Scott K. Powers • Edward T. HowleyScott K. Powers • Edward T. Howley
Theory and Application to Fitness and PerformanceTheory and Application to Fitness and PerformanceSEVENTH EDITION
Chapter
Presentation prepared by:
Brian B. Parr, Ph.D.University of South Carolina Aiken
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Measurement of Work, Measurement of Work, Power, and Energy Power, and Energy
ExpenditureExpenditure
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ObjectivesObjectives1. 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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ObjectivesObjectives
4. Discuss the procedure used to estimate energy expenditure during horizontal treadmill walking and running.
5. Define the following terms: (a) kilogram-meter, (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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OutlineOutline
Units of MeasureMetric SystemSI Units
Work and Power DefinedWorkPower
Measurement of Work and PowerBench StepCycle ErgometerTreadmill
Measurement of Energy ExpenditureDirect CalorimetryIndirect Calorimetry
Estimation of Energy Expenditure
Calculation of Exercise EfficiencyFactors That Influence Exercise Efficiency
Running Economy
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Units of MeasureUnits 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
Units of Measure
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Common Metric System Common Metric System PrefixesPrefixes
Units of Measure
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Important SI UnitsImportant SI UnitsUnits of Measure
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In SummaryIn 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.
Units of Measure
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WorkWork• 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
Work and Power Defined
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Common Units Used to Express Work Common Units Used to Express Work Performed or Energy ExpenditurePerformed or Energy Expenditure
Work and Power Defined
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PowerPower
• 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
Work and Power Defined
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Common Units Used to Express PowerCommon Units Used to Express Power
Work and Power Defined
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Measurement of Work and PowerMeasurement of Work and Power
• Ergometry– Measurement of work output
• Ergometer– Device used to measure work
• Bench step ergometer• Cycle ergometer• Arm ergometer• Treadmill
Measurement of Work and Power
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Ergometers used in the Measurement of Ergometers used in the Measurement of Human Work Output and PowerHuman Work Output and Power
Figure 6.1
Measurement of Work and Power
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Bench StepBench 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
– Force = 70 kg x 9.79 N•kg–1 = 685.3 N– Distance = 0.5 m•step–1 x 30 steps•min–1 x 10 min = 150
m
• Power = work ÷ time
Measurement of Work and Power
685 N x 150 m = 102,795 J (or 102.8 kJ)
102,795 J ÷ 600 s = 171.3 W
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Cycle ErgometerCycle 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
• Power
14.7 N x 6 m•rev–1 x 60 rev•min–1 x 10 min = 52,920 J52, 290 J ÷ 600 s = 88.2 W
Measurement of Work and Power
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Treadmill 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
Measurement of Work and Power
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Determination of Percent Grade on a Determination of Percent Grade on a TreadmillTreadmill
Figure 6.2
Measurement of Work and Power
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Treadmill 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
Measurement of Work and Power
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In SummaryIn 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
Measurement of Work and Power
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• Direct calorimetry– Measurement of heat production as an
indication of metabolic rate
– Commonly measured in calories• 1 kilocalorie (kcal) = 1,000 calories• 1 kcal = 4,186 J or 4.186 kJ
Measurement of Energy ExpenditureMeasurement of Energy Expenditure
Foodstuffs + O2 ATP + heatcell work
Heat
Measurement of Work and Power
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Diagram of a Simple CalorimeterDiagram of a Simple Calorimeter
Measurement of Work and Power
Figure 6.3
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• Indirect calorimetry– Measurement of oxygen consumption as an
estimate of resting metabolic rate
• 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
Measurement of Energy ExpenditureMeasurement of Energy Expenditure
Foodstuffs + O2 Heat + CO2 + H2O
Measurement of Work and Power
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Open-Circuit SpirometryOpen-Circuit SpirometryMeasurement of Work and Power
Figure 6.4
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In SummaryIn 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.
Measurement of Work and Power
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Estimation of Energy ExpenditureEstimation 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
Estimation of Energy Expenditure
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The Relationship Between Walking or The Relationship Between Walking or Running Speed and VORunning Speed and VO22
Figure 6.5
Estimation of Energy Expenditure
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Estimation of the OEstimation of the O22 Requirement of Treadmill Walking 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
– Horizontal VO2:
Vertical VO2:
– Total VO2:
Estimation of Energy Expenditure
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
1.8 ml•kg–1•min–1 x 80 m•min–1 x 0.05 = 7.2 ml•kg–1•min–1
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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Estimation of the OEstimation of the O22 Requirement of Treadmill Running 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:
– Vertical VO2:
– Total VO2:
Estimation of Energy Expenditure
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
0.9 ml•kg–1•min–1 x 160 m•min–1 x 0.05 = 7.2 ml•kg–1•min–1
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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Relationship Between Work Rate and VORelationship Between Work Rate and VO2 2
for Cyclingfor Cycling
Figure 6.6
Estimation of Energy Expenditure
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• 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:
• Work rate in kpm•min–1
• M = body mass in kg• 7 = sum of resting VO2 and VO2 of unloaded cycling
Estimation of Energy Expenditure
VO2 (ml•kg–1•min–1) = 1.8 x work rate x M–1 + 7
Estimation of the OEstimation of the O22 Requirement of Cycling Requirement of Cycling
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In SummaryIn 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).
Estimation of Energy Expenditure
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• Net efficiency– Ratio of work output divided by 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
Work outputEnergy expended
above rest
% net efficiency = x 100
Calculation of Exercise EfficiencyCalculation of Exercise EfficiencyCalculation of Exercise Efficiency
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Calculation of Exercise Efficiency
Factors That Influence Exercise EfficiencyFactors 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 Net Efficiency During Arm Crank ErgometeryErgometery
Calculation of Exercise Efficiency
Figure 6.7
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Relationship Between Energy Expenditure Relationship Between Energy Expenditure and Work Rateand Work Rate
Calculation of Exercise Efficiency
Figure 6.8
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Effect of Speed of Movement of Net Effect of Speed of Movement of Net EfficiencyEfficiency
Calculation of Exercise Efficiency
Figure 6.9
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In SummaryIn 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.
Calculation of Exercise Efficiency
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Running EconomyRunning 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
Running Economy
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Comparison of RunningComparison of Running Economy Between Economy Between Males and FemalesMales and Females
Running Economy
Figure 6.10
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In SummaryIn 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.
Running Economy
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