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Fig. 2. Model predictions of metabolic energy expenditure as a function of
frequency of leg swinging. A simple pendulum model shows that (A) setting
target amplitudes to decrease with swing frequency (according to
Eqn 1) will result in (B) a
constant rate of positive work performed on the leg. (C) The work hypothesis
predicts that a constant rate of work will result in a constant rate of
metabolic energy expenditure (Eqn
6). (D) In contrast, the cyclic work hypothesis, where energy is
expended to produce force for short durations, predicts that metabolic rate
will increase with swing frequency (Eqn
7). Both hypotheses predict trends (rather than absolute metabolic
rates) that are to be tested against experimental data with least-squares
fits. The ability to predict energy expenditure may independently be tested at
a different combination of swing frequency and amplitude (extrapolation point,
denoted by open circles). The extrapolated model, fitted from the original
data, may be compared against the extrapolation data. All predictions apply to
swing frequencies at least as fast as the natural frequency, labeled in A, of
the leg swinging freely under gravity, as computed from leg inertial
properties.
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