Biomechanical analysis of movement strategies in human forward trunk bending. II. Experimental study

 The large mass of the human upper trunk, its elevated position during erect stance, and the small area limited by the size of the feet, stress the importance of equilibrium control during trunk movements. The objective of the present study was to perform a biomechanical analysis of fast forward trunk movements in order to understand the coordination between movement and posture. The analysis is based on a comparison between experimentally observed bending and hypothetical “optimal bending” performed on an infinitely narrow support, as presented in a companion paper. The experimental data were obtained from 16 subjects who performed fast forward bending while standing on a wide platform or on a narrow beam. The analysis is performed by decomposition of the movement into three dynamically independent components, each representing a movement along one of the three eigenvectors of the motion equation. The eigenmovements are termed “hip”, “ankle”, and “knee” eigenmovements, according to the dominant joint. The experimentally observed movement is characterized mainly by the hip and ankle eigenmovements, whereas the knee eigenmovement is negligible. Similarly to the “optimal bending” the ankle eigenmovement starts earlier and lasts longer than the hip eigenmovement. An early forward acceleration of the center of gravity in the ankle eigenmovement is caused by anticipatory changes in the ankle joint torque. This clarifies the role of the early tibialis anterior burst and/or soleus inhibition usually observed in electromyographic recordings during forward bending. The results suggest that the hip and the ankle eigenmovements can be treated as independently controlled motion units aimed at functionally different behavioral goals: the bending per se and postural adjustment. It is proposed that the central nervous system has to control these motion units sequentially in order to perform the movement and maintain equilibrium. It is also suggested that the hip and ankle eigenmovements can be regarded as a biomechanical background for the hip and ankle strategies introduced by Horak and Nashner (1986) on the basis of electromyographic recordings and kinematic patterns in response to postural perturbations. Received: 1 July 1999 / Accepted in revised form: 23 October 2000     

Feedback equilibrium control during human standing

Equilibrium maintenance during standing in humans was investigated with a 3-joint (ankle, knee and hip) sagittal model of body movement. The experimental paradigm consisted of sudden perturbations of humans in quiet stance by backward displacements of the support platform. Data analysis was performed using eigenvectors of motion equation. The results supported three conclusions. First, independent feedback control of movements along eigenvectors (eigenmovements) can adequately describe human postural responses to stance perturbations. This conclusion is consistent with previous observations (Alexandrov et al., 2001b) that these same eigenmovements are also independently controlled in a feed-forward manner during voluntary upper-trunk bending. Second, independent feedback control of each eigenmovement is sufficient to provide its stability. Third, the feedback loop in each eigenmovement can be modeled as a linear visco-elastic spring with delay. Visco-elastic parameters and time-delay values result from the combined contribution of passive visco-elastic mechanisms and sensory systems of different modalities     

Closed-loop and open-loop control of posture and movement during human trunk bending

Closed-loop (CL) and open-loop (OL) types of motor control during human forward upper trunk bending are investigated. A two-joint (hip and ankle) biomechanical model of the human body is used. The analysis is performed in terms of the movements along eigenvectors of the motion equation (“eigenmovements” or “natural synergies”). Two analyzed natural synergies are called “H-synergy” (Hip) and “A-synergy” (Ankle) according to the dominant joint in each of these synergies. Parameters of CL control were estimated using a sudden support platform displacement applied during the movement execution. The CL gain in the H-synergy increased and in the A-synergy decreased during the movement as compared with the quiet standing. The analysis of the time course of OL control signal suggests that the H-synergy (responsible for the prime movement, i.e. bending per se) is controlled according to the EP theory whereas for the associated A-synergy (responsible for posture adjustment, i.e. equilibrium maintenance) muscle forces and gravity forces are balanced for any its final amplitude and therefore the EP theory is not applicable to its control.     

