Exercise Physiology Quiz

Essentials of Bioenergetics and Anaerobic Metabolic Pathways

• Students should be able to define three major metabolic substrates and how they are metabolized to produce energy.
• Students should be able to determine which metabolic substrates predominate during rest and exercise.
• Students should be able to describe energy production from the ATP-phosphocreatine system and glycolysis.
• Students should be able to describe the positive and negative features of the phosphagen and glycolytic pathways.
• Students should be able to explain the energy system adaptations that accompany training.

Metabolism: Applications

• Sprinters can only sprint "all out" for a short time.
• Marathon runners can sustain a race pace for over two hours.
• Energy comes from the body's fuel sources (substrates)
• Performance limitations are determined by several factors, and can be overcome.

Why do we need energy?

• Muscle contraction
• Digestion
• Reproduction

Energy

• It is the ability to do work
• This is the capacity of work
• Examples include various forms of energy:

How do we get energy?

• We use food to make energy

Through Metabolism

• Metabolism, also known as bioenergetics, refers to the total of all chemical reactions within cells.
• Food provides energy.

Where does the energy come from?

• The sun, through photosynthesis, plants convert sunlight to carbohydrates.
• Humans and animals consume plants and animals to get carbs, protein, and fats.
• The body then breaks down these substances into usable forms which helps in the production of energy

Energy Sources

• Chemical energy from food is converted to produce mechanical energy
• This results in muscle contractions and bodily movement.
• Three essential chemical energy types that the body consumes are carbohydrates, fats, and proteins.
• Carbohydrates are broken into simple sugars, (glucose, fructose, and galactose)
• Fats are broken down into triglycerides and fatty acids
• Proteins are converted into amino acids

Macronutrients

• Carbohydrates, which are broken into simple sugars (glucose, fructose, and galactose).
• Fats, which are broken down into triglycerides and fatty acids.
• Proteins, which are converted into amino acids.
  • These are broken down into usable forms to form high-energy compounds like ATP

Adenosine Triphosphate (ATP)

• The energy currency for biological useful work/processes
• Breaking phosphate bonds releases energy for other biological work.
• ATP breaks down to release energy for muscle contraction.

When a Phosphate is Broken Off

• ATP releases energy
• This is called an exergonic reaction
• ADP is formed
• This reaction needs energy (endergonic)

What does a muscle need to contract and keep contracting?

• A continuous supply of ATP to match demand

ATP Supply

• ATP stored in limited amounts.
• Enough for 1-2 seconds of all-out effort.
• Nutrients are broken down to replace it.

Fuels (substrates) for Exercise

• Carbohydrates (CHO)
• Fats
• Proteins
• Creatine phosphate (CPR, PC, CP)

Carbohydrates

• Rapid and readily available.
• 4 kcal/g
• 3 forms:
  • Monosaccharides (single) like glucose, fructose, galactose
  • Disaccharides (two sugars) like sucrose, lactose, maltose
  • Polysaccharides (many sugars) like starch, glycogen
• Blood sugar (monosaccharides), primary fuel for the brain, only source of energy for some cells

Polysaccharides

• Many monosaccharides bonded together
  • Starch: stored in plants (grains, legumes, and tubers)
  • Glycogen: stored in animals (liver and muscles)
  • Cellulose: insoluble fiber, plants

Glycogenesis

• Formation of glycogen from glucose

Glycogenolysis

• Breaking down glycogen into glucose

Glycogen Storage

• When blood glucose drops, fatigue occurs.
• Muscle glycogen provides energy for muscle
• Liver glycogen helps to maintain stable blood sugar

Carbohydrates for Energy

• Essential fuel during exercise, vital for the brain (CNS).
• ATP quickly produced from them
• Can be depleted after about 2 hours of extended exercise.
• Influenced by dietary carbohydrate content.

Fats

• Can be metabolized for energy.
• Triglycerides: main form of fat storage (1 glycerol + 3 fatty acids).
• Fat stores are large and not readily depleted.
• Slower ATP production than carbohydrates. Used more at rest.
  • Useful for long duration activity

Lipolysis

• Breakdown of triglycerides to release energy in the form of fatty acids

Lipolysis (Continued)

• Fats are broken down to produce ATP energy
• ATP is slowly produced, important at rest, but not useful in intense exercise

Proteins

• Used for energy in small amounts
• Made from amino acids linked together.
• Needed for various bodily functions, not primarily for energy.

Enzymes

• Enzymes facilitate chemical reactions by speeding them up.
• They have a unique shape that allows them to bind with substrates and catalyze reactions.
• They end in '-ase' (e.g., protease, lipase).

