The Jumping Mechanism of Salticid Spiders

1959 ◽  
Vol 36 (4) ◽  
pp. 654-664 ◽  
Author(s):  
D. A. PARRY ◽  
R. H. J. BROWN
Keyword(s):  
Direct Evidence ◽  
Jumping Spider ◽  
Multiple Image ◽  
Extensor Muscles ◽  
The Moment ◽  
Salticid Spiders ◽  
Fourth Pair

1. Photographs of the jumping spider Sitticus pubescens (Salticidae) show that the jump is almost entirely due to the sudden straightening of the fourth pair of legs. Multiple-image photographs show the importance of a silk drag-line in controlling the jump. 2. The torques at the leg joints have been estimated. Extension torques occur at the two hinge joints although these lack extensor muscles. 3. The erection of leg spines at the moment of the jump provides direct evidence that hydraulic forces are involved in the jump. This view is supported by estimates of the pressures involved, which fall within a factor of about two of those previously measured in the legs of the spider Tegenaria.

Trunk Posture Influences Neck Angle When Reading A Tablet Computer

2016 ◽  
Vol 60 (1) ◽  
pp. 942-942
Author(s):  
Kaitlin M. Gallagher ◽  
Ethan C. Douglas
Keyword(s):  
Muscle Activity ◽  
Erector Spinae ◽  
Flexion Angle ◽  
Neck Flexion ◽  
Handheld Computer ◽  
Extensor Muscles ◽  
Head Flexion ◽  
The Moment ◽  
Trunk Position ◽  
Gravitational Moment

In 2013, 64% of American households owned a handheld computer device (e-reader, tablet, smartphones, etc.). The presence of these devices has grown more quickly than our understanding of their effects on musculoskeletal disorders. Their use on a tabletop or a person’s lap causes increased head and neck flexion, as well as an inreased gravitational moment produced by the weight of the head (Straker et al., 2009, Young et al., 2012, Vasavada et al., 2015). A limitation to these studies is that they keep a standard trunk position throughout all tasks; however, people can also assume a semi-reclined position when reading a tablet. The purpose of this study was to determine the influence of a semi-reclined trunk position on neck and head flexion angle, and cervical erector spinae muscle activity. Nineteen participants (10 male, 9 female) read off of a tablet in four postures: with the tablet in their lap, on a tabletop, off of a standard computer monitor, and semi-reclined to an angle of 30 degrees from the vertical. Having the tablet on the lap ( M=16%MVC, SD=8%MVC) significantly increased muscle activity of the cervical erector spinae ( p=.0023) compared to reading off of a monitor or in the semi-reclined position (approximately 10%MVC). Neck and head flexion angles significantly increased ( p<.001) when reading the tablet off the lap (neck M=56.8o, SD=17.3o; head M=53.4o, SD=12.9o) versus the computer (neck M=6.4o, SD=6.4o; head M=8.2o, SD=7.4o), however, the head angle during semi-reclined reading stayed more vertical despite having the highest increase in neck flexion angle (neck M=71.6o, SD=14.0o; head M=19.7o, SD=9.2o). In the semi-reclined position, the gravitational moment of the head is second smallest for the four reading positions. In theory, this is desired as the moment that must be produced by the musculature and surround tissues would be less. The downside to this posture is that many of the neck extensor muscles may still not be in optimal force and moment production position. Many of the neck muscles that assist with extension originate from C5 to T5 and insert on C5 and above (Vasavada et al., 1998). At 30 degrees of neck flexion, the moment generating capability of the spenius and semispinalis muscles are decreased compared to when at a neutral position and fascicle length of splenius cervicis, capitis, and semispinalis capitis muscles experience changes of more than 70% of optimal length (Vasavada et al., 1998). While many of the extensor muscles only show moment arms that vary by 1 cm or less, for some there can be about a 2-3 cm changes as one goes from a flexed to extended neck posture (Vasavada et al., 1998). These combined changes mean that the force producing capabilities of the neck extensor muscles may be compromised a semi-reclined position. Future studies should report torso angle to properly analyze biomechanical risk factors during handheld computer use and compare results between studies.

