Metabolic Calculations - Purpose

Estimate energy expenditure during steady Estimate energy expenditure during steady state exercisestate exercise

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 Calculations (S=Speed in m/min; G= % Grade) MODE Horizonal + Vertical + Rest• Walking VO2 = (0.1• S) + (1.8 • S • G) +

3.5• Running VO2 = (0.2• S) + (0.9 • S • G) + 3.5• Cycle VO2 = 1.8 (work rate) + 3.5 + 3.5

Body Weight (kgs)

• Arm VO2 = 3 (Work Rate) + 3.5 Body Weight (kgs)

• Stepping VO2 = (0.2• f) + (1.33 • 1.8 • h • f) + 3.5

CARRY OUT EACH STEP TO 2 DECIMAL PLACESMonark Cycle Work Rate: Resistance X Revs/min x 6m/revMonark Arm Work Rate: Resistance X Revs/min x 2.4m/rev

• 1L= 1000 mL• 1kg= 2.2 lbs• 1mph= 26.8 mmin-1

• 1 MET = 3.5 mLkg-1min-1

• 1 W= 6 kgmmin-1

• 1 in = 0.0254m=2.54 cm• Pace: min/mile to mph = 60/time• Ex: 7.5 min/mile / 60 min/hr = 8mph

• Kcal/min = METS * 3.5 * BW

200

• 1L O2min-1 = 5 kcalmin-1

• 1 lb of fat= 3500kcal

Metabolic Calculations (S=Speed; G=Grade)

• Walking (most accurate from 1.9-3.7 mph)– VO2 = (0.1• S) + (1.8 • S • G) + 3.5

• Treadmill and Outdoor Running (for speeds > 5 mph)– VO2 = (0.2• S) + (0.9 • S • G) + 3.5

• Leg Ergometry – VO2 = 1.8 (work rate)/(BM) + 3.5 + 3.5

• Arm Ergometry– VO2 = 3 (Work Rate)/(BM) + 3.5

• Stepping– VO2 = (0.2• F) + (1.33 • 1.8 • H • f) + 3.5

CARRY OUT EACH STEP TO 2 DECIMAL PLACES

Assumptions and Limitations• Measured VO2 is highly reproducible at a given steady

state workload. Failure to achieve steady state is an overestimation of VO2.

• Accuracy of equations is unaffected by most environmental conditions such as heat and cold.

• However, variables that change mechanical efficiency (gait abnormalities, wind, snow or sand) result in a loss of accuracy.

• Assumption that ergometers are calibrated and no holding on to hand rails occur during on treadmill.

Met Calc - Key Points

• Estimates oxygen requirement (VO2) for various workloads– Linear relationship– Some variability

(S.E.E. 7%)

assumptions

500

1000

1500

2000

2500

0 50 100 150 200

Watts

VO

2 (

ml/m

in)

S.E.E. 7%

Met Calc - Key Points (con’t)

• “Steady State” or submax exercise:O2 cost = O2 uptake

• “Maximal” ExerciseO2 cost > O2 uptake

O2 R

equirement

Workload

AnaerobicComponent

Max Exer

=

VO2max

Predicted

VO2max

you cannot predict maximal

Met Calc - General Principle

MechanicalWorkload

MetabolicEquivalent

• Meters.min-1

• kgm.min-1

• VOVO22

• METs• kcals.min-1

We estimate one value based onWe estimate one value based onknowledge of the otherknowledge of the other

Metabolic Units

Gross vs. NET

All equations give Gross VO2 values.

For weight loss use the NET VO2 vales.

NET: Gross – resting valueVO2 NET : 40 ml/kg/min – 3.5 ml/kg/min = 36.5 ml/kg/min

OR

: 11.4 METS – 1 MET = 10.4 METS

Metabolic Calculations (S=Speed in m/min; G= % Grade) MODE Horizonal + Vertical + Rest• Walking VO2 = (0.1• S) + (1.8 • S • G) +

3.5• Running VO2 = (0.2• S) + (0.9 • S • G) + 3.5

• Cycle VO2 = 1.8 (work rate) + 3.5 + 3.5 Body Weight

• Arm VO2 = 3 (Work Rate) + 3.5 Body Weight

• Stepping VO2 = (0.2• f) + (1.33 • 1.8 • h • f) + 3.5

CARRY OUT EACH STEP TO 2 DECIMAL PLACESMonark Cycle Work Rate: Resistance X Revs/min x 6m/revMonark Arm Work Rate: Resistance X Revs/min x 2.4m/rev

ACSM Walking Equation• Speeds 50-100 m/min; 1.9-3.7 mph

– (1 mph = 26.8 m/min)

• “Relative” VO2 unit (ml/kg/min; ml.kg-1.min -1)

