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ACSM Exercise Specialist Workshop
Metabolic Calculations
Tutorial
Purpose of Metabolic Calculations
Under steady-state conditions, VO2 provides a measure of the energy cost of exercise
The rate of O2 uptake at maximal exercise indicates the capacity for O2 transport and utilization
Peak VO2 serves as the gold standard criterion measure of cardiorespiratory fitness
At steady state, and in combination with CO2 output, VO2 can provide information about type of fuel use during exercise
Determine work rates to be used in the development of exercise prescription
Expression of VO2
Absolute- Liters per minute (Lmin-1) Used to convert consumption to a rate of energy expenditure
Relative- mL per kg body weight per min (mLkg-1min-1) Used to compare VO2 among varying body sizes
Gross oxygen consumption- Total consumption rate under any circumstances, either in absolute or relative; describes rest plus exercise
Net oxygen consumption- Consumption rate above resting oxygen uptake (approx. 3.5 mLkg-1min-1); describes exercise
RER and RQ RER-Respiratory
Exchange Ratio Ventilatory
measurement Reflects gas exchange
between lungs and pulmonary blood
Exceeds 1.0 during heavy exercise due to buffering of lactic acid which produces CO2
RQ-Respiratory Quotient Cellular Respiration and
substrate utilization• 0.7 = Fat• 1.0 = Carbohydrate• 0.8 = Protein
Equivalent to RER only under resting or steady-state conditions
Can never exceed 1.0 RQ is used to estimate
energy expenditure, however, when RQ is not available, assume 5 kcal L-1
Estimation of Energy Expenditure
When VO2 cannot be measured directly, estimations can be made during steady-state exercise (will overestimate VO2 if not at steady-state)
Equations are based on relating mechanical work rate to metabolic equivalents
Equations are appropriate for general clinical and lab use
Estimation of Energy Expenditure
Equations can be used for: Estimating or predicting energy
expenditure Designing an exercise prescription to
determine the exercise intensity associated with a desired level of energy expenditure
Cautionary Notes The inter-subject variability for VO2 may be as
high as 7% Appropriate for steady-state submaximal
aerobic exercise Any variable that changes the metabolic
efficiency results in loss of accuracy (e.g., orthopedic limitations, holding handrail on treadmill, etc.)
Assumes that a metabolic cart or gas analyzers and flow indicators are calibrated and used properly
Despite these caveats, metabolic equations provide a valuable tool for exercise professionals
Conversion Factors
1L= 1000 mL 1kg= 2.2 lbs 1mph= 26.8 mmin-1
1lb of fat= 3500kcal 1 MET=3.5 mLkg-1min-1
1 W= 6 kgmmin-1
1L O2min-1 = 5 kcalmin-1
1 in= 0.0254m=2.54 cm
Located in Appendix D of GETP6
Conversion Flowchart
METS
mLkg-1min-1
mLmin-1 L min-1 Kcalmin-1
Total kcal
lb fat loss/gain
X 3.5
X BW
X 1000 X 5
X Tot min
3500 3.5
BW
1000 5
Tot min
X 3500
Walking (1.93.75 mph) VO2= (0.1S) + (1.8 S G) + 3.5
Horizontal Vertical Rest
S= speed in mmin-1 (convert if needed)G= grade in decimal form (i.e., 5% is
