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 rate
Energy 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 off
Calories – measure of heat
Caloric value of nutrients is equivalent to
the heat released
Bomb 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 oC
Oxygen 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
metabolized
Estimates 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 = .95
Zuntz table (Fig 4.4, p. 83)
O2 Consumption and Recovery
Steady state exercise
– Oxygen deficit
– Oxygen debt
Excess post-exercise oxygen consumption
Oxygen 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)