Biomedical subjects

Reinhard Blickhan

Publications and source records attributed to Reinhard Blickhan.

13 recordsLinked to original sources

PubMed2007

Intelligence by mechanics.

Research on the biomechanics of animal and human locomotion provides insight into basic principles of locomotion and respective implications for construction and control. Nearly elastic operation of the leg is necessary to reproduce the basic dynamics in walking and running. Elastic leg operation can be modelled with a spring-mass model. This model can be used as a template with respect to both gaits in the construction and control of legged machines. With respect to the segmented leg, the humanoid arrangement saves energy and ensures structural stability. With the quasi-elastic operation the leg inherits the property of self-stability, i.e. the ability to stabilize a system in the presence of disturbances without sensing the disturbance or its direct effects. Self-stability can be conserved in the presence of musculature with its crucial damping property. To ensure secure foothold visco-elastic suspended muscles serve as shock absorbers. Experiments with technically implemented leg models, which explore some of these principles, are promising.

Artificial Intelligence↗

PubMed2006

Compliant leg behaviour explains basic dynamics of walking and running.

The basic mechanics of human locomotion are associated with vaulting over stiff legs in walking and rebounding on compliant legs in running. However, while rebounding legs well explain the stance dynamics of running, stiff legs cannot reproduce that of walking. With a simple bipedal spring-mass model, we show that not stiff but compliant legs are essential to obtain the basic walking mechanics; incorporating the double support as an essential part of the walking motion, the model reproduces the characteristic stance dynamics that result in the observed small vertical oscillation of the body and the observed out-of-phase changes in forward kinetic and gravitational potential energies. Exploring the parameter space of this model, we further show that it not only combines the basic dynamics of walking and running in one mechanical system, but also reveals these gaits to be just two out of the many solutions to legged locomotion offered by compliant leg behaviour and accessed by energy or speed.

Biomechanical Phenomena↗

PubMed2006

The tri-segmented limbs of therian mammals: kinematics, dynamics, and self-stabilization--a review.

The evolution of therian mammals is to a large degree marked by changes in their motion systems. One of the decisive transitions has been from the sprawled, bi-segmented to the parasagittal, tri-segmented limb. Here, we review aspects of the tri-segmented limb in locomotion which have been elucidated in our research groups in the last 10 years. First, we report the kinematics of the tri-segmented therian limb from mouse to elephant in order to explore general principles of the therian limb configuration and locomotion. Torques will be reported from a previous paper (Witte et al., 2002. J Exp Biol 205:1339-1353) for a better understanding of the anti-gravity work of all limb joints. The stability of a limb in z-configuration will be explained and its advantage with respect to other potential solutions from modeling will be discussed. Finally, we describe how the emerging concept of self-stability can be explained for a tri-segmented leg template and how it affects the design of the musculoskeletal system and the operation of legs during locomotion. While locomotion has been considered as mainly a control problem in various disciplines, we stress the necessity to reduce control as much as possible. Central control can be cheap if the limbs are "intelligent" by means of their design. Gravity-induced movements and self-stability seem to be energy-saving mechanisms.

Animals↗

PubMed2006

Analysis of complex physiological systems by information flow: a time scale-specific complexity assessment.

In the last two decades conventional linear methods for biosignal analysis have been substantially extended by non-stationary, non-linear, and complexity approaches. So far, complexity is usually assessed with regard to one single time scale, disregarding complex physiology organised on different time scales. This shortcoming was overcome and medically evaluated by information flow functions developed in our research group in collaboration with several theoretical, experimental, and clinical partners. In the present work, the information flow is introduced and typical information flow characteristics are demonstrated. The prognostic value of autonomic information flow (AIF), which reflects communication in the cardiovascular system, was shown in patients with multiple organ dysfunction syndrome and in patients with heart failure. Gait information flow (GIF), which reflects communication in the motor control system during walking, was introduced to discriminate between controls and elderly patients suffering from low back pain. The applications presented for the theoretically based approach of information flow confirm its value for the identification of complex physiological systems. The medical relevance has to be confirmed by comprehensive clinical studies. These information flow measures substantially extend the established linear and complexity measures in biosignal analysis.

Adult↗

PubMed2005

Lumbar spine intersegmental motion analysis during lifting.

