Chapter 7 - Energy for Muscular Activity

ATP resynthesis

process where muscle cells are able to continually resynthesize ATP by recombination of ADP with a free phosphate

3 energy systems of ATP synthesis

• Phosphagen System (or Immediate)

• Glycolytic system (Short-term)

• Oxidative System (Long-term)

Phosphagen system (Anaerobic Alactic)

• supports high-power-output activities

• advantages: produces large amounts of energy in a really short amount of time and rate of recovery is relatively rapid

  • can provide immediate energy for muscle contractions only in the first 7-12 seconds of high-intensity activity

    • which is why you get tired after running near the end of a 100m dash

• disadvantages: Limited amount of ATP produced

• energy process: hydrolysis + ATP synthesis

• fuel source: creatine phosphate

• does not produce any byproducts LIKE LACTIC ACID

• ATP output: 1 molecule (very limited)

Glygolytic System (Anaerobic lactic)

• supports high-intensity activity

• energy system: glycolysis

  • if happening at a high rate, lactic acid is produced

• advantages: not limited by oxygen delivery

• disadvantages buildup of lactic acid contributes to fatigue

• fuel source: Glycogen and blood glucose

• produces pyruvic acid

• byproduct: lactic acid

  • if rate of pyruvic acid production exceeds rate at which pyruvate can be processed in mitochondria, excess pyruvic acid is turned into lactic acid

• ATP output: 2 molecules per glucose molecule

pyruvic acid

product of glycolysis

• can go down 2 paths:

  • converted into pyruvate

  • can go into the mitochondria

pyruvate

buffered salt form of pyruvic acid

mitochondria

specialized cellular organelles where the reactions of aerobic metabolism occur

blood glucose

circulating form of carbohydrate

Lactate

salt compound that forms when lactic acid rapidly dissociates

what does lactic acid rapidly dissociates into

Lactate and hydrogen ions

How does Lactic acid contribute to fatigue

• glycolytic system produces lactic acid as a byproduct

• lactic acid rapidly dissociates into lactate and hydrogen ions

  • hydrogen ions are known to induce muscle fatigue

    • compete with calcium for cross-bridge binding sites which limits strength of muscle fibre activation

effects of training on the Glycolytic system

an endurance trained individual will have a decreased rate of lactic acid accumulation

• which means anaerobic threshold is higher

• individual can work at higher rate of activity before lactic acid builds up

• sprinters benefit from lactic acid production

  • don’t need to worry about buildup since they compete in such short events

why is it important to increase rate of lactic acid removal

allows people to exercise at higher intensities for longer periods of time

factors that increase rate of lactic acid removal

• increased rate of lactic acid diffusion from active muscle fibres into circulatory system

• increased muscle blood flow

• increased ability to metabolize lactate in the heart, liver, and non-working muscle fibres

metabolic pathways of oxidative phosphorylation

• Krebs cycle

• Electron transport chain (ETC)

Oxidative system (Aerobic)

• supports long-duration activities

• energy process: oxidative phosphorylation to resynthesize ATP (occurs in the mitochondria)

• advantages: high ATP yield and can remove lactic acid

• disadvantages: needs oxygen and is slower to meet energy demands

• fuel sources: glucose, amino acids, fatty acids

• ATP output: 36 molecules ATP per glucose molecule

• byproducts: water, CO2

Krebs Cycle (Citric Acid cycle)

metabolic process where pyruvate is metabolized along with other fuel sources like carbohydrate, protein, and fat

electron transport chain (ETC)

final step in oxidation system where large amounts of ATP are produced

which system is the most efficient energy system and why

Oxidative system

• aerobic breakdown of glucose molecule is approx. 18x more efficient than that of glycolytic’s system

Lactic acid removal in Oxidative system

2 ways:

1. can be transported to the liver for processing

• Cori cycle - lactate is metabolized to pyruvate and then glucose

2. lactate is transported in the blood from Type II glycolytic muscle fibres and then to Type I oxidative muscle fibres

• here it is converted back to pyruvate and then metabolized in Krebs cycle

which type of exercise is most effective for training oxidative system

endurance exercise

4 major effects that endurance training has on oxidative system

• increases vascularization within the muscles so that there is an enhanced delivery of nutrients and oxygen to the muscle

• increases the number and size of mitochondria within the muscle fibres

• increases the activity of the enzymes involved in the aerobic metabolic pathways

• results in the preferential use of fats over glycogen during exercise

  • which saves the limited storage of glycogen that the muscles have

How do the 3 energy systems interact

• phosphagen and glycolytic systems are more important for short-term, high-intensity activities

  • ex. diving, sprinting, jumping

• oxidative system is more important for longer-lasting, less-intensive endurance activities

  • ex. marathon running, triathlon

• the longer the duration of the activity, the more contribution that oxidative metabolism has to the energy supply

which system contributes (and how much) energy to high-intensity work lasting 6-9 minutes?

half from glycolytic and the other half from oxidative