scholarly journals Musculoskeletal modeling of an ostrich (Struthio camelus) pelvic limb: Influence of limb orientation on muscular capacity during locomotion

2014 ◽  
Author(s):  
John R Hutchinson ◽  
Jeffery W Rankin ◽  
Jonas Rubenson ◽  
Kate H Rosenbluth ◽  
Robert A Siston ◽  
...  
Keyword(s):  
Muscle Function ◽  
Sagittal Plane ◽  
Dynamic Properties ◽  
Three Dimensional ◽  
Limb Muscle ◽  
Struthio Camelus ◽  
Moment Arms ◽  
Extensor Muscles ◽  
Pelvic Limb ◽  
The Moment

We developed a three-dimensional, biomechanical computer model of the 36 major pelvic limb muscle groups in an ostrich (Struthio camelus) to investigate muscle function in this, the largest of extant birds and model organism for many studies of locomotor mechanics, body size, anatomy and evolution. Combined with experimental data, we use this model to test two main hypotheses. We first query whether ostriches use limb orientations (joint angles) that optimize the moment-generating capacities of their muscles during walking or running. Next, we test whether ostriches use limb orientations at mid-stance that keep their extensor muscles near maximal, and flexor muscles near minimal, moment arms. Our two hypotheses relate to the control priorities that a large bipedal animal might evolve under biomechanical constraints to achieve more effective static weight support. We find that ostriches do not use limb orientations to optimize the moment-generating capacities or moment arms of their muscles. We infer that dynamic properties of muscles or tendons might be better candidates for locomotor optimization. Regardless, general principles explaining why species choose particular joint orientations during locomotion are lacking, raising the question of whether such general principles exist or if clades evolve different patterns (e.g. weighting of muscle force-length or force-velocity properties in selecting postures). This leaves theoretical studies of muscle moment arms estimated for extinct animals at an impasse until studies of extant taxa answer these questions. Finally, we compare our model’s results against those of two prior studies of ostrich limb muscle moment arms, finding general agreement for many muscles. Some flexor and extensor muscles exhibit self-stabilization patterns (posture-dependent switches between flexor/extensor action) that ostriches may use to coordinate their locomotion. However, some conspicuous areas of disagreement in our results illustrate some cautionary principles. Importantly, tendon-travel empirical measurements of muscle moment arms must be carefully designed to preserve 3D muscle geometry lest their accuracy suffer relative to that of anatomically realistic models. The dearth of accurate experimental measurements of 3D moment arms of muscles in birds leaves uncertainty regarding the relative accuracy of different modelling or experimental datasets such as in ostriches. Our model, however, provides a comprehensive set of 3D estimates of muscle actions in ostriches for the first time, emphasizing that avian limb mechanics are highly three-dimensional and complex, and how no muscles act purely in the sagittal plane. A comparative synthesis of experiments and models such as ours could provide powerful synthesis into how anatomy, mechanics and control interact during locomotion and how these interactions evolve. Such a framework could remove obstacles impeding the analysis of muscle function in extinct taxa.

Finding Secrets: Inference

1996 ◽  
Author(s):  
Harvey S. Wiener
Keyword(s):  
Direct Evidence ◽  
Prior Experience ◽  
Body Language ◽  
Reading Process ◽  
Monday Morning ◽  
Complex Process ◽  
Usual Behavior ◽  
The Moment ◽  
Definition Of ◽  
Straight Ahead

