week 3-energy expenditure

why measure energy expenditure

assesses metabolic needs

insight into the demands of exercise

fuel utilisation

thermic effects of food

nutritional intervention

assessment of economy

calories

amount of energy required to raise temperature of 1g of water by 1 degree Celsius

bomb calorimeter

measures heat of combustion under controlled conditions

direct calorimetry

water around the walls of the exercise chamber, measure heat

advantages of direct calorimetry

direct measure of heat

accurate for steady state measures

disadvantages of direct calorimetry

expensive

slow to generate results

few in operation

accurate for exercise? calculates average over time

indirect calorimetry

predicts substrate use, kilocalories and O2 efficiency

advantages of indirect calorimetry

can detect changes during exercise with breath by breath systems

no longer affected by the heat of equipment

easy to administer

fairly accurate for aerobic measures

direct assessments of gas exchange

caloric equivalents for oxygen

fat gives us the most energy per gram

fat also costs the most oxygen per kilocalorie

disadvantages of indirect calorimetry

ASSUMES:- Body’s O2 content constant- CO2 exchange in lung is proportional to release from cells aerobic processes

BUT:- CO2 released in the lung may not be representative of CO2 released by working cells.- Body has O2 stores not directly reflected in pulmonary measures

ASSUMES:- Little contribution from protein during exercise (Non protein RER)

BUT:- Protein contributes up to 5% of total energy in prolonged exercise.

RER values >1 won’t provide a valid estimation of energy expenditure.- even values approaching 1 may be inaccurate in assessing energy expenditure

Gluconeogenesis from catabolism of fat and amino acid produces RER < 0.7

RER not appropriate for EE estimations outside range of 0.7-1

Basal Metabolic Rate

2-3% decrease in metabolic rate per decade

Decrease in fat free mass

Depression of metabolic activity of lean tissues

Altered by change in body composition (increase FFM)

Altered by physical activity (independent of change in body comp)

Resting Metabolic Rate

less tightly controlled v BMR

more accessible/applicable

MET

multiples of RMR

1 MET = 3.5ml/kg/min

Fat max

Facilitation of fat metabolism important for health and performance

Exercise intensity at which maximal fat oxidation is observed “Fatmax” Explained by:

Lower availability of plasma FFA

Reduced entry of fatty acids into mitochondria

EE for performance

Slower recreational runners (3h 45m) run at 60-65% VO2max - RER = 0.9 – CHO 68%

Faster athletes (2h 45min) run at 70-75% VO2max RER = 0.95 – CHO 84%

Elite runners run at 80-90% of VO2max for 2.02 to 2.10

Possible that these athletes could compete marathon using only CHO as fuel (RER = 1)

Mechanical efficiency

(external work accomplished) ÷ (energy expenditure)

Average value for cycling, running, walking: 20 – 25% Example:

- Cycling: 160 Watts: ~ 2.29 kcal/min

- Oxygen uptake at 160 Watts: ~2.0 L/min

- 2.0 L/min equivalent to 10 kcal/min (as ~5kcal per litre O2)

Mechanical efficiency: 2.29/10 =22.9%

Swimming (more drag): <20%

importance of efficiency

Relationship between ̇ VO2max and performance not evident in homogenous group of runners

BUT there is a relationship between running economy and performance

Although V ̇O2max similar between elites RE varies up to 30% (Morgan et al., 1995)

EPOC

Excess Post Oxygen Consumption

oxygen deficit

fast portion: 2-3-mins after exercise

slow portion: up to an hour following exercise

ultraslow portion: lasts several hours

fast portion of EPOC

• resynthesis of ATP and PC

• O2 levels restored to myoglobin and haemoglobin

• thermogenic effects of hormones

slow portion of EPOC

• thermogenic effects of elevated core temperature

• resynthesis of lactate to glycogen

• HR and VE remain elevated for several minutes after exercise