VO2 walking = Horizontal Walking (HW) + Vertical Climb (VC) + Resting

VO2 walking = Speed (m/min) x 0.1 + % grade x Speed (m/min) x 1.8 + 3.5

ACSM Walking Equation• Example: VO2 for walking @ 3.0 mph at 5% grade

• Convert 3.0 mph to m/min– 3.0 x 26.8 = 80.4 m/min

VO2 walking = Horizontal Component + Vertical Component + Resting

VO2 walking = Speed (m/min) x 0.1 + % grade x Speed (m/min) x 1.8 + 3.5

• VO2 = 80.04 x 0.1 + 80.04 x .05 x 1.8 + 3.5

• VO2 = 8.04 + 7.20 + 3.5

• VO2 = 18.74 ml.kg-1.min-1

• VO2 = 18.74 ml.kg-1.min-1 / 3.5 = 5.4 METS

ACSM Running Equation • Speeds > 134 m/min; > 5.0 mph (1 mph = 26.8 m/min)

VO2 for running at 6.0 mph at a 5% grade• Convert 6.0 mph to m/min

– 6.0 x 26.8 = 160.8 m/minVO2 running = Horizontal Component + Vertical Component + Resting

VO2 running = Speed (m/min) x 0.2 + % grade x Speed (m/min) x 0.9 + 3.5

VO2 running = 160.8 x 0.2 + 0.05 x 160.8 x 0.9 + 3.5

VO2 running = 32.16 + 7.24 + 3.5

VO2 running = 42.9 ml/kg/min

VO2 running = 42.9 ml/kg/min / 3.5 = 12.26 METS

ACSM Leg Cycling Equation

• Loads 300-1200 kgm/min; 50-200 wattsWork Rate = kg x meters/rev x RPM

Use 6 meters/revolution for the Monark Ergometer

Add resting twice : 1 for resting and 1 for unloadedQ: What is the VO2 for a 90 kg subject pedaling at 2.0 kgs at 60 rpms

Work Rate: 2.0 kg x 6 m/rev x 60 rpms = 720 kgmVO2 Cycling = 1.8 x WR + 3.5 + 3.5

BW

VO2 Cycling = 1.8 x 720 + 3.5 + 3.5

90 kgs

VO2 Cycling = 14.4 + 3.5 + 3.5

VO2 Cycling = 21.4 ml/kg/min or 6.1 METS

ACSM Arm Cycling Equation• Loads 150 to 750 kgm/min; 25-125 watts

– 3.0 = ml.min-1 per kpm/min ( from leg cycling)– Only 1 resting component (3.5) – Monark™ Rehab Trainer: 2.4 meter/rev

Work Rate: kg x 2.4 meters/rev x rpm

Q: What is the VO2 of a 100 kg person who uses a Monark arm ergometer at 3 kg at 50 rpms.

Work Rate: 3 kg x 2.4 meters/rev x 50 revs/min = 360 kgm

• VO2 arm= 3 x WR + 3.5 ml.kg-1.min-1

BW• VO2 arm= 3 x 360 + 3.5 ml.kg-1.min-1 = 14.3 ml/kg/min

100

ACSM Stepping Equation• VO2stepping = 0.2 x f + 1.33 x 1.8 x h x f + 3.5

• VO2 varies with Step height & rate• “Relative” VO2 unit (ml.kg-1.min-1)• VO2 (ml.kg-1.min- 1 ) = Horizontal + Vertical + Resting• Horizontal = steps/min x 0.2• Vertical = step ht x steps/min x 1.33 x 1.8

– Down cycle 0.33 VO2 of the up cycle (add this in by multiplying by “1.33”)

– 1.8 is the constant for vertical work• Step height is entered in meters

– 1 in = 0.0254m=2.54 cm

ACSM Stepping EquationQ: What is the VO2 for a 55 kg woman who is stepping on a 12” bench

at 30 steps per minute

• Calculate step height in meters– 12” x 0.0254 = 0.31 meters

VO2stepping = 0.2 x f + 1.33 x 1.8 x h x f + 3.5

VO2stepping = 0.2 x 30 + 1.33 x 1.8 x 0.31 x 30 + 3.5

VO2stepping = 6 + 22.26 + 3.5VO2stepping = 31.76 ml/kg.min

VO2stepping = 31.76/3.5 = 9.1 METS

Question: What is the kcal expenditure (kcal.min-1) for this 55 kg person exercising at the above VO2 or METS? This person exercises at this rate 3 times per week for 30 minutes each session.

How long will it take this person to lose 10 pounds exercising at this rate?

Kcal conversion example

Q: What is the kcal expenditure (kcal.min-1) for a 55 kg person exercising at an oxygen uptake of 9.1 METs? This person exercises at this rate 3 times per week for 30 minutes each session. How long will it take this person to lose 10 pounds exercising at this rate?

kcal.min-1 = METs x 3.5 x BW (kg)

200

kcal.min-1 = 8.1 x 3.5 x 55 (Why did we use 8.1 METS?) 200 (For weight loss use the NET)

kcal.min-1 = 7.8

1 pound of fat = 3,500 kcals 10 pounds = 35,000 kcals

Answer: 35,000 kcals = 4,487.18 minutes

7.8 kcals/min

4,487.18 minutes = 49.9 weeks

90 minutes/week