Metabolic Calculations - Purpose

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Metabolic Calculations - Purpose. Estimate energy expenditure during steady state 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.

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Metabolic Calculations - Purpose

Estimate energy expenditure during steady state 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.
1L= 1000 mL

1kg= 2.2 lbs

1mph= 26.8 mmin-1

1 lb of fat= 3500kcal

1 MET = 3.5 mLkg-1min-1

1 W= 6 kgmmin-1

1L O2min-1= 5 kcalmin-1

1 in = 0.0254m=2.54 cm

Pace: min/mile to mph = 60/time

7.5 min/mile / 60 min/hr = 8mph

Kcal/min =

METS * 3.5 * BW

200

1L O2min-1= 5 kcalmin-1

MEMORIZE

MEMORIZE

MEMORIZE

• 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 tm.
Met Calc - Key Points
• Estimates oxygen requirement (VO2) for various workloads
• Linear relationship
• Some variability (S.E.E. ­ 7%)

assumptions

S.E.E. ­ 7%

Met Calc - Key Points (con’t)

Anaerobic

Component

• “Steady State” or submax exercise:

O2 cost = O2 uptake

• “Maximal” Exercise

O2 cost > O2 uptake

=

Predicted

VO2max

VO2max

O2Requirement

Max Exer

you cannot predict maximal

Met Calc - General Principle

Metabolic

Equivalent

Mechanical

• Meters.min-1
• kgm.min-1
• VO2
• METs
• kcals.min-1

We estimate one value based on

knowledge of the other

Metabolic Units
• Absolute vs. Relative VO2 units
• Absolute
• independent of body weight
• non-weight bearing activities
• leg and arm ‘cycling’
• liters of O2 per minute (l.min-1)
• milliliters of O2 per minute (ml.min-1)
Metabolic Units (cont.)
• Absolute vs. Relative VO2 units
• Relative
• dependent on body weight
• weight bearing activities
• walking, jogging, stepping equations
• milliliters of O2 per kg per minute
• (ml.kg-1.min-1)
• METs: 1 MET = 3.5 ml.kg-1.min-1
Metabolic Units - Energy
• 1 calorie = the heat energy required to raise 1 gm H20, 1o C (@ 15o C)
• 1000 “small” calories = 1 “large” calorie or kilocalorie (kcal)
• Kilocalories per min (kcals . min-1)
• Application to Weight Control
Energy Conversions
• 1 liter O2 , VO2 ~ 5.0 kcals
• 1 lb of fat ~ 3500 kcals
• 1 MET ­ 1.0 kcals . kg . hr-1
• Kcal.min-1 = METs x 3.5 x ( BW(kg) / 200)
• “caloric thresholds” for adaptation during training (200-300 kcals per session; 1000+ for week)
Mechanical Units - Force
• Force = mass x acceleration
• “Weight” ~ mass undergoing gravitation acceleration
• examples: lbs. and kgs
• Kilopond (kp) ­ 1 kg mass under normal gravitational acceleration
• 1 kp ­ 1 kg (cycle work - resistance)
Mechanical Units - Work
• Work = force x distance
• Units:
• kilogram meters (kg.m or kgm)
• kilopond meters (kp.m or kpm)
• foot pounds (ft.lbs)
• Walking/Running: we carry our mass (kg) a given distance (meters) and therefore we can estimate the “work” performed
Mechanical Units - Power
• Power = Work / Time
• Units:
• kilogram meters per min (kg. m. min-1)
• kilopond meters per min (kp. m.min-1)
• watts (1 watt ­ 6 kg. m. min-1)
• Cycle workloads or work rates
• Metabolic (Aerobic) Power = Oxygen Consumption; VO2
ACSM Metabolic Equations: Equation set-up
• Regression equations: estimate Y based upon X
• Y = a + bx
• a = intercept
• “y” value when x = 0
• b = slope of line
• unit change in “y”, for every one unit change in “x”

Y = a + b x

a

Y

b

X

Y Unit = oxygen cost

X Unit = power output

ACSM recommendations

Conversion to units: lb to kg, mph to m.min-1; etc. (metric)

