Transcript Chapter 6

Scott K. Powers • Edward T. Howley
Theory and Application to Fitness and Performance
SEVENTH EDITION
Chapter
Measurement of Work,
Power, and Energy
Expenditure
Presentation prepared by:
Brian B. Parr, Ph.D.
University of South Carolina Aiken
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Chapter 6
Objectives
1. Define the terms work, power, energy,
and net efficiency.
2. Give a brief explanation of the procedure
used to calculate work performed during:
(a) cycle ergometer exercise and (b)
treadmill exercise.
3. Describe the concept behind the
measurement of energy expenditure
using: (a) direct calorimetry and (b)
indirect calorimetry.
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Chapter 6
Objectives
4. Discuss the procedure used to estimate
energy expenditure during horizontal
treadmill walking and running.
5. Define the following terms: (a) kilogrammeter, (b) relative VO2, (c) MET, and (d)
open-circuit spirometry.
6. Describe the procedure used to calculate
net efficiency during steady-state
exercise.
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Chapter 6
Outline
 Units of Measure
Metric System
SI Units
 Work and Power
Defined
Work
Power
 Measurement of
Work and Power
 Measurement of
Energy
Expenditure
Direct Calorimetry
Indirect Calorimetry
 Estimation of
Energy
Expenditure
 Calculation of
Exercise
Efficiency
Factors That Influence
Exercise Efficiency
 Running Economy
Bench Step
Cycle Ergometer
Treadmill
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Chapter 6
Units of Measure
Units of Measure
• Metric system
– The standard system of measurement for
scientists
– Used to express mass, length, and volume
• System International (SI) units
– For standardizing units of measurement
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Chapter 6
Units of Measure
Common Metric System
Prefixes
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Chapter 6
Units of Measure
Important SI Units
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Chapter 6
Units of Measure
In Summary
 The metric system is the system of
measurement used by scientists to
express mass, length, and volume.
 In an effort to standardize terms for the
measurement of energy, force, work,
and power, scientists have developed a
common system of terminology called
System International (SI) units.
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Chapter 6
Work and Power Defined
Work
• Work = force x distance
• In SI units:
– Work (J) = force (N) x distance (m)
• Example:
– Lifting a 10-kg (97.9-N) weight up a distance
of 2 m
• 1 kg = 9.79 N, so 10 kg = 97.9 N
97.9 N x 2 m = 195.8 N-m = 195.8 J
• 1 N-m = 1 J, so 195.8 N-m = 195.8 J
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Chapter 6
Work and Power Defined
Common Units Used to Express Work
Performed or Energy Expenditure
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Chapter 6
Work and Power Defined
Power
• Power = work ÷ time
• In SI units:
– Power (W) = work (J) ÷ time (s)
• Example:
– Performing 20,000 J of work in 60 s
20,000 J ÷ 60 s = 333.33 J•s–1 = 333.33 W 1
W = 1 J•s–1, so 333.33 J•s–1 = 333.33 W
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Chapter 6
Work and Power Defined
Common Units Used to Express Power
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Chapter 6
Measurement of Work and Power
Measurement of Work and Power
• Ergometry
– Measurement of work output
• Ergometer
– Device used to measure work
•
•
•
•
Bench step ergometer
Cycle ergometer
Arm ergometer
Treadmill
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Chapter 6
Measurement of Work and Power
Ergometers used in the Measurement of
Human Work Output and Power
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Figure 6.1
Chapter 6
Measurement of Work and Power
Bench Step
• Subject steps up and down at specified rate
• Example:
– 70-kg subject, 0.5-m step, 30 steps•min–1 for 10
min
• Total work = force x distance
–1 = 685.3 N
– Force
= 150
70 kg
9.79 N•kg
685 N x
m =x102,795
J (or 102.8
kJ)
– Distance = 0.5 m•step–1 x 30 steps•min–1 x 10 min
= 150 m
102,795 J ÷ 600 s = 171.3 W
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Chapter 6
Measurement of Work and Power
Cycle Ergometer
• Stationary cycle that allows accurate
measurement of work performed
• Example:
– 1.5-kg (14.7-N) resistance, 6 m•rev–1, 60
rev•min–1 for 10 min
• Total work
14.7 N x 6 m•rev–1 x 60 rev•min–1 x 10 min = 52,920 J
52, 290 J ÷ 600 s = 88.2 W
• Power
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Chapter 6
Measurement of Work and Power
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
• 10% grade means 10 m vertical rise for 100 m of
belt travel
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Chapter 6
Measurement of Work and Power
Determination of Percent Grade on a
Treadmill
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Figure 6.2
Chapter 6
Measurement of Work and Power
Treadmill
• Example
– 60-kg (587.4-N) subject, speed 200 m•min–1,
7.5% grade for 10 min
– Vertical displacement = % grade x distance
0.075 x (200 m•min–1 x 10 min) = 150 m
– Work = body weight x total vertical distance
587.4 N x 150 m = 88,110 J
– Power = work ÷ time
88,110 J ÷ 600 s = 146.9 W
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Chapter 6
Measurement of Work and Power
In Summary
 An understanding of terms work and power
is necessary in order to compute human
work output and the associated exercise
efficiency.
