Animal Locomotion: An Electro-photographic Investigation of Consecutive Phases of Animal Movements is a series of scientific photographs by Eadweard Muybridge made in 1884 and 1885 at the University of Pennsylvania, to study motion in animals (including humans).[2][3] Published in 1887, the chronophotographic series comprised 781 collotype plates, each containing up to 36 pictures of the different phases of a specific motion of one subject (over 20,000 images in total).[4]
muybridge complete human and animal locomotion pdf 14
The Animal Locomotion project was a collaborative endeavor between the photographer and the institutional commissioning committee at the University of Pennsylvania.[8] In 1883, Muybridge met with William Pepper and J.B. Lippincott to discuss a plan for a scientific study focused on the analysis of animal and human movement. The university contributed $5,000, seeing the proposed project as important research that would benefit anthropology, physiology, medicine and sports.[7] The commission was appointed in march 1884 and included the University's professors Pepper, Joseph Leidy, George Frederick Barker, Lewis M. Haupt and emeritus Harrison Allen, as well as Thomas Eakins and Edward Hornor Coates of the Pennsylvania Academy of the Fine Arts. The project would eventually last more than three years, and costs rose to almost $30,000, but the University believed the unexpected amount of time and money to be well spent. The huge body of work was thought to be of everlasting importance to science and art and it would take years to examin all the material critcially.[9]
From spring 1884 to autumn 1885, Muybridge and his team produced over 100,000 images,[10] mostly at an outdoor studio on the University grounds' northeast corner of 36th and Pine, recording the motions of animals from the veterinary hospital, and from humans: University professors, students, athletes, Blockley Almshouse patients, and local residents.[11] Thomas Eakins worked with him briefly, although the painter preferred working with multiple exposures on a single negative, whereas Muybridge preferred capturing motion through the use of multiple cameras.[12]
The published portfolio contained 19 by 24 inch plates in 36 by 36-inch frames, numbered from 1 to 781 in an order mostly based on types of movement (starting with "Walking" followed by "Walking and turning around", "Starting for a run", "Running", et cetera).[26] The plates came in eleven categorized volumes with title pages: Vol. I. & II. Males (nude)., Vol. III. & IV. Females (nude)., Vol. V. Males (pelvis cloth)., Vol. VI. Females (semi-nude and transparent drapery) and Children., Vol. VII. Males and Females (draped) and Miscellaneous Subjects., Vol. VIII. Abnormal Movements. Men and Women (nude and semi-nude)., Vol. IX. Horses., Vol. X. Domestic Animals., and Vol. XI. Wild Animals and Birds.[27] Alternatively, individual subscribers had the option of selecting 100 plates of their choosing from the portfolio's prospectus and complete catalog for $100.[11] The classification and order of the subjects seems to suggest a hierarchy from nude human males down to chickens.
In many cases the human images featured nude or partially-nude men or women, directly confronting a local controversy over the use of nude models in art.[7] Though the animals were typically photographed running or walking across the frame, human subjects were also portrayed performing activities ranging from typical daily tasks to competitive athletics.[11]
Historians and theoreticians have proposed that Muybridge's work on animal locomotion influenced a number of other artists, photographers and filmmakers, including Marcel Duchamp, Thomas Eakins, Walt Disney, among others.[34][35][36][37]
The force interference model for integer numbers of walking legs (Weihmann, 2018) predicts decreasing total force amplitudes when ipsilateral leg coordination deviates from the strict alternating pattern. Shifting away from perfect alternation, results in symmetric minima of the total force amplitudes (cp. also Figure 2, left column). The position of these minima in the phase range are specific for the numbers of propulsive legs and closer to ipsilateral phase values of 0.5 the more legs an animal has. These minima are exploited by quadru-, hexa- and octopedal animals for energetic optimisation of their fast locomotion if storage-recovery cycles of kinetic and potential energy are not applicable (Weihmann et al., 2016; Weihmann et al., 2017; Weihmann, 2018).
Though there are quite a few studies on the emergence of bipedalism (e.g. Harcourt-Smith and Aiello, 2004; Hirasaki et al., 2004; Crompton et al., 2008), particularly in view of our own preferred mode of locomotion, changes in the numbers of propulsive legs are much less studied with regard to multi-legged animals. Nevertheless, the underlying mechanisms have tremendous importance for both understanding the drivers of evolutionary processes affecting the locomotor system of multi-legged organisms, as well as the meaningful development of swiftly moving robots with polypedal designs.