Analysis of kinematically redundant reaching movements using the equilibrium-point hypothesis

 Six subjects performed a planar reaching arm movement to a target while unpredictable perturbations were applied to the endpoint; the perturbations consisted of pulling springs having different stiffness. Two conditions were applied; in the first, subjects had to reach for the target despite the perturbation, in the second condition, the subjects were asked to not correct the motion as a perturbation was applied. We analyzed the kinematics profiles of the three arm segments and, by means of inverse dynamics, calculated the joint torques. The framework of the equilibrium-point (EP) hypothesis, the λ model, allowed the reconstruction of the control variables, the “equilibrium trajectories”, in the “do not correct” condition for the wrist and the elbow joints as well as for the end point final position, while for the other condition, the reconstruction was less reliable. The findings support and extend to a multiple-joint planar movement, the paradigm of the EP hypothesis along with the “do not correct” instruction. Received: 3 May 1999 / Accepted in revised form: 19 May 2000     

Reconstruction of equilibrium trajectories during whole-body movements

The framework of the equilibrium-point hypothesis was used to reconstruct equilibrium trajectories (ETs) of the ankle, hip and body center of mass during quick voluntary hip flexions (`Japanese courtesy bow') by standing subjects. Different spring loads applied to the subject's back were used to introduce smooth perturbations that are necessary to reconstruct ETs based on a series of trials at the same task. Time patterns of muscle torques were calculated using inverse dynamics techniques. A second-order linear model was employed to calculate the instantaneous position of the spring-like joint or center of mass characteristic at different times during the movement. ETs of the joints and of the center of mass had significantly different shapes from the actual trajectories. Integral measures of electromyographic bursts of activity in postural muscles demonstrated a relation to muscle length corresponding to the equilibrium-point hypothesis. Received: 3 March 1997 / Accepted in revised form: 2 November 1998     

Ecological explanations for successful invasion of exotic plants

The intentional introduction of exotic species can increase the level of local biodiversity, enrich people’s material lives, and bring significant social and economic benefits that are also the symbols of human progress. However, along with the frequent intercourse among countries and regions, the frequency of uncontrolled crossregional migration of species is increased and there is a lack of scientific management strategy for the intentional introduction of exotic species. Exotic species invasion, which is behind habitat fragmentation, has become the second largest threatening factor to the maintenance of the global-scale level of biological diversity. Exotic species invasion can destroy the structure of an ecosystem, disturb the economic life of a society, and do harm to human health. In this paper, the authors review some of the ecological explanations for issues such as “what causes or mechanisms have led to the successful invasion of exotic species”, including the “ideal weeds characteristics”, “biodiversity resistance hypothesis”, “enemies release hypothesis”, “evolution of increased competitive ability hypothesis”, “niche opportunity hypothesis”, and “novel weapon hypothesis”. The authors also analyze and evaluate the background and theoretical basis of the hypotheses, providing explanations for some phenomena, as well as the deficiencies of these explanations.     

Md-ACS1 and Md-ACO1 genotyping of apple (<Emphasis Type="Italic">Malus</Emphasis> x <Emphasis Type="Italic">domestica</Emphasis> Borkh.) breeding parents and suitability for marker-assisted selection

Fruit ethylene production genotypes for Md-ACS1 and Md-ACO1 were determined for 60 apple cultivars and 35 advanced breeding selections. Two alleles for each gene are commonly found in cultivated apple. Earlier studies showed that genotypes homozygous for the ACS1-2 allele produce less ethylene and have firmer fruit than ACS1-1/2 and ACS1-1/1 genotypes. ACO1 plays a minor role compared to ACS1, with homozygous ACO1-1 having lower ethylene production. In this study, ACS1-2 and ACO1-1 homozygotes had firmer fruit at harvest and after 60 days of 0–1°C cold storage compared to other genotypes. These genotypes, ACS1-2/2 and ACO1-1/1, were observed for the following 8 of 95 cultivars/selections: “Delblush”, “Fuji”, “Pacific Beauty”, “Sabina” and four breeding selections. Cultivars/selections that were homozygous ACS1-2 but not ACO1-1 were: “Ambrosia”, “Aurora Golden Gala”, “CrimsonCrisp”, “Gala”, “GoldRush”, “Huaguan”, “Pacific Rose, “Pacific Queen”, “Pinova”, “Sansa”, “Sonja”, “Sundance”, “Zestar”, and 17 breeding selections. Cultivars with the heterozygous ACS1-1/2 genotype were “Arlet”, “Braeburn”, “Cameo”, “Delicious”, “Delorgue”, “Empire”, “Enterprise”, “Ginger Gold”, “Golden Delicious”, “Granny Smith”, “Honeycrisp”, “Orin”, “Pink Lady”, “Silken”, “Suncrisp”, “Sundowner”, “Sunrise” and 11 breeding selections. No cultivars were detected homozygous for both ACS1-1 and ACO1-1, or for both ACS1-2 and ACO1-2. This study is the first large-scale allelic genotyping of both ethylene synthesis genes for a comprehensive set of apple breeding parents used in an ongoing breeding project. The data reported here are important for informative selection of parent combinations and marker-assisted selection of progeny for breeding low ethylene-producing apple cultivars for better storability and improved consumer acceptance.     

