

Source of fuel• We have 90 grams (same weight as a large egg) of ATP in

our body• This is sufficient to power the muscles required in one

explosive movement such as a jump, start or throw. • Allows for 1-2 seconds of hard work• Following that, we rely on 120 grams of reserve fuel, CP,

stored in our cells• Creatine phosphate, then, is the fuel of the ATP/PC

system

Efficiency of atp production• The alactacid system function to ATP rapidly available.

Occurs whether or not oxygen is available.• This is primarily possible by a concentration of CP within

muscle cells that is approximately 5 times greater than that of ATP.

• Supply of ATP is very limited if the demand is high, sustained, near maximal or maximal.

• But the system can recover quickly.• That is why it is integral to short, explosive movements

such as weight-lifting, discus throwing and sprint starts.

DURATION OF SYSTEM• ATP supplies are exhausted after, 1-2 seconds of hard

work• CP supplies are exhausted in a further 10-15 seconds• At rest, CP supplies are almost fully restored in 2 mins.

Cause of fatigue• Fatigue is caused by inability of system to continually

resynthesise ADP from CP because CP supplies are quickly exhausted.

• This is why we are unable to run at maximal effort for distances longer than 100m.

By-PRODUCTS OF ENERGY PRODUCTION• No fatiguing by-products but hear is produced during

muscle contraction

RATE OF RECOVERY• ATP/PC system recovers quickly from exercise. Within 2

minutes, most ATP and CP supplies have been fully restored, with 50% of CP replenishment occuring in first 30 seconds of rest recovery.

• This is why high jumpers, weight lifters and discus throwers can ‘back up’ almost immediately after their 1st and 2nd attemptsVideo: ATP & How it works

Lactic acid system• Following 10-12 seconds of maximal exercise, CP

supplies are exhausted• ATP still needs to be produced to provide energy,

assuming activity requires effort for longer than this eg. 400m

• Oxygen is not readily available (even though breathing rate has increased) as it takes time for the blood to move fro lungs around the body, then to working muscles where oxygen is in high demand

• CP supplies are at a low level, so a different source must be used

• Immediate sugar supplies circulating in the blood (blood sugar), as well as, our sugar storage supplies in the muscle and liver. We refer to our blood sugar as glucose.

Lactic acid system• Pancreas constantly regulates our levels of glucose, when

we accumulate too much in the body stores, the excess in the liver and muscle. Stored glucose is called glycogen.

• The process of using glycogen or glucose as fuel is called glycolysis

• As the system works without oxygen, and glycogen is the only fuel, the system of degradation is referred to as anaerobic glycolysis.

• During intense exercise – lactic acid levels rise and continue to rise as intensity increases

• Lactic acid is produced because insufficient oxygen results in the partial breakdown of glucose -> provides quick but limited ATP, as well as the by-product, lactic acid

Examples of activities: 200m, 400m, 800m, 200m freestyle and gymnastic routines

sources OF FUELThe only fuel that can be used by the lactic acid system

is carbohydrate. This exists in two forms:• as glucose in the blood• in the storage form called glycogen.

Glycogen is broken down, producing ATP and energy for muscular contraction.

Efficiency of systemThe lactic acid system provides ATP quickly, but this requires large quantities of glucose. In other words, ATP is rapidly available but at considerable cost.

For example, 1 mole of ATP is produced for 180grams of glycogen.

DURATION of systemThe duration (work span) of the system depends on the intensity of the activity.Generally speaking, the lactic acid system produces energy for highintensity activities lasting from 10 seconds to 1 minute or more depending on the effort involved. It is the dominant system for all maximal activity performed between 30 seconds and 2 minutes

For example, 200 metre sprint, 400 metre running, 800 metre running, 200 metre freestyle and gymnastic routines

Cause of fatigueFatigue occurs when lactic acid build up within the muscle cells. Although, it is not directly lactic acid that hinders performance, rather it’s the rate of removal – this varies on an individual basis.

Lactic acid is produced whenever the body uses carbohydrate as a fuel, and this occurs most of the time, even at rest. Lactic acid is produced because the carbohydrate is being metabolised.

The speed of lactic acid production depends on exercise intensity. The faster you work, the more rapidly lactic acid accumulates.

Cause of fatigueExcessively high levels of lactic acid prevent muscle fibres from contracting and result in rapid deterioration in performance. However, while lactic acid levels cause fatigue, tolerable levels can enhance performance because lactate is a fuel source. Finding a balance and building a tolerance, comes with training, as do removal rates.

Work sheetRelationship between lactic acid and fatigue.

Rate of recoveryDuring the post-exercise period, lactic acid diffuses from the muscle and into the bloodstream where its use as a by-product is important.

