Energy systems – Improving PDHPE
Study Notes

ENERGY Production

  • ATP is made up of two types of molecules: adenosine (big) and three phosphates (small).
  • The ATP stores energy within it’s bonds. Energy is released when the connection between the last two phosphates is broken. This release of energy makes movement possible.
  • However, now ATP is ADP (adenosine diphosphate) = powerless to supply energy.
  • ADP needs to be rebuilt back to ATP for muscles to keep working.
  • Rebuilding of the ADP molecule back to ATP = re-synthesis.

– Alactacid System

Source of fuel

Creatine Phosphate

Efficiency of ATP production

Rapid supply of ATP through the availability of PC and short explosive movements (e.g. sprinting)

Duration that the system can operate

ATP exhausted after 1-2 seconds

Further activity relies on CP (creatine/phosphate molecule) which is bound by high-energy bonds, when bonds break, energy released. This energy is used to join the phosphate molecule back to ADP so it becomes ATP again (re-synthesis) – CP exhausted after 10-12 seconds

Cause of fatigue

At maximal/near maximal HR (effort), fatigue caused by inability to continually re-synthesise = ATP from PC, because PC supplies are quickly exhausted

By-products of energy production

No by-products in Alactacid system

Process and rate of recovery

At rest, CP supplies fully restored within 2 minutes

– Lactic Acid System

Source of fuel

Sugar supplies (carbohydrates)

– As glucose (in blood)

– As glycogen (stored in muscle cells and liver)

Use of glucose/glycogen is glycolysis

Breakdown of glucose/glycogen occurs without O2

Glycogen much more plentiful than CP

Higher quantity of glycogen = more energy available

Efficiency of ATP production

Provides ATP quickly, but requires large amounts of glucose

Duration that the system can operate

High intensity activities lasting 10-30 seconds

Moderate intensity lasting approx. 3 minutes(e.g. 400/800m)

Cause of fatigue

Build up of lactic acid in the muscle

By-products of energy production

Lactic acid

Process and rate of recovery

Depends on intensity/duration of activity. Somewhere around 20 mins – 2 hours, with shorter recovery assisted by active cool down. After exercise, lactic acid leaves muscles and returns to bloodstream to be stored in kidney, for fuel later on.

– Aerobic System

Source of fuel

Carbs preferred fuel, fats become important after an hour, also protein (all broken down by oxygen)

Virtually unlimited fats in well trained athlete, body will mix carbs/fats

Efficiency of ATP production

Extremely efficient for activity of a lower intensity and prolonged duration

Duration that the system can operate

More than a few minutes

Hours if individual is trained

Cause of fatigue

Depletion of carbs

Depletion of glucose to working muscles

Poor circulation/respiration (fats require more oxygen, thus faster breathing is needed)

By-products of energy production

Water and Carbon Dioxide

Process and rate of recovery

Rate of recovery depends on the duration/intensity of the activity.

Could take longer than 24 hours.

Replenishment of glycogen is required, which can take several days to digest

Full Written Content

Critical Question 1: How does training affect performance?
Energy Systems

Alactacid System (ATP-PC System)

The ATP system comprises of a large molecule called adenosine and 3 smaller molecules called phosphates. They are all held together by high energy bands; when the last phosphate becomes detached energy stored within the bonds is released. However, after the process, ATP transitions to ADP (adenosine diphosphate), meaning it can no longer supply energy. Accordingly, ADP must be rebuilt, or re-synthesised, back to ATP in order for muscles to keep working.

Source of fuel
Creatine Phosphate

Efficiency of ATP production
Rapid supply of ATP through the availability of PC and short explosive movements (e.g. sprinting).

Duration that the system can operate
ATP has a short duration and is exhausted after 1-2 seconds. Further work relies on CP (creatine/phosphate molecule), which is held together by high-energy bonds. When these bonds break, energy is released. Re-synthesis occurs when the energy is used to join the phosphate back to ADP, so it becomes ATP again.

CP has a longer duration and is exhausted after 10-12 seconds.

Cause of fatigue
At maximal/near maximal HR (effort), fatigue is caused by an inability to continually re-synthesise ATP from PC, because PC supplies are quickly exhausted

By-products of energy production
There are no by-products in the Alactacid system

Process and rate of recovery
CP processing rates are relatively quick at rest; supplies are fully restored within 2 minutes.

Lactic Acid System

Source of fuel
Sugar supplies (carbohydrates) in the body consist of glucose, in the blood, and glycogen, stored in muscle cells and liver. The process of using glucose/glycogen is called glycolysis. The breakdown of glucose and glycogen occurs without exposure to oxygen and glycogen much more abundant than CP. The higher the quantity of glycogen, the more energy available to individual.

Efficiency of ATP production
Provides ATP quickly, but requires large amounts of glucose

Duration that the system can operate
High intensity activities lasting 10-30 seconds. Moderate intensity lasting approx. 3 minutes (e.g. 400/800m)

Cause of fatigue
Pyruvic acid – producing lactate (due to insufficient O2). Increase in hydrogen ion concentration

By-products of energy production
Pyruvic acid – producing lactate and hydrogen ions

Process and rate of recovery
Depends on intensity/duration of activity. Somewhere around 20 mins – 2 hours, with shorter recovery assisted by active cool down. After exercise, lactic acid leaves muscles and returns to bloodstream to be stored in kidney, for fuel later on

Aerobic System

Source of fuel
Carbs preferred fuel, fats become important after an hour, also protein (all broken down by oxygen). Virtually unlimited fats in well trained athlete, body will mix carbs/fats

Efficiency of ATP production
Extremely efficient for activity of a lower intensity and prolonged duration

Duration that the system can operate
More than a few minutes. Hours if individual is trained

Cause of fatigue
Depletion of carbs. Depletion of glucose to working muscles. Poor circulation/respiration (fats require more oxygen, thus faster breathing is needed)

By-products of energy production
Water and Carbon Dioxide

Process and rate of recovery
Rate of recovery depends on the duration/intensity of the activity. Could take longer than 24 hours. Replenishment of glycogen is required, which can take several days to digest