A colleague arrives at work one Monday morning at 9:30. She's usually there at 8:00 A.M., ahead of everyone else. She mumbles under her breath and shakes her head from side to side, biting her lip. She doesn't say "Hello" as she usually does, but instead, staring straight ahead, she storms past your desk. At her office she turns the knob roughly, throws open the door, and then slams it loudly behind her. What's going on here? This is a classic bad mood scene, isn't it? No direct evidence, of course—your colleague doesn't say anything to you—but you can add up the pieces to figure out some important information for yourself. Clearly, she's angry or upset about something. To reach that judgment, you relied on what you saw and heard at the moment, but also on what you know about her usual behavior. No one had to tell you that she was furious. From her appearance, her actions, her body language, and her behavior, it was safe to infer that something irritated her. You were assessing the scene, and your natural ability to draw inferences fed you information that you needed in order to figure out her behavior. What is inference? When we infer, we derive information by a complex process of reasoning that balances assumptions, induction and deduction, instinct, prior experience, perception, hunches—even, some believe, ESP. Many people define inference as reading between the lines. This definition, of course, is figurative. It says that being able to determine information in this way is like figuring out hidden meanings—beyond the apparent ideas expressed by words and sentences. More information resides on a page of text than what the lines of print say. You can tell from this familiar metaphor—reading between the lines—that inference is usually intertwined with the reading process. In other words, we conceive of the act of inference as print-bound. Much of the essential meaning from a page does come to us as cues and clues in a writer's discourse.

existing code correlating a whistle with the information that now is the moment to attack. The information is obvious enough: it is the only information that A could conceivably have intended to make manifest in the circumstances. Could not the repetition of such a situation lead to the development of a code? Imagine that the two prisoners, caught again, find themselves in the same predicament: again a whistle, again an escape, and again they are caught. The next time, prisoner B, who has not realised that both guards are distracted, hears pris-oner A whistle: this time, fortunately, B does not have to infer what the whistle is intended to make manifest: he knows. The whistle has become a signal associ-ated by an underlying code to the message ‘Let us overpower our guards now!’ Inferential theorists might be tempted to see language as a whole as having developed in this way: to see conventional meanings as growing out of natural inferences. This is reminiscent of the story of how Rockefeller became a million-aire. One day, when he was young and very poor, Rockefeller found a one-cent coin in the street. He bought an apple, polished it, sold it for two cents, bought two apples, polished them, sold them for four cents . . . After one month he bought a cart, after two years he was about to buy a grocery store, when he inherited the fortune of his millionaire uncle. We will never know how far hominid efforts at conventionalising inference might have gone towards establishing a full-fledged human language. The fact is that the development of human languages was made possible by a specialised biological endowment. Whatever the origin of the language or code employed, a piece of coded behaviour may be used ostensively – that is, to provide two layers of information: a basic layer of information, which may be about anything at all, and a second layer con-sisting of the information that the first layer of information has been intentionally made manifest. When a coded signal, or any other arbitrary piece of behaviour, is used ostensively, the evidence displayed bears directly on the individual’s intention, and only indirectly on the basic layer of information that she intends to make manifest. We are now, of course, dealing with standard cases of Gricean communication. Is there a dividing line between instances of ostension which one would be more inclined to describe as ‘showing something’, and clear cases of communica-tion where the communicator unquestionably ‘means something’? One of Grice’s main concerns was to draw such a line: to distinguish what he called ‘natural meaning’ – smoke meaning fire, clouds meaning rain, and so on – from ‘non-natural meaning’: the word ‘fire’ meaning fire, Peter’s utterance meaning that it will rain, and so on. Essential to this distinction was the third type of communi-cator’s intention Grice mentioned in his analysis: a true communicator intends the recognition of his informative intention to function as at least part of the audi-ence’s reason for fulfilling that intention. In other words, the first, basic, layer of information must not be entirely recoverable without reference to the second. What we have tried to show so far in this section is that there are not two distinct and well-defined classes, but a continuum of cases of ostension ranging from ‘showing’, where strong direct evidence for the basic layer of information is provided, to ‘saying that’, where all the evidence is indirect. Even in our very

2005 ◽  
pp. 158-158
Keyword(s):  
Direct Evidence ◽  
Grocery Store ◽  
Human Language ◽  
Know How ◽  
The Third ◽  
Basic Layer ◽  
Gricean Communication ◽  
The Moment ◽  
Clear Cases ◽  
Dividing Line