Transform VO2 units to needed units: ml.min-1 to l.min- 1 to ml.kg-1.min-

Write down the equation in appropriate form

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 = Horizontal Walking (HW) + Vertical Climb (VC) + Resting
• HW (ml.kg-1.min-1) = m/minx 0.1
• VC(ml.kg-1.min-1) = % grade (decimal) x m/minx 1.8
• Resting (ml.kg-1.min-1) = 3.5
ACSM Walking Equation
• Example: VO2 for walking @ 3.0 mph
• Convert 3.0 mph to m/min
• 3.0 x 26.8 = 80.4 m/min
• Calculate HW
• 80.4 m/min x 0.1
• 8.04 ml.kg-1.min-1
• Total VO2 = 8.04 + 3.5 = 11.54 ml.kg-1.min-1
VO2 for walking 3.0 mph / 5% grade
• HW + Resting = 11.5 ml.kg-1.min-1
• Calculate VC
• 0.05 % grade x 80.4 m/min x 1.8
• 0.05 x 80.4 x 1.8
• 4.02 x 1.8
• 7.2 ml.kg-1.min-1
• Total VO2 = 8.04 + 7.2 + 3.5 = 18.7 ml.kg-1.min-1
• To convert to METs: 18.7 / 3.5 = 5.3 METs
ACSM Running Equation
• Speeds > 134 m/min; > 5.0 mph
• (1 mph = 26.8 m/min)
• “Relative” VO2 unit (ml.kg-1.min-1)
• VO2 = Horizontal Run + Vertical Climb+ Resting
• HR (ml.kg-1.min-1) = m/minx 0.2
• VC (ml.kg-1.min-1) = % grade (decimal) x m/minx 0.9
• Resting (ml.kg-1.min-1) = 3.5
ACSM Running Equation
• Example: VO2 for running @ 6.0 mph
• Convert 6.0 mph to m/min
• 6.0 x 26.8 = 160.8 m/min
• Calculate HR
• 160.8 m/min x 0.2
• 32.2 ml.kg-1.min-1
• Total VO2 = 32.2 + 3.5 = 35.7 ml.kg-1.min-1
• HR + Resting = 35.7 ml.kg-1.min-1
• Calculate VC
• 0.05 % grade x 160.8 m/min x 0.9
• 0.05 x 160.8 x 0.9
• 8.04 x 0.9
• 7.2ml.kg-1.min-1
• Total VO2 = 32.2 + 7.2 + 3.5 = 42.9 ml.kg-1.min-1
• To convert to METs: 42.9 / 3.5 = 12.3 METs
ACSM Leg Cycling Equation
• Loads 300-1200 kgm/min; 50-200 watts
• VO2 ml.kg-1.min-1= 1.8x kgm/min / BW + 3.5 ml.kg-1.min-1 + 3.5 ml.kg-1.min-1
• kgm/min = kg x meters/rev x RPM
• Add resting twice : 1 for resting and 1 for unloaded
• Monark™ bike: 6.0 meter/rev
ACSM Leg Cycling Equation
• Example: VO2 for an 80 kgperson cycling on a Monark™ cycle at 50 RPM, 2.0 kg load.
• kgm/min = 2 x 6 x50
• kgm/min = 600
• Calculate VO2
• ml.kg-1.min-1= 1.8 x 600 / 80 + 3.5 + 3.5
• ml.kg-1.min-1 = 1.8 x 7.5 + 3.5 + 3.5
• ml.kg-1.min-1 = 20.5 (5.86 METS)
Different Body Weights?
• Compare “relative” VO2 during leg cycling at 600 kpm/min for 80 kg vs. 60 kg persons
• 80 kg ~ 5.86 METs
• 60 kg:
• ml.kg-1.min-1 = 1.8 x 600 / 60 + 3.5 + 3.5
• ml.kg-1.min-1 = 18 + 7
• ml.kg-1.min-1 = 25
• 25 / 3.5 = 7.14 METs

1.72 > METs for

lighter person

Kcal conversion example
• What is the kcal expenditure (kcal.min-1) for an 85 kg person exercising at an oxygen uptake of 5.86 METs?
• kcal.min-1 = METs x 3.5 x (BW (kg)/200)
• kcal.min-1 = 5.86 x 3.5 x (85/200)
• kcal.min-1 = 8.72
ACSM Weekly kcal threshold: Exercise Prescription
• Minimum caloric threshold ­ 1000 kcals
• Minutes of exercise: 1000/8.72 = 114.7 min week
• 3 Workouts: 115/3 = 38.3 minutes
• 4 Workouts: 115/4 = 28.75 minutes

This is for an 85 kg individual @ 5.86 METs

Achieving the “minimal” kcal threshold

ACSM Arm Cycling Equation
• Loads 150 to 750 kgm/min; 25-125 watts
• VO2 ml.kg-1.min-1= 3x kgm/min / BW + 3.5 ml.kg-1.min-1
• 3.0 = ml.min-1 per kpm/min ( from leg cycling)
• Only 1 resting component (3.5)
• kgm/min = kg x meters/rev x RPM
• Monark™ Rehab Trainer: 2.4 meter/rev
ACSM Stepping Equation
• 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/minx 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
ACSM Stepping Equation
• Example: VO2 for stepping on a 12” bench at 30 steps per minute
• Calculate step height in meters
• 12” x 2.54 = 30.5 cm / 100 = 0.305 meters
• Calculate Horiz VO2
• ml.kg-1.min-1= 30 steps/min x 0.2
• ml.kg-1.min-1 = 6
ACSM Stepping Equation (cont.)
• Horiz VO2 ml.kg-1.min-1 = 6
• Calculate Vert VO2 ml.kg-1.min-1
• 0.305 meters x 30 steps/min x 1.33 x 1.8
• 0.305 x 30 x 1.33 x 1.8
• 21.9 ml.kg-1.min-1
• Total VO2 = 6 + 21.9 + 3.5
• Total VO2 = 31.4 ml.kg-1.min-1
• METs = 31.4/3.5 = 8.9