0.05); if 0% grade, then vertical=0R= resting component NOTE: VO2 is reported as mLkg-1min-1
Running (>5.0mph) VO2= (0.2 S) + (0.9 S G) + 3.5 Horizontal Vertical Rest
All variables are the same as for walking
NOTE: VO2 is reported as mLkg-1min-1
Leg Ergometry VO2= (10.8 W/M) + 7 M= mass (weight) of subject in kg W= Work rate in watts,
convert when necessary 1 W= 6 kgmmin-1
kgmmin-1=R D f• R= resistance in kg• D= distance of the fly wheel
• 6m for Monark• 3m for Tunturi
• f= frequency in rpm
NOTE: VO2 is reported as mLkg-1min-1
Arm Ergometry
VO2= 18(W/M) + 3.5
Find work rate the same as leg ergometry
Major difference: D=2.4 for Monark
NOTE: VO2 is reported as mLkg-1min-1
Stepping Ergometry
VO2= (0.2 f) + (1.33 1.8 f h) + 3.5 f=stepping rate h=height of step in m
NOTE: VO2 is reported as mLkg-1min-1
Question #1
VO2= (0.1x85.76)+(1.8x85.76x.06)+3.5
VO2= 8.576 + 9.26 + 3.5
VO2= 21.34 mLkg-1min-1
21.34/3.5 = 6.1 METs
Question #2 VO2 = (0.2x241.2)+(0.9x241.2x.01)+3.5
VO2 = 48.24 + 2.17 + 3.5
VO2 = 53.9 mLkg-1min-1
VO2 = 53.9 mLkg-1min-1 x 68.0 kg=3665.2 mLmin-1
VO2(Lmin-1) =3665.2 mLmin-1/1000 mLL-1 = 3.67 Lmin-1
Kcalsmin-1 = 3.67 Lmin-1x5 kcals L-1 =18.4 Kcalsmin-1 Kcals in 40 minutes = 18.4 Kcalsmin-1 x 40min.= 736 kcals
expended in 40 minutes
Question #3 50 kg man walking at 75% VO2 reserve.
Max VO2 = 2.4 Lmin-1. What speed at a grade of 12%.
2.4 Lmin-1 = 2400 mLmin-1
2400 mLmin-1 ÷ 50 kg = 48 mLkg-1min-1 48 mLkg-1min-1 x 0.75 = 36 mLkg-1min-1
• 36 = (0.1)(x) + (1.8)(x)(0.12) + 3.5• 36 = 0.1x + 0.21x + 3.5• 32.5 = 0.31x• x = 104.8 mmin-1/26.8 mmin-1 = 3.9 mph
Question #4 VO2 = (0.2xS)+(0.9xSxG)+3.5 45.0 mLkg-1min-1 = 0.2x87.6)+(0.9x187.6xG)
+3.5 45.0 mLkg-1min-1 = 37.52 + 168.8(G) + 3.5 3.98 = 168.8 (G) 0.024 = G or 2.4%
Question #5
VO2 = (18 x W/M) + 3.5 where W = 0.5kg x 2.4m x 50rpm w=60 kgmmin-1 or 10 watts
VO2 mLkg-1min-1 = (18 x 10)/50 + 3.5
VO2 = 180/50 + 3.5
VO2 = 3.6 + 3.5
VO2 = 7.1 mLkg-1min-1
Question #6 176 lbs/2.2 = 80 kg Warm Up 2.5 x 3.5 = 8.75 mLkg-1min-1
8.75 mLkg-1min-1x80 kg=700 mLmin-1
700 mLmin-1 /1000 mLL-1 =0.7 Lmin-1
0.7 Lmin-1 x 5 kcalsL-1 = 3.5 kcalsmin-1 x 5 min. = 17.5 kcals in 5 min.
Question #6... continued Exercise 4.5 METs = 15.75 mLkg-1min-1
15.75mLkg-1min-1
x 80kg = 1260 mLmin-1 = 1.26 Lmin-1
1.26 Lmin-1 x 20 min =25.2 L x 5 kcal L-1 = 126 kcals in 20 min.
4 METs = 14 mLkg-1min-1
14 mLkg-1min-1 x 80 kg = 1120 mLmin-1 = 1.12 Lmin-1
1.12 Lmin-1 x 15 min = 16.8 L x 5 kcal L-1 = 84 kcals
Question # 6…continued Cool Down 2 METs = 7 mLkg-1min-1/80kg =560 mLmin-1
560 mLmin-1/1000 mLL-1 = 0.56 Lmin-1
0.56 Lmin-1 x 5 min = 2.8 L 2.8 L x 5 = 14 kcals
17.5 + 126 + 84 + 14= 241.5 Kcals
Question #7 140 lbs = 63.6 kg TM @ 3.2/0%
VO2 = 8.576+3.5=12.08 mLkg-1min-1
12.08 x 63.6 = 768.29 mLmin-1
768.29/1000 = 0.768 Lmin-1
0.768 x 10 = 7.7 l = 38.5 kcals• TM @ 3.4/2% = 50.5 kcals• TM @ 3.0/5% = 59.5 kcals
• Total Kcals = 148.5 • 148.5 x 3 = 445.5/week• 3500 x 15 = 52,500 kcals• 52, 500 kcals/445.5 = 118 weeks @ 3 days/week
Question # 8
•MET level of person with VO2 of 55 mLkg-1min-1?
