Math Modeling of Interlimb Coordination in Cat Locomotion

Locomotion is an evolutionary adaptation that allows animals to move in 3-D space. The way that mammalian locomotion is controlled has been studied for generations. It remains unclear how the neuronal network that controls locomotion is structured and how the mammalian locomotor network keeps balance in the face of a changing environment. In this body of research, we build mathematical models of locomotion and fit our models to experimental data of walking cats to gain understanding of network connectivity and of balance control. Specifically, we test the biological plausibility of a particular connectivity of the mammalian locomotor network by matching network activity to phases of walking in different experimental conditions. We gain understanding of balance control with an inverted pendulum model that fits the center of mass oscillations during walking in different experimental conditions

Intra-individual movement variability during skill transitions: A useful marker?

Applied research suggests athletes and coaches need to be challenged in knowing when and how much a movement should be consciously attended to. This is exacerbated when the skill is in transition between two more stable states, such as when an already well learnt skill is being refined. Using existing theory and research, this paper highlights the potential application of movement variability as a tool to inform a coach’s decision-making process when implementing a systematic approach to technical refinement. Of particular interest is the structure of co-variability between mechanical degrees-of-freedom (e.g., joints) within the movement system’s entirety when undergoing a skill transition. Exemplar data from golf are presented, demonstrating the link between movement variability and mental effort as an important feature of automaticity, and thus intervention design throughout the different stages of refinement. Movement variability was shown to reduce when mental effort directed towards an individual aspect of the skill was high (target variable). The opposite pattern was apparent for variables unrelated to the technical refinement. Therefore, two related indicators, movement variability and mental effort, are offered as a basis through which the evaluation of automaticity during technical refinements may be made

Postural adjustments to self-triggered perturbations under conditions of changes in body orientation

We studied anticipatory and compensatory postural adjustments (APAs and CPAs) associated with self-triggered postural perturbations in conditions with changes in the initial body orientation. In particular, we were testing hypotheses on adjustments in the reciprocal and coactivation commands, role of proximal vs. distal muscles, and correlations between changes in indices of APAs and CPAs. Healthy young participants stood on a board with full support or reduced support area and held a standard load in the extended arms. They released the load in a self-paced manned with a standard small-amplitude arm movement. Electromyograms of 12 muscles were recorded and used to compute reciprocal and coactivation indices between three muscle pairs on both sides of the body. The subject's body was oriented toward one of three targets: straight ahead, 60° to the left, and 60° to the right. Body orientation has stronger effects on proximal muscle pairs compared to distal muscles. It led to more consistent changes in the reciprocal command compared to the coactivation command. Indices of APAs and CPAs showed positive correlations across conditions. We conclude that the earlier suggested hierarchical relations between the reciprocal and coactivation command could be task-specific. Predominance of negative or positive correlations between APA and CPA indices could also be task-specific

Postural Synergies and Their Development

The recent developments of a particular approach to analyzing motor synergies based on the principle of motor abundance has allowed a quantitative assessment of multieffector coordination in motor tasks involving anticipatory adjustments to self-triggered postural perturbations and in voluntary posturalsway. This approach, the uncontrolled manifold (UCM) hypothesis, is based on an assumption that the central nervous system organizes covariation of elemental variables to stabilize important performance variables in a task-specific manner. In particular, this approach has been used to demonstrate and to assess the emergence of synergies and their modification with motor practice in typical persons and persons with Down syndrome. The framework of the UCM hypothesis allows the formulation of testable hypotheses with respect to developing postural synergies in typically and atypically developing persons

Is Power Grasping Contact Continuous or Discrete?

During power grasp, the number of local force maxima reflects either the central nervous system's preferential use of particular hand regions, or anatomical constraints, or both. Previously, both bimodal and trimodal force maxima have been hypothesized for power grasp of a cylindrical handle. Here we measure the number of local force maxima, with a resolution of 4.8 degrees, when performing pushing and pulling efforts in the plane perpendicular to the cylinder's long axis. Twelve participants produced external forces to eight targets. The number of contacts was defined as the number of local maxima exceeding background variance. A minimum of four and a maximum of five discrete contacts were observed in all subjects at the distal phalanges and metacarpal heads. We thus reject previous hypotheses of bimodal or trimodal force control for cylindrical power grasping. Since we presently observed only 4-5 contacts, which is rather low considering the hand's kinematic flexibility in the flexion plane, we also reject hypotheses of continuous contact, which are inherent to current grasping taxonomy. A modification to current grasping taxonomy is proposed wherein power grasp contains separate branches for continuous and discrete contacts, and where power and precision grasps are distinguished only by grasp manipulability.ArticleJOURNAL OF APPLIED BIOMECHANICS. 29(5):554-562 (2013)journal articl

