Chapter 6 Measurement of Work, Power, and Energy Expenditure

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Chapter 6Measurement of Work, Power, and Energy
Expenditure

• EXERCISE PHYSIOLOGY
• Theory and Application to Fitness and
  Performance, 6th edition
• Scott K. Powers Edward T. Howley

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Units of Measure

• Metric system is the standard system of
  measurement for scientists
• Used to express mass, length, and volume
• System International units or SI units
• For standardizing units of measurement

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Important SI Units

• Units for Quantifying
• Human Exercise SI Unit
• Mass kilogram (kg)
• Distance meter (m)
• Time second (s)
• Force Newton (N)
• Work joule (J)
• Energy joule (J)
• Power Watt (W)
• Velocity meters per second (m . s-1)
• Torque newton-meter (N . m)

Table 6.2
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Work and Power

• Work force x distance
• Example
• Lifting a 5 kg (5 kp) weight up a distance of 2
  m
• 5 kp is the force acting on a 5 kg mass
• 5 kp x 2 m 10 kpm
• Power work time
• Example
• Performing 2,000 kgm of work in 60 sec
• 2,000 kgm 60s 33.33 kgms-1
• Expressed in SI Units
• 1 Watt (W) 0.102 kpms-1, so 326.8 W

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Measurement of Work and Power

• Ergometry
• Measurement of work output
• Ergometer
• Device used to measure work
• Bench step ergometer
• Cycle ergometer
• Treadmill

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Ergometer
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Bench Step

• Subject steps up and down at specified rate
• Example
• 70 kg subject, 0.5 m step, 30 stepsmin-1 for 10
  min
• Total work
• 70 kg x 0.5 mstep-1 x 30 stepsmin-1 x 10 min
  10,500 kpm
• Power
• 10,500 kpm 10 min 1,050 kpmmin-1 or 171.6 W

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Cycle Ergometer

• Stationary cycle that allows accurate measurement
  of work performed
• Example
• 1.5 kp resistance, 6 mrev-1, 60 revmin-1 for 10
  min
• Total work
• 1.5 kp x 6 mrev-1 x 60 revmin-1 x 10 min
  5,400 kpm
• Power
• 5,400 kpm 10 min 540 kpmmin-1 or 88.2 W

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Treadmill

• Calculation of work performed while a subject
  runs or walks on a treadmill is not generally
  possible when the treadmill is horizontal
• Even though running horizontal on a treadmill
  requires energy
• Quantifiable work is being performed when walking
  or running up a slope
• Incline of the treadmill is expressed in percent
  grade
• Amount of vertical rise per 100 units of belt
  travel

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Determination of Percent Grade on a Treadmill
Figure 6.2
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Treadmill

• Example
• 70 kg subject, treadmill speed 200 mmin-1, 7.5
  grade for 10 min
• Vertical displacement grade x distance
• 0.75 x 200 mmin-1 15 m
• Total vertical distance vertical displacement x
  time
• 15 m x 10 min 150 m
• Work body weight x total vertical distance
• 70 kg x 150 m 10,500 kpm
• Power work time
• 10,500 kpm 10 min 1,050 kpmmin-1

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Measurement of Energy Expenditure

• Direct calorimetry
• Measurement of heat production as an indication
  of metabolic rate
• Indirect calorimetry
• Measurement of oxygen consumption as an estimate
  of resting metabolic rate
• Open-circuit spirometry

Foodstuffs O2 ? Heat CO2 H2O
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Diagram of a Simple Calorimeter
Figure 6.3
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Open-Circuit Spirometry
Figure 6.4
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Estimation of Energy Expenditure

• Energy cost of horizontal treadmill walking or
  running
• O2 requirement increases as a linear function of
  speed
• Expression of energy cost in METs
• 1 MET energy cost at rest
• 1 MET 3.5 mlkg-1min-1

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The Relationship Between Walking or Running Speed
and VO2
Figure 6.5
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Relationship Between Work Rate and VO2 for Cycling
Figure 6.6
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Calculation of Exercise Efficiency

• Net efficiency
• Ratio of work output divided by energy expended
  above rest
• Net efficiency of cycle ergometry
• 15-27

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Factors That Influence Exercise Efficiency

• Exercise work rate
• Efficiency decreases as work rate increases
• Speed of movement
• There is an optimum speed of movement and any
  deviation reduces efficiency
• Muscle fiber type
• Higher efficiency in muscles with greater
  percentage of slow fibers

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Net Efficiency During Arm Crank Ergometery
Figure 6.8
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Relationship Between Energy Expenditure and Work
Rate
Figure 6.9
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Effect of Speed of Movement of Net Efficiency
Figure 6.10
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Running Economy

• Not possible to calculate net efficiency of
  horizontal running
• Running Economy
• Oxygen cost of running at given speed
• Lower VO2 (mlkg-1min-1) indicates better
  running economy
• Gender difference
• No difference at slow speeds
• At race pace speeds, males may be more
  economical that females

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Comparison of Running Economy Between Males and
Females
Figure 6.11