Air movement preferences observed in office buildings

Office workers’ preferences for air movement have been extracted from a database of indoor environmental quality surveys performed in over 200 buildings. Dissatisfaction with the amount of air motion is very common, with too little air movement cited far more commonly than too much air movement. Workers were also surveyed in a detailed two-season study of a single naturally ventilated building. About one-half the building’s population wanted more air movement and only 4% wanted less. This same ratio applied when the air movement in workspaces was higher than 0.2 m/s, the de facto draft limit in the current ASHRAE and ISO thermal environment standards. Preference for “less air motion” exceeded that for “more” only at thermal sensations of −2 (cool) or colder. These results raise questions about the consequences of the ASHRAE and ISO standards’ restrictions on air movement, especially for neutral and warm conditions.     

Hypothalamic regulation of pituitary secretion of luteinizing hormone—II feedback control of gonadotropin secretion

A general mathematical model describing the biochemical interactions of the hormones luteinizing hormone releasing hormone (LHRH), luteinizing hormone (LH) and testosterone (T) in the male is presented. The model structure consists of a negative feedback system of three ordinary differential equations, in which the qualitative behavior is either a stable constant equilibrium solution or oscillatory solutions. A specific realization of the model is used to describe the experimental observations of pulsatile hormone release, its experimental suppression, the onset of puberty, the effects of castration, and several other qualitative and quantitative results. This model is presented as a first step in understanding the physicochemical interactions of the hypothalamic-pituitary-gonadal axis. Based on a paper presented at the conference “Mathematics in the Medical Sciences”, Dalhousie University, Halifax, Nova Scotia, June, 1976.     

Decline in energy storage in the Antarctic minke whale (<Emphasis Type="Italic">Balaenoptera bonaerensis</Emphasis>) in the Southern Ocean

The annual trend in energy storage in the Antarctic minke whale was examined using catch data from all 18 survey years in the Japanese Whale Research Program (JARPA). Regression analyses clearly showed that blubber thickness, girth and fat weight have been decreasing for nearly 2 decades. The decrease per year is estimated at approximately 0.02 cm for mid-lateral blubber thickness and 17 kg for fat weight, corresponding to 9% for both measurements over the 18-year period. Furthermore, “date”, “extent of diatom adhesion”, “sex”, “body length”, “fetus length”, “latitude”, “age” and “longitude” were all identified as partially independent predictors of blubber thickness. The direct interpretation of this substantial decline in energy storage in terms of food availability is difficult, since no long-term krill abundance series is available. However, an increase in the abundance of krill feeders other than minke whales and a resulting decrease in the krill population must be considered as a likely explanation.     

Non-equivalent role of TM2 gating hinges in heteromeric Kir4.1/Kir5.1 potassium channels

Comparison of the crystal structures of the KcsA and MthK potassium channels suggests that the process of opening a K⁺ channel involves pivoted bending of the inner pore-lining helices at a highly conserved glycine residue. This bending motion is proposed to splay the transmembrane domains outwards to widen the gate at the “helix-bundle crossing”. However, in the inwardly rectifying (Kir) potassium channel family, the role of this “hinge” residue in the second transmembrane domain (TM2) and that of another putative glycine gating hinge at the base of TM2 remain controversial. We investigated the role of these two positions in heteromeric Kir4.1/Kir5.1 channels, which are unique amongst Kir channels in that both subunits lack a conserved glycine at the upper hinge position. Contrary to the effect seen in other channels, increasing the potential flexibility of TM2 by glycine substitutions at the upper hinge position decreases channel opening. Furthermore, the contribution of the Kir4.1 subunit to this process is dominant compared to Kir5.1, demonstrating a non-equivalent contribution of these two subunits to the gating process. A homology model of heteromeric Kir4.1/Kir5.1 shows that these upper “hinge” residues are in close contact with the base of the pore α-helix that supports the selectivity filter. Our results also indicate that the highly conserved glycine at the “lower” gating hinge position is required for tight packing of the TM2 helices at the helix-bundle crossing, rather than acting as a hinge residue.     

