Ch 4 Energy
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100 Terms
Energy
The capacity to do work.
Forms of energy
Light energy, chemical energy, heat, and electrical energy.
ATP
The energy currency of the cell.
Calorie (cal)
A unit of energy; the amount of heat needed to raise 1 g of water by 1°C.
Kilocalorie (kcal)
1,000 calories; what is commonly called a “Calorie” with a capital C on food labels.
Joule (J)
A metric unit of energy.
Kilojoule (kJ)
1,000 joules; commonly used instead of joules because a joule is a small amount of energy.
1 calorie
4.184 joules.
1 kilocalorie
4.184 kilojoules.
Food energy
Energy stored in the chemical bonds of carbohydrate, fat, and protein.
Direct calorimetry
A method that measures the heat produced by combusting food to determine its energy content.
Bomb calorimeter
A device used to measure the chemical energy content of food by combusting it.
Chemical energy of food
The total potential energy in food before accounting for losses during digestion, absorption, and metabolism.
Energy from carbohydrate
Carbohydrate provides about 4.2 kcal per gram in the average diet.
Energy from fat
Fat provides about 9.4 kcal per gram in the average diet.
Energy from protein
Protein has a potential energy content of about 5.65 kcal/g, but only about 4.6 kcal/g is available to the body.
Nitrogen in protein
Nitrogen cannot be oxidized for energy, so it reduces the amount of usable energy obtained from protein.
Available food energy
The amount of energy that can actually be obtained from food after digestion and absorption.
Coefficient of digestibility
The proportion of consumed food that is actually digested and absorbed.
Average carbohydrate digestibility
About 97%.
Average fat digestibility
About 95%.
Average protein digestibility
About 92%.
Atwater factors
The standard energy values used for carbohydrate, fat, and protein: 4, 9, and 4 kcal/g.
Atwater factor for carbohydrate
4 kcal/g.
Atwater factor for fat
9 kcal/g.
Atwater factor for protein
4 kcal/g.
Energetic efficiency
The percentage of energy from food that is converted into useful work.
Energy efficiency during cycling
About 20% of energy is converted into power; most of the rest becomes heat.
Heat during exercise
Energy that is not converted into mechanical work; some helps maintain body temperature, but excess heat must be dissipated.
Energy expenditure
The amount of calories burned by the body.
Direct calorimetry
Measures energy expenditure by directly measuring the heat produced by the body.
Human calorimeter
A well-insulated chamber that measures heat produced by a person to estimate metabolic rate.
Indirect calorimetry
Measures oxygen uptake and carbon dioxide production to estimate energy expenditure.
Why is indirect calorimetry called “indirect”?
Because it measures O2 consumption and CO2 production rather than directly measuring heat.
VO2
Oxygen uptake or oxygen consumption.
VCO2
Carbon dioxide production.
Respiratory quotient (RQ)
The ratio of CO2 produced to O2 consumed during metabolism.
RQ formula
RQ = VCO2 ÷ VO2.
Respiratory exchange ratio (RER)
The ratio of CO2 produced to O2 consumed measured at the mouth during exercise.
RQ vs RER
RQ refers to gas exchange at the tissue level, while RER is measured from gases breathed at the mouth.
Normal RQ/RER range when using mixed fuels
Usually between 0.7 and 1.0.
RQ of carbohydrate
About 1.0.
RQ of fat
About 0.7.
RQ of protein
Protein has a different RQ depending on the amino acid being oxidized.
What does an RQ/RER closer to 1.0 indicate?
More carbohydrate is being used as fuel.
What does an RQ/RER closer to 0.7 indicate?
More fat is being used as fuel.
Glucose RQ
About 1.0.
Fatty acid RQ
About 0.7.
Why can RER exceed 1.0?
Hyperventilation or high-intensity exercise can increase CO2 production beyond what would normally occur from substrate oxidation.
Hyperventilation and RER
Hyperventilation increases CO2 expiration while O2 uptake stays about the same, causing RER to rise above 1.0.
High-intensity exercise and RER
Above about 80–85% VO2max, increased glycolysis and buffering of hydrogen ions produce extra CO2, causing RER to rise.
RER during very high-intensity exercise
Can reach approximately 1.0–1.3.