Hijerarhije sinergija u ljudskim pokretima

This brief review addresses the problem of motor redundancy, which exists at many levels of the neuro-motor hierarchies involved in the production of voluntary movements. An approach to this problem is described based on the principle of abundance. This approach offers an operational definition for motor synergies using the framework of the uncontrolled manifold hypothesis. It is shown that hierarchical systems have inherent trade-offs between synergies at different control levels. These trade-offs have been demonstrated in experimental studies of human multi-finger pressing and prehension. They are likely to be present in other hierarchical systems, for example, those involved in the control of large groups of muscles. The framework of the equilibrium-point hypothesis offers a physiologically based mechanism, which may form the basis for hierarchies of synergies.Ovaj se pregledni rad bavi problemom motoričke redundancije (zalihosti) koja postoji na više razina neuromotoričkih hijerarhija uključenih u realizaciju voljnih pokreta. Opisan je pristup utemeljen na principu obilja (brojnosti). Pristup nudi operativnu definiciju za motoričke sinergije korištenjem okvira što ga pruža hipoteza neupravljanih slojeva (ljusaka). Pokazuje se da hijerarhijski sustavi posjeduju inherentne kompromise između sinergija na različitim razinama upravljanja. Ti se kompromisi mogu pokazati pomoću eksperimentalnih studija pritiska prstima ljudske šake. Vjerojatno je da su isti prisutni i u drugim hijerarhijskim sustavima, npr. onima uključenima u upravljanje velikim skupinama mišića. Okvir hipoteze ravnotežne točke nudi fiziološki utemeljen mehanizam koji može predstavljati osnovu za hijerarhije sinergija. Problem motoričke redundancije Svi neuromotorički procesi unutar ljudskoga ti-jela povezani s izvođenjem prirodnih voljnih pokreta uključuju nekoliko preslikavanja (mapiranja) tipa “od nekoliko na više”, kakva se uobičajeno smatraju problemom redundancije. Drugim riječima, ograničenja definirana ulazom (npr. zadatkom) ne definiraju jednoznačno uzorak izlaza (npr. uzorci rotacije zglobova, mišićne sile, aktivacije motoričkih neurona itd.) na način da postoji više (beskonačan broj, uobičajeno) rješenja. Problem je uočio Bernstein (1935, 1967), smatrajući ga središnjim problemom motoričkog upravljanja: “Na koji način središnji živčani sustav (SŽS) odabire jednoznačna rješenja iz brojnih, naizgled jednakih mogućnosti?” Tradicionalni način shvaćanja problema motoričke redundancije pretpostavljao je da SŽS rabi skup kriterija da bi pronašao jednoznačna rješenja takvih problema. Konkretno, mnoštvo optimizacijskih tehnika uporabljeno je za pristup tim problemima uključujući optimizaciju funkcija troškovi-korist, temeljenu na mehaničkim, psihologijskim i neuropsihologijskim varijablama (vidjeti pregled u Prilutsky, 2000; Osenbaum i sur., 1993; Latash, 1993). Princip obilja Gelfand i Tselin (1966) su usporedili mnoge ele-mente uključene na bilo kojem koraku generiranja pokreta s razredom studenata koji žele sa što manje rada izvršiti zadatak. Uveli su princip minimalnog međudjelovanja da bi opisali takve oblike velikih skupina elemenata. Prema tom načelu svaki element nastoji minimizirati svoje međudjelovanje s ostalima, s upravljačkim dijelom te s okolinom. Drugim riječima, svaki element nastoji minimizirati ulaz koji prima iz svih spomenutih izvora. Taj je princip u novije vrijeme razvijen u princip obilja (Gelfand i Latash, 1998). Prema njemu su problemi motoričke redundancije pogrešno formulirani. Preslikavanja tipa “od nekoliko na više”, tipična za takve probleme, ne bi trebalo gledati kao problem računalne naravi za upravljački sustav, nego pak više kao svojevrsni luksuz koji dozvoljava kombiniranje stabilnog funkcioniranja zadatka uz obavljanje ostalih zadataka i reagiranje na moguće ometajuće utjecaje okoline. Rješavanje problema motoričke redundancije ne uključuje izbor jednoznačnog, optimalnog rješenja, nego prije olakša-vanje čitave obitelji rješenja koje mogu biti jedna-ko uspješne u rješavanju problema. Broj tih obitelji rješenja puno je manji od ukupnog broja mogućih rješenja, što znači da se ipak događa neka vrsta selekcije. Taj pomak od traženja jedinstvenog rješenja prema definiranju pravila kojima se organiziraju obitelji rješenja rezultirao je novim pogledom na motoričke sinergije, paradigmatskim pomakom koji je doveo do izvedbene definicije sinergija i do stvaranja novog računalnog pristupa identifikaciji i kvantifikaciji sinergija. Sinergija - radna definicija Riječ “sinergija” rabila se u studijima ljudskog kretanja, kao i za opis motoričkih poremećaja