Energy Costs of Physical Activity Flashcards
Direct Calorimetry requires that…
requires that the person performs an activity within a specially constructed chamber
chamber is insulated and has water flowing through its walls
Direct Calorimetry
considered the gold standard, but difficult to do
Direct Calorimetry chamber
water flowing through walls of the chamber is warmed by the heat given off by the subject
chamber is insulated and has water flowing through its walls
–by knowing the V of water flowing through the chamber per minute and the change in water temp from entry to exit, calorimetry is determined…
It takes 1 kcal…
to raise the temperature of 1 L of water 1deg C
additional heat producing adjustments for direct calorimetry
subject loses additional heat though evaporation of water from skin and respiratory passages
equipment utilized produces heat
indirect calorimetry
estimates energy by measuring O2 consumption
uses certain constants for converting liters of O2 consumption to calories expended
Constants Derived From Bomb Calorimeter
1g CHO = 4.0 kcal
1g of FAT = 9.0 kcal
1g of PROTEIN = 4.0 kcal
energy density of CHO
4.0 kcal
energy density of fat
9.0 kcal
energy density of protein
4.0 kcal
caloric equivalent of O2
the number of calories of energy produced when 1L of O2 is consumed
CHO vs FAT
CHO gives 6% more energy / LO2 than Fat (5 kcal/L vs 4.7 kcal/L)
fat gives more than 2x the energy per gram than CHO (9 kcal vs 4 kcal)
Respiratory Quotient (RQ)
the ratio of CO2 produced to O2 consumed at the cell
Volume CO2 produced / Volume O2 consumed
Respiratory Exchange Ratio (RER)
RQ measured by conventional gas exchange procedure
used to indicate fuel use (CHO vs fat) during exercise
caloric equivalent of 1L O2 for CHO
5.0 kcal
caloric equivalent of 1L O2 for FAT
4.7 kcal
caloric equivalent of 1L O2 for PROTEIN
4.5 kcal
RQ for CHO
1.0
RQ for FAT
0.7
RQ for PROTEIN
0.8
types of indirect calorimetry
closed-circuit spirometry
open-circuit spirometry
closed-circuit spirometry
subject breaths 100% O2 from a spirometer and the exhaled air passes through a chemical that absorbs the CO2
over time, the O2 in the spirometer decreases, giving a measure of the O2 consumption in ml/min
Because the CO2 is absorbed, R can’t be calculated and caloric equivalent of 4.82 kcal/L is used to indicate a mixture of CHO, fat, and protein producing the energy
R used for Closed-circuit spirometry? why?
4.82 kcal/L O2
because the CO2 is absorbed, R can’t be calculated
represents a mixture of CHO, fat, and protein used to produce energy
What is the old system of indirect calorimetry?
Closed-circuit spirometry
What is the most common technique for indirect calorimetry? (currently)
open-circuit spirometry
Open-circuit spirometry
O2 is calculated by subtracting O2 exhaled from O2 inhaled (O2 inhaled - O2 exhaled)
CO2 is calculated by: CO2 inhaled - CO2 exhaled
Allows for calculation of R and determination of which fuel (CHO and fat) is primary energy source
Which indirect calorimetry allows for the calculation of R?