On the equilibrium distribution of population in space

Spatial equilibrium distributions of population are derived from the spatial distribution of net rates of reproduction, and from a relationship between migratory flow and gradients of population density and of locational “attractiveness.” Conditions are discussed for which population approaches a uniform spatial density. Under certain conditions a particularly simple statement of the equilibrium conditions is possible in terms of the “potential of population,” a concept introduced by demographers (J. Q. Stewart,Geographical Review,37, 46–85, 1947) to measure the proximity of a point to people. This paper was first written at the Center for Advanced Study in the Behavioral Sciences.     

The structure of social behaviour inTheropithecus gelada

Through the use of principal components analysis of the correlation matrix between excentricity quotients of intra- and inter-individual transitions between pairs of the 22 most frequent behaviour elements of male and female gelada baboons observed in captivity, the total variance could be described in terms of a low number of causal factors. In intra-individual sequences the five factors requested of the analysis explain 74 per cent of the total variance. The following intra-individual groupings were found: (I) “autostimulation”, (II) “intensive social” versus “groom”, (III) “male sexual”, (IV) “attack” versus “sexual presentation”, and (V) “greeting” versus “threat”. In inter-individual transitions, the five factors explain 68 per cent of the variance. The following communicative sets were found: (1) “female-sexual releasing”, (2) “greeting and approaching releasing” versus “groom releasing”, (3) “austostimulation releasing” versus “male-sexual releasing”, (4) “fight releasing”, and (5) “conflict”. Mimetic induction of same acts or acts within one particular intra-individual set was frequent.     

Terahertz vibrational properties of water nanoclusters relevant to biology

Water nanoclusters are shown from first-principles calculations to possess unique terahertz-frequency vibrational modes in the 1–6 THz range, corresponding to O–O–O “bending,” “squashing,” and “twisting” “surface” distortions of the clusters. The cluster molecular-orbital LUMOs are huge Rydberg-like “S,” “P,” “D,” and “F” orbitals that accept an extra electron via optical excitation, ionization, or electron donation from interacting biomolecules. Dynamic Jahn–Teller coupling of these “hydrated-electron” orbitals to the THz vibrations promotes such water clusters as vibronically active “structured water” essential to biomolecular function such as protein folding. In biological microtubules, confined water-cluster THz vibrations may induce their “quantum coherence” communicated by Jahn–Teller phonons via coupling of the THz electromagnetic field to the water clusters’ large electric dipole moments.     

Physics,biology and sociology: II. Suggestion for a synthesis

In continuation of previous studies (Bull. Math. Biophysics,28, 283–308; 655–661, 1966;29, 139–152, 1967) it is shown that the difference between the “metric” aspects of physics and the “relational” aspects of biological and social sciences disappear by accepting the broader definition of “relation”, such as that given in mathematics and logic. A conceptual superstructure then becomes possible from which all three branches of knowledge may be derived, though none of them can be derived from the others.     

Theoretical Assessment of Public Health Impact of Imperfect Prophylactic HIV-1 Vaccines with Therapeutic Benefits

This paper presents a number of deterministic models for theoretically assessing the potential impact of an imperfect prophylactic HIV-1 vaccine that has five biological modes of action, namely “take,” “degree,” “duration,” “infectiousness,” and “progression,” and can lead to increased risky behavior. The models, which are of the form of systems of nonlinear differential equations, are constructed via a progressive refinement of a basic model to incorporate more realistic features of HIV pathogenesis and epidemiology such as staged progression, differential infectivity, and HIV transmission by AIDS patients. The models are analyzed to gain insights into the qualitative features of the associated equilibria. This allows the determination of important epidemiological thresholds such as the basic reproduction numbers and a measure for vaccine impact or efficacy. The key findings of the study include the following (i) if the vaccinated reproduction number is greater than unity, each of the models considered has a locally unstable disease-free equilibrium and a unique endemic equilibrium; (ii) owing to the vaccine-induced backward bifurcation in these models, the classical epidemiological requirement of vaccinated reproduction number being less than unity does not guarantee disease elimination in these models; (iii) an imperfect vaccine will reduce HIV prevalence and mortality if the reproduction number for a wholly vaccinated population is less than the corresponding reproduction number in the absence of vaccination; (iv) the expressions for the vaccine characteristics of the refined models take the same general structure as those of the basic model.     

