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Measure of Work, Power, Energy Expenditure

Measure of Work, Power, Energy Expenditure. Week 1-2. Measurements. Metric System: standard for scientists SI (System International) Units Standardize units of measurement. Common Formulas and Conversions. 1 kilogram (kg) = 2.2 pounds (1bs) 1 mile per hour (mph) = 26.8 meters/min

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Measure of Work, Power, Energy Expenditure

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  1. Measure of Work, Power, Energy Expenditure Week 1-2

  2. Measurements • Metric System: standard for scientists • SI (System International) Units • Standardize units of measurement

  3. Common Formulas and Conversions 1 kilogram (kg) = 2.2 pounds (1bs) 1 mile per hour (mph) = 26.8 meters/min 1 Watt = 6.12 kgm/min* 1 Watt = .01433 kcal/min* 1 kgm = .00235 kcal 1 kcal = 4.186 kj 1 mile = 1.6129 km 1 lb fat = ~3,500 kcal 60 / “minutes per mile” = mph

  4. Measurement of Work & Power • Ergometry • Measurement of work output • Ergometer • Device used to measure work • Bench step ergometer • Cycle ergometer “bike, bicycle” • Arm ergometer “arm bike” • Treadmill

  5. Work • Work = force x distance • In SI units: • Work (J) = force (N) x distance (m) • Example: • Lifting a 10 kg weight up a distance of 5 m • 1 kg = 9.81 N, so 10 kg = 98.1 N • 1 N•m = 1 J, so 490.5 N•m = 490.5 J

  6. Power • Power = work ÷ time • In SI units: • Power (W) = work (J) ÷ time (s) • Example: • Performing 20,000 J of work in 60 s 20,000 J ÷ 60 s = 333.33 J•s–1 = 333.33 W

  7. Measurement of Work and Power: Bench Step Work = body weight (kg) x distance per step x steps/min x min Example: A 50 kg female performs a step test. Each step height is 40 cm and she performs 25 steps/min. Total test time is 5 minutes. How much work did she perform? What is her power output? Work = 50kg X 40 cm X 25 steps/min X 5 minutes = 250,000 J or 250kJ Power = 250,000J / 300 s = 833.3 W

  8. Measurement of Work and Power: Cycle Ergometer Work = resistance (kg) x (distance/revolution X revolutions) Normal distance per revolution on Monark = 6m Example: A 60 kg male performs a workout on a bicycle. He pedals for 10 minutes performing 50 revolutions per minute at 6 kg resistance. What is the work performed and power output produced? Work = 6kg X (6m X 500) = 18000 J Power = 18000J / 600 seconds = 30W

  9. Measurement of Work and Power: Treadmill • Calculation of work performed while a subject runs or walks on a treadmill is not generally possible when the treadmill is horizontal. • Even though running horizontal on a treadmill requires energy • Complicated measurements (i.e. 0% will negate mathematics) • Quantifiable work is being performed when walking or running up a slope

  10. Measurement of Work and Power: Treadmill • Incline of the treadmill is expressed in percent grade • Percent grade is the amount of vertical rise per 100 units of belt travel • Vertical displacement = % grade x Distance Example Treadmill speed = 200m/min Percent Grade = 7.5% or 0.075 Exercise time = 10 mins Total vertical distance traveled = 200m/min X 0.075 x 10 mins = 150 m

  11. Measurement of Work and Power: Treadmill Work = body weight (kg) x total vertical distance traveled Example: A 75 kg male is doing a TM workout. He has been walking for 15 minutes at 10% grade with a treadmill speed of 100m/min. What is the work performed and power output? Total distance = .10 X 100 m/min X 15 min= 150 m Work = 75 kg X 150m = 11250J Power = 11250J / 900s = 12.5 W

  12. Measurement of Energy Expenditure • Direct Calorimetry • Measurement of heat production as an indication of metabolic rate • Indirect Calorimetry • Estimation by measuring amount of O2 consumed

  13. Direct Calorimetry

  14. Indirect Calorimetry • Open-circuit spirometry • Determines estimate of VO2 by measuring amount of O2 consumed • VO2 consumed = volume of O2 inspired – volume of O2 expired

  15. Open Circuit Spirometry • Subject inhales ambient air 20.93% O2, 0.03% CO2, 79.04% N • O2 is used during energy-yielding reactions and CO2 produced (exhaled air contains less O2 and more CO2) • Difference in composition between inspired and expired gas volume reflects release of energy through aerobic metabolic reactions

  16. Common Expressions of Energy Expenditure • Absolute VO2 (mL/min or L/min) • Oxygen consumption at a given rate/intensity • Submaximal • = Ventilation (L/min) X (inspired O2 % – expired O2 %) • Relative VO2 (mL/kG•min) • Takes into account body weight and allows better comparisons • Submaximal • Absolute VO2 (L/min) X 1000 mL / weight in kg = ml/kg/min

  17. Common Expressions of Energy Expenditure • VO2max • Maximal rate of oxygen consumption during incremental exercise • Reflects aerobic physical fitness of individual • “Physiological ceiling” • Can be expressed as either absolute or relative (like VO2) • METs • Metabolic equivalents – another way to compare • 1 MET represents resting metabolism • Research: 3.5 mL/kG•min of O2 = 1 MET • Energy cost of different activities can be expressed as multiples of MET

  18. MET Values for Common ActivitiesAinsworth et al., MSSE 25: 71-80, 1993. LOWMODERATEHIGH < 4 METs 4-6 METs > 6 METs Sewing 1.5 Sweeping garage 4.0 Shoveling snow 7.0 Fishing 2.5 Painting house 5.0 Running 6mph 10.0 Shower 2.5 Ballroom dancing 5.5 Chopping wood 17.0 Driving 2.0 Walking 3.5mph 4.5 Handball 12.0