više od stotinu godina. Općenito, definicija je bila sukladna s grčkim prijevodom “raditi zajedno”. U posljednje vrijeme, međutim, ta je riječ poprimila određenije značenje ukorijenjeno u principu obilja (detalj-no vidjeti u Latash, 2008). Postoje, naime, tri vrste sinergija. Prvo, kada je u zadatak uključen privi-dno redundantni skup elemenata, odabire se srednji uzorak raspodjele koji će karakterizirati prosječni doprinos svakog elementa. Drugo, kada se analizira nekoliko pokušaja izvedbe zadatka, izlazi elemenata mogu kovarirati, što je za zadatak korisno, tj. smanjuje se varijabilnost važne varijable u usporedbi sa situacijom koja bi se mogla očekivati kada kovarijacije ne bi bilo. To se svojstvo ponekad naziva kompenzacijom pogreške ili stabilnošću. Treće, isti skup elemenata može se rabiti za formiranje različitih sinergija, tj. različitih uzoraka kovarijacije koji su povoljni za različite varijable cjelokupnog sustava. To se svojstvo može nazvati stabilnošću. Samo sustavi koji mogu pokazati sva tri svojstva nazivat će se sinergijama. Nema apstraktnih sinergija – one uvijek nešto čine. Sinergija se, prema tomu, definira kao neuralna organizacija skupa elementarnih varijabla s ciljem osiguranja svojevrsnih svojstava stabilnosti (stabilizirati ili destabilizirati) varijable koja je izlaz sustava kao cjeline. Hipoteza neupravljanih ljusaka (UCM – uncontrolled manifold hypothesis) i hijerarhijsko upravljanje Uvedena definicija sinergije zahtijeva kvantitativnu metodu koja bi mogla razlikovati sinergiju od nesinergije, kao i kvantificirati sinergije. Takva je metoda razvijena u sklopu nekontroliranih višeslojnih hipoteza. Ona pretpostavlja da neuralni kontroler djeluje u prostoru elementarnih varijabla i u tom prostoru izabire potprostore koji odgovaraju željenoj vrijednosti uspješno izvedene varijable. Nadalje, kontroler organizira interakcije među elementima tako da je varijanca među elementarnim varijablama uglavnom ograničena UCM-om. Bilo je nekoliko pokušaja da se ponude mehanizmi koji mogu organizirati takvu vrstu kontrole – feedback perifernih senzora, feedback koji koristi uparivanje centralnih i povratnih neuralnih petlji, kontrolni anticipacijski program. Pojam referentne konfiguracije pruža privlačan okvir za analizu motoričkih sinergija. Taj okvir pretpostavlja hijerarhijski kontrolni sustav u kojemu je , na svakom stupnju hijerarhije, taj sustav redundantan, tj. proizvodi puno više izlaznih varijabli od broja ograničenja specificiranih ulaznim varijablama (kao na slici 3). Ostale karakteristike akcije mogu varirati na temelju sekundarnih zakonitosti, koje vjerojatno odražavaju optimizaciju nekih osobina izvedbe. Zato što je sustav redundantan, referentna konfiguracija na višem hijerarhijskom stupnju ne specificira sasvim nedvojbeno sve referentne konfiguracije na nižim stupnjevima. Izranjanje određenih nižerazinskih referentnih trajektorija može se temeljiti na mehanizmu povratne sprege ili na mehanizmu anticipacije (feed-forward). Stoga se hijerarhija kontrolnih razina, gdje svaka razina funkcionira na na-čelu kontrole ravnotežne točke, čini vrlo vjerojatnom strukturom koja podržava motoričke sinergije

Analysis of finger motion coordination during packaging interactions

Packaging accessibility is a significant problem for many older people. Whilst the majority of studies have focused on issues surrounding strength, work has shown that dexterity required to open a pack is also a major issue for many older people. Hence, the work undertaken here, reports a quantitative study that aimed to analyse motion coordination patterns across digits 2–5 (index to little finger) during interactions with three of the most common types of packaging: plastic bottles, jars, and crisps packets, and comparing those interactions to a common measure of dexterity, the Perdue Pegboard. Ten subjects (6 males and 4 females) were examined while reaching forward to grasp and open a 300ml plastic bottle and a 500g jar. A ten-camera opto-electronic motion capture system measured trajectories of 25 miniature reflective markers placed on the dorsal surface landmarks of the hand. Joint angular profiles for 12 involved flexion–extension movements were derived from the measured coordinates of surface markers. The results showed that finger correlations vary widely across the differing pack formats with the crisps having the lowest finger movement correlation and the jar having the highest. Speed and jerk metrics were also seen to vary across the various pack formats. However, finger correlations were seen to be more relevant to perceived dexterity of pack opening than finger speeds and jerk motions