Measurement Of Work, Power, And Energy Expenditure

Question 1

_______________ is a measure of energy transfer that occurs when an object is moved over a distance by an external force .

Answer 1

Work

Question 2

How to calculate work ?

Answer 2

Work = Force x Distance

Force → kiloponds kp
Distance → meter m
Work → kpm

Question 3

A person lifting 25 kg weight from the floor up to a height (distance) of 2 meter has performed a work equal to what ?

Answer 3

F x D = W

25 kp x 2 m = 50 kpm

(NOTE: 1 kp = 1 kg)

Question 4

Unit of work

Answer 4

Kiloponds-meter Kpm

Question 5

Answer 5

Question 6

___________ is the amount of work performed per unit of time.

Answer 6

Power

Question 7

How to calculate power

What is the unit of power

Answer 7

Power = Work / Time

Unit of power = Watt = 6.12 kpm/min

Question 8

Two people may perform the same amount of work but take different durations to perform this work

For example :

Person A performs 1000 kpm in one hour
Person B performs the same work in one minute

Which person has greater power ?

Answer 8

• Person A : 1000 / 60 = 16.7 kpm/min = 2.73 Watt
• Person B: 1000/1 = 1000 kpm/min = 163 Watt

Person B has greater power because he was able to perform the same work in a SHORTER time

(Remember: 1 Watt = 6.12 kpm/min)

Question 9

Answer 9

Question 10

_______________ is the measurement of work output

_______________ is the device which is used to measure specific type of work.

Answer 10

Ergometry

Ergometer

Question 11

Different types of ergometer devices

Answer 11

They all provide measurements/quantification of human physical performance

Question 12

Bench step ergometry

• explain how it’s done
• what are the required parameters

Answer 12

Subject steps up and down a bench with specific height at a certain rate (steps/min)

Required parameters:
- height of steps (meter)
- number of steps/min
- total duration (minutes)
- weight of subject (force kp)

Question 13

Bench step ergometry :

A 70 kg subject steps up and down a 50 cm bench at a rate of 30 steps per minute for 10 minutes. Calculate the amount of power output for this subject.

Answer 13

Power = Work / Time
But we have to calculate work first
Work = Force x Distance
We have force ☑️ but we dont have distance so lets calculate distance first :

1. Find distance:
   Distance = height x speed x duration
   Distance = 0.5 m x 30 steps/min x 10 min = 150 m
2. Find work:
   Work = Force x Distance
   Work = 70 kp x 150 m = 10500 kpm
3. Find power:
   Power = Work / Time
   Power = 10500 kpm / 10 min = 1050 kpm/min = 171.6 W

Question 14

When converting the work this subject did into kcal, it only came out as a total of 24.6 kcal.

Is that really the energy expenditure (calories burned) for this entire workout?

Answer 14

No

That is just the work. The energy expenditure is much higher (ex: 200 kcal)

Question 15

What is the earliest method of measuring work capacity in humans?

Answer 15

Bench step ergometry

Question 16

What is the most commonly used ergometer that allows for accurate measurement of work and power output ?

Answer 16

Cycle ergometer

Question 17

Cycle ergometer

• Explain what it is.
• How is distance measured?
• what is the force considered as?

Answer 17

Adjustable friction braked cycle with a belt around the wheel, which can be loosened or tightened to adjust the friction, therefore changing the resistance.

Distance can be measured by the number of revolutions the wheel makes

Force is the resistance

Question 18

Cycle ergometer :

A subject does 10 minutes of pedaling at a resistance of 1.5 kp. The distance traveled at each revolution is 6 m. The pedaling speed is 60 rev/min. What will be the total work and power of the subject?

Answer 18

1. Calculate distance
   Distance = distance travelled/revolution x pedaling speed x duration
   Distance = 6 m x 60 rev/min x 10 min = 3600 m
2. Calculate work.
   Work = Force x Distance
   Work = 1.5 kp x 3600 m = 5400 kpm
3. Calculate power
   Power = Work / Time
   Power = 5400 kpm / 10 min = 540 kpm/min = 88.2 W

(The work in kcal here is 12.6 , but remember that the energy expenditure is much higher)

Question 19

True or false
We can measure work performed in treadmill ergometry at zero inclination.

Answer 19

False

It is complicated at zero inclination .

Therefore, treadmill ergometry is performed at predetermined incline angles (percent grade)

Question 20

Determination of percent grade on a treadmill:

A subject walking 100 m at 10% grade climbs how many meters vertically ?