 Work is defined as the product of force times
distance:
Work = force x distance
 Power is defined as work divided by time:
Power = work ÷ time
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Chapter 6
Measurement of Work and Power
Measurement of Energy Expenditure
• Direct calorimetry
– Measurement of heat production as an
indication of metabolic rate
Foodstuffs + O2  ATP + heat
cell work
Heat
– Commonly measured in calories
• 1 kilocalorie (kcal) = 1,000 calories
• 1 kcal = 4,186 J or 4.186 kJ
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Chapter 6
Measurement of Work and Power
Diagram of a Simple Calorimeter
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Figure 6.3
Chapter 6
Measurement of Work and Power
Measurement of Energy Expenditure
• Indirect calorimetry
– Measurement of oxygen consumption as an
estimate of resting metabolic rate
Foodstuffs + O2  Heat + CO2 + H2O
• VO2 of 2.0 L•min–1 = ~10 kcal or 42 kJ per minute
– Open-circuit spirometry
• Determines VO2 by measuring amount of O2
consumed
• VO2 = volume of O2 inspired – volume of O2
expired
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Chapter 6
Measurement of Work and Power
Open-Circuit Spirometry
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Figure 6.4
Chapter 6
Measurement of Work and Power
In Summary
 Measurement of energy expenditure at rest
or during exercise is possible using either
direct or indirect calorimetry.
 Direct calorimetry uses the measurement of
heat production as an indication of metabolic
rate.
 Indirect calorimetry estimates metabolic rate
via the measurement of oxygen
consumption.
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Chapter 6
Estimation of Energy Expenditure
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 metabolic
equivalents (MET)
– 1 MET = energy cost at rest
– 1 MET = 3.5 ml•kg–1•min–1
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Chapter 6
Estimation of Energy Expenditure
The Relationship Between Walking or
Running Speed and VO2
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Figure 6.5
Estimation of Energy Expenditure
Chapter 6
Estimation of the O2 Requirement of Treadmill Walking
•
•
•
Horizontal VO2 (ml•kg–1•min–1)
– 0.1 ml•kg–1•min–1/m•min–1 x speed (m•min–1) + 3.5 ml•kg–1•min–1
Vertical VO2 (ml•kg–1•min–1)
– 1.8 ml•kg–1•min–1 x speed (m•min–1) x % grade
Example:
– Walking at 80 m•min–1 at 5% grade
0.1 ml•kg–1•min–1 x 80 m•min–1 + 3.5 ml•kg–1•min–1 = 11.5 ml•kg–1•min–1
– Horizontal VO2:
1.8 ml•kg–1•min–1 x 80 m•min–1 x 0.05 = 7.2 ml•kg–1•min–1
Vertical VO2:
– Total VO2:
11.5 ml•kg–1•min–1 + 7.2 ml•kg–1•min–1 = 18.7 ml•kg–1•min–1
(or 5.3 METs)
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Chapter 6
Estimation of Energy Expenditure
Estimation of the O2 Requirement of Treadmill Running
• Horizontal VO2 (ml•kg–1•min–1)
– 0.2 ml•kg–1•min–1/m•min–1 x speed (m•min–1) + 3.5 ml•kg–1•min–1
• Vertical VO2 (ml•kg–1•min–1)
– 0.9 ml•kg–1•min–1 x speed (m•min–1) x % grade
• Example:
– Running at 160 m•min–1 at 5% grade
– Horizontal VO2:
0.2 ml•kg–1•min–1 x 160 m•min–1 + 3.5 ml•kg–1•min–1 = 35.5 ml•kg–1•min–1
– Vertical VO2:
0.9 ml•kg–1•min–1 x 160 m•min–1 x 0.05 = 7.2 ml•kg–1•min–1
– Total VO2:
11.5 ml•kg–1•min–1 + 7.2 ml•kg–1•min–1 = 42.7 ml•kg–1•min–1
(or 12.2 METs)
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Chapter 6
Estimation of Energy Expenditure
Relationship Between Work Rate and VO2
for Cycling
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Figure 6.6
Chapter 6
Estimation of Energy Expenditure
Estimation of the O2 Requirement of Cycling
• Comprised of three components:
– Resting VO2