Walking energy expenditure rule
A person expends about 1 kcal per kilogram of body mass per kilometer walked or run.
Walking energy expenditure formula
EE (kcal) = distance covered (km) × body mass (kg).
Accelerometer
A small device that measures body acceleration to estimate physical activity.
Triaxial accelerometer
Measures acceleration along three axes and is generally more accurate than one- or two-axis devices.
Resting metabolic rate (RMR)
The energy needed to maintain basic physiological functions such as breathing and pumping blood.
Diet-induced thermogenesis (DIT)
The energy used to process the food we eat.
Thermic effect of food (TEF)
Another name for diet-induced thermogenesis.
Thermic effect of exercise (TEE)
The energy used to power muscles during movement and exercise.
Activity thermogenesis (TEA)
Energy expenditure related to physical activity and movement.
Largest component of daily energy expenditure
Resting metabolic rate, especially in relatively sedentary people.
RMR contribution to daily energy expenditure
About 60–75% in relatively sedentary people.
DIT contribution to daily energy expenditure
About 10%.
Exercise-related energy expenditure
About 15–30% in relatively sedentary people.
Lean body mass (LBM)
Body tissues including muscle and organs, along with bone and body fluids.
Why does lean body mass affect RMR?
Muscle and organ tissue require energy to maintain their metabolic activity.
Factors that can alter RMR
Age, gender, exercise, body size, and changes in lean body mass.
Energy balance
The difference between energy intake and energy expenditure.
Positive energy balance
Energy intake is greater than energy expenditure; generally results in weight gain.
Negative energy balance
Energy intake is less than energy expenditure; generally results in weight loss.
Energy balance should usually be considered over
Several days or weeks rather than a single meal or day.
Energy balance and athletic performance
Energy intake needs to be sufficient to support training, recovery, and normal physiological functions.
Problem with extremely low energy intake
It can impair performance and increase the risk of nutrient deficiencies and illness.
Low energy availability
When not enough energy is available to support normal physiological functions after exercise demands are considered.
Female athlete triad
A condition associated with sustained negative energy balance in female athletes involving menstrual dysfunction and low bone density, along with low energy availability.
REDs
Relative Energy Deficiency in Sport; impaired physiological functioning caused by inadequate energy availability.
REDs can occur in
Both male and female athletes.
REDs energy availability threshold
Below about 30 kcal/kg fat-free mass/day.
Very high energy expenditure
Some endurance sports can require extremely high daily energy expenditures.
Sports with very high energy expenditures
Cycling, triathlon, and ultraendurance running can reach around 8,600 kcal/day.
Why is eating enough difficult during extreme endurance events?
Limited eating time, fatigue, reduced hunger, and gastrointestinal problems can make consuming enough food difficult.
Factors that can increase energy needs
Cold or heat exposure, fear, stress, high altitude, injury/wound healing, stimulant drugs, and increased fat-free mass.
Factors that can decrease energy needs
Aging-related decreases in movement, decreased fat-free mass, sedentary behavior between training sessions, and decreased training volume.
Resting activity energy cost
About 1 kcal/min.
Very light activity energy cost
About 3–5 kcal/min.
Light activity energy cost
About 5–7 kcal/min.
Moderate activity energy cost
About 7–9 kcal/min.
Strenuous activity energy cost
About 9–13 kcal/min.
Very strenuous activity energy cost
More than 13 kcal/min.
Example of very light activity
Sitting, standing, driving, cooking, typing.
Example of light activity
Walking 3–5 km/h, baseball, bowling, golf.
Example of moderate activity
Jogging, basketball, soccer, tennis, volleyball, walking 7–8 km/h.
Example of strenuous activity
Running 10–13 km/h or cross-country skiing.
Example of very strenuous activity
Cycling around 35 km/h or running faster than 14 km/h.
Carbohydrate energy value
About 4 kcal/g using the Atwater factor.
Fat energy value
About 9 kcal/g using the Atwater factor.
Protein energy value
About 4 kcal/g using the Atwater factor.
Why does fat provide more energy per gram than carbohydrate?
Fat contains more energy stored in its chemical bonds.
Why isn't all food energy available to the body?
Some food cannot be completely digested or absorbed, and some potential energy is lost during metabolism.