1. Chapter 6 Measurement of Work, Power, and Energy Expenditure
EXERCISE PHYSIOLOGY
Theory and Application to Fitness and Performance, 6th edition
Scott K. Powers & Edward T. Howley

2. 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

3. 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

4. Work and Power Work = force x distance Power = work ÷ time 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
Performing 2,000 kgm of work in 60 sec
2,000 kgm ÷ 60s = kgm•s-1
Expressed in SI Units:
1 Watt (W) = kpm•s-1, so W

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

6. Ergometer

7. 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
70 kg x 0.5 m•step-1 x 30 steps•min-1 x 10 min = 10,500 kpm
Power
10,500 kpm ÷ 10 min = 1,050 kpm•min-1 or W

8. Cycle Ergometer
Stationary cycle that allows accurate measurement of work performed
Example:
1.5 kp resistance, 6 m•rev-1, 60 rev•min-1 for 10 min
Total work
1.5 kp x 6 m•rev-1 x 60 rev•min-1 x 10 min = 5,400 kpm
Power
5,400 kpm ÷ 10 min = 540 kpm•min-1 or 88.2 W

9. 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. Determination of Percent Grade on a Treadmill
Figure 6.2

11. Treadmill
Example
70 kg subject, treadmill speed 200 m•min-1, 7.5% grade for 10 min
Vertical displacement = % grade x distance
0.75 x 200 m•min-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 kpm•min-1

12. 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  ATP + heat
cell work
Heat
Foodstuffs + O2  Heat + CO2 + H2O

13. Diagram of a Simple Calorimeter
Figure 6.3

14. Open-Circuit Spirometry
Figure 6.4

15. 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 ml•kg-1•min-1

16. The Relationship Between Walking or Running Speed and VO2
Figure 6.5

17. Relationship Between Work Rate and VO2 for Cycling
Figure 6.6

18. Calculation of Exercise Efficiency
Net efficiency
Ratio of work output divided by energy expended above rest
Net efficiency of cycle ergometry
15-27%
Work output
Energy expended above rest
% net efficiency =
x 100

19. 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

20. Net Efficiency During Arm Crank Ergometery
Figure 6.8

21. Relationship Between Energy Expenditure and Work Rate
Figure 6.9

22. Effect of Speed of Movement of Net Efficiency
Figure 6.10

23. 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) indicates better running economy
Gender difference
No difference at slow speeds
At “race pace” speeds, males may be more economical that females

24. Comparison of Running Economy Between Males and Females
Figure 6.11