Agonistic and courtship behaviour patterns in the skink Chalcides viridanus (Fam. Scincidae) from Tenerife

There have been relatively few attempts to quantitatively describe behaviours in scincid lizards. Chalcides viridanus is a small body-sized skink endemic of Tenerife (Canary Islands). We describe and quantify 18 behaviour patterns (both social and agonistic) of this species, some of which have not been described before for other scincids. Video recordings of male–male, female–female, and male–female interactions were made under laboratory conditions, with controlled light–dark cycle and temperature. We describe several agonistic and courtship behaviour patterns. Within the first context, we detected a new agonistic behaviour for a scincid, “Snout to body”, that appeared at the beginning of agonistic sequences; it consisted of each animal placing its snout in contact with the other individual’s lateral side of the body. The amplitude of head movement during “Head bobbing” was lower than that described for many other lizard species. Agonistic behaviours were shown in intrasexual staged encounters both within males and females. The comparison of behaviour patterns of both types of intrasexual encounters showed that females were more active, exhibiting significantly higher frequencies of behaviour than males. Specifically, females showed the “Snout to body” pattern more frequently than males. In male–female encounters we detected courtship and copulation patterns only in April, when males performed “Bites” and “Snout to body” directed at females.     

A note on energy expenditure in walking on level ground and uphill

In walking, energy is wasted in the process of up-and-down movement of the center of gravity of the body during each step, as well as in the kinetic energy involved in the swinging forward of each extrèmity. In this paper the frictional loss in muscles is not considered. It is shown that for a prescribed available amount of metabolic power expenditure there exists an optimal size of the step and an optimal (maximal) speed of walking for the size of the step. Calculated values are of the correct order of magnitude. In walking uphill there exists a type of step for which there is no “lost” up-and-down motion of the center of gravity of the body. This step is optimal for walking up a hill of a given incline.     

Interrelations between early child development,gestational age and birth weight

Five traits of early child development were studied in 656 infants from the day of birth till 2 years of age. The infants selected for follow-up were born at 26–42 weeks of gestational age and with a birth weight accordingly ranging from 860 to 4560g. Analysis of variance was carried out for each of the following five traits which entailed the age at which a child: 1) turned himself over (turned); 2) sat unsupported for a few seconds (sat); 3) stood up (stood); 4) walked unsupported (walked); and 5) cut its first tooth (tooth). The results of this survey show no significant sex differences in the age of initial occurrence of any of the studied traits. Comparison with older siblings of the surveyed infants indicated a significant sibling resemblance component for all 5 trais, with the respective intraclass correlation coefficients ranging between 0.34 and 0.53. Gestational age and birth weight, but not “tooth”, appeared to be important messages of an infant's motor development, insofar as onset of the studied traits. The separate correlations of “turned”, “sat”, “stood” and “walked” with gestational age or weight were all negative and statistically highly significant. Research Unit — Human Population Biology, Division of Anatomy and Anthropology     

Consistency of optimal sequence alignments

Pairwise optimal alignments between three or more sequences are not necessarily consistent as a whole, but consistent and inconsistent residues are usually distributed in clusters. An efficient method has been developed for locating consistent regions when each pairwise alignment is given in the form of a “skeletal representation” (Bull. math. Biol. 52, 359–373). This method is further extended so that the combination of pairwise alignments that gives the greatest consistency is found when possibly many alignments are equally optimal for each pairwise comparison. A method for acceleration of simultaneous multiple sequence alignment is proposed in which consistent regions serve as “anchor points” limiting application of direct multi-way alignment to the rest of “inconsistent” regions. Dedicated to Prof. Akiyoshi Wada on the occasion of his 60^th birthday.