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Exercise Physiology > Energy Balance and Substrate Metabolism > Flashcards

Energy Balance and Substrate Metabolism Flashcards

1
Q

Energy Intake

A

Protein - 15%

Fat - 30-35%

Carbohydrate - 45-50%

Ethanol - 5%

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2
Q

Energy Expenditure

A

Resting metabolic rate

Diet induced thermogenesis

Physical activity energy expenditure

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3
Q

Energy stores

A

Fat

Carbohydrate

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4
Q

Energy store - Fat

A

4.4g in blood

12kg in adipose tissue

300g in muscle - intramuscular triglyceride

> 100,000 kcal

Can be increased to >400,000 kcal

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5
Q

Energy store - Carbohydrate

A

5g in blood

350-700g in muscle - stored alongside water

100g in liver - can be released in circulation

<3200 kcal

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6
Q

What is leptin?

A

Hormone secreted by adipocytes and enterocytes

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7
Q

Function of leptin

A

Regulates energy balance by inhibiting hunger

Acts on cell receptors of the hypothalamus

By injecting leptin, fat mass starts to decrease

Increase in leptin, leads to increase in leptin in order to decrease energy intake

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8
Q

FTO Gene

A

Fat mass and obesity

Having both alleles predisposes you to carry extra weight

Genetic variations act through energy balance

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9
Q

Methods of measuring intake

A

Covert

Overt

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10
Q

Covert methods of measuring intake

A

Researcher weighs food without participants knowing

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11
Q

Overt methods of measuring intake

A

Researcher weighs food and tells participant

Participant weighed

Participant recall

Participant Food Frequency Questionnaire

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12
Q

Energy density of food

A

CHO ~ 4 kcal/g

Fat ~ 9 kcal/g

Protein ~ 4 kcal/g

Ethanol ~ 7 kcal/g

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13
Q

Impact of Macronutrient Composition

A

Alters energy intake independent of energy density

Higher protein intake can suppress appetite and energy intake when in exchange of CHO

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14
Q

Measuring energy expenditure

A

Laboratory

Free Living

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15
Q

Laboratory methods of measuring energy expenditure

A

Indirect calorimetry

  • Foodstuff
  • O2

Direct calorimetry

  • Heat
  • CO2
  • H2O
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16
Q

Free living methods of measuring energy expenditure

A

Physical activity questionnaires

Doubly labelled water

Pedometers

Accelerometer

Actiheart

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17
Q

Accelerometers and Actiheart

A

Allow to see difference between intensities of exercise and sedentary time

18
Q

Doubly labelled water

A

Ingest 2H218O - heavy water - extra neuron

18O is lost in expired CO2 and water

2H lost in water only

Difference represents average expired CO2 over time period

19
Q

Strength of doubly labelled water

A

CO2 production over free-living conditions

20
Q

Weaknesses of doubly labelled water

A

Assume RER to determine O2 consumption

Average VCO2 over time

21
Q

Lean Mass

A

Primary determinant of resting metabolic rate

Each kg of muscle is responsible for ~13 kcal/d

22
Q

Metabolic Adaptation

A

The reduction in RMR during energy restriction

Attenuated when adjusted for body cell mass

23
Q

Diet Induced Thermogenesis

A

Fat - 0-3%

Carbohydrate - 5-10%

Protein - 20-30%

Ethanol

  • Dehydrogenase pathway ~ 12%
  • Microsomal ethanol oxidising system ~ 28%
24
Q

Physical activity

A

Most variable component of energy expenditure

Major determinant of muscle mass

25
Q

Tissue Specific Substrate Metabolism

A

Muscle biopsy

[6,6-2H2] glucose, stable isotope injection

[U-13C] glucose drink

26
Q

Muscle biopsy

A

CHO utilisation

Calculate pre- and post- glycogen levels

27
Q

[6,6-2H2] glucose, stable isotope injection

A

Fatty acid kinetics

Liver glucose output

28
Q

[U-13C] glucose drink

A

CHO oxidation detected in breath

29
Q

Measuring liver glycogen use

A

Liver glycogen concentration decreases with CHO restriction

Increases dramatically with CHO refeeding

Liver biopsy is too dangerous

13C Magnetic Resonance Spectrometry

30
Q

Exercise Intensity

A

Primary regulator of substrate metabolism

As intensity increases, oxidation rate of plasma glucose and muscle glycogen increases

Fat oxidation decreases as intensity increases

Most elite events would be mainly reliant on CHO

31
Q

Factors that influence substrate metabolism

A

Intensity and duration of exercise

Nutritional status

Training status

Biological sex

Mode of exercise

Environmental temperature and altitude

32
Q

Wallis et al., 2006

A

CHO intake suppresses fat oxidation during cycling exercise

Found that women oxidise more fat than men - linked to oestrogen

33
Q

Areta & Hopkins, 2018

A

Training status and diet influence muscle glycogen content

Even on low CHO diet, those with a higher VO2max have higher muscle glycogen content

Training status and exercise intensity influence muscle glycogen utilisation

People that are more endurance trained use muscle glycogen more sparingly during moderate to high intensity exercise

Untrained individuals rely more on liver glycogen

34
Q

Increasing contribution from circulating fuels with exercise duration

A

Diagram

35
Q

Regulation of glycogen metabolism

A

Diagram

36
Q

Muscle Glycogen Stores

A

Subsarcolemmal stores

Intermyofibrillar stores

Intramyofibrillar stores

37
Q

Buchholz & Schoellar, 2004

A

The substitution of one macronutrient for another has been shown to have a statistically significant effect on energy expenditure part of energy balance equation, mainly high-protein diets.

38
Q

Hall & Guo, 2017

A

Meta-analysis of 32 controlled feeding studies with substitution of CHO for fat to review components of energy balance and mechanisms to resist weight loss

Influence of exercise on energy expenditure and body weight

Reductions in energy intake lead to decreased energy expenditure greater than expected due to metabolic adaptation

Energy expenditure (26 kcal/d) and fat loss (16 g/d) were greater with low fat diets

39
Q

Influence of exercise on energy expenditure and body weight (Hall & Guo, 2017)

A

Large amounts of exercise are required to result in modest weight loss

Leads to loss of body fat and maintenance of FFM

Individual weight changes are highly variable

Energy expended during exercise is variably compensated by changes in food intake and non-exercise physical activity behaviours

Biomechanical efficiency improvements may decrease cost of exercise, meaning energy expenditure does not progress as exercise does

40
Q

Jeppesen & Kiens, 2012

A

Focus on the limitations in fatty acid oxidation in the transition from moderate to high intensity exercise

Inability of fatty acid oxidation to support energy demand during high intensity exercise could be due to:

  • Failure of adipose tissue lipolysis
  • Limitation in skeletal muscle to oxidise fatty acids

Regulatory candidate for fatty acid oxidation is muscle metabolite carnitine, which is essential for CPT-1 regulation

At high intensity exercise, rapid glycolysis provides mitochondria with excessive acetyl-CoA, which is buffered by free carnitine to form acetylcarnitine

Fall in concentration of free carnitine may reduce CPT-1 activity, so the ability to transport fatty acids into mitochondria

Therefore, rapid glycogen breakdown and glycolysis are suggested to have a major impact on inhibiting fatty acid oxidation

Exercise Physiology (1 decks)

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