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Power

Power. Power is how much work is accomplished per unit time. The unit for power is watt (W) It is defined as 1 joule per second Power = work ÷ time Power describes the rate at which work is being done  describes the intensity of exercise. Work.

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Power

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  1. Power • Power is how much work is accomplished per unit time. • The unit for power is watt (W) • It is defined as 1 joule per second • Power = work ÷ time • Power describes the rate at which work is being done • describes the intensity of exercise.

  2. Work • Work = product of force multiplied by distance: Work = force x distance • The SI unit for force is Newtons (N) • Lifting a 10kg weight up a distance of 2m the work performed • Work = 97.9N x 2m = 195.8 Joules • 1kg = 9.79N so 10kg = 97.9N

  3. Measurement of Work and Power • Ergonometry= to the measurement of work output. • Ergometer = to an apparatus or device used to measure a specific type of work

  4. Bench Step • The bench = form of ergometer • It involves stepping up and down on a bench at a specified rate. • E.g 70kg man steps up and down on a 50cm(0.5m) bench for ten minutes at a rate of 30 steps per minute. Work performed: • Force = 685.3 N (i.e., 70kg x 9.79 N/kg) • Distance = 0.5m/step x 30 steps/min x 10min =150m Total work performed : • 685.3 N x 150m = 102 795 Joules or 102.8kilojoules • The power output during this exercise can be calculated as: • Power = 102 795 Joules/600seconds = 173.3 watts

  5. Cycle Ergometer • =stationary exercise bicycle that permits accurate measurement of the amount of work performed. • It incorporates a belt wrapped around the wheel (flywheel). • Distance traveled = distance covered per revolution of the pedal(6 meters per revolution on a standard Monarch) • This is multiplied by the number of pedal revolutions.

  6. Evaluating Immediate Energy System • Power = F x D/time • Short term muscular power: e.g sprinting up flight of steps • Jumping power tests: may not measure anaerobic power = too brief to evaluate ATP & PCr.

  7. Evaluating Immediate Energy Systems • Other power tests last 6 to 8 seconds. • Power tests = high degree of task specificity. Best sprinter may not be the best repetitive volleyball leaper.

  8. Evaluating Short-Term Glycolytic Energy System • Glycogen depletion in specific muscles activated = indication of contribution of glycolysis to exercise • Tests demanding maximal work for up to 3min = best estimate of glycolytic power.

  9. Measuring Anaerobic Capacity • No clear method for measuring anaerobic capacity • Accepted methods: • Maximal accumulated O2 deficit • Wingate anaerobic test • Critical power test

  10. Wingate test:Peak power output, average power output, anaerobic fatigue • What is anaerobic fatigue?= percentage decline in power relative to peak power.

  11. Energy Expenditure During Maximal Anaerobic Exercise • No activity = 100% aerobic or anaerobic • Estimates of anaerobic effort involved • Excess post exercise O2 consumption (EPOC) • Lactate threshold

  12. Anaerobic Energy Expenditure:EPOC • O2demand > O2consumed in early exercise • Body = experiences O2 deficit • Occurs when anaerobic pathways used for ATP production • O2consumed> O2demand in early recovery • Excess post-exercise O2 consumption (EPOC)

  13. Anaerobic Energy Expenditure:Lactate Threshold • Lactate threshold: point at which blood lactate accumulation  • Lactate production rate > lactate clearance rate • Good indicator of potential for endurance exercise

  14. Anaerobic Energy Expenditure:Lactate Threshold • Lactate accumulation  fatigue • Ability to exercise hard without accumulating lactate = beneficial to athletic performance • Higher lactate threshold = higher sustained exercise intensity = better endurance performance • For 2 athletes with same VO2max higher lactate threshold predicts better performance

  15. Measuring & Evaluating the Aerobic System Direct Calorimetry: = Process of measuring metabolic rate via measurement of heat

  16. Direct Calorimetry • Theory: when body uses energy to do work, heat is given off. measure heat production (calorimetry) gives a direct measurement of metabolic work.

  17. Measuring & Evaluating the Aerobic System • Airtight chamber (calorimeter) insulated from environment • Exchange O2 & CO2 • Body temperature raises temperature of water • Heat production calculated

  18. Measuring & Evaluating the Aerobic System Indirect Calorimetry • Theory: Since direct relationship between O2 consumed & amountof heat produced by body  measurement of O2 consumption provides estimate of metabolic rate. • Measurement of O2 consumption is indirect, since heat not measured directly.

  19. Respiratory Quotient • Respiratory quotient (RQ) is ratio of volume of carbon dioxide produced to volume of oxygen consumed. RQ for Carbohydrate is 1.0.

  20. Respiratory Exchange Ratio Respiratory Exchange Ratio is ratio of carbon dioxide exhaled to oxygen consumed when CO2 and O2 exchange does not reflect food oxidation.

  21. Measuring Maximal Oxygen Consumption Test of Aerobic Power • Two general criteria needed: • Test that is independent of muscle strength, speed, body size, skill • Test that consists of graded exercise to point of exhaustion (without muscular fatigue)

  22. Measuring Maximal Oxygen Consumption Criteria for true max VO2 is leveling off or peaking in oxygen uptake. • Other criteria: • Oxygen uptake fails to increase by some value • Maximum lactic acid • Maximum predicted HR • R > 1.0

  23. Maximal Oxygen Consumption • The highest maximal oxygen uptakes generally recorded for cross-country skiers, runners, swimmers & cyclists. • Lance Armstrong VO2 max = 83.3 ml/kg/min

  24. Measuring Maximal Oxygen Consumption Factors that affect Maximal Oxygen Uptake: • Mode • Heredity • State of training • Gender • Body composition • Age

  25. Energy Expenditure DuringMaximal Aerobic Exercise • VO2max : • Point at which O2 consumption doesn’t  with further  in intensity • Best single measurement of aerobic fitness • Not best predictor of endurance performance • Plateaus after 8 to 12 weeks of training • Performance continues to improve • More training = compete at higher percentage of VO2max

  26. Energy Expenditure:Energy Cost of Various Activities • Varies with type and intensity of activity • Calculated from VO2, expressed in kilocalories/minute • Values ignore anaerobic aspects, EPOC • Daily expenditures depend on • Activity level (largest influence) • Inherent body factors (age, sex, size, weight, FFM)

  27. Energy Expenditure:Successful Endurance Athletes 1. High VO2max 2. High lactate threshold (as % VO2max) 3. High economy of effort 4. High percentage of type I muscle fibers (Slow, oxidative, fatigue resistant)

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