Metabolic Calculations Importance of Metabolic Calculations

Metabolic Calculations
Chapter 5 and Appendix D
Importance of Metabolic Calculations
ƒ It is imperative that the exercise physiologist is
able to interpret test results and estimate energy
expenditure.
ƒ Optimizing exercise protocols.
ƒ Exercise prescription.
ƒ Weight loss.
Metabolic Topics
ƒ Work, Energy, Power as they relate to
calorimetry
ƒ Expressions of oxygen uptake
ƒ Concept of the MET
ƒ Metabolic calculations
ƒ Case studies
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Work and Energy
ƒ Work - Application of force through distance
ƒ Work = Force x distance (i.e.kg x m)
ƒ Force is constant
ƒ W = 70 kg x 0.75 meters
52.5 kg•
kg•m or 515 Joules
ƒ Energy – capacity to perform work
ƒ 1 kcal = 4,186 J
ƒ CHO = 5.05 kcal • LO2
ƒ 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
ƒ Understanding energy expenditure is important
for weight loss, work tasks, exercise
prescription, etc.
ƒ Calorie - basic unit of measure of energy
expenditure
ƒ Direct and Indirect Calorimetry can be used to
estimate energy expenditure
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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
ƒ Oxygen consumption and carbon dioxide production
(VO2, VCO2)
ƒ Respiratory exchange ratio (RER
(RER or R)R)ƒ Noninvasive method to estimate the relative contribution of
fat and CHO to energy metabolism
ƒ RQ during steady state conditions
ƒ VCO2/VO2
ƒ Calorie/ energy expenditure
ƒ i.e. 1 liter of VO2 = ~ 5 kcals
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Need a link
ƒ 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.
ƒ For example, we can use oxygen consumption
measures to help us determine caloric
expenditure during exercise.
Expressions for O2 uptake (VO2)
ƒ Absolute – (L·
(L·min-1 or ml·
ml·min-1): Can be
used in a form that will yield rate of
energy expenditure
ƒ (1 L of O2 = 5 kcal)
ƒ Relative – (ml•
(ml•kg-1•min-1): used to
compare individuals of different body size
and to better quantify aerobic fitness level
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MET
ƒ Clinically, the MET or “Metabolic equivalent”
equivalent”
is used to express energy expenditure and to
prescribe exercise in clinical settings.
settings.
1
1
ƒ 1 MET = 3.5 ml•
ml•kg •min
ƒ For example
ƒ
ƒ
ƒ
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
ƒ Man weighing 176 lbs has pk O2 uptake = 4.4 L•min-1
ƒ What is his relative oxygen consumption?
ƒ How many METs is this?
ƒ A woman weighing 140 lbs has VO2 pk = 36.7 ml•
ml•kg
-1 • min-1
ƒ What is her absolute oxygen uptake?
ƒ How many METs is this?
ƒ How many METs would 70% of her peak capacity be
equivalent to?
ƒ How many calories per minute is she burning at her peak?
ƒ How many calories per minute is she burning at 70%?
Quiz – Met Calc (3 points per
question)
ƒ Man weighing 200 lbs has pk O2 uptake = 4.0 L•min-1
ƒ What is his relative oxygen consumption?
ƒ How many METs is this?
ƒ A woman weighing 155 lbs has VO2 pk = 32.1 ml•
ml•kg
-1 • min-1
ƒ What is her absolute oxygen uptake?
ƒ How many METs is this?
ƒ What is the difference between indirect and direct
calorimetry?
calorimetry?
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Estimation of Energy Expenditure
ƒ We can estimate energy expenditure through
American College of Sports MedicineSM Metabolic
Equations
ƒ Special considerations for these equations
ƒ Need to assure that person is at steady state in order to use
equations
ƒ There is a variance in prediction
ƒ Need to consider environmental considerations
ƒ No railrail-holding and make sure equipment is calibrated
ƒ Gross Vs. Net O2 cost
ACSM Metabolic Calculations
ƒ Can estimate energy expenditure if you have
ƒ Vertical component
ƒ Horizontal component
ƒ Resting component
ƒ Useful conversions (Memorize) /
ƒ
ƒ
ƒ
ƒ
ƒ
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
ƒ Watts to kgm •min-1
ƒ kcals (3,500 kcals = 1 lb of fat gain or loss)
ƒ 1 L O2 = 5 kcals
ƒ For weight loss purposes, always account for resting metabolic rate,
rate, weekly physical
activity and energy expenditure, and food intake
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Metabolic Calculations
ƒ Walking
(S=Speed; G=Grade)
ƒ VO2 = (0.1•
(0.1• S) + (1.8 • S • G) + 3.5
ƒ Treadmill and Outdoor Running
ƒ VO2 = (0.2•
(0.2• S) + (0.9 • S • G) + 3.5
ƒ Leg Ergometry
ƒ VO2 = (10.8 • W • M-1) + 7 OR
ƒ VO2 = ((kgm • min-1) • 2) + (3.5 • W)
ƒ Arm Ergometry
ƒ VO2 = (18 • W • M-1) + 3.5
ƒ Stepping
ƒ VO2 = (0.2•
(0.2• F) + (1.33 • 1.8 • H • f) + 3.5
Useful calculation tips to live by
ƒ Write down all known’
known’s and do any necessary
conversions first.
ƒ Calculate each component separately, then
complete the calculation
ƒ I.e. vertical, horizontal, resting
ƒ Make sure your answer agrees with the
question in numerical and unit form (always
provide units!!!)
Practice Calculation (from pg 311)
ƒ 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?
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More Practice Calculations
ƒ A client weighs 155 lbs was determined to
have a VO2 pk of 45 ml/kg/min.
ƒ What is his oxygen consumption in
absolute terms?
ƒ In METs?
ƒ How many kcals/min is he expending?
ƒ More on pages 309 - 312
…and Even More Practice
Calculations
ƒ 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
ƒ
ƒ
ƒ
ƒ
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
ƒ CHO (glucose) C6H12O6
ƒ Oxidation C6H12O6 + 6O2 × 6 CO2 + 6 H2O
ƒ R = VCO2 /VO26 = 6 VCO2 / 6 VO2 = 1.0
ƒ FAT (C16H32O2)
ƒ Oxidation C16H32O2 + 23O2 × 16 CO2 + 16 H2O
ƒ R = VCO2 /VO26 = 16 VCO2 / 23 VO2 = 0.70
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