1. Measurement of Work, Power, and Energy Expenditure

2. Objectives Define the terms work, power, energy, and net efficiency.
Give a brief explanation of the procedure used to calculate work performed during: (a) cycle ergometer exercise and (b) treadmill exercise.
Describe the concept behind the measurement of energy expenditure using: (a) direct calorimetry and (b) indirect calorimetry.

3. Objectives
Discuss the procedure used to estimate energy expenditure during horizontal treadmill walking and running.
Define the following terms: (a) kilogram-meter, (b) relative VO2, (c) MET, and (d) open-circuit spirometry.
Describe the procedure used to calculate net efficiency during steady-state exercise.

4. Outline Units of Measure Measurement of Energy Expenditure
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

5. 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

6. Common Metric System Prefixes
Units of Measure
Common Metric System Prefixes

7. Units of Measure
Important SI Units

8. 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.

9. Work Work = force x distance In SI units:
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 = N-m = J
1 N-m = 1 J, so N-m = J

10. Common Units Used to Express Work Performed or Energy Expenditure
Work and Power Defined
Common Units Used to Express Work Performed or Energy Expenditure

11. Power Power = work ÷ time In SI units: Power (W) = work (J) ÷ time (s)
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 = J•s–1 = W
1 W = 1 J•s–1, so J•s–1 = W

12. Common Units Used to Express Power
Work and Power Defined
Common Units Used to Express Power

13. Measurement of Work and Power
Ergometry
Measurement of work output
Ergometer
Device used to measure work
Bench step ergometer
Cycle ergometer
Arm ergometer
Treadmill

14. Ergometers used in the Measurement of Human Work Output and Power
Measurement of Work and Power
Ergometers used in the Measurement of Human Work Output and Power
Figure 6.1

15. Bench Step Subject steps up and down at specified rate Example:
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
Force = 70 kg x 9.79 N•kg–1 = N
Distance = 0.5 m•step–1 x 30 steps•min–1 x 10 min = 150 m
Power = work ÷ time
685 N x 150 m = 102,795 J (or kJ)
102,795 J ÷ 600 s = W

16. 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
Power
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

17. 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

18. Determination of Percent Grade on a Treadmill
Measurement of Work and Power
Determination of Percent Grade on a Treadmill
Figure 6.2

19. 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 = W

20. 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

21. Measurement of Energy Expenditure
Measurement of Work and Power
Measurement of Energy Expenditure
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
Foodstuffs + O2  ATP + heat
cell work
Heat

22. Diagram of a Simple Calorimeter
Measurement of Work and Power
Diagram of a Simple Calorimeter
Figure 6.3

23. Measurement of Energy Expenditure
Measurement of Work and Power
Measurement of Energy Expenditure
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
Foodstuffs + O2  Heat + CO2 + H2O

24. Open-Circuit Spirometry
Measurement of Work and Power
Open-Circuit Spirometry
Figure 6.4

25. 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.

26. 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

27. The Relationship Between Walking or Running Speed and VO2
Estimation of Energy Expenditure
The Relationship Between Walking or Running Speed and VO2
Figure 6.5

28. Estimation of Energy Expenditure
A Closer Look 6.1 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) 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:
0.1 ml•kg–1•min–1 x 80 m•min– 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– ml•kg–1•min–1 = 18.7 ml•kg–1•min–1
(or 5.3 METs)

29. Estimation of Energy Expenditure
A Closer Look 6.2 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) 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:
0.2 ml•kg–1•min–1 x 160 m•min– 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– ml•kg–1•min–1 = 42.7 ml•kg–1•min–1
(or 12.2 METs)

30. Relationship Between Work Rate and VO2 for Cycling
Estimation of Energy Expenditure
Relationship Between Work Rate and VO2 for Cycling
Figure 6.6

31. A Closer Look 6.3 Estimation of the O2 Requirement of Cycling
Estimation of Energy Expenditure
A Closer Look 6.3 Estimation of the O2 Requirement of Cycling
Comprised of three components:
Resting VO2
3.5 ml•kg–1•min–1
VO2 for unloaded cycling
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
VO2 (ml•kg–1•min–1) = 1.8 x work rate x M–1 + 7

32. 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 VO (3.5 ml•kg–1•min–1).

33. Calculation of Exercise Efficiency
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

34. Factors That Influence Exercise Efficiency
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

35. Net Efficiency During Arm Crank Ergometery
Calculation of Exercise Efficiency
Net Efficiency During Arm Crank Ergometery
Figure 6.7

36. Relationship Between Energy Expenditure and Work Rate
Calculation of Exercise Efficiency
Relationship Between Energy Expenditure and Work Rate
Figure 6.8

37. Effect of Speed of Movement of Net Efficiency
Calculation of Exercise Efficiency
Effect of Speed of Movement of Net Efficiency
Figure 6.9

38. 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.

39. 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

40. Comparison of Running Economy Between Males and Females
Figure 6.10

41. 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.

42. Study Questions
Define the following terms: a. work e. net efficiency b. power f. metric system c. percent grade g. SI units d. relative VO2
Calculate the total amount of work performed in five minutes of exercise on the cycle ergometer, given the following: Resistance on the flywheel = 25 N Cranking speed = 60 rpm Distance traveled per revolution = 6 m
Compute total work and power output per minute for ten minutes of treadmill exercise, given the following: Treadmill grade = 15% Horizontal speed = 200 m•min– Subject’s weight = 70 kg

43. Study Questions
Briefly, describe the procedure used to estimate energy expenditure using (a) direct calorimetry and (b) indirect calorimetry.
Compute the estimated energy expenditure during horizontal treadmill walking for the following examples: a. Treadmill speed = 50 m•min– Subject’s weight = 62 kg b. Treadmill speed = 100 m•min– Subject’s weight = 75 kg c. Treadmill speed = 80 m•min– Subject’s weight = 60 kg
Calculate the estimated O2 cost of horizontal treadmill running for a 70-kg subject at 150, 200, and 235 m•min–1.

44. Study Questions
Calculate net efficiency, given the following: Exercise VO2 = 3.0 L•min–1 Resting VO2 = 0.3 L•min–1 Work rate = 200 W
Calculate the power output during one minute of cycle ergometer exercise, given the following: Resistance on the flywheel = 50 N Cranking speed = 50 rpm Distance traveled per revolution = 6 m
Calculate the total work performed during ten minutes of cycle ergometer exercise, given the following: Resistance on the flywheel = 20 N Cranking speed = 70 rpm Distance traveled per revolution = 6 m

45. Study Questions
Calculate net efficiency, given the following: Resting VO2 = 0.3 L•min– Exercise VO2 = 2.1 L•min–1 Work rate = 150 W
Compute power output for three minutes of treadmill exercise, given the following: Treadmill grade = 10% Horizontal speed = 100 m•min– Subject’s weight = 60 kg
Calculate the power output (expressed in watts) for a subject who performed ten minutes of cycle ergometer exercise, given the following: Resistance on the flywheel = 20 N Cranking speed = 60 rpm Distance traveled per revolution = 6 m
Compute the oxygen cost of cycling at work rates of 50, 75, 100, and 125 W for a 60-kg person.