Importance of Metabolic Calculations
It is imperative that the exercise physiologist is
Metabolic Calculations
Chapter 5 and Appendix D
Metabolic Topics
Work, Energy, Power as they relate to
calorimetry
Expressions of oxygen uptake
C
Concept
off the
h MET
Metabolic calculations
Case studies
able to interpret test results and estimate energy
expenditure.
di
Optimizing exercise protocols.
Exercise prescription.
Weight loss.
Work and Energy
Work - Application of force through distance
Work = Force x distance (i
(i..e.kg x m)
Force is constant
W = 70 kg x 0.75 meters
52..5 kg
52
kg••m or 515 Joules
Energy – capacity to perform work
1 kcal = 4,186 J
CHO = 5.05 kcal • LO2
Fat = 4.74 kcal • LO2
Each L of O2 consumed
= 5 kcal
1
Power (on different modes)
• Power – Amount of work per unit time
• Bike
• work/time (I.e. kgm/min; Watt)
• 1 W = 6 kgm•min-1
• Note = For cycle
l ergometry you must account for
f
• kg
• distance the flywheel moves the kg with one turn
• rev•min-1
• I.e. Monarch = 6 m • rev -1
• Power = (2 kg x 6 m • rev -1 x 60 rev•min-1)
= 720 kgm•min-1 or
W
Power (on different modes)
• Power – Amount of work per unit time
• Step –
• step height (m)
• 4 cycle steps / minute (f)
• Treadmill
• Speed (m/min)
• Grade (% grade – use decimal)
Energy Expenditure
Understanding energy expenditure is important
for weight loss, work tasks, exercise
pprescription,
p
, etc.
Calorie - basic unit of measure of energy
expenditure
Direct and Indirect Calorimetry can be used to
estimate energy expenditure
Calorimetry
Direct Calorimetry
Metabolic Chamber
(enclosed)
Slide 8
Indirect Calorimetry
Closed or Open Circuit
Spirometry Indirect Calorimetry,
Slide 11, Slide 10
2
Calorimetry
Calorimetry
Indirect Calorimetry
Calorimetry
Calorimetry
3
Indirect Calorimetry: Variables Obtained
Oxygen consumption and carbon dioxide production
(VO2, VCO2)
Respiratory exchange ratio (RER
(RER or R)
R)- Noninvasive method to estimate the relative contribution of
fat and CHO to energy metabolism
RQ during steady state conditions
VCO2/VO2
Calorie/ energy expenditure
Need a link
In research and in practice, we use information
obtained from openopen-circuit spirometry to give
us estimates of energy expenditure, aerobic
power and fuel utilization.
power,
utilization
For example, we can use oxygen consumption
measures to help us determine caloric
expenditure during exercise.
i.e. 1 liter of VO2 = ~ 5 kcals
For example:
How many calories are you burning
if you exercise in a step class using
an 8 inch bench?
If we need to know the oxygen
consumption (workload) for
someone exercising at 6 mph at 5%
grade…..
If we need to figure out, how long it
will take an individual to loose a
certain amount of weight….
4
Expressions for O2 uptake (VO2)
Expressions for O2 uptake (VO2)
We will be using metabolic calculations to
calculate oxgyen consumption and calories
Oxygen consumption in humans can be
expressed in two different forms
Absolute – (L
(L··min-1 or ml
ml··min-1): Can be used in a
form that will yield rate of energy expenditure
(1 L of O2 = 5 kcal)
Relative – (ml
(ml•kg
•kg-1•min-1): used to compare
individuals of different body size and to better
quantify aerobic fitness level
MATH AND UNITS ??
Make sure that you have your answer is in the
right units.
Make sure your answer units make physiological
sense
Make sure your answer units agree with the
problem (i.e. apples = apples NOT apples =
oranges)
Make sure you cancel out units correctly
i.e. 3 L/K
X
5
K/ P =
15 L/Ps
Absolute – (L
(L··min-1 or ml
ml··min-1): Can be
! UNITS
UNITS
usedUNITS
in a form
that will! yield
rate!of
energy expenditure ; good for converting
oxygen consumption into calories
(1 L of O2 = 5 kcal)
Relative – (ml
(ml•kg
•kg-1•min-1): used to
compare individuals of different body size
and to better quantify aerobic fitness level
Example
5 apple/oranges X 6 orange/ bananas = ???
30 apple / bananas ÷
6
oranges = ???
5 apple/ banana/ oranges
Expressions of units
a/ b/ c is the same as a•b-1•c-1
5
MET
METs
Clinically, the MET or “Metabolic equivalent”
is used to express energy expenditure and to
prescribe exercise in clinical settings.
settings.