Answer 20

(Percent grade/100) x distance

10/100 x 100 = 10 meters vertically

Question 21

What is the information required to calculate work performed in treadmill ergometry?

Answer 21

• Weight of the subject (kg)
• “Distance traveled “ (meters/min)
• Percent grade of treadmill

(Distance travelled is a mistake in the note . It should be speed meters/min)

Question 22

Treadmill ergometry

A 70 kg subject runs at a speed of 200 m/min on a treadmill at a percent grade of 7.5 for 10 minutes. What is the total work performed and power?

Answer 22

1. Calculate the distance.
   Distance = speed x time
   Distance = 200 m/min x 10 min = 2000 m
2. Calculate the vertical displacement:
   Vertical displacement = (percent grade/100) x distance
   Vertical displacement = (7.5/100) x 2000 m = 150 m
3. Calculate work.
   Work = Force x Distance
   Work = 70 kp x 150 m = 10,500 kpm
4. Calculate power.
   Power = Work / Time
   Power = 10,500 kpm / 10 min = 1050 kpm = 171.5 W

(Note: the work in kcal for this example is 24.6 but that is only the work and not the total energy expenditure!)

Question 23

What is the SI unit of heat?

Answer 23

Joules

But for biological systems, we use Calorie

Question 24

Which unit is used for the body and value of foods (heat energy when metabolized) ?

Answer 24

Kilocalorie ( kcal )

1 kcal = 4.186 KJ

Question 25

What are two techniques used to measure human energy expenditure? What is the difference between them?

Answer 25

Question 26

Explain how direct calorimetry works?

Answer 26

A subject is in a special tight chamber where heat cannot escape. The change in temperature of water is equal to the heat emitted by the body of the subject.

Question 27

Explain how indirect calorimetry works - how is the amount of oxygen consumption measured? - What does the amount of heat produced depend on? - what are the two types of spirometry used? - How much is the caloric expenditure of exercise?

Answer 27

The amount of O2 consumed = the amount of heat produced - oxygen consumed per minute = the subtractive volume of O2 inspired from O2 expired - amount of heat produced depends on the type of fuel the body is using: Fat produces 4.7 kcal/l O2 CHO produces 5.05 kcal/l O2 - closed circuit spirometry and open circuit spirometry - approximately 5 kcal/L or 21 kJ/L

Question 28

True or false Energy cost of any activity is measured at a steady-state

Answer 28

True

Question 29

True or false O2 consumption is equivalent to energy expenditure

Answer 29

True

Question 30

What can be understood from this graph

Answer 30

Oxygen requirement of walking and running (as a function of SPEED) show a linear relationship As speed increases (walking → running) , more O2 is consumed = more energy expenditure Hence “O2 consumption is equivalent to energy expenditure” Also O2 consumption increases with increasing power output !!

Question 31

_______________ expresses the energy cost of an exercise as simple units.

Answer 31

Metabolic equivalent MET

Question 32

What is 1 MET equivalent to?

Answer 32

1 MET = the energy requirement AT REST = 3.5 ml O2/kg/min So 1 MET = resting VO2 consumption

Question 33

If a subject is performing an activity which requires 35 ml O2/kg/min then how much MET is the subject working at?

Answer 33

10 MET Why? Because⁣⁣⁣⁣⁣ 1 MET = 3.5 ? MET = 35 (Then cross multiply and solve)

Question 34

A 70 kg subject is running on a treadmill for 12 minutes. Total consumption of O2 (VO2) is measured to be 90 L. What is the average energy expenditure of this subject in MET.

Answer 34

1. Find out how many O2 he consumes in ONE minute: 12 minutes = 90 L 1 minute = ? Answer: 7.5 L/min 2. Convert L to ml 7.5 L = 7500 ml/min 3. Divide O2 consumption per minute by body weight (7500 ml/min) / 70 kg = 107 ml/kg/min 4. Convert ml/kg/min into METS 1 MET = 3.5 ? MET = 107 Answer: 30.5 MET

Question 35

Efficiency of exercise is often described as NET EFFICIENCY How can we calculate net efficiency ? - what is work rate and how can we calculate it? - how can we calculate energy expenditure ?

Answer 35

Question 36

The net efficiency of cycle ergometry is how much ?