open-circuit spirometry
Caloric equivalent of 1 L of O2 in calculation of energy expenditure
5.0 kcal/ L is typically used to convert O2 uptake to kcal
per ACSM guidelines
expressing energy expenditure
the energy requirement for an activity is calculated from the subject’s steady-state O2 consumption (VO2) measured during an activity
5 most common ways to express energy expenditure
- VO2 (L/min)
- Kcal/min
- VO2 (mL/kg*min)
- METs
- kcal/kg*hr
VO2 (L/min)
“Volume of O2 in L/min”
the calculation of O2 uptake yields a value expressed in L of O2 per minute
ABSOLUTE
this does not account for body mass, so is not good for comparing individuals
Kcal/min
The caloric equivalent of 1 L O2 ranges from 4.7 kcal/L for fat to 5.0 kcal/L for CHO
5.0 kcal.L IS USED TO CONVERT THE O2 UPTAKE TO KCAL/L
Energy expenditure is calculated by multiplying the kcal expended per min (kcal/L) by the duration of the activity in minutes
VO2 (ml/kg*min
“Volume of O2 in ml/kg*min”
this expression allows you to compare values for people of different body sizes
calculated by taking the O2 uptake expressed in L/min multiplied by 1000 and divided by the subjects body weight in kg
METs
metabolic equivalent is a term used to describe resting metabolism
1 MET = 3.5 ml/kg*min
Activities are expressed in terms of multiples of the MET unit
1 MET =
3.5 mL/kg*min
Kcal/kg*hr
you can use the MET value to calculate this
convert the MET value back to the number of mL/kg*min and multiply by 60min/hr
Who prefers METs? Who prefers mL/kg*min
Doctors prefer to talk in terms of METs. exercise professionals prefer to express in terms of ml/kg*min
Equations for estimating the energy cost of activities
In mid 1970s, ACSM identified some simple equations to estimate the steady-state energy requirements associated with common modes of activities used in GXTs
EQUATIONS PROVIDE ESTIMATES OF ENERGY COSTS WITH STD DEVIATIONS OF ~7-9%
Standard deviation of equations for estimating energy costs
7-9%
Additional error when using ACSM equations can happen when… (3 examples)
- when the equations are used to estimate maximal aerobic power and the increments between the stages are too large
- When the person tested is somewhat unfit
- when the person is “diseased” (i.e. cardiac patients)
when the ACSM equations used to estimate maximal aerobic power have increments between stages that are too long…
equations overestimate actual measured O2 uptake
O2 uptake cant keep pace with the stage of the test
ex. jumping from 3.2mph to 6.0mph in consecutive stages
when the person being tested is somewhat unfit, ACSM equations…
equations overestimate the actual measured O2 uptake
O2 uptake cant keep pace with the stage of the test
this is probably because tests were developed in fit individuals
when the person is “diseased” ACSM equations…
ex. cardiac disease
equations overestimate the actual measured O2 uptake
The GXT is too aggressive
The O2 uptake can’t keep pace with the stage of the test
Gross (Total) O2 consumption =
Net O2 consumption + Resting O2 consumption
Net O2 consumption vs. Resting O2 consumption
Net = O2 consumed to complete an activity Resting = baseline measure = 3.5 ml/kg*min
Resting O2 consumption =
3.5 ml/kg*min
1 MET
Net O2 cost of the activity - components
Includes horizontal and vertical components of work
ex. treadmill, accounting for speed and grade of incline
Note for GXT
Subjects must follow instructions (don’t hold on to the treadmill railing, maintain pedal cadence)
work instruments MUST BE CALIBRATED so the settings are known to be correct
WALKING EQUATION
- used for walking speeds between 1.9 and 3.7 mph and the client must be walking
- -eliminate vertical component if walking on flat surface or 0% incline
VO2 ml/kg*min =
3.5+ 2.68 (speed in mph) + 0.48 (speed in mph)(%grade)
TREADMILL RUNNING EQUATION
–used for jogging speeds greater than 3.7mph
VO2 ml/kg*min =
3.5+ 5.36(speed in mph) + 0.24(speed in mph)(%grade)
OUTDOOR RUNNING EQUATION
–if you don’t have a steady grade or if it is unknown, eliminate the vertical component of the equation
VO2 mL/kg*min=
3.5+ 5.36(speed in mph) + 0.48(speed in mph)(%grade)
LEG ERGOMETRY EQUATION
ACSM equation comes out (is reported in) ml/min, while the simplified equation reports it in mL/kgmin
workload or power is in the units kgm/min (ACSM refers to these units as kgm/m (min))
Vo2 ml/kg*min=
3.5+ 2(workload)/BW
Workload for arm and leg ergometry equations
ACSM refers to the units as kgm/m
The power depends on how fast the flywheel is moving against the set amount of resistance
Resistance generally reported in kg (technically should be N)
Speed of the flywheel depends on how fast the subject is pedaling and on the gearing used to drive the flywheel
Monarch bike
flywheel moves 6 m per revolution
Proper unit for expressing workload vs ACSM expression for ergometry (leg and arm) equations
proper unit is watts
ACSM expresses in kgm/m
ACSM conversion is 1 watt = 6 kgm/m
watt conversion
1 watt = 6 kgm/min
technically 6.12
ARM ERGOMETRY EQUATION
ACSM equation reported in ml/min, while simplified equation is reported in mL/kg*min
VO2 mL/kg*min=
3.5+ 3(workload)/BW
workload = (resistance setting)(flywheel setting per revolution)(rpm)