1 MET = 3.5 ml•
ml•kgg-1•min-1
For example
80 kg man working at 2.5 L•min-1
2,500 mL•min
mL•min-1 / 80kg = 31.25 ml
ml••kg-1•min-1
1
1
31.25 ml•
ml•kg •min / 3.5 = 8.9 METs
Met Calc warming up
Man weighing 200 lbs has pk O2 uptake = 4.0 L•min-1
What is his relative oxygen consumption?
How many METs is this?
A woman weighing 155 lbs has VO2 pk = 32.1 ml
ml••kg
-1 • min-1
What is her absolute oxygen uptake?
How many METs is this?
What is the difference between indirect and direct
calorimetry??
calorimetry
6
Practice with O2 calculations
Man weighing 176 lbs has pk O2 uptake = 4.4 L•min-1
What is his relative oxygen consumption?
How many METs is this?
A woman weighing
i hi 140 lbs
lb has
h VO2 pkk = 36.7
36 7 ml
ml••kg
-1 • min-1
What is her absolute oxygen uptake?
How many METs is this?
How many METs would 70% of her peak capacity be
equivalent to?
How many calories per minute is she burning at her peak?
How many calories per minute is she burning at 70%?
ACSM Metabolic Calculations
Can estimate energy expenditure if you have
Vertical component
Horizontal component
Resting component
Useful conversions (Memorize) /
Always convert lb to kg (lb/2.2)
Centimeters
C i
= in
i x 2.54
2 54
Convert speed from mph to m/min (mi/h X 26.8)
1Watt = 6 kgm•min
kgm•min-1
Remember equivalents
Watts to kgm •min-1
kcals (3,500 kcals = 1 lb of fat gain or loss)
1 L O2 = 5 kcals
For weight loss purposes, always account for resting metabolic rate, weekly
physical activity and energy expenditure, and food intake
Estimation of Energy Expenditure
We can estimate energy expenditure through
American College of Sports MedicineSM Metabolic
Equations
Special considerations for these equations
Need
N d tto assure th
thatt person is
i att steady
t d state
t t in
i order
d to
t use
equations
There is a variance in prediction
Need to consider environmental considerations
No rail
rail--holding and make sure equipment is calibrated
Gross Vs. Net O2 cost
Metabolic Calculations – (see also page 216)
Walking
(S=Speed; G=Grade)
VO2 = (0.1•
(0.1• S) + (1.8 • S • G) + 3.5
Treadmill and Outdoor Running
VO2 = (0.2•
(0.2• S) + (0.9 • S • G) + 3.5
Leg
L Ergometry
E
t (watch
( t h the
th units
it here)
h )
VO2 = (10.8 • W • M-1) + 7 OR
VO2 = ((kgm
((kgm • min-1) • 2) + (3.5 • W)
Arm Ergometry
VO2 = (18 • W • M-1) + 3.5
Stepping
VO2 = (0.2
(0.2•• F) + (1.33 • 1.8 • H • f) + 3.5
7
Break it down – Walking equation
oxygen
consumption
(ml/kg/min)
VO2 = [(0.1•
[(0.1• S)] + [(1.8 • S • G)] + 3.5
Horizontal component –
i.e. oxygen cost of
Speed (units are
Speed (units are
carrying
m/min)
m/min)
body in horizontal
direction over distance
Vertical component – i.e.
(units are ml/kg/m)
oxygen cost of carrying
body in vertically(units are
ml/kg/m)
grade
Resting oxygen
consumption
(ml/kg/min)
Useful calculation tips to live by
Practice Calculation (from pg 311)
Write down all known’s and do any necessary
A 7171-yearyear-old man weighing 180 lb walks on a
conversions first.
Calculate each component separately, then
complete the calculation
I.e. vertical, horizontal, resting
Make sure your answer agrees with the
motor--driven treadmill at 3.5 mph and a 15%
motor
grade.
What is the oxygen consumption
What is the MET level
How many calories is he burning at this level?
question in numerical and unit form (always
provide units!!!)
8
…and Even More Practice
Calculations - bonus
More Practice Calculations
A client weighs 155 lbs was determined to
have a VO2 pk of 45 ml/kg/min.
What is his oxygen consumption in absolute terms?
In METs?
How many kcals
kcals/min
/min is he expending?
expending?
A 2323-yearyear-old woman weighing 150 lb jogs
on a motormotor-driven treadmill at 5.8 mph and
a 0% grade.
What is the oxygen consumption?
What is her MET level?
How many kcals
kcals/min
/min is she expending?
A cardiac patient has just entered your cardiac
rehabilitation program and has an exercise
prescription to exercise 40 minutes at 6 METs,
4 days per week and the client weight 210 lbs.
Calculate the following
Treadmill grade for a speed of 2.5 mph
Step rate for a 4 inch bench
Resistance for a monarch bike at 50 rpm
Total caloric expenditure for each workout session
9
0
