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

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Presentation on theme: "Physiology, Health & Exercise Lesson 14 zEnergy Expenditure & it’s Measurement."— Presentation transcript:

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

2 2 Exercise & metabolism Includes: zBasal Metabolic Rate zThermic effect of food zEffect of physical activity zFactors affecting total energy expenditure zMeasurement of energy expenditure

3 3 Basal Metabolic Rate (BMR) zIs the energy required for body’s essential processes when fasting and at rest zVaries between individuals zHigher in: yLeaner/fatter people yMales/Females yLighter/heavier people yYounger/older people yLess/more active people

4 4 BMR- How do different factors have their effect? Body size & composition & BMR zDepends also on ratio of lean (muscle) to fat tissue zLean tissue more metabolically active than fat (adipose tissue) zHigher proportion of lean tissue  higher BMR

5 5 BMR- How do different factors have their effect? Gender & BMR zBMR 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

6 6 BMR- How do different factors have their effect? Body Mass & BMR zAs body weight increases… zMore body tissue…. zMore energy expended to do same activities zIncreased BMR

7 7 BMR- How do different factors have their effect? Age & BMR zBMR is highest in children due to energy cost of growth zFrom years BMR decreases at a rate of 2% per decade zDue mainly to changes in body composition as we age (i.e. tendency to put on extra fat)

8 8 BMR- How do different factors have their effect? Age & BMR

9 9 BMR- How do different factors have their effect? Level of activity & BMR zAthletes have a higher BMR than untrained people

10 10 BMR- How do different factors have their effect? Nutritional status & BMR zBMR is reduced by fasting or being on a low energy intake for any length of time zRemember probably also combined with loss of lean tissue as negative energy balance  Reason why most diets don’t work

11 11 Measuring BMR zVery difficult to measure: y12-18 hours after eating & digestion yat complete physical & mental rest yin a comfortable resting position ycomplex apparatus required zinstead use an equation to estimate

12 12 Measuring BMR  variety of equations- couple of examples: Males: AgeBMR (MJ/day) x body mass (kg) x body mass (kg)

13 13 Measuring BMR Females: AgeBMR (MJ/day) x body mass (kg) x body mass (kg)

14 14 Total Energy Expenditure (EE) Sum of 3 components: 1.BMR 2.Thermic effects of food 3.Physical activity

15 15 Thermic effects of Food zBody needs energy to digest, absorb, metabolise & store ingested nutrients zThis energy is eventually converted to heat & causes an increase in EE zThermogenesis means heat production zEnergy expenditure (EE) can increase up to 30% above BMR in the 2-3 hours after a meal zOver 24 hour period, thermic effects of food can account for approx 10% of total EE

16 16 Thermic effects of Food zDepends also on type & quantity of food eaten High fat meal 3% increase in EE High carbohydrate meal 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.

17 17 Thermic effects of Food zThermogenesis can be increased by eating several small meals a day compared to 2 or 3 larger ones zEvery 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

18 18 Effects of Physical Activity zRemember BMR is measured at rest zAny activity uses up energy in addition to the BMR zExercise is the most variable component of EE zCan be changed voluntarily!!

19 19 Effects of Physical Activity zFor sedentary people physical activity accounts for approx 30% total EE zFor people working in heavy manual work or vigorous exercise programmes it accounts for more than 50% total EE zDifferent activities have different energy costs zEE also depends on intensity & duration of the activity

20 20 Effects of Physical Activity zIndividuals own BMR zOften expressed as a multiple of BMR  Physical Activity Ratio (PAR) zE.g. lying at rest has a PAR of 1.0

21 21 Effects of Physical Activity V zsquash energy cost = 42 kJ/min zgolf energy cost = 16.7 kJ/min zsquash game of 30 mins = 1260 kJ zgolf round of 3 hours = 3010 kJ zbetter 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 of strenuous activity moderate activity of longer duration

22 22 What happens to EE when activity stops? zDoes not return to baseline immediately after exercise zInstead have a post-exercise elevation of EE zSize depends on intensity of exercise zIf exercise is severe, EE remains elevated above resting levels for longer

23 23 What happens to EE when activity stops? zElevated EE called post-exercise oxygen consumption (EPOC) zNeeded to enable body to replenish its glycogen stores in liver & muscles zLasts 5-40 mins for non-athletes & can account for additional kJ energy zAlso exercise can temporarily increase BMR for several hours after exercise- so more energy expended if regular exercise taken

24 24 Factors affecting total EE zBody size zBody composition zAge zGender zNutritional status zPregnancy & lactation both increase total EE zActivity zClimate

25 25 Measurement of EE EE can be measured in various ways including: zDirect calorimetry zIndirect calorimetry zHeart rate recording

26 26 Direct calorimetry zAll energy eventually converted to heat, including energy released by metabolism zTotal energy expended can be measured by measuring heat energy produced  calorimetry zIndividual placed inside an insulated chamber & measure temperature rise of known mass of water. 1 calorie = energy required to raise temperature of 1g water by 1 0 C

27 27 Direct calorimetry Pros & cons: zVery accurate method zVery expensive zVery difficult to operate zNot suitable for most situations

28 28 Indirect calorimetry zO 2 required to release energy during respiration zSo must be a relationship between O 2 consumption and EE zUsed as an indirect measure of EE- if know volume of O 2 taken in over a period of time & composition of expired air 20kJ (4.8 kcal) of energy released for every litre of O 2 used

29 29 Indirect calorimetry zVolume of expired air is measured using a spirometer which collects air breathed out. zCan use a respirometer to measure total volume of expired air passing through it. Also collects a small gas sample for analysis of O 2 and CO 2 Inhaled Air 20.93% O % CO % N 2 Exhaled Air 16-18% O 2 3-5% CO % N 2

30 30 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 O 2 consumed. Assume O 2 in inhaled air is 21% & exhaled air is 18% What is their EE? 1.Calculate % O 2 in inhaled & exhaled air 2.Calculate volume of O 2 used per min 3.Multiply by 20 (kJ) Answer 6kJ/min

31 31 Indirect calorimetry Pros & cons: zNot as accurate as direct calorimetry zStill fairly accurate zCheaper zEasier to carry out

32 32 Indirect calorimetry

33 33 Heart Rate Recording zThis method relates to indirect calorimetry zUses heart rate recorders zRelationship between HR & O 2 consumption during activity zGreater O 2 consumption –-> higher HR (linear relationship) zActual relationship depends on fitness of the individual and type of activity undertaken

34 34 Heart Rate Recording 1.Measure HR over the period of exercise 2.Read off graph to get O 2 consumption 3.Remember- 20kJ of energy is released when 1 litre of O 2 consumed.

35 35 Heart Rate Recording Pros & cons: zNot as accurate as direct calorimetry zStill fairly accurate zEasier to carry out than direct calorimetry

36 36 Homework Energy Expenditure PS Questions zHand in on 10 th April 2008


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