A Role for Hip Position in Initiating the Swing-to-Stance Transition in Walking Cats

2005 ◽  
Vol 94 (5) ◽  
pp. 3497-3508 ◽  
Author(s):  
D. A. McVea ◽  
J. M. Donelan ◽  
A. Tachibana ◽  
K. G. Pearson
Keyword(s):  
Hip Joint ◽  
Direct Evidence ◽  
Swing Phase ◽  
Strongly Correlated ◽  
Flexor Muscle ◽  
Extensor Muscles ◽  
Ankle Joints ◽  
Hip Flexion ◽  
Hip Flexor ◽  
Decerebrate Cats

In this investigation, we obtained data that support the hypothesis that afferent signals associated with hip flexion play a role in initiating the swing-to-stance transition of the hind legs in walking cats. Direct evidence came from observations in walking decerebrate cats. Assisting the flexion of the hip joint during swing advanced the onset of activity in ankle extensor muscles, and this advance was strongly correlated with a reduction in the duration of hip flexor muscle activity. The hip angle at the time of onset of the flexion to extension transition was similar during assisted and unassisted steps. Additional evidence for the hypothesis that sensory signals related to hip flexion are important in regulating the swing-to-stance transition came from four normal animals trained to walk in a variety of situations designed to alter the coordination of movements at the hip, knee, and ankle joints during the swing phase. Although there were exceptions in some tasks and preparations, the angle of the hip joint at the time of onset of extensor activity was generally less variable than that of the knee and ankle joints. We also found no clear relationships between the angle of the limb and body axes, or the length of the limb axis, and the time of onset of extensor activity. Finally, there were no indications that the stretching of ankle extensor muscles during swing was a factor in regulating the transition from swing-to-stance.

scholarly journals Musculoskeletal modeling of an ostrich (Struthio camelus) pelvic limb: Influence of limb orientation on muscular capacity during locomotion

2014 ◽  
Author(s):  
John R Hutchinson ◽  
Jeffery W Rankin ◽  
Jonas Rubenson ◽  
Kate H Rosenbluth ◽  
Robert A Siston ◽  
...  
Keyword(s):  
Muscle Function ◽  
Sagittal Plane ◽  
Dynamic Properties ◽  
Three Dimensional ◽  
Limb Muscle ◽  
Struthio Camelus ◽  
Moment Arms ◽  
Extensor Muscles ◽  
Pelvic Limb ◽  
The Moment

We developed a three-dimensional, biomechanical computer model of the 36 major pelvic limb muscle groups in an ostrich (Struthio camelus) to investigate muscle function in this, the largest of extant birds and model organism for many studies of locomotor mechanics, body size, anatomy and evolution. Combined with experimental data, we use this model to test two main hypotheses. We first query whether ostriches use limb orientations (joint angles) that optimize the moment-generating capacities of their muscles during walking or running. Next, we test whether ostriches use limb orientations at mid-stance that keep their extensor muscles near maximal, and flexor muscles near minimal, moment arms. Our two hypotheses relate to the control priorities that a large bipedal animal might evolve under biomechanical constraints to achieve more effective static weight support. We find that ostriches do not use limb orientations to optimize the moment-generating capacities or moment arms of their muscles. We infer that dynamic properties of muscles or tendons might be better candidates for locomotor optimization. Regardless, general principles explaining why species choose particular joint orientations during locomotion are lacking, raising the question of whether such general principles exist or if clades evolve different patterns (e.g. weighting of muscle force-length or force-velocity properties in selecting postures). This leaves theoretical studies of muscle moment arms estimated for extinct animals at an impasse until studies of extant taxa answer these questions. Finally, we compare our model’s results against those of two prior studies of ostrich limb muscle moment arms, finding general agreement for many muscles. Some flexor and extensor muscles exhibit self-stabilization patterns (posture-dependent switches between flexor/extensor action) that ostriches may use to coordinate their locomotion. However, some conspicuous areas of disagreement in our results illustrate some cautionary principles. Importantly, tendon-travel empirical measurements of muscle moment arms must be carefully designed to preserve 3D muscle geometry lest their accuracy suffer relative to that of anatomically realistic models. The dearth of accurate experimental measurements of 3D moment arms of muscles in birds leaves uncertainty regarding the relative accuracy of different modelling or experimental datasets such as in ostriches. Our model, however, provides a comprehensive set of 3D estimates of muscle actions in ostriches for the first time, emphasizing that avian limb mechanics are highly three-dimensional and complex, and how no muscles act purely in the sagittal plane. A comparative synthesis of experiments and models such as ours could provide powerful synthesis into how anatomy, mechanics and control interact during locomotion and how these interactions evolve. Such a framework could remove obstacles impeding the analysis of muscle function in extinct taxa.