It has been shown earlier, that the width of the central region in the phase graphs increases with decreasing numbers of leg pairs. This means that animals with a higher number of legs are less able to use vertical oscillations of the body for the energetic optimisation of their locomotion (Weihmann, 2018). However, in contrast to the general trend, at the transition from two to one propulsive leg pair, the position of the amplitude minimum in the phase space remains unchanged. Nonetheless, with gradually decreasing GRF under a pair of legs, the depth of the minima diminishes and the slope of the amplitude decrease continues to decline, particularly when contact durations of all legs were kept constant. Therefore, reducing GRF under one of the leg pairs increases the ability of quadrupeds to exploit vertical oscillations for energy recovery, even at phase relations where animals with more legs and even quadrupeds that equally distribute GRFs among their legs are affected by oscillation minima. However, this also means that oscillation minimisation can no longer be used as an energy optimisation tool.
Long hindlegs, which are typical for bipedal species, allow for longer contact phases and therefore increased power generation and higher maximum running speeds (Günther et al., 2021). Long hindlegs and backward shift of the COM often have co-evolved and have mutually conditioned each other (Clemente et al., 2018). Correspondingly, tailless lizards cannot employ bipedal locomotion even if they would otherwise have been able to do so (Savvides et al., 2017). However, originally tailless species, like some monkeys, great apes or technical implementations like humanoid robots, can bring their COM over the hind limbs by raising the body. Like in cockroaches, this automatically reduces the GRFs generated by the forefeet and increases the stability of vertical body oscillations (see above). However, increasing bipedalism decreases the ability of a locomotor system, be it biological or mechanical, to employ asymmetrical gaits, i.e., gallop gaits and the employment of the lumbar spine for functional elongation of the legs (Günther et al., 2021). This functional lengthening gives the galloping gaits an advantage over symmetrical gaits when it comes to maximum speed performance. Accordingly, quadrupeds must choose between increased inherent stability of bipedal locomotion and higher maximum speed of quadrupedal gallop like locomotion.
However, exclusive amplitude reduction while contact durations are maintained might also be relevant in the locomotion of animals that do not necessarily reduce the number of propulsive leg pairs, particularly when anatomical characteristics cause an unbalanced weight distribution between rear and forelegs. Such imbalances are known for a number of ungulates, where typically the forelegs bear the greater weight (e.g. Biknevicius et al., 2004; Basu et al., 2019), but also for crocodiles, where the heavy tails cause higher load on the rear legs (Willey et al., 2004). Roughly equal contact durations for all propulsive legs, then, would facilitate a constant position of total force amplitude maxima at θ = 0.5 (Figure 2) and therefore predictable responses of total GRF and body dynamics to ipsilateral phase changes. The same applies to robots with uneven weight distribution either being caused by the mass distribution within their body or when carrying loads (see introduction).
However, by reversing the reasoning, animals and legged machines aiming at smooth COM trajectories by using ipsilateral phase relations deviating from θ = 0.5 can experience sudden force and COM amplitude increases when the contact durations of some legs are accidentally delayed or terminated prematurely. Shortened contact durations can cause a sudden shift of the maximum total force amplitude away from the alternating coordination pattern, which has the potential to destabilise locomotion dynamics. Fortunately, pronounced phase shifts and therefore high relative changes in total force amplitudes are to be expected only at higher duty factors and lower speeds, where COM amplitudes are generally small. At higher speeds, the position of the total force amplitude maxima deviates only little from θ = 0.5. Interestingly, gradual reductions in the number of propulsive legs occur mainly when animals shift to higher running speeds (Burrows and Hoyle, 1973; Full and Tu, 1991; Clemente et al., 2008), i.e., when locomotor systems are less vulnerable against truncated contact phases.
Those hoofbeats reverberated in art and science and are still being heard today. In pursuing for Stanford the secrets of equine gait, Muybridge unwittingly set the stage for a spectacular invention a decade later--the motion picture. The racehorse experiment also taught scientists to see photos as data, launching the study of animal locomotion. And the images shook the art world by exposing postural errors in classic equine sculptures and paintings. 2ff7e9595c
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