4 Energy Transformations

Energy define

The capacity to do work

Energy is derived from:

lipid, carbs and proteins stores in body

What kind of work is chemical energy from food

Mechanical work

• Muscular contraction

Chemical work

• Anabolism, catabolism

Osmotic work

• Active transport

Heat energy

Major product of nutrient metabolism

Important for maintaining body temp

Free Energy

Potential energy in chemical bonds of nutrients

Released by combustion or oxidation within cell

How is ATP made?

Substrate level phosphorylation

Oxidative phosphorylation

• Respiratory chain, ETC

Chemiosmotic theory

Flow of protons into the matrix drives ATP production

How many protons does it take to make 1 ATP?

3 protons

What are the components of energy expenditure (EE)?

Basal metabolic rate (BMR)

Thermic effect of food

Energy expenditure of exercise

Thermoregulation

Basal metabolic rate (BMR)

Rate at which the body expends energy to sustain basic life processes

• Ex. heartbeat

60% of total EE

Exercise increases BMR

Mostly related to lean body mass

How is BMR measured?

Person is fasting 12 hours

Lying down and relaxed

Neutral temp

Increase in EE associated with food processing by the body due to:

Digestion

Absorption

Transport

Metabolism

Storage of energy from ingested food

Thermic effect of food

Increase of EE due to food processing by body

Protein increase EE more than carbs or fats

10% of total EE

Effect lasts for 1 hour after eating

Energy expenditure of exercise

Most variable

• Depends on frequency, intensity and duration, body mass, efficiency of performing the activity

30% of total EE

Can remain elevated after exercise is stopped because of oxygen consumption

What variables effect energy expenditure of exercise?

Intensity

Duration

Frequency

Body mass

Efficiency of performing the activity

Thermoregulation

Changes in metabolism that occurs when body works to maintain temp

0 - 10% total EE

Takes energy to cool and heat body

Ways of measuring energy expenditure?

Direct calorimetry

Indirect calorimetry

Doubly labelled water

Derived formulas

Direct calorimetry (Measuring energy expenditure)

Measure the heat given off by the body

Indirect calorimetry

Uses the respiratory quotient (RQ)

Used to estimate how much carbs and lipids are being used

CO2 produced divided by O2 consumed

What is the RQ value of Lipids?

0.7

What is the RQ value of proteins?

~0.9

Hard to measure because of different amino acids

iF the RQ is measured under resting conditions it reflects _____

the proportion of carb and lipid intake

Carbs vs Fats in Exercise Intensity

Carbs

• Used in high intensity

Fats

• Used in low intensity, high duration

Fuel Crossover

Transition of using fats to carbs

Primary reasons is because fats cannot be used for anaerobic metabolism

• Required for high intensity

Other reasons

• Recruitment of fast twitch muscle fibers (fat metabolism)

• Increase level of epinephrine (Increase rate of muscle glycogen breakdown)

Glycogen loading

Used by athletes to increase glycogen stores in muscles

Goal is to reduce hypoglycemia and metabolic stress

Studies found that preoperative carb loading is associated with:

Higher wellbeing

Less insulin resistance

Improved body temp maintenance

Ways of Measuring Energy Expenditure: Doubly labeled water

Give a known amount of doubly labeled water

• 2H2O and H218O, or 2H218O)

At a later time, measure the amount of each isotope remaining

• Disappearance of 18O represents the disappearance of body water (H2O) and disappearance of CO2 (Production)

• Disappearance of 2H represents the disappearance of body water (H2O) only

Ways of Measuring Energy Expenditure: Derived Formulas

Formulas based off weight, height, gender and age for BMR

Estimated energy requirement (EER)

EER used in DRI are based on equations that include

Weight, height, gender, age and physical activity

Direct and Indirect calorimetry vs doubly labelled water and derived formulas

Direct and indirect calorimetry have less potential of errors but are much more invasive than doubly labelled water and derived formulas

Energy requirements

Proportional to lean body mass

Depends on age, growth, gender, and physioglocial state

• Pregnancy/lactation, stress

Influenced by physical activity and environmental conditions

Units of Energy

Calorie

• Amount of heat required to raise the temp of 1 gram of water to 1 C

• 4.2 joules (int units)

Kilocalorie

• Amount of heat required to raise the temp of 1 kg of water to 1 C

• Calories with a capital C

What does a bomb calorimeter measures

Measures energy content of food

Gross energy given off upon combustion of food

Energy density of food components derived by human metabolism gives the physiological fuel values:

• Carbs

• Lipid

• Protein

• Alcohol

Carbs

• 4 kcal/g

Lipid

• 9 kcal/g

Protein

• 4 kcal/g

Alcohol

• 7 kcal/g

Energy Use During Rest

During rest, most energy comes from fat

Most of the balance comes from carbs with a small amount coming from protein

What energy sources are used during low physical activity

Aerobic metabolism (Major)

ATP (minor)

• Creatine phosphate stores

Increased ________ improve ability to exercise

glycogen stores

More ____ is used with longer exercise. Why does this happen?

Fat

This is caused by epinephrine which is secreted during exercise and increases activity of hormone sensitive lipase

Energy Systems used during exercise

1. ATP-CP system used initially

2. Then anaerobic metabolism becomes the greater source of energy

   • Lactate produced from pyruvate

   • If exercise is strenuous, lactate can build up

3. Aerobic metabolism then takes over

   • Pyruvate enters mitochondria and converted to acetyl CoA → TCA cycle

   • Limited to amount of O₂ available

Respiratory Quotient

Indicates which macronutrients are being metabolized

Different pathways used for fats, carbs and proteins