Chapter 6 Measurement of Work, Power, and Energy Expenditure

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1 Bewegungseffizienz und Laufökonomie Bedeutung im Spitzensport Aktueller Forschungsstand Donnerstag, 15. Mai 2008, Uhr, PVT Nächste Woche: Dr. Vogt Michael! Bereiten Sie sich bitte anhand der angeführten Präsentation (ppt) von Scott et al. (siehe Hinweis) und aktueller wissenschaftlicher Literatur vor. Chapter 6 Measurement of Work, Power, and Energy Expenditure EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 6 th edition Units of Measure English system used in United States Metric system is the standard system of measurement for scientists Used to express Mass kg length m Volume l System International units or SI units Standardized terms for measurement of: Energy J (kj) Force N Work Nm (J, kj) Power Watt (J/s) Work Work is the product of force and distance Work = Kraft x Weg Lifting a 5 kg weight up a distance of 2 m Work = force x distance Work = 5 kp x 2 m (~50 N x 2 m) ~ 100 Nm Work = 10 kpm (~100 Nm) Kg measure of mass, not force Kp = force acting on a mass of 1 kg at normal gravity 1

2 Power Power is how much work is done per unit of time Power = _Arbeit / Zeit Performing 2,000 kpm of work in 60 seconds Power = work/time Power = 2,000 kpm/60s (~20,000 Nm/60s) Power = 33.3 kpm s -1 (333.3 Watt) SI Units = 1 Watt (W) = kpm s -1 Power = W Measurement of Work and Power Bench Step Work = Kraft x Weg Gewicht x Höhe Work = body weight (kg) x distance (m) = 70 kp x 150 m (25 cm Stufe, 1 x /sek) = 10,500 kpm or ~ 103 kilojoules Power = work minutes = 10,500 kpm/10 min (~ 105 kj) = 1,050 kpm/min or W (105 kj/600 s 175 W) Physikalische Basis 100 Vorgabe: N + 0,25 m = 25 Nm X 6,28 Leistung x 80 / oder 60 = 25 x 8,37 ~ 210 Watt Bremsmoment 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. Although running horizontal on a treadmill requires energy Work performed during horizontal walking or running is complicated Quantifiable work is being performed when walking or running uphill! 2

3 Determination of Percent Grade on a Treadmill Measurement of Work and Power Treadmill Work = = 70 kp x 150 m = 10,500 kpm or ~103 kilojoules Fig 6.2 P = G x v x sin O 700 N x 200 m/min /60 x 0,1 = 233 Watt (Achtung: sin 0 = 0) Power = work minutes = 10,500 kpm/10 mins = 1,050 kpm/min or ~ 175 Watts Measurement of Energy Expenditure Measurement of heat production as an indication of metabolic rate Foodstuff + O 2 ATP + Heat Cell work Heat Measurement of oxygen consumption as an estimate of resting metabolic rate Foodstuff + O 2 Heat + CO 2 + H 2 O Estimation of Energy Expenditure Energy cost of horizontal treadmill walking or running O 2 requirement increases as a linear function of speed Expression of energy cost in METs 1 MET = 3,5 mlo 2 /min/kg 1 MET = Absolute O 2 requirement of activity at 10 METS >>> example p

4 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 Fiber composition of muscles Higher efficiency in muscles with greater percentage of????? Gross efficiency = Power output / Total energy expenditure Net efficiency = Power output / Total energy exp. resting energy exp.) Work efficiency = Power output / Total energy exp. unloaded energy exp.) Delta efficiency = Delta Power output / delta energy expenditure Running economy = Oxygen consumption / km/h Relationship Between Energy Expenditure and Work Rate Net Efficiency During Arm Crank Ergometery Fig 6.8 4

5 Effect of Speed of Movement of Net Efficiency Running Economy Running Economy Oxygen cost of running at given speed Lower VO 2 (ml kg -1 min -1 ) indicates better running economy Gender difference in running economy No difference at slow speeds At race pace speeds, males may be more economical than females Fig 6.10 Comparison of Running Economy Between Males and Females BEDEUTUNG: Hohe Laufökonomie und Laufgeschwindigkeit von Spitzenläufern aus Kenya Fig

6 Was macht die Laufökonomie bzw. Arbeitseffizienz aus? Zusammenhang mit Fasertypenverteilung der Arbeitsmuskulatur Typ II Fasern sind weniger effizient! (Hunter et al. Muscle Nerve 2001). Muskelsehnensteifigkeit korreliert positiv mit der Laufökonomie (Lichtwark and Wilson. J Biomech 2007). Negative Korrelation zw. Effizienz und VO 2 max. (Lucía et al. Med Sci Sports Exerc 2002). Geschlechts- und altersspezifische Unterschiede. Welche?? Verbesserung durch?? Intensives Krafttraining (Storen et al. Med Sci Sports Exerc 2008): Warum? Höhentraining? Ja: Sauders et al. JAP 2003; Nein: Truijens et al. JAP 2008 Siehe auch Point-Counterpoint JAP 2006! Warum? Hitzetraining?? Warum? Saunders et al., JAP, 2003 Eigene Untersuchungen: Storen et al. Maximal strength training imroves running economy in distance runners. Med Sci Sports Exerc 2008 Probanden: 17 gut trainierte Läufer (8 männl, 9 weibl; ~ 29 Jahre) 5-km Zeit: 18,7 min (Interventions + Kontrollgruppe) Intervention: 4 sets 4RM half-squats; 3 min rest; 3 x / week; 8 weeks Beide Gruppen: Übliches Lauftraining (ca. 400 min / Woche) Ergebnisse: 5 % verbesserte RE bei 70%VO2max; TTE: 21,3 % Verbesserung Diskussion: Verbesserte Maximalkraft kürzere Kontraktionszeit verbesserte Durchblutung weniger zentrale Ermüdung Sehnenelastizität? Intensives Krafttraining, plyometrisches Training?? Siehe auch Zitate im besprochenen Artikel! Bitte lesen Sie diesen Beitrag (Beilage) für eine kritische Diskussion! B 6