Physiology, Health & Exercise

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

2. Exercise & metabolism Includes: • Basal Metabolic Rate • Thermic effect of food • Effect of physical activity • Factors affecting total energy expenditure • Measurement of energy expenditure

3. 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

4. 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

5. 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

6. 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

7. 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)

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

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

10. 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

11. 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

12. Measuring BMR • variety of equations- couple of examples: Males: Age BMR (MJ/day) 10-17 0.074 x body mass (kg) + 2.754 18-29 0.063 x body mass (kg) + 2.896

13. Measuring BMR Females: Age BMR (MJ/day) 10-170.056 x body mass (kg) + 2.898 18-29 0.062 x body mass (kg) + 2.036

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

15. 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

16. Thermic effects of Food • Depends also on type & quantity of food eaten High carbohydrate meal 9% increase in EE High fat meal 3% 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. 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

18. 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!!

19. 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

20. 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

21. Effects of Physical Activity Short bursts of strenuous activity moderate activity of longer duration 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

22. 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

23. 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

24. Factors affecting total EE • Body size • Body composition • Age • Gender • Nutritional status • Pregnancy & lactation both increase total EE • Activity • Climate

25. Measurement of EE EE can be measured in various ways including: • Direct calorimetry • Indirect calorimetry • Heart rate recording

26. 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

27. Direct calorimetry Pros & cons: • Very accurate method • Very expensive • Very difficult to operate • Not suitable for most situations

28. 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

29. 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 20.93% O2 0.03% CO2 79.04% N2 Exhaled Air 16-18% O2 3-5% CO2 79.04% N2

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 O2 consumed. Assume O2 in inhaled air is 21% & exhaled air is 18% What is their EE? • Calculate % O2 in inhaled & exhaled air • Calculate volume of O2 used per min • Multiply by 20 (kJ) Answer 6kJ/min

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

32. Indirect calorimetry

33. 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

34. Heart Rate Recording • Measure HR over the period of exercise • Read off graph to get O2 consumption • Remember- 20kJ of energy is released when 1 litre of O2 consumed.

35. Heart Rate Recording Pros & cons: • Not as accurate as direct calorimetry • Still fairly accurate • Easier to carry out than direct calorimetry

36. Homework Energy Expenditure PS Questions • Hand in on 10th April 2008