ATP-PC System

• Energy source for high-intensity activities requiring quick energy
• Brief duration (3-15 seconds)
• Examples include sprinting.
• Phosphocreatine (PCr) is composed of creatine and phosphate.
• PCr stores energy in the sarcoplasm for quick ATP production.

ATP-PC Mechanism

• Energy from phosphocreatine breaks down to produce ATP.
• This ATP is then broken down releasing the energy to fuel muscle contraction.
• The rate of ATP formation in this system is high.

Glycolysis

• Breakdown of glucose or glycogen into pyruvate.
• A 10-step, anaerobic reaction that occurs in the absence of oxygen
• A small amount of ATP is produced (but rapid). Used in high intensive, short duration activity
• In the absence of oxygen, Pyruvate is converted to Lactate
• In the presence of oxygen, Pyruvate is converted to Acetyl CoA (then into Krebs Cycle/Electron Transport Chain)

Glycolysis Overview

• Anaerobic (fast): Does not utilize oxygen, used in short duration, high intensity activities
• Aerobic (slow): Utilizes oxygen, used in low intensity, long duration activities

Glycolysis (Glucose to Pyruvate)

• Occurs in 2 ways; Fast (anaerobic) & Slow (aerobic).
• Fast when cells need quick energy.
• Slow when cells do not need as much energy, but need it over a longer time.

Glycolysis: Substrate

• ATP use to transform glucose into glucose-6-phosphate
• Glycogen breakdown does not need ATP

Glycolysis: Key Points

• Rapid ATP production
• Limited capacity due to acidity
• Dominant energy system in activities from 20-30 seconds to 2-3 minutes.

Glycolysis: Enzyme Adaptations

• Changes in glycolytic enzymes may improve performance
• Increase in ATP availability
• Key studied enzymes:
  • Glycogen phosphorylase
  • Phosphofructokinase (rate-limiting enzyme)
  • Lactate dehydrogenase

Glycolysis: Intramuscular Glycogen Adaptations

• Endurance training increases muscle glycogen. More glycogen means it will take longer to run out of stored fuel.

Glycolysis: Buffering Adaptations

• Endurance and sprint training increases buffering capabilities
• Buffers H+ (which causes acidity) for better performance and recovery in activities that produce a lot of lactic acid
• More ATP production before fatigue.

Interactions of Aerobic and Anaerobic Metabolism

• Anaerobic system creates ATP rapidly for short, high-intensity activities
• Aerobic system makes most ATP for long duration, low intensity activities

A 3-Second Sprint

• A 3-second sprint is mostly powered by the ATP-PC system.
• Other processes like glycolysis contribute to a lesser extent.

3-Second Sprint and Other Sprints

• The ratio of contribution from ATP-PC, glycolysis, and aerobic metabolism changes depending on the length of the sprint.

Energy for Longer High-Intensity Efforts

• If exercise goes beyond ATP-PC system capacity then other systems (like glycolysis) are involved

Lactate Response to Exercise

• Lactate buildup occurs during exercise and plateaus after a while.
• It increases then falls back to baseline

What's causing fatigue?

• Accumulation of H+ (from lactic acid) increases acidity, causes fatigue
• Breakdown of ATP that exceeds production will accumulate H+ which increases acidity

Replenishing PC Stores

• Recovery process occurs when PC stores are depleted via other energy systems (Anaerobic and Aerobic)

Why can a sprinter only sprint "all out" for a brief period of time?

• The ATP-PC system is quickly depleted because of the high energy demands needed for quick, intense movements
• Hydrogen accumulation causes fatigue during sprinting

ATP-PC: Adaptations to Exercise

• Mixed results in studies
• Endurance training has no impact on creatine kinase activity
• Increased content of intramuscular ATP and PC might not enhance short-term, high-intensity performance

Creatine: Mechanism of Action

• Creatine combines with ATP to help produce more for muscle contraction

Common Adaptations

• Improved enzyme function (enzyme activity)
• Improved substrate availability means the enzymes can work at higher efficiency rates

Glycolysis: Enzymes Adaptations

• Enzymes increase due to weight and sprint training, not just endurance training
• Enzymes (like glycogen phosphorylase & Phosphofructokinase) change depending on type, volume, duration, intensity, and frequency of exercise. Muscle hypertrophy can also change PFK activity.

Glycolysis: Intramuscular Glycogen Adaptations

• Endurance training increases Muscle glycogen
• More glycogen available means it takes longer to run out/fatigue

Test your knowledge on key concepts in exercise physiology, including energy systems, metabolism, and muscle function. This quiz covers essential topics such as anabolism, catabolism, and the roles of ATP during physical activity.