Answer 36

15-27%

Question 37

A subject is performing cycle ergometer exercise. The following data were obtained: Resistance of flywheel : 2 kp Cycle speed : 50 rpm Distance per Revolution : 6 m Steady state resting VO2: 0.25 L/min Steady state exercise VO2: 1.5 L/min Calculate the work rate and net efficiency %. Keep in mind 1 kpm = 9.81 joules

Answer 37

1. Calculate work rate Work rate = force x distance/min Work rate = 2 kp x (50 rpm x 6 m) = 600 kpm/min or 5.89 KJ/min 2. Calculate VO2 above rest VO2 = 1.5 - 0.25 = 1.25 L/min 3. Calculate energy expenditure Energy expenditure = VO2 x 21 kJ = 1.25 x 21 = 26.5 kJ/min 4. Calculate % Net efficiency % Net efficiency = (work rate / energy expenditure ) x 100 % Net efficiency = (5.89 kJ/min / 26.5 kJ/min) x 100 = 22.4%

Question 38

Just read this slide . The point of this slide is to appreciate the insane amounts of energy expenditure athletes can utilize and it provided examples like 9000 kcal/d Tour de France 10,000+ kcal/d extreme long distance running If well planned, energy requirements can be met by most athletes

Answer 38

Easy ✅

Question 39

What are some factors that affect exercise efficiency ?

Answer 39

Question 40

True or false The greater the exercise work rate = the higher the efficiency

Answer 40

False The LOWER the efficiency

Question 41

True or false The speed of exercise maneuver affects the efficiency

Answer 41

True

Question 42

True or false Fast twitch muscles have greater efficiency compared to slow-twitch muscles

Answer 42

False Slow-twitch has greater efficiency than fast-twitch muscles

Question 43

What is understood from this graph

Answer 43

Net efficiency of an exercise DECREASES as the work rate INCREASES Net efficiency ↓ = work rate ↑ / ↑ energy expenditure (Obviously if both work rate and energy expenditure increase in a parallel manner , then net efficiency would remain constant) Also, notice that energy expenditure increases as work rate increases (curvilinear relationship)

Question 44

What is understood from this graph?

Answer 44

There is an OPTIMUM speed of movement and any deviation reduces efficiency Low speed: inertia, repeated stop and start ❌ High speed : friction ❌

Question 45

Interpret the graph (Focus mostly on the left one)

Answer 45

Eritrean runners are consuming less oxygen = so less energy expenditure for the same work = MORE EFFICIENCY

Question 46

This chart portrays the oxygen cost of running among groups differing in running ability, from elite runner to untrained individuals. What do you notice ?

Answer 46

The average difference between the elite runners and the untrained individuals is only 10%, suggesting that systematic training has a limited effect on running economy However, the difference within a single group is more than 10% , so there is more incredible variability within each group

Question 47

Higher efficiency is seen in muscles with the greater percentage of ___________ fibers. A. Fast. B. Slow.

Answer 47

B. Slow

Question 48

Difference between slow twitch and fast twitch muscle types

Answer 48

Slow twitch (type 1) - Generates ATP by oxidative metabolism - A lot of myoglobin, mitochondria, and blood capillaries - Used for continuous muscle contraction over a long time - Fatigues slower - Good for endurance sports (marathons, bicycling for hours) Fast twitch (type 2) - Generates ATP using anaerobic metabolism - For short strength or speed required movements - Fatigues faster - Good for short bursts of activity (sprinter, weightlifter)

Question 49

Which muscle type is more efficient in generating ATP by oxidative metabolism

Answer 49

Slow twitch

Question 50

Which muscle type utilizes anaerobic metabolism to generate ATP

Answer 50

Fast twitch

Question 51

Which muscle type contains a lot of myoglobin, mitochondria, and blood capillaries

Answer 51

Slow twitch

Question 52

Which muscle type is used for continuous muscle contraction over a long time?

Answer 52

Slow twitch

Question 53

Which muscle type is used for short strength or speed required movements

Answer 53

Fast twitch

Question 54

Which muscle type fatigues slower

Answer 54

Slow twitch

Question 55

Which muscle type fatigues faster

Answer 55

Fast twitch

Question 56

Which muscle type is great for endurance sports

Answer 56

Slow twitch

Question 57

Which muscle type is great for marathons and bicycling for hours

Answer 57

Slow twitch

Question 58

Which muscle type is great for short bursts of activity

Answer 58

Fast twitch

Question 59

Which muscle type is great for sprinters and weight lifters

Answer 59

Fast twitch

Question 60

What are the types of exercise? Provide examples

Answer 60

Question 61

What is work rate?

Answer 61

Power output