Scott K. Powers Edward T. Howley Theory and Application to Fitness and Performance SEVENTH EDITION Chapter Copyright ©2009 The McGraw-Hill Companies, Inc. Permission required for reproduction or display outside of classroom use. Measurement of Work, Power, and Energy Expenditure

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. 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.

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Objectives 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 VO 2, (c) MET, and (d) open-circuit spirometry. 6.Describe the procedure used to calculate net efficiency during steady-state exercise.

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Outline  Units of Measure Metric System SI Units  Work and Power Defined Work Power  Measurement of Work and Power Bench Step Cycle Ergometer Treadmill  Measurement of Energy Expenditure Direct Calorimetry Indirect Calorimetry  Estimation of Energy Expenditure  Calculation of Exercise Efficiency Factors That Influence Exercise Efficiency  Running Economy

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. 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 Units of Measure

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Common Metric System Prefixes Units of Measure

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Important SI Units Units of Measure

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. 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. Units of Measure

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. 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 = N-m = J 1 N-m = 1 J, so N-m = J Work and Power Defined

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Common Units Used to Express Work Performed or Energy Expenditure Work and Power Defined

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. 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 = Js –1 = W 1 W = 1 Js –1, so Js –1 = W Work and Power Defined

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Common Units Used to Express Power Work and Power Defined

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Measurement 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

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Ergometers used in the Measurement of Human Work Output and Power Figure 6.1 Measurement of Work and Power

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. 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 = force x distance –Force = 70 kg x 9.79 Nkg –1 = N –Distance = 0.5 mstep –1 x 30 stepsmin –1 x 10 min = 150 m Power = work ÷ time Measurement of Work and Power 685 N x 150 m = 102,795 J (or kJ) 102,795 J ÷ 600 s = W

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Cycle Ergometer Stationary cycle that allows accurate measurement of work performed Example: –1.5-kg (14.7-N) resistance, 6 mrev –1, 60 revmin –1 for 10 min Total work Power 14.7 N x 6 mrev –1 x 60 revmin –1 x 10 min = 52,920 J 52, 290 J ÷ 600 s = 88.2 W Measurement of Work and Power

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. 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

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Determination of Percent Grade on a Treadmill Figure 6.2 Measurement of Work and Power

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Treadmill Example –60-kg (587.4-N) subject, speed 200 mmin –1, 7.5% grade for 10 min –Vertical displacement = % grade x distance x (200 mmin –1 x 10 min) = 150 m –Work = body weight x total vertical distance N x 150 m = 88,110 J –Power = work ÷ time 88,110 J ÷ 600 s = W Measurement of Work and Power

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. 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 Measurement of Work and Power

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. 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 kJ Measurement of Energy Expenditure Foodstuffs + O 2  ATP + heat cell work Heat Measurement of Work and Power

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Diagram of a Simple Calorimeter Measurement of Work and Power Figure 6.3

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Indirect calorimetry –Measurement of oxygen consumption as an estimate of resting metabolic rate VO 2 of 2.0 Lmin –1 = ~10 kcal or 42 kJ per minute –Open-circuit spirometry Determines VO 2 by measuring amount of O 2 consumed VO 2 = volume of O 2 inspired – volume of O 2 expired Measurement of Energy Expenditure Foodstuffs + O 2  Heat + CO 2 + H 2 O Measurement of Work and Power

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Open-Circuit Spirometry Measurement of Work and Power Figure 6.4

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. 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. Measurement of Work and Power

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Estimation of Energy Expenditure Energy cost of horizontal treadmill walking or running –O 2 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 mlkg –1 min –1 Estimation of Energy Expenditure

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. The Relationship Between Walking or Running Speed and VO 2 Figure 6.5 Estimation of Energy Expenditure

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Estimation of the O 2 Requirement of Treadmill Walking Horizontal VO 2 (mlkg –1 min –1 ) –0.1 mlkg –1 min –1 /mmin –1 x speed (mmin –1 ) mlkg –1 min –1 Vertical VO 2 (mlkg –1 min –1 ) –1.8 mlkg –1 min –1 x speed (mmin –1 ) x % grade Example: –Walking at 80 mmin –1 at 5% grade –Horizontal VO 2 : Vertical VO 2 : –Total VO 2: Estimation of Energy Expenditure 0.1 mlkg –1 min –1 x 80 mmin – mlkg –1 min –1 = 11.5 mlkg –1 min –1 1.8 mlkg –1 min –1 x 80 mmin –1 x 0.05 = 7.2 mlkg –1 min – mlkg –1 min – mlkg –1 min –1 = 18.7 mlkg –1 min –1 (or 5.3 METs)

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Estimation of the O 2 Requirement of Treadmill Running Horizontal VO 2 (mlkg –1 min –1 ) –0.2 mlkg –1 min –1 /mmin –1 x speed (mmin –1 ) mlkg –1 min –1 Vertical VO 2 (mlkg –1 min –1 ) –0.9 mlkg –1 min –1 x speed (mmin –1 ) x % grade Example: –Running at 160 mmin –1 at 5% grade –Horizontal VO 2 : –Vertical VO 2 : –Total VO 2: Estimation of Energy Expenditure 0.2 mlkg –1 min –1 x 160 mmin – mlkg –1 min –1 = 35.5 mlkg –1 min –1 0.9 mlkg –1 min –1 x 160 mmin –1 x 0.05 = 7.2 mlkg –1 min – mlkg –1 min – mlkg –1 min –1 = 42.7 mlkg –1 min –1 (or 12.2 METs)

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Relationship Between Work Rate and VO 2 for Cycling Figure 6.6 Estimation of Energy Expenditure

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Comprised of three components: –Resting VO mlkg –1 min –1 –VO 2 for unloaded cycling 3.5 mlkg –1 min –1 –VO 2 of cycling against external load 1.8 mlmin –1 x work rate x body mass –1 Equation: Work rate in kpmmin –1 M = body mass in kg 7 = sum of resting VO 2 and VO 2 of unloaded cycling Estimation of Energy Expenditure VO 2 (mlkg –1 min –1 ) = 1.8 x work rate x M –1 + 7 Estimation of the O 2 Requirement of Cycling

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. In Summary  The energy cost of horizontal treadmill walking or running can be estimated with reasonable accuracy because the O 2 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 VO 2 (3.5 mlkg – 1 min –1 ). Estimation of Energy Expenditure

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. 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 output Energy expended above rest % net efficiency = x 100 Calculation of Exercise Efficiency

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. 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

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Net Efficiency During Arm Crank Ergometery Calculation of Exercise Efficiency Figure 6.7

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Relationship Between Energy Expenditure and Work Rate Calculation of Exercise Efficiency Figure 6.8

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Effect of Speed of Movement of Net Efficiency Calculation of Exercise Efficiency Figure 6.9

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. 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. Calculation of Exercise Efficiency

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Running Economy Not possible to calculate net efficiency of horizontal running Running Economy –Oxygen cost of running at given speed –Lower VO 2 (mlkg –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

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. Comparison of Running Economy Between Males and Females Running Economy Figure 6.10

Chapter 6 Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved. In Summary  Although is is not easy to compute efficiency during horizontal running, the measurement of the O 2 cost of running (mlkg –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