WHAT IS ATP ?

Carbohydrates, Fats and Protein – contain energy, however we can’t use it directly. These nutrients are used to form a chemical compound called ATP (adenosine triphosphate). When broken down it releases energy for body functions eg. muscle contraction, nerve impulse transmission, cell division, secretion by organs).

THE FUNCTION OF ATP

When an electrical impulse arrives at the muscle, it stimulates the ATP to break down into ADP and phosphate and to release its energy. The energy is used to power the rowing motion of the myosin crossbridges, making the muscle contract. Only a small amount of ATP is stored in the muscle, so chemical reactions take place to produce more ATP to

allow the muscles to keep contracting.

THE FUNCTION OF ATP

To produce or re-synthesise ATP, energy is obtained from food or from Creatine Phosphate (CP) (also known as phosphocreatine or phosphagen)

ATP production during resting conditions

* Demand for ATP is low so produced aerobically. Major food fuels is fats (2/3) and carbohydrates (1/3).

* ATP is produced in the mitochondria and transported to the myosin crossbridges.

THE ENERGY SYSTEMS

The body has three different ATP manufacturing systems or energy pathways:

• ATP-PC system

• Lactic acid system

• Aerobic or oxygen system

Each of these systems have the same purpose – to produce or re-synthesise ATP that is used for energy.

ATP-PC SYSTEM

ATP stored in the muscle is broken down to release energy for muscle contraction. There is a large amount of energy that is released from the breakdown of the bond between the 2nd and 3rd phosphate molecules.

ATP-PC SYSTEM

If you continue to exercise, the left over ADPs and phosphates must be recombined to produce ATP. Initially this is done by creatine phosphate. This does not require O2.

To re-synthesise ATP to it’s original state, creatine (stored in the muscle) and energy obtained from food provides the energy to allow the free phosphate molecule to reattach to the adenosine and 2 phosphates.

Creatine phosphate stores are exhausted after about 10 seconds of high intensity exercise and so are not replensished until after 2 mins of rest.

LACTIC ACID SYSTEM• Provides energy for events of up to 3 minutes.

• Carbohydrates (glycogen/glucose) are the primary fuel for re-building ATP.

•Produces 1-3 ATP molecules for each glucose molecule.

Glycogen

Glucose

Pyruvic acid

Lactic acid

Energy

ADP + Pi

ATP

LACTIC ACID SYSTEM

MAIN STEPS:

•Glycogen is broken down chemically by a series of reactions into pyruvic acid.

•Energy is released which is used to re-synthesise ATP (ADP + Pi = ATP).

•Absence of oxygen = pyruvic acid converted to lactic acid.

THE AEROBIC SYSTEM

•After 2-3 mins of vigorous activity the body is able to take in sufficient oxygen to meet it’s energy requirements aerobically – provided the intensity of the activity does not exceed 85% of maximal heart rate. This is the point at which lactic acid starts to accumulate – known as the anaerobic threshold.

•Activity between 85-100% HR max = accumulation of lactic acid, fatigue of muscles, cannot continue exercise.

•Reduce intensity to enable individual to continue (reduce to 60% HR max).

THE AEROBIC SYSTEM

RESPIRATION

•Process of breaking down glycogen in cells using O2 to produce ATP. Aerobic glycolysis occurs in the mitochondria (specialised components in aerobic muscle cells).

•ATP produced in mitochondria – transported to myosin crossbridges to provide energy for muscular contraction.

STAGES IN AEROBIC ENERGY PRODUCTION

Glycogen/Glucose

Pyruvic acid

Kreb’s Cycle

Electron transport chain

Protein

FatsATP

C02

ADP + Pi

ATP

ATP

CO2

H20

ATP

Heat

H20

ATP

Heat ATP

First Stage – Breakdown of glycogen and glucose to pyruvic acid in the presence of O2 , with some energy released for ATP re-synthesis.

Second Stage – Kreb’s cycle. Pyruvic acid is broken down into CO2 with further energy release.

Third Stage – Electron transport system. Water (H20) in the form of perspiration, heat and substantial ATP is formed (total 38 moles of ATP from 1 mole of glycogen)

During prolonged events, in the presence of O2, fat and protein can be broken down to CO2 and H2O to provide energy for ATP re-synthesis. This only happens after glycogen stores have been exhausted first.

MAIN STEPS OF AEROBIC ENERGY PRODUCTION

FACTORS LIMITING THE AEROBIC SYSTEM

FACTORS LIMITING THE AEROBIC SYSTEMOxygen Deficit = the period after the onset of exercise where O2 consumption is below that required to produce all the ATP required aerobically.

Steady State = the point during exercise when oxygen supply equals oxygen demand.

Oxygen Debt = oxygen consumed during recovery. The amount consumed is above what is required at rest to repay the O2 deficit and replenish the body’s energy stores.

Hitting the wall = when glycogen is depleted in endurance events, the body is able to use fats for ATP production. Fats require more O2 to produce the same amount of ATP. The cardio-respiratory system has to work harder and the athlete will have to slow down and fight hard to keep going.

ENERGY CONTRIBUTION OF EACH SYSTEM