The Energy Systems

What is the primary ‘currency’ of energy in the body?

• Adenosine triphosphate (ATP)

ATP structure

• Adenosine molecule bonded to 3 inorganic phosphate molectules

ATP chemical reaction to release energy worded formula

• ATP + water + ATPase → ADP + 1 phosphate + energy

Power stroke

• Myosin head binds to actin filament

• Energy from ATP used to ‘tilt’ myosin head which drags actin filament towards it, shortening it (the power stroke)

ADP cycle def

The breakdown of ATP results in adenosine diphosphate (ADP) and a free phosphate molecule (Pi​). To continue work, the body must re-synthesise these components back into ATP.

Why is ATP vital at all times? (2)

• Muscle Tone: Maintaining a baseline level of contraction even during rest.

• Rapid Response: Enabling immediate reactions to perturbations, such as a spinal reflex response to touching a hot object or tripping.

2 ways in which ATP synthesis is categorised

• Aerobic (O2 required)

• Anaerobic (O2 not required)

2 anaerobic systems

• ATP-PCr (phosphocreatine system)

• Lactic system

ATP-Cr system: fuel, O2 requirements, speed of ATP production, ATP yield, duration

• Phosophocreatine

• Nil

• Fastest

• Very limited

• 3-15 seconds (usually during very beginning of intense activity)

Lactic/glycolytic system: fuel, O2 requirements, speed of ATP production, ATP yield, duration

• Glucose/glycogen

• Nil

• Fast

• Limited (2-3 ATP)

• 30 sec - 2 mins

ATP yield from glycolysis of free glucose vs glucose released from glycogen chain

• 2 ATP

VS

• 3 ATP

Note on lactic system + O2 (3)

• Doesn’t require O2, but without sufficient O2 → pyruvic acid converts to lactic acid

• Lactic acid accumulation causes acidosis (decrease in muscle pH) → which inhibits further glycogen breakdown for energy + decreases muscle contractility (fatigue noticeable after 30 seconds of maximal effort)

• In presence of O2, pyruvic acid is used for fuel in oxidative system

What happens to excess lactate during recovery? (1)

Re-synthesised to form glucose by liver + returned to muscle

Where do processes of oxidative system take place?

Mitochondria

2 types of oxidation that occur for energy production

• Carbohydrate oxidation

• Fat oxidation

Carbohydrate oxidation description + how many ATP it can yield

• In presence of O2 → pyruvic acid enters mitochondria

• Up to 39 ATP/glucose molecule

Fat oxidation: main energy source, benefit + note

• Triglycerides

• Can provide more kcals of energy compared to carb stores

• Preferred source of fuel during rest (save carb stores for exercise)

Example of triglyceride + no. of ATP produced

• Palmitic acid

• 129 ATP per molecule

Cons of fat oxidation

• Requires more O2

• Slower

• Can’t exercise as intensely if carb stores are depleted

What is ‘hitting the wall’? (2)

• When glycogen stores (~2,500 kcal capacity) are depleted

• Must rely solely on fat oxidation, which produces ATP too slowly to maintain high-intensity work

• Leading to a forced reduction in pace

Factor that influences rate of aerobic metabolism (1) + benefit

• Size + number of mitochondria

• Greater size + number of mitochondria → can metabolise pyruvic acid faster and exercise at higher intensities without accumulating too much lactic

Note on protein metabolism

Protein is not a primary energy source and is only utilised significantly during starvation or severe energy depletion

Fuel reserves greatest to smallest (5)

• Adipose tissue (fat

• Protein

• Muscle glycogen

• Liver glycogen

• Blood glucose

Note on interplay between systems

• The system that is used doesn’t depend on exercise intensity; during all out exercise, every system will be active

Summary of energy systems (table)