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=0

R= 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 METS

Pete (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