The efficiency of bicycle‐pedalling, as affected by speed and load

Dickinson, Sylvia

doi:10.1113/jphysiol.1929.sp002565

Cited by 118 publications

(52 citation statements)

References 7 publications

(9 reference statements)

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“…Since a single contraction cannot be studied, but only a long series of contractions, the absolute value depends largely on the " base line " assumed in the calculation for those normal meta bolic processes which are unchanged in muscular work. The maximum value obtained in Dickinson's (1929) investigation, by what is probably the most reliable method, was about 21-5 %, and this occurred at an optimum speed corresponding to a time for one leg movement of 0-9 sec. The absolute value is only slightly higher than in frog's muscle.…”

Section: Discussionmentioning

confidence: 97%

The mechanical efficiency of frog’s muscle

Hill

1939

Proc. R. Soc. Lond. B

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The factors determining the maximum work and the mechanical efficiency of muscle were discussed by Hartree and Hill in 1928. Work was measured with the Levin-Wyman ergometer (Levin and Wyman 1927), the muscle being allowed to shorten at constant speed, adjustable as required, and recording a tension-length curve on a smoked surface. The whole of the work which the muscle can do in a single shortening at the given speed is thus obtained, as in no other method. The mechanical efficiency, therefore, should be the highest possible.The efficiencies given by Hartree and Hill, however, were considerably too low, probably owing to an error in the heat measurements: their thermopile was not " protected" against temperature differences along the muscle (cf. Hill 1937(cf. Hill , 1938. The part of the muscle off the thermopile being warmer than the part on it would cause too large a temperature deflexion when it shortened on to the thermopile, so making the observed heat too great. The highest efficiency they found for the initial process in frog's muscle was about 26 %, or for the whole cycle, including recovery, about 13 %. This is low compared with measured efficiencies in man, where values as high as 22 % seem to be authentic. It was desirable, therefore, to repeat the measurements on frog's muscle with a protected thermopile.Recent work (Hill 1938) on the energetics of muscular shortening has made it possible to give a theoretical treatm ent of the present problem, and from known data to calculate approximately the most efficient speed, the optimum load, and the absolute value of the efficiency. We will con sider the initial process only, and assume th at the muscle shortens at a constant speed v, through a distance x, th at the relation between speed of shortening and force exerted is given by the characteristic equationand th at the heat given out is independent of the work done and is made up of two terms, one, the heat of maintenance, being proportional to the [ 434 ] on May 12, 2018 http://rspb.royalsocietypublishing.org/ Downloaded from

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Section: Discussionmentioning

confidence: 97%

The mechanical efficiency of frog’s muscle

Hill

1939

Proc. R. Soc. Lond. B

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“…These values are in good agreement with those of Cavagna and Kaneko (1977) and Willems et al (1995). At speeds greater than ~1·m·s -1 , the efficiency of positive work production is greater than the maximal efficiency of the conversion of chemical energy into positive work by muscles (≤0.25; Dickinson, 1929), suggesting that elastic energy is stored during the phase of negative work to be recovered during the following phase of positive work (Willems et al, 1995).…”