  19. Linear Relationship Between VO2 and Walking or Running Speed

  20. Estimating O2 Consumption and Energy Expenditure from Submaximal Steady-State Exercise = R (rest) + H (horizontal) + V (vertical) Running R = 3.5ml/kg/min H = 0.2 (running speed in m/min) V = 0.9 (running speed in m/min) x (grade as %) Walking R = 3.5ml/kg/min H = 0.1 (walking speed in m/min) V = 1.8 (walking speed in m/min) x (grade as %) Answer is in ml/kg/min of oxygen consumption

  21. Estimating O2 Consumption and Energy Expenditure from Submaximal Steady-State Exercise = R (rest) + H (horizontal) + V (vertical) Cycling R = 3.5ml/kg/min x body weight in kg H = 0 V = 2 x (power output in kgm/min) Answer is in ml or L of oxygen consumption per min*

  22. REMINDER: Common Formulas and Conversions 1 kilogram (kg) = 2.2 pounds (1bs) 1 mile per hour (mph) = 26.8 meters/min 1 Watt = 6.12 kgm/min* 1 Watt = .01433 kcal/min* 1 kgm = .00235 kcal 1 kcal = 4.186 kj 5 kcal = 1 L O2 consumed 1 mile = 1.6129 km 1 lb fat = ~3,500 kcal 60 / “minutes per mile” = mph

  23. Estimating O2 Consumption and Energy Expenditure from Submaximal Steady-State Exercise Sample calculations: Q: What is the estimated oxygen consumption and how many kcal/min does a person (70kg) burn when running a 9-minute mile pace on a flat surface? How?

  24. Estimating O2 Consumption and Energy Expenditure from Submaximal Steady-State Exercise Sample calculations: Q: What is the estimated oxygen consumption and how many kcal/min does a person (70kg) burn when running a 9-minute mile pace on a flat surface? How? R = 3.5ml/kg/min H = .2 (60 / 9min/mile = 6.66mph x 26.8 = 178.66m/min) = 35.7 ml/kg/min V = 0 3.5 + 35.7 = 39.2 ml/kg/min x 70kg = 2744ml/min / 1000 = 2.744 L/min x 5kcal/L = 13.7 kcal/min

  25. Estimating O2 Consumption and Energy Expenditure from Submaximal Steady-State Exercise Sample calculations: Q: A person (180 lbs) walks on a treadmill at 3.5 mph and at a 15% grade for 20 minutes. What is the estimated oxygen consumption? How many kcal did they burn? What is their average MET level? How?

  26. Estimating O2 Consumption and Energy Expenditure from Submaximal Steady-State Exercise Sample calculations: Q: A person (180 lbs) walks on a treadmill at 3.5 mph and at a 15% grade for 20 minutes. What is the estimated oxygen consumption? How many kcal in total did they burn? What is their average MET level? How? R = 3.5ml/kg/min H = .1 (3.5mph x 26.8 = 93.8m/min) = 9.38 V = 1.8 (93.8m/min) x (.15) = 25.33 180 lbs/2.2 = 81.8 kg 3.5 + 9.38 + 25.33 = 38.2 ml/kg/min x 81.8 kg = 3124ml/min / 1000 = 3.124 L/min x 5kcal/L = 15.62kcal/min x 20min = 312 kcal 38.2 ml/kg/min / 3.5 ml/kg/min (1 MET) =10.9 METs

  27. Estimating O2 Consumption and Energy Expenditure from Submaximal Steady-State Exercise Sample calculations: Q: A person (150 lbs) pedals at 60 rev/min on a Monark* cycle ergometer against a resistance of 2.5 kg for 30 minutes. What is the estimated oxygen consumption and how many kcal did this person burn? Keeping all other things constant, how long (days) will it take this person to lose 1 kg of body fat if they continue daily? How?

  28. Estimating O2 Consumption and Energy Expenditure from Submaximal Steady-State Exercise Sample calculations: Q: A person (150 lbs) pedals at 60 rev/min on a Monark* cycle ergometer against a resistance of 2.5 kg for 30 minutes. What is the estimated oxygen consumption and how many kcal did this person burn? Keeping all other things constant, how long (days) will it take this person to lose 1 kg of body fat if they continue daily? How? 150 lbs/2.2 lbs/kg = 68.18 kg R = 3.5ml/kg/min x 68.18 kg = 238.6 ml/min H = 0 V = 2 X (2.5kg x 6m/rev x 60 rev/min = 900kgm/min) = 1800 ml/min 238.6 + 1800 = 2038.6ml/min /1000 = 2.038 L/min x 5kcal/L = 10.19 kcal/min x 30min = 306 kcal 7700kcal (2 lbs fat) / 306 kcal/day = 25 days

  29. Work output % net efficiency = x 100 Energy expended above rest Net Efficiency • Ratio of work output divided by energy expended above rest • Efficiency decreases with increasing work rate • Curvilinear relationship between work rate and energy expenditure

  30. Net Efficiency During Arm Crank Ergometery

  31. Factors that Influence Exercise Efficiency • Exercise work rate • Efficiency decreases as work rate increases • Speed of movement • There is an optimum speed of movement and any deviation reduces efficiency – “bell curve” • Muscle fiber type • Higher efficiency in muscles with greater percentage of slow fibers

  32. Effect of Speed of Movement of Net Efficiency

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