Measurement Of Work, Power, And Energy Expenditure Flashcards
_______________ is a measure of energy transfer that occurs when an object is moved over a distance by an external force .
Work
How to calculate work ?
Work = Force x Distance
Force → kiloponds kp
Distance → meter m
Work → kpm
A person lifting 25 kg weight from the floor up to a height (distance) of 2 meter has performed a work equal to what ?
F x D = W
25 kp x 2 m = 50 kpm
(NOTE: 1 kp = 1 kg)
Unit of work
Kiloponds-meter Kpm
___________ is the amount of work performed per unit of time.
Power
How to calculate power
What is the unit of power
Power = Work / Time
Unit of power = Watt = 6.12 kpm/min
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 ?
- 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)
_______________ is the measurement of work output
_______________ is the device which is used to measure specific type of work.
Ergometry
Ergometer
Different types of ergometer devices
They all provide measurements/quantification of human physical performance
Bench step ergometry
- explain how it’s done
- what are the required parameters
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)
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.
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 :
- Find distance:
Distance = height x speed x duration
Distance = 0.5 m x 30 steps/min x 10 min = 150 m - Find work:
Work = Force x Distance
Work = 70 kp x 150 m = 10500 kpm - Find power:
Power = Work / Time
Power = 10500 kpm / 10 min = 1050 kpm/min = 171.6 W
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?
No
That is just the work. The energy expenditure is much higher (ex: 200 kcal)
What is the earliest method of measuring work capacity in humans?
Bench step ergometry
What is the most commonly used ergometer that allows for accurate measurement of work and power output ?
Cycle ergometer
Cycle ergometer
- Explain what it is.
- How is distance measured?
- what is the force considered as?
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
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?
- Calculate distance
Distance = distance travelled/revolution x pedaling speed x duration
Distance = 6 m x 60 rev/min x 10 min = 3600 m - Calculate work.
Work = Force x Distance
Work = 1.5 kp x 3600 m = 5400 kpm - 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)
True or false
We can measure work performed in treadmill ergometry at zero inclination.
False
It is complicated at zero inclination .
Therefore, treadmill ergometry is performed at predetermined incline angles (percent grade)
Determination of percent grade on a treadmill:
A subject walking 100 m at 10% grade climbs how many meters vertically ?
(Percent grade/100) x distance
10/100 x 100 = 10 meters vertically
What is the information required to calculate work performed in treadmill ergometry?
- 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)
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?
- Calculate the distance.
Distance = speed x time
Distance = 200 m/min x 10 min = 2000 m - Calculate the vertical displacement:
Vertical displacement = (percent grade/100) x distance
Vertical displacement = (7.5/100) x 2000 m = 150 m - Calculate work.
Work = Force x Distance
Work = 70 kp x 150 m = 10,500 kpm - 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!)
What is the SI unit of heat?
Joules
But for biological systems, we use Calorie
Which unit is used for the body and value of foods (heat energy when metabolized) ?
Kilocalorie ( kcal )
1 kcal = 4.186 KJ
What are two techniques used to measure human energy expenditure?
What is the difference between them?
Explain how direct calorimetry works?
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.
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?
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
True or false
Energy cost of any activity is measured at a steady-state
True
True or false
O2 consumption is equivalent to energy expenditure
True
What can be understood from this graph
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 !!
_______________ expresses the energy cost of an exercise as simple units.
Metabolic equivalent MET
What is 1 MET equivalent to?
1 MET = the energy requirement AT REST = 3.5 ml O2/kg/min
So 1 MET = resting VO2 consumption
If a subject is performing an activity which requires 35 ml O2/kg/min then how much MET is the subject working at?
10 MET
Why? Because
1 MET = 3.5
? MET = 35
(Then cross multiply and solve)
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.
- Find out how many O2 he consumes in ONE minute:
12 minutes = 90 L
1 minute = ?
Answer: 7.5 L/min - Convert L to ml
7.5 L = 7500 ml/min - Divide O2 consumption per minute by body weight
(7500 ml/min) / 70 kg = 107 ml/kg/min - Convert ml/kg/min into METS
1 MET = 3.5
? MET = 107
Answer: 30.5 MET
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 ?
The net efficiency of cycle ergometry is how much ?
15-27%
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
- 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 - Calculate VO2 above rest
VO2 = 1.5 - 0.25 = 1.25 L/min - Calculate energy expenditure
Energy expenditure = VO2 x 21 kJ = 1.25 x 21 = 26.5 kJ/min - 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%
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
Easy ✅
What are some factors that affect exercise efficiency ?
True or false
The greater the exercise work rate = the higher the efficiency
False
The LOWER the efficiency
True or false
The speed of exercise maneuver affects the efficiency
True
True or false
Fast twitch muscles have greater efficiency compared to slow-twitch muscles
False
Slow-twitch has greater efficiency than fast-twitch muscles
What is understood from this graph
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)
What is understood from this graph?
There is an OPTIMUM speed of movement and any deviation reduces efficiency
Low speed: inertia, repeated stop and start ❌
High speed : friction ❌
Interpret the graph
(Focus mostly on the left one)
Eritrean runners are consuming less oxygen = so less energy expenditure for the same work = MORE EFFICIENCY
This chart portrays the oxygen cost of running among groups differing in running ability, from elite runner to untrained individuals.
What do you notice ?
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
Higher efficiency is seen in muscles with the greater percentage of ___________ fibers.
A. Fast.
B. Slow.
B. Slow
Difference between slow twitch and fast twitch muscle types
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)
Which muscle type is more efficient in generating ATP by oxidative metabolism
Slow twitch
Which muscle type utilizes anaerobic metabolism to generate ATP
Fast twitch
Which muscle type contains a lot of myoglobin, mitochondria, and blood capillaries
Slow twitch
Which muscle type is used for continuous muscle contraction over a long time?
Slow twitch
Which muscle type is used for short strength or speed required movements
Fast twitch
Which muscle type fatigues slower
Slow twitch
Which muscle type fatigues faster
Fast twitch
Which muscle type is great for endurance sports
Slow twitch
Which muscle type is great for marathons and bicycling for hours
Slow twitch
Which muscle type is great for short bursts of activity
Fast twitch
Which muscle type is great for sprinters and weight lifters
Fast twitch
What are the types of exercise?
Provide examples
What is work rate?
Power output