Section: Discussionmentioning

confidence: 99%

Mechanical work and muscular efficiency in walking children

Schepens

Bastien

Heglund

et al. 2004

Journal of Experimental Biology

109

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Children consume more energy per unit body mass to walk at a given speed than do adults (DeJaeger et al., 2001). The difference in the net mass-specific metabolic energy cost per unit distance (i.e. the cost of transport, the energy required to operate the locomotory machinery) between adults and children is greater the higher the speed and the younger the subject. For example, at a speed of 1·m·s -1 , a 3-4-year-old has a net oxygen consumption 33% greater than adults. This difference disappears by the age of 11-12·years.In order to take into account the difference in size between children and adults, the speed of progression can be normalised using the dimensionless Froude number, V -f 2 /(gl), where V -f is mean walking speed, g is acceleration of gravity and l is leg length (Alexander, 1989). In this case, the difference in the cost of transport between children and adults for the most part disappears. This indicates that, after the age of 3-4·years, the difference in the cost of transport may be explained mostly on the basis of body size (DeJaeger et al., 2001).As previously observed in running (Schepens et al., 2001), body size can also affect the positive muscle-tendon work (W tot) performed during walking. Wtot naturally falls into two categories: the external work (Wext), which is the work necessary to sustain the displacement of the centre of mass of the body (COM) relative to the surroundings, and the internal work (W int), which is the work that does not directly lead to a displacement of the COM. Only some of Wint can be measured: (1) the internal work done to accelerate the body segments relative to the COM (Wint,k) and (2) the internal work done during the double contact phase of walking by the back leg, which generates energy that will be absorbed by the front leg (Wint,dc). On the contrary, the internal mechanical work done for stretching the series elastic components of the muscles during isometric contractions, to overcome antagonistic cocontractions, to overcome viscosity and friction cannot be directly measured (although this unmeasured internal work will affect the efficiency of positive work production; Willems et al., 1995).Walking is characterised by a pendulum-like exchange between the kinetic and potential energy of the COM. In children, the 'optimal speed' at which these pendulum-like transfers are maximal increases progressively with age from 0.8·m·s -1 in 2-year-olds up to 1.4·m·s -1 in 12-year-olds and adults (Cavagna et al., 1983). At all ages, the optimal speed is close to the speed at which the mass-specific work to move the COM a given distance, Wext, is at a minimum. Above the optimal speed, the energy transfers decrease. This decrease is greater the younger the subject. The decreased transfers result in a greater power required to move the COM: at 1.25·m·s -1 , The effect of age and body size on the total mechanical work done during walking is studied in children of 3-12·years of age and in adults. The total mechanical work per stride (W tot ) is measured as the sum of the ex...

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“…In addition, humans can reduce drastically the cost of transport by means of a bicycle indicating that the limiting factor is the propulsive efficiency, not the efficiency of muscular contraction. In fact, by using a bicycle, i.e., a clever lever system applied to the leg, the overall efficiency attains 0.22, a value approaching the maximum efficiency of muscular contraction [5]. According to equation (2) It is therefore the propulsive efficiency, which is much smaller in walking and running than in flying and swimming.…”

Section: The Problem Of Terrestrial Locomotionmentioning

confidence: 99%

Symmetry and Asymmetry in Bouncing Gaits

Cavagna

2010

Symmetry

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Abstract:In running, hopping and trotting gaits, the center of mass of the body oscillates each step below and above an equilibrium position where the vertical force on the ground equals body weight. In trotting and low speed human running, the average vertical acceleration of the center of mass during the lower part of the oscillation equals that of the upper part, the duration of the lower part equals that of the upper part and the step frequency equals the resonant frequency of the bouncing system: we define this as on-offground symmetric rebound. In hopping and high speed human running, the average vertical acceleration of the center of mass during the lower part of the oscillation exceeds that of the upper part, the duration of the upper part exceeds that of the lower part and the step frequency is lower than the resonant frequency of the bouncing system: we define this as on-off-ground asymmetric rebound. Here we examine the physical and physiological constraints resulting in this on-off-ground symmetry and asymmetry of the rebound. Furthermore, the average force exerted during the brake when the body decelerates downwards and forwards is greater than that exerted during the push when the body is reaccelerated upwards and forwards. This landing-takeoff asymmetry, which would be nil in the elastic rebound of the symmetric spring-mass model for running and hopping, suggests a less efficient elastic energy storage and recovery during the bouncing step. During hopping, running and trotting the landing-takeoff asymmetry and the mass-specific vertical stiffness are smaller in larger animals than in the smaller animals suggesting a more efficient rebound in larger animals.

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The efficiency of bicycle‐pedalling, as affected by speed and load

Cited by 118 publications

References 7 publications

The mechanical efficiency of frog’s muscle

The mechanical efficiency of frog’s muscle

Mechanical work and muscular efficiency in walking children

Symmetry and Asymmetry in Bouncing Gaits

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