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

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

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

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 = 33.33 kgm•s-1 Expressed in SI Units: 1 Watt (W) = 0.102 kpm•s-1, so 326.8 W

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

Ergometer

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 171.6 W

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

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

Determination of Percent Grade on a Treadmill Figure 6.2

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

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

Diagram of a Simple Calorimeter Figure 6.3

Open-Circuit Spirometry Figure 6.4

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

The Relationship Between Walking or Running Speed and VO2 Figure 6.5

Relationship Between Work Rate and VO2 for Cycling Figure 6.6

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

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

Net Efficiency During Arm Crank Ergometery Figure 6.8

Relationship Between Energy Expenditure and Work Rate Figure 6.9

Effect of Speed of Movement of Net Efficiency Figure 6.10

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

Comparison of Running Economy Between Males and Females Figure 6.11