Biomechanical Determinants of Pedaling Energetics: Internal and External Work Are Not Independent
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KAUTZ, S.A., and R.R. NEPTUNE. Biomechanical determinants of pedaling energetics: Internal and external work are not independent. Exerc. Sport Sci. Rev., Vol. 30, No. 4, pp. 159–165, 2002. Simulation analyses of pedaling demonstrate how individual muscle forces act to accelerate and decelerate the leg segments and the crank to perform external work. The work done by the muscles to accelerate the leg segments ultimately drives the pedals because when the legs decelerate, their mechanical energy is used to overcome the external load.Keywords:
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KAUTZ, S.A., and R.R. NEPTUNE. Biomechanical determinants of pedaling energetics: Internal and external work are not independent. Exerc. Sport Sci. Rev., Vol. 30, No. 4, pp. 159–165, 2002. Simulation analyses of pedaling demonstrate how individual muscle forces act to accelerate and decelerate the leg segments and the crank to perform external work. The work done by the muscles to accelerate the leg segments ultimately drives the pedals because when the legs decelerate, their mechanical energy is used to overcome the external load.
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Introduction: Previous research has explored muscle function during gait and this work has shown that more positive mechanical muscle work is produced in gait tasks that primarily raise the center of mass (incline gait tasks) compared to the amount of negative mechanical muscle work dissipated in gait tasks that primarily lower the center of mass (decline gait tasks). This has led to the hypothesis that skeletal muscles generate more mechanical energy in gait tasks that raise the center of mass compared to mechanical energy dissipated by muscles in gait tasks that lower the center of mass. The purpose of this study was to compare the positive and negative muscle work produced during incline and decline running at three speeds in healthy young adults.
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ABSTRACT Moving about in nature often involves walking or running on a soft yielding substratum such as sand, which has a profound effect on the mechanics and energetics of locomotion. Force platform and cinematographic analyses were used to determine the mechanical work performed by human subjects during walking and running on sand and on a hard surface. Oxygen consumption was used to determine the energetic cost of walking and running under the same conditions. Walking on sand requires 1.6–2.5 times more mechanical work than does walking on a hard surface at the same speed. In contrast, running on sand requires only 1.15 times more mechanical work than does running on a hard surface at the same speed. Walking on sand requires 2.1–2.7 times more energy expenditure than does walking on a hard surface at the same speed; while running on sand requires 1.6 times more energy expenditure than does running on a hard surface. The increase in energy cost is due primarily to two effects: the mechanical work done on the sand, and a decrease in the efficiency of positive work done by the muscles and tendons.
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From the point of wiew of energetics the input of a press-tool- billet system is the electric power, and the output parameter is the mechanical power of forming. The comparison of the momentary values of the total and useful power characterises the energy flow of forming process, the integral of the electric and mechanical powers, referring to one stroke of the ram, gives the total and useful work.
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SUMMARY Muscles generate forces that redistribute segmental energybetween the leg segments and the crank. They accelerate anddecelerate the legs resulting in an increase and decrease oftheir total energy. Increases in the mechanical energy of thelegs are predominantly due to work done by the uniarticularhip and knee extensor muscles. Decreases in mechanicalenergy of the legs are predominantly the result of concentricactivity by the ankle plantar flexors that acts to transferenergy from the legs to the crank to overcome the externalresistance with no significant dissipation by eccentric muscleactivity. Thus, changes in the mechanical energy of the legsare neither independent of external work production norpredictive of the mechanical work required to move the legs;instead they are an integral part of producing the externalwork. Therefore, the internal work hypothesis is inappropri-ate for scientific investigations of pedaling. Furthermore, byshowing how muscles accelerate and decelerate the legs, andhow they transfer energy from the legs to the crank, it waspossible to address several misconceptions in the literaturerelated to pedaling biomechanics and energetics. Our analysisof pedaling also suggests that internal work measures will besimilarly flawed in other locomotor tasks where muscles causesignificant external work to be done by the deceleration ofthe body segments (
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The energetics of human locomotion can be studied by calculating mechanical efliciency defined as the ratio of mechanical work performed and the net energy consumed. The efficiency values vary with several factors related not only to human machinery but also to methodological problems in determining either work or net energy cost. Using the method described by Fenn (1930), Cavagna and Kaneko (1977) reported the efficiency values for walking and running were 0.35-0.45 and 0.45-0.70 for level walking and running, respectively. One strong criticism is given to mechanical work determined as the sum of external work (Wext) to accelerate the body and internal work (Wint) performed by limbs around the body's center of mass, because of a possible energy transformation between Wext and Wint. The joint power method by Winter (1979) can be used as an appropriate alternative method. Another serious problem exists in determining energy cost for anaerobic metabolism. The most classical way of measuring oxygen debt (Hill, 1924) may lead to over-estimation, and the value of 1 kcal/kg/km obtained by extrapolation of aerobic metabolism (Margaria, 1963) might cause an under-estimation. There are many other elusive factors such as mechanical energy transfer, elastic energy utilization, the so called 'base-line' problem in metabolism and so on. Although several theories have been presented, it would be a more fruitful approach to obtain experimental data by applying a given method with assumptions. The data we obtained on energetics could contribute to a better understanding of human locomotion.
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The sections in this article are: 1 Thermodynamics 1.1 Heat, Work, and Efficiency 1.2 Energy Balance 1.3 Energetics and Limitation of Airflow 2 Energy Supply 2.1 Blood Flow 2.2 Substrate Metabolism 2.3 Estimation of Energy Change 2.4 Tension-Time Index 3 Work of Breathing 3.1 Definitions 3.2 Positive Work, Negative Work, and No Work 3.3 Graphical Analysis of Work 3.4 Theoretical Estimation of Work 3.5 Measurement of Mechanical Work 3.6 Work Rate (Power) 3.7 Maximal Available Work and Power 4 Efficiency of Breathing 4.1 Mechanical Work 4.2 Metabolic Cost 5 Physiological Considerations 5.1 Optimal Breathing Frequency 5.2 Respiratory Muscle Energetics and Exercise 5.3 Respiratory Muscle Energetics in Health and Disease
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Energetics and Mechanics of Terrestrial Locomotion, Page 1 of 1 < Previous page | Next page > /docserver/preview/fulltext/physiol/44/1/annurev.ph.44.030182.000525-1.gif
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