Metabolic Calculations
Chapter 5 and Appendix D
Importance of Metabolic Calculations
It is imperative that the exercise physiologist is
able to interpret test results and estimate energy
expenditure.
Optimizing exercise protocols.
Exercise prescription.
Weight loss.
Metabolic Topics
Work, Energy, Power as they relate to
calorimetry
Expressions of oxygen uptake
Concept of the MET
Metabolic calculations
Case studies
1
Work and Energy
Work - Application of force through distance
Work = Force x distance (i.e.kg x m)
Force is constant
W = 70 kg x 0.75 meters
52.5 kg•
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
Power
• Power – Amount of work per
•6 unit time
• work/time (I.e. kgm/min; Watt)
• 1 W = 6 kgm•min-1
• Note = For cycle ergometry you must account for
• 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)
W
= 720 kgm•min-1 or
Energy Expenditure
Understanding energy expenditure is important
for weight loss, work tasks, exercise
prescription, etc.
Calorie - basic unit of measure of energy
expenditure
Direct and Indirect Calorimetry can be used to
estimate energy expenditure
2
Calorimetry
Direct Calorimetry
Metabolic Chamber
(enclosed)
Slide 8
Indirect Calorimetry
Closed or Open Circuit
Spirometry Indirect Calorimetry,
Slide 11, Slide 10
Calorimetry
Calorimetry
3
Calorimetry
Indirect Calorimetry
Calorimetry
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
i.e. 1 liter of VO2 = ~ 5 kcals
4
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.
For example, we can use oxygen consumption
measures to help us determine caloric
expenditure during exercise.
Expressions for O2 uptake (VO2)
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-1•min-1): used to
compare individuals of different body size
and to better quantify aerobic fitness level
5
MET
Clinically, the MET or “Metabolic equivalent”
equivalent”
is used to express energy expenditure and to
prescribe exercise in clinical settings.
settings.
1
1
1 MET = 3.5 ml•
ml•kg •min
For example
80 kg man working at 2.5 L•min-1
2,500 mL•
ml•kg-1•min-1
mL•min-1 / 80kg = 31.25 ml•
1
1
31.25 ml•
•
kg
•
min
/
3.5
=
8.9
METs
ml
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 140 lbs has VO2 pk = 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%?
Quiz – Met Calc (3 points per
question)
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
Estimation of Energy Expenditure
We can estimate energy expenditure through
American College of Sports MedicineSM Metabolic
Equations
Special considerations for these equations
Need to assure that person is at steady state in order to use
equations
There is a variance in prediction
Need to consider environmental considerations
No railrail-holding and make sure equipment is calibrated
Gross Vs. Net O2 cost
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 = in x 2.54
Convert speed from mph to m/min (mi/h X 26.8)
1Watt = 6 kgm•
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,
rate, weekly physical
activity and energy expenditure, and food intake
7
Metabolic Calculations
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 Ergometry
VO2 = (10.8 • W • M-1) + 7 OR
VO2 = ((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
Useful calculation tips to live by
Write down all known’
known’s and do any necessary
conversions first.
Calculate each component separately, then
complete the calculation
I.e. vertical, horizontal, resting
Make sure your answer agrees with the
question in numerical and unit form (always
provide units!!!)
Practice Calculation (from pg 311)
A 7171-yearyear-old man weighing 180 lb walks on a
motormotor-driven treadmill at 3.5 mph and a 15%
grade. What is his gross MET level?
8
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/min is he expending?
More on pages 309 - 312
…and Even More Practice
Calculations
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
Indirect Calorimetry for Estimation of Fuel
Utilization During Exercise
CHO (glucose) C6H12O6
Oxidation C6H12O6 + 6O2 × 6 CO2 + 6 H2O
R = VCO2 /VO26 = 6 VCO2 / 6 VO2 = 1.0
FAT (C16H32O2)
Oxidation C16H32O2 + 23O2 × 16 CO2 + 16 H2O
R = VCO2 /VO26 = 16 VCO2 / 23 VO2 = 0.70
9
0