In the liver, lactic acid is reconverted to glycogen and can once again be used as a source of fuel .The process takes about 30 minutes to an hour.

This further contributes to the body’s efficiency by resynthesising waste for use at a later stage.

AEROBIC SYSTEM• Physical activity lasting more than a few minutes requires

the presence of oxygen to ensure the continuation of muscular contraction

• Oxygen is not immediately available at the onset of activity but becomes gradually available as the oxygen-rich blood fills the muscle cells.

• This allows the aerobic pathway or oxidative system to become the predominant supplier of ATP. This process of fuel degradation is sometimes called aerobic metabolism because oxygen is present. In the breakdown of glucose and fat (sometimes protein) to produce ATP.

• Lactic acid does not accumulate as oxygen is present.

Sources of fuel• Aerobic system can use carbohydrate, fat, even protein

as fuel• During early stages, carbohydrate is the preferred fuel, if

exercise continues beyond an hour or so, fat becomes increasingly important as a fuel and reigns as the dominant energy source if glycogen supllies become exhausted

Efficiency of atp production• Lactic acid system is able to generate only 3 moles of

ATP from 180 grams of glycogen, the aerobic system is able to generate 39 moles of ATP from 180g of glycogen.

• Enables us to continue sustained work for longer periods of time

DURATION OF THE SYSTEMThe total amount of glycogen in the body is approximately 350 grams. This is sufficient for 12 hours of rest or one hour of hard work.

In intermittent exercise, such as football or netball, glycogen supplies last for approximately four to six hours. However, in the case of marathon runners, supplies could be exhausted in about two hours.

The body has virtually unlimited supplies of fat and this is used as a fuel source as glycogen supplies are depleted. In well-trained athletes, the body mixes carbohydrate and fat in endurance events. This process, called glycogen sparing, results in some fat fuel being used earlier so that glycogen can be available at a later stage, such as for a sprint finish. These fuels used jointly, yet sparingly, ensure that the body can operate using this system for long periods of time.

DURATION OF THE SYSTEMThe aerobic system is the predominant system for use during extended endurance events such as marathons and low demand activities such as walking, sitting and reading.

But how does it work exactly?

Worksheet: Aerobic System explained

CAUSE OF FATIGUEThe aerobic system is so versatile in fuel usage (remember it can use carbohydrate, fat and even protein to produce energy), it is not a lack of fuel but other factors that contribute to fatigue while this system predominates.

 During endurance work, slow-twitch muscle fibres will do most of the work. These fibres have many capillaries and a rich oxygen supply. Before a run, these fibres may be saturated with glucose. However, activity beyond an hour or so results in depletion of fuel and, although some is replaced from the liver, glycogen is exhausted. Glycogen is premium fuel for muscles. When it runs out, the body tires.

 

CAUSE OF FATIGUE  A second cause of fatigue is the exhaustion of carbohydrate

and subsequent reliance on the secondary fuel, fat. Although fat is much higher in energy than carbohydrate, its use as a sole fuel can cause problems. Fatigue occurs because fat requires more oxygen for metabolism than does carbohydrate. This increases the runner’s body temperature and rate of respiration.

BY-PRODUCTS OF ENERGY PRODUCTIONDuring aerobic activity, oxygen is required to burn the fuels in the body(carbohydrate and fat). As with most fuels that are burnt, by-products are produced, in this case, carbon dioxide and water.

The carbon dioxide is breathed out through the process of respiration and the water is available to the cells. These by-products are not harmful to performance.

RATE OF RECOVERYThe recovery rate of the aerobic system depends on the duration

of use. Ifused for a short period of time, the system recovers quickly

because glycogenstores have not been depleted. However, if used for hours,

glycogen storageareas could well be exhausted. In this case, it may take days to

fully replenishglycogen reserves.

ENERGY SYSTEMS SUMMARYThe energy systems should not be thought of as individual

metabolic unitsthat operate independently of one another. Although the systems

have beenreferred to individually, they actually function together (see

figure 5.15). Thisgives rise to the term predominant energy system, or the system

that is being mostutilised at that point in time. This concept is further illustrated in

figure 5.15,where, after 120 seconds of running time, the ATP/PC system is

contributinglittle to energy supply and the lactic acid system is in decline,

although stillassisting to some extent. The contribution of the aerobic system

at this point ispredominant and rising gradually.

Applying the energy systems

Group 1 Group 2

Sham Ferah Pisu Jerod Jazz Haani

Ulia So’o Derek Chantelle Billy Vaoesea

Group 3

Luke Nahren Vinnie Katerina Janita Adrian

Split into the following groups and work together to complete your assigned task, groups will need to report back to class with their findings.