Transcript Physiology, Health & Exercise

Physiology, Health & Exercise
Lesson 14
Energy Expenditure & it’s
Measurement
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:
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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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BMR- How do different factors
have their effect?
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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BMR- How do different factors
have their effect?
Body Mass & BMR
 As body weight increases…
 More body tissue….
 More energy expended to do same activities
 Increased BMR
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BMR- How do different factors
have their effect?
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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BMR- How do different factors
have their effect?
Age & BMR
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BMR- How do different factors
have their effect?
Level of activity & BMR
 Athletes have a higher BMR than untrained
people
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BMR- How do different factors
have their effect?
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:
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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
18-29
0.074 x body mass (kg) + 2.754
0.063 x body mass (kg) + 2.896
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Measuring BMR
Females:
Age
BMR (MJ/day)
10-17
18-29
0.056 x body mass (kg) + 2.898
0.062 x body mass (kg) + 2.036
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Total Energy Expenditure (EE)
Sum of 3 components:
1. BMR
2. Thermic effects of food
3. 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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Thermic effects of Food
 Depends also on type & quantity of food
eaten
High carbohydrate
High fat meal
meal
3% increase in EE
9% increase in EE
High protein meal
17% 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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Thermic effects of Food
 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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Effects of Physical Activity
 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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Effects of Physical Activity
 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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Effects of Physical Activity
Short bursts of
strenuous activity
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moderate activity
of
V
longer duration
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
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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
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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
20kJ (4.8 kcal) of energy released for every
litre of O2 used
 Used as an indirect measure of EE- if know
volume of O2 taken in over a period of time &
composition of expired air
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Indirect calorimetry
 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
Exhaled Air
20.93% O2
16-18% O2
0.03% CO2
3-5% CO2
79.04% N2
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?
Answer
1. Calculate % O2 in inhaled & exhaled air
2. Calculate volume of O2 used per min
3. Multiply by 20 (kJ)
6kJ/min
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Indirect calorimetry
Pros & cons:
 Not as accurate as direct calorimetry
 Still fairly accurate
 Cheaper
 Easier to carry out
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Indirect calorimetry
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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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Heart Rate Recording
1. Measure HR over the period of exercise
2. Read off graph to get O2 consumption
3. Remember- 20kJ of energy is released when
1 litre of O2 consumed.
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Heart Rate Recording
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
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