Chapter 6

Measurement of Work, Power, and Energy Expenditure

Energy Consumption

Measures of energy consumption– Volume of oxygen consumed = VO2

– Maximal volume of oxygen consumed = VO2max

– L – min-1

– ml-kg-1-min-1

How do we measure energy?

Energy Consumption

Basal metabolic rate– Energy expended by all cells at rest

Exercise metabolic rateEnergy expended (ATP hydrolyzed) provides:– Kcals to perform work (e.g. muscular

contraction)– Heat

Energy Consumption

Fixed amount of energy results in a fixed amount of heat given offCalories – measure of heatCaloric value of nutrients is equivalent to the heat releasedBomb calorimeter-measured heat production in terms of calories– Bomb – chamber shape– Calorimetry – measurement of liberated heat

Energy Consumption

1 calorie is the heat required to raise the temperature of 1 g of water 1 oCOxygen consumption equals heat production– The amount of heat given off by the body

(whether rest or exercise) equals the volume of oxygen consumed (VO2)

Direct Calorimetry

Indirect Calorimetry

Measuring Energy

Direct calorimetry– Measure heat during various activities– Measure food energy values– Measure oxygen needed to metabolize food

Problems– Expensive and slow

Indirect calorimetry– Measures expired oxygen and carbon dioxide– Caloric expenditure

Indirect Calorimetry

Knowing the volume of oxygen consumed and carbon dioxide produced provides information about the fuel being metabolizedEstimates energy expenditure (kcal) based on the respiratory exchange of O2 and CO2

Respiratory Exchange Ratio (RER)

RER

Example– VO2 = 3.0 L-min-1

– VCO2 = 2.85 L-min-1

– 2.85/3.0 = .95Zuntz table (Fig 4.4, p. 83)

O2 Consumption and Recovery

Steady state exercise– Oxygen deficit– Oxygen debt

Excess post-exercise oxygen consumptionOxygen recovery

Gross oxygen consumption – Prior to deducting resting metabolic rate

Net oxygen consumption– After deducting resting metabolic rate

Oxygen Consumption and Recovery

Resting metabolic rate– VO2 for entire time (rest, exercise, recovery)

Total resting VO2– Add VO2 for each min of rest

.357 L-min-1 + .289 L-min-1 + .325 L-min-1 = .971 L

Mean resting VO2– Sum of VO2 for rest ÷ # minutes of rest– .971 L ÷ 3 min = .323 L-min-1

Oxygen Consumption and Recovery

Gross exercise VO2– Total VO2 for exercise time– 16.5 L– Mean VO2 for exercise time– 16.5 L ÷ 12 min = 1.375 L-min-1

Gross recovery VO2– Total VO2 for recovery– 11.0 L– Mean VO2 for recovery time– 11.0 L ÷ 5 min = 2.2 L-min-1

Oxygen Consumption and Recovery

Net oxygen cost of exercise– 16.5 L total oxygen cost of exercise– Subtract RMR– .323 L-min-1

– 12 min of exercise– .323 L-min-1 x 12 min = 3.876 L– 16.5 L – 3.876 = 12.62 L

Oxygen Consumption and Recovery

Net oxygen cost of recovery– 11 L total oxygen cost of recovery– Subtract RMR– .323 L-min-1

– 5 min of recovery– .323 L-min-1 x 5 min = 1.62 L– 11 L – 1.615 L = 9.39 L = oxygen debt

Oxygen Consumption and Recovery

Net oxygen cost of exercise per minute– 12.62 L ÷ 12 min = 1.05 L-min-1

Net oxygen cost of recovery per minute– 9.39 L ÷ 5 min = 1.88 L-min-1

Metabolic Equivalent

Energy cost of activities– Absolute oxygen consumption (L-min-1)– Relative oxygen consumption (ml-kg-1-min-1)