55 mLkg-1min-1 ÷ 3.5 mLkg-1min-1 per MET = 15.7 METs
Question # 9
60 kg women with a VO2 of 2400 mLmin-1. What is her MET level?
2400 mLmin-1 ÷ 60kg = 40 mLkg-1min-1
40 mLkg-1min-1 ÷ 3.5 mLkg-1min-1 per MET = 11.4 METS
Question #10 70 kg person using Stepper @ 18
stepsmin-1, 25 cm step• VO2 = (0.2 x f)+(1.33 x 1.8 x H x F) +3.5
• VO2 = (0.2 x 18) + (1.33x1.8x0.25x18)
• VO2 = 3.6 + 10.8
• VO2 = 14.4 mLkg-1min-1 or 4.1 METs
Question 10…continued 70 kg person on Monark @ 750 kgmmin-1
750 kgmmin-1 / 6 kgmmin-1 per watt= 125 watts
• VO2 = (10.8x125)/70 + 7
• VO2 = 18.9 + 7 = 25.9 mLkg-1min-1 or 7.5 METs
• (NOTE: may get 7.4 METS if use 6.12 kgmmin-1 as 1 watt)
Question #10…continued 70 kg person on Monark arm
ergometer @ 350 kgmmin-1. 350 kgmmin-1 = 58.3 watts
• VO2 = (18x58.3)/70 + 3.5
• VO2 = 14.99 + 3.5
• VO2 = 18.49 or 5.3 METs
Question # 11 Who is exercising harder, Fred or Pete?
Fred(72 kg)• VO2 = (0.2x160.8) + (0.9x160.8x0.1)+3.5
• VO2 = 32.16 + 14.47 + 3.5
• VO2 = 50.13 mLkg-1min-1 or 14.3 METSPete (55 kg)
•Power = 2.5kg x 6m x 60rpm= 900 kgmmin-
1 or 150 watts•VO2 = (10.8 x 150)/55 + 7 = 36.45 mLkg-
1min-1 or 10.4 METS•FRED is working harder
Question # 12 Desired exercise intensity = 8 METs;
what is the grade at 3 mph 3 mph x 26.8 mmin-1 per MPH = 80.4 mmin-1
•28 mLkg-1min-1 = (0.1x80.4) + (1.8x80.4xG) + 3.5•28 = 8.04 + 144.7(G)+ 3.5•16.46 = 144.7 (G)•G= 11.4%
Question # 13 Functional capacity of 70 kg male
completing stage 5 (3mph/12%) of Balke protocol. 3 mph = 80.4 mmin-1
• VO2 = (0.1x80.4) + (1.8x80.4x0.12)+3.5
• VO2 = 8.04 + 17.37 + 3.5
• Relative VO2 = 28.9 mLkg-1min-1 or 8.3 METs
• Absolute VO2 = 2023 mLmin-1 or 2.02 Lmin-1
Question # 14 MET level of man running @ 7mph
and 5% grade 7 mph = 187.6 mmin-1
• VO2 = (0.2x187.6)+(0.9x187.6x0.05)+3.5
• VO2 = 37.52 + 8.44 + 3.5
• VO2 = 49.46 mLkg-1min-1 or 14.1 METs
Question # 15 What is kcal utilization over 20
minutes on the cycle ergometer if VO2 = 1745 mLmin-1.
• 1745 mLmin-1 = 1.75 Lmin-1
• 1.75 Lmin-1 x 5 kcalsL-1 = 8.75 kcalsmin-1
• 8.75 kcalsmin-1 x 20 min = 175 kcals expended over 20 minutes
Questions