• 3.5 ml•kg–1•min–1
– VO2 for unloaded cycling
• 3.5 ml•kg–1•min–1
– VO2 of cycling against external load
• 1.8 ml•min–1 x work rate x body mass–1
• Equation:
VO2 (ml•kg–1•min–1) = 1.8 x work rate x M–1 + 7
• Work rate in kpm•min–1
• M = body mass in kg
• 7 = sum of resting VO2 and VO2 of unloaded
cycling
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Chapter 6
Estimation of Energy Expenditure
In Summary
 The energy cost of horizontal treadmill
walking or running can be estimated with
reasonable accuracy because the O2
requirements of both walking and running
increase as a linear function of speed.
 The need to express the energy cost of
exercise in simple terms has led to the
development of the term MET. One MET is
equal to the resting VO2
(3.5 ml•kg–
1•min–1).
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Chapter 6
Calculation of Exercise Efficiency
Calculation of Exercise Efficiency
• Net efficiency
– Ratio of work output divided by energy expended
above rest
Work output
% net efficiency =
x 100
Energy expended
above rest
• Net efficiency of cycle ergometry
– 15–27%
• Efficiency decreases with increasing work rate
– Curvilinear relationship between work rate and energy
expenditure
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Chapter 6
Calculation of Exercise Efficiency
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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Chapter 6
Calculation of Exercise Efficiency
Net Efficiency During Arm Crank Ergometery
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Figure 6.7
Chapter 6
Calculation of Exercise Efficiency
Relationship Between Energy Expenditure
and Work Rate
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Figure 6.8
Chapter 6
Calculation of Exercise Efficiency
Effect of Speed of Movement of Net
Efficiency
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Figure 6.9
Chapter 6
Calculation of Exercise Efficiency
In Summary
 Net efficiency is defined as the mathematical ratio of
work performed divided by the energy expenditure
above rest, and is expressed as a percentage.
 The efficiency of exercise decreases as the exercise
work rate increases. This occurs because the
relationship between work rate and energy
expenditure is curvilinear.
 To achieve maximal efficiency at any work rate, there
is an optimal speed of movement.
 Exercise efficiency is greater in subjects who
possess a high percentage of slow muscle fibers
compared to subjects with a high percentage of fast
fibers. This is due to the fact that slow muscle fibers
are more efficient than fast fibers.
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Chapter 6
Running Economy
Running Economy
• Not possible to calculate net efficiency of
horizontal running
• Running Economy
– Oxygen cost of running at given speed
– Lower VO2 (ml•kg–1•min–1) at same speed
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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Chapter 6
Running Economy
Comparison of Running Economy Between
Males and Females
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Figure 6.10
Chapter 6
Running Economy
In Summary
 Although is is not easy to compute efficiency
during horizontal running, the measurement
of the O2 cost of running (ml•kg–1•min–1) at
any given speed offers a measure of running
economy.
 Running economy does not differ between
highly trained men and women distance
runners at slow running speeds. However, at
fast “race pace” speeds, male runners may
be more economical than females. The
reasons for this are unclear.
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