Ant Mimicry Lessens Predation on a North American Jumping Spider by Larger Salticid Spiders

2011 ◽  
Vol 40 (5) ◽  
pp. 1223-1231 ◽  
Author(s):  
Caitlin A. Durkee ◽  
Martha R. Weiss ◽  
Divya B. Uma
Keyword(s):  
North American ◽  
Jumping Spider ◽  
Salticid Spiders ◽  
Ant Mimicry

An Inverse Dynamic Analysis of the Pole Vault

1986 ◽  
Vol 2 (3) ◽  
pp. 186-201 ◽  
Author(s):  
Peter M. McGinnis ◽  
Lawrence A. Bergman
Keyword(s):  
Shoulder Joint ◽  
High Speed ◽  
Left Knee ◽  
Joint Moment ◽  
Two Dimensions ◽  
Inverse Dynamic ◽  
Extensor Muscles ◽  
Rigid Body Model ◽  
The Moment ◽  
Pole Vault

An inverse analysis of the pole vault was completed using a nine-segment rigid-body model of the vaulter in two dimensions. Competitive vaults by five elite vaulters were recorded on film using a high-speed 16-mm motion picture camera. The films were digitized and the digitized data were smoothed. The resultant joint moment histories at the shoulder, left hip, left knee, right hip, and right knee were computed for each vaulter. The moments produced about the top hand by the lower hand on the pole were also computed. The resultant joint moments at each joint were compared between vaulters and related to observed vault techniques. The moment produced by the lower hand on the pole and the resultant shoulder moment showed the most variance between vaulters. The pole moment indicated that the lower arm pulled on the pole throughout much of the vault. The resultant shoulder joint moment indicated the need for strength in the shoulder joint extensor muscles. Variations in the resultant moments at the lower extremity joints were small despite large apparent differences in the observed kinematics between vaulters.

scholarly journals Evidence of superfluidity in a dipolar supersolid from nonclassical rotational inertia

Science ◽  
2021 ◽  
pp. eaba4309
Author(s):  
L. Tanzi ◽  
J. G. Maloberti ◽  
G. Biagioni ◽  
A. Fioretti ◽  
C. Gabbanini ◽  
...  
Keyword(s):  
Direct Evidence ◽  
Lattice Structure ◽  
Oscillation Mode ◽  
Quantum Gases ◽  
Moment Of Inertia ◽  
Rotational Inertia ◽  
Rotational Oscillation ◽  
Superfluid Fraction ◽  
Supersolid Phase ◽  
The Moment

A key manifestation of superfluidity in liquids and gases is a reduction of the moment of inertia under slow rotations. Non-classical rotational effects have also been considered in the context of the elusive supersolid phase of matter, in which superfluidity coexists with a lattice structure. Here we show that the recently discovered supersolid phase in dipolar quantum gases features a reduced moment of inertia. Using a dipolar gas of dysprosium atoms, we study a peculiar rotational oscillation mode in a harmonic potential, the scissors mode, previously investigated in ordinary superfluids. From the measured moment of inertia, we deduce a superfluid fraction that is different from zero and of order of unity, providing direct evidence of the superfluid nature of the dipolar supersolid.

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