Physiology, Health & Exercise Lesson 14 zEnergy Expenditure & it’s Measurement.

Physiology, Health & Exercise

Lesson 14Energy Expenditure & it’s Measurement

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Exercise & metabolism

Includes: Basal Metabolic Rate Thermic effect of food Effect of physical activity Factors affecting total energy expenditure Measurement of energy expenditure

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Basal Metabolic Rate (BMR)

Is the energy required for body’s essential processes when fasting and at rest

Varies between individuals Higher in:

Leaner/fatter people Males/Females Lighter/heavier people Younger/older people Less/more active people

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BMR- How do different factors have their effect?

Body size & composition & BMR Depends also on ratio of lean (muscle) to

fat tissue Lean tissue more metabolically active

than fat (adipose tissue) Higher proportion of lean tissue higher

BMR

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Gender & BMR BMR higher in males because tend to

have a higher proportion of lean tissue E.g. average % body fat for 20year old 60kg

male = 12-15% compared to 25-30% for 20 year old 60kg

female

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Body Mass & BMR As body weight increases… More body tissue…. More energy expended to do same

activities Increased BMR

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Age & BMR BMR is highest in children due to energy

cost of growth From 18-20 years BMR decreases at a

rate of 2% per decade Due mainly to changes in body

composition as we age (i.e. tendency to put on extra fat)

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Age & BMR

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Level of activity & BMR Athletes have a higher BMR than

untrained people

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Nutritional status & BMR BMR is reduced by fasting or being on a

low energy intake for any length of time Remember probably also combined with

loss of lean tissue as negative energy balance

Reason why most diets don’t work

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Measuring BMR

Very difficult to measure: 12-18 hours after eating & digestion at complete physical & mental rest in a comfortable resting position complex apparatus required

instead use an equation to estimate

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Measuring BMR

variety of equations- couple of examples: Males:

Age BMR (MJ/day)

10-17 0.074 x body mass (kg) + 2.75418-29 0.063 x body mass (kg) + 2.896

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Measuring BMR

Females:

Age BMR (MJ/day)

10-17 0.056 x body mass (kg) + 2.898

18-29 0.062 x body mass (kg) + 2.036

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Total Energy Expenditure (EE)

Sum of 3 components:1. BMR2. Thermic effects of food3. Physical activity

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Thermic effects of Food

Body needs energy to digest, absorb, metabolise & store ingested nutrients

This energy is eventually converted to heat & causes an increase in EE

Thermogenesis means heat production Energy expenditure (EE) can increase up to

30% above BMR in the 2-3 hours after a meal Over 24 hour period, thermic effects of food

can account for approx 10% of total EE

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Depends also on type & quantity of food eatenHigh fat meal3% increase in

EE

High carbohydrate meal

9% increase in EE

High protein meal17% increase in EE

if on a high fat diet will not use up as much energy to digest & absorb the meal as someone on a healthier high carbohydrate diet.

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Thermogenesis can be increased by eating several small meals a day compared to 2 or 3 larger ones

Every time you eat, thermogenesis increases, so if increase number of times you eat without increasing your calorific intake you will increase energy required to digest & metabolise food

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Effects of Physical Activity

Remember BMR is measured at rest Any activity uses up energy in addition to

the BMR Exercise is the most variable component

of EE Can be changed voluntarily!!

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For sedentary people physical activity accounts for approx 30% total EE

For people working in heavy manual work or vigorous exercise programmes it accounts for more than 50% total EE

Different activities have different energy costs

EE also depends on intensity & duration of the activity

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Individuals own BMR Often expressed as a multiple of BMR

Physical Activity Ratio (PAR) E.g. lying at rest has a PAR of 1.0

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V squash energy cost = 42 kJ/min golf energy cost = 16.7 kJ/min squash game of 30 mins = 1260 kJ golf round of 3 hours = 3010 kJ better to exercise moderately (w.r.t. EE)

for 30-40mins 3-5 times a week rather than exercise intensely for 2 hours once a week

Short bursts ofstrenuous

activity

moderate activity of

longer duration

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What happens to EE when activity stops?

Does not return to baseline immediately after exercise

Instead have a post-exercise elevation of EE

Size depends on intensity of exercise If exercise is severe, EE remains elevated

above resting levels for longer

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What happens to EE when activity stops?

Elevated EE called post-exercise oxygen consumption (EPOC)

Needed to enable body to replenish its glycogen stores in liver & muscles

Lasts 5-40 mins for non-athletes & can account for 20-100 additional kJ energy

Also exercise can temporarily increase BMR for several hours after exercise- so more energy expended if regular exercise taken

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Factors affecting total EE

Body size Body composition Age Gender Nutritional status Pregnancy & lactation both increase total

EE Activity Climate

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Measurement of EE

EE can be measured in various ways including:

Direct calorimetry Indirect calorimetry Heart rate recording

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Direct calorimetry

All energy eventually converted to heat, including energy released by metabolism

Total energy expended can be measured by measuring heat energy produced calorimetry

Individual placed inside an insulated chamber & measure temperature rise of known mass of water.

1 calorie = energy required to raise temperature of 1g water by 10C

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Direct calorimetry

Pros & cons: Very accurate method Very expensive Very difficult to operate Not suitable for most situations

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Indirect calorimetry

O2 required to release energy during respiration

So must be a relationship between O2 consumption and EE

Used as an indirect measure of EE- if know volume of O2 taken in over a period of time & composition of expired air

20kJ (4.8 kcal) of energy released for every litre of O2 used

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Volume of expired air is measured using a spirometer which collects air breathed out.

Can use a respirometer to measure total volume of expired air passing through it. Also collects a small gas sample for analysis of O2 and CO2 Inhaled Air

20.93% O2

0.03% CO2

79.04% N2

Exhaled Air16-18% O2

3-5% CO2

79.04% N2

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Indirect calorimetry- an example

Person exercises for 10 minutes and breathes out 100 litres of air.

Remember- 20kJ of energy is released when 1 litre of O2 consumed.

Assume O2 in inhaled air is 21% & exhaled air is 18%

What is their EE?1. Calculate % O2 in inhaled & exhaled air

2. Calculate volume of O2 used per min

3. Multiply by 20 (kJ)

Answer6kJ/min

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Pros & cons: Not as accurate as direct calorimetry Still fairly accurate Cheaper Easier to carry out

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Heart Rate Recording

This method relates to indirect calorimetry

Uses heart rate recorders Relationship between HR & O2

consumption during activity Greater O2 consumption –-> higher HR

(linear relationship) Actual relationship depends on fitness of

the individual and type of activity undertaken

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1. Measure HR over the period of exercise2. Read off graph to get O2 consumption

3. Remember- 20kJ of energy is released when 1 litre of O2 consumed.

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Pros & cons: Not as accurate as direct calorimetry Still fairly accurate Easier to carry out than direct calorimetry

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Homework

Energy Expenditure PS Questions Hand in on 10th April 2008

Physiology, Health & Exercise Lesson 14 zEnergy Expenditure & it’s Measurement.

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Transcript of Physiology, Health & Exercise Lesson 14 zEnergy Expenditure & it’s Measurement.