Transcript Measuring and Evaluating Energy Expenditure

Power
• Power is how much work is accomplished per
unit time.
• The unit for power is watt (W)
• It is defined as 1 joule per second
• Power = work ÷ time
• Power describes the rate at which work is
being done
• describes the intensity of exercise.
1
Work
• Work = product of force multiplied by distance:
Work = force x distance
• The SI unit for force is Newtons (N)
• Lifting a 10kg weight up a distance of 2m the
work performed
• Work = 97.9N x 2m = 195.8 Joules
• 1kg = 9.79N so 10kg = 97.9N
2
Measurement of Work and Power
• Ergonometry = to the measurement of work
output.
• Ergometer = to an apparatus or device used to
measure a specific type of work
3
Bench Step
• The bench = form of ergometer
• It involves stepping up and down on a bench at a specified rate.
• E.g 70kg man steps up and down on a 50cm(0.5m) bench for ten
minutes at a rate of 30 steps per minute.
Work performed:
• Force = 685.3 N (i.e., 70kg x 9.79 N/kg)
• Distance = 0.5m/step x 30 steps/min x 10min =150m
Total work performed :
• 685.3 N x 150m = 102 795 Joules or 102.8kilojoules
• The power output during this exercise can be calculated as:
• Power = 102 795 Joules/600seconds = 173.3 watts
4
Cycle Ergometer
• =stationary exercise bicycle that permits accurate
measurement of the amount of work performed.
• It incorporates a belt wrapped around the wheel
(flywheel).
• Distance traveled = distance covered per revolution of
the pedal
(6 meters per revolution on a standard Monarch)
• This is multiplied by the number of pedal
revolutions.
5
Evaluating Immediate Energy
System
• Power = F x D/time
• Short term muscular
power: e.g sprinting up
flight of steps
• Jumping power tests:
may not measure
anaerobic power = too
brief to evaluate ATP &
PCr.
6
Evaluating Immediate Energy
Systems
• Other power tests last 6 to
8 seconds.
• Power tests = high degree
of task specificity.
Best sprinter may not be
the best repetitive volleyball
leaper.
7
Evaluating Short-Term Glycolytic
Energy System
• Glycogen depletion in specific muscles
activated = indication of contribution of
glycolysis to exercise
• Tests demanding maximal work for up to 3min
= best estimate of glycolytic power.
8
Measuring Anaerobic Capacity
• No clear method for measuring anaerobic
capacity
• Accepted methods:
– Maximal accumulated O2 deficit
– Wingate anaerobic test
– Critical power test
9
• Wingate test:
Peak power output, average power output,
anaerobic fatigue
• What is anaerobic fatigue?
= percentage decline in power relative to peak
power.
10
Energy Expenditure During
Maximal Anaerobic Exercise
• No activity = 100% aerobic or anaerobic
• Estimates of anaerobic effort involved
– Excess post exercise O2 consumption (EPOC)
– Lactate threshold
11
Anaerobic Energy Expenditure:
EPOC
• O2 demand > O2 consumed in early exercise
– Body = experiences O2 deficit
– Occurs when anaerobic pathways used for ATP
production
• O2 consumed > O2 demand in early recovery
– Excess post-exercise O2 consumption (EPOC)
12
Anaerobic Energy Expenditure:
Lactate Threshold
• Lactate threshold: point at which blood
lactate accumulation 
• Lactate production rate > lactate clearance
rate
– Good indicator of potential for endurance
exercise
13
Anaerobic Energy Expenditure:
Lactate Threshold
• Lactate accumulation  fatigue
– Ability to exercise hard without accumulating
lactate = beneficial to athletic performance
– Higher lactate threshold = higher sustained
exercise intensity = better endurance
performance
• For 2 athletes with same VO2max  higher
lactate threshold predicts better performance
14
Measuring & Evaluating the Aerobic
System
Direct Calorimetry:
= Process of measuring metabolic rate via
measurement of heat
15
Direct Calorimetry
• Theory: when body uses energy to do work,
heat is given off.
 measure heat production (calorimetry)
gives a direct measurement of metabolic
work.
16
Measuring & Evaluating the
Aerobic System
• Airtight chamber
(calorimeter) insulated
from environment
• Exchange O2 & CO2
• Body temperature raises
temperature of water
• Heat production
calculated
17
Measuring & Evaluating the Aerobic
System
Indirect Calorimetry
• Theory: Since direct relationship between
O2 consumed & amount of heat produced
by body
 measurement of O2 consumption provides
estimate of metabolic rate.
• Measurement of O2 consumption is indirect,
since heat not measured directly.
18
Respiratory Quotient
• Respiratory quotient (RQ) is ratio of volume of
carbon dioxide produced to volume of oxygen
consumed.
RQ for Carbohydrate is 1.0.
19
Respiratory Exchange Ratio
Respiratory Exchange Ratio is ratio of carbon
dioxide exhaled to oxygen consumed when CO2
and O2 exchange
does not reflect food oxidation.
20
Measuring Maximal Oxygen
Consumption
Test of Aerobic Power
• Two general criteria needed:
– Test that is independent of muscle strength, speed,
body size, skill
– Test that consists of graded exercise to point of
exhaustion (without muscular fatigue)
21
Measuring Maximal Oxygen
Consumption
Criteria for true max VO2 is
leveling off or peaking in oxygen
uptake.
• Other criteria:
– Oxygen uptake fails to
increase by some value
– Maximum lactic acid
– Maximum predicted HR
– R > 1.0
22
Maximal Oxygen Consumption
• The highest maximal
oxygen uptakes
generally recorded for
cross-country skiers,
runners, swimmers &
cyclists.
• Lance Armstrong VO2
max = 83.3 ml/kg/min
23
Measuring Maximal Oxygen
Consumption
Factors that affect
Maximal Oxygen
Uptake:
–
–
–
–
–
–
Mode
Heredity
State of training
Gender
Body composition
Age
24
Energy Expenditure During
Maximal Aerobic Exercise
• VO2max :
– Point at which O2 consumption doesn’t  with
further  in intensity
– Best single measurement of aerobic fitness
– Not best predictor of endurance performance
– Plateaus after 8 to 12 weeks of training
• Performance continues to improve
• More training = compete at higher percentage of
VO2max
25
Energy Expenditure:
Energy Cost of Various Activities
• Varies with type and intensity of activity
• Calculated from VO2, expressed in
kilocalories/minute
• Values ignore anaerobic aspects, EPOC
• Daily expenditures depend on
– Activity level (largest influence)
– Inherent body factors (age, sex, size, weight, FFM)
26
Energy Expenditure:
Successful Endurance Athletes
1. High VO2max
2. High lactate threshold (as % VO2max)
3. High economy of effort
4. High percentage of type I muscle fibers
(Slow, oxidative, fatigue resistant)
27