UNLABELLED: There are a lot of in vitro and also in vivo studies under strictly restricted and subject-demanding laboratory conditions using X-ray or MRI recordings, but very few studies give information about the lumbar spine intersegmental behavior in daily life activities. Aims of this study were to measure the intersegmental lumbar spine motions during lifting trials and to determine the different motion patterns of different subjects performing comparable lifting tasks. First, 11 healthy volunteers had to perform lifting tasks (box weight 4-15 kg) using their favorite lifting technique (no instructions by the researcher). The coordinates of skin-markers attached on lumbar spines of the subjects were measured using 3D-motion capturing and then transformed to Cardan-angles. Second, 23 volunteers performed lifting tasks (box weight 4-15 kg) with the instruction to bend their knees during lifting. Coordinates of this smaller set of markers on lumbar spines of the subjects were transformed to intersegmental angles using a spline-method. From the first experiment three groups of motion patterns are distinguishable: subjects who used only small intersegmental range of motion within their upper lumbar spine and bended their knees during lifting were in contrast to subjects who used 3.25 times wider range of motion in the upper lumbar spine and did not bend the knees (cluster analysis, c = 0.76). The third group was not assignable to these other two groups. Within all lifting trials of the second experiment different groups were detectable also: in spite of all subjects bended their knees, there were subjects with wide range of motion of lumbar spine motion segments. Other subjects were able to reduce intersegmental range of motion (k-means clustering, msv > 0.47). From this it follows that the intersegmental motion of lumbar spine is individually different and not equal for all lumbar levels. Furthermore, lifting technique influenced the motion of the lumbar spine. But not for all subjects, the advice to bend the knees during the lifting effectively reduced the lumbar motion ranges. IN CONCLUSION: special instructions to reduce lumbar spinal motion are recommended. Due to different lumbar spine motion patterns, different loading situations are anticipated because of changing lever arms and angular accelerations. This understanding is important in reducing spinal loading and to prevent spinal disorders in manual material handling tasks.

Journal Article↗

PubMed2005

Three-dimensional relation of skin markers to lumbar vertebrae of healthy subjects in different postures measured by open MRI.

The debate is to which extent external skin markers represent true underlying vertebral position and motion. Skin markers and lumbar vertebrae L3 and L4 were examined by vertically open magnetic resonance imaging (MRI) within different postures to investigate whether, and to which extent the position and orientation of skin markers represent the corresponding information of assigned underlying vertebra. Nine healthy volunteers sat within an open MRI scanner in five different seating postures: upright, low flexion, heavy flexion, upright left turn and upright right turn. Skin markers were fixed at lumbar levels L3 and L4. A set of landmarks defines corresponding positions on the vertebrae. Translation-vectors quantify the change of co-ordinates while changing position. Orientation (Cardan-angles) of each level in space was calculated from co-ordinates of three skin-markers and the corresponding vertebral landmarks respectively. The close relation between the position of the individual skin marker and its corresponding landmark on the vertebrae is conserved through all postures (regression coefficients: 0.720<b<0.972, 0.916<r<0.993, p<0.0001). Despite the high sensitivity to measurement errors there is a strong relation between the translation-vectors of external markers and the corresponding translation of the landmark on the vertebrae (0.68<r<0.99, p<0.0001). Within the resolution of the MR-imaging the orientation of the vertebrae can be predicted from the external markers (regression coefficients: 0.936<b<1.189, 0.769<r<0.959, p<0.0001). Positions and motions of skin markers can be taken as a first estimate to calculate the position and spatial orientation of underlying vertebrae. The use of skin markers may help to investigate spinal positions in daily life situations where internal imaging is not possible.

Adult↗

PubMed2005

Gait information flow indicates complex motor dysfunction.

Gait-related back movements require coordination of multiple extremities including the flexible trunk. Ageing and chronic back pain influence these adjustments. These complex coordinations can advantageously be quantified by information theoretically based communication measures such as the gait information flow (GIF). Nine back pain patients (aged 61+/-10 yr) and 12 controls (aged 38+/-10 yr) were investigated during normal walking across a distance of 300 m. The back movements were measured as distances between characteristic points (cervical spine CS, thoracic spine TS, lumbar spine LS) by the sonoSens Monitor, a system for mobile motion analysis. Gait information flow and regularity indices (RI1: short prediction horizon of 100 ms, RI2: longer prediction horizon of walking period) were assessed as communication characteristics. All indices were non-parametrically tested for group differences. Sensitivity and specificity were assessed by bivariate logistic regression models. We found regularity indices systematically dependent on measurement points, information flow horizon and groups. In the patients RI1 was increased, but RI2 was decreased in comparison to the control group. These results quantitatively characterize the altered complex communication in the patients. We conclude that ageing and/or chronic back pain related dysfunctions of gait can advantageously be monitored by gait information flow characteristics of back movements measured as distances between characteristics points at the back surface.

Adult↗

PubMed2005

Spring-mass running: simple approximate solution and application to gait stability.

The planar spring-mass model is frequently used to describe bouncing gaits (running, hopping, trotting, galloping) in animal and human locomotion and robotics. Although this model represents a rather simple mechanical system, an analytical solution predicting the center of mass trajectory during stance remains open. We derive an approximate solution in elementary functions assuming a small angular sweep and a small spring compression during stance. The predictive power and quality of this solution is investigated for model parameters relevant to human locomotion. The analysis shows that (i), for spring compressions of up to 20% (angle of attack > or = 60 degree, angular sweep < or = 60 degree) the approximate solution describes the stance dynamics of the center of mass within a 1% tolerance of spring compression and 0.6 degree tolerance of angular motion compared to numerical calculations, and (ii), despite its relative simplicity, the approximate solution accurately predicts stable locomotion well extending into the physiologically reasonable parameter domain. (iii) Furthermore, in a particular case, an explicit parametric dependency required for gait stability can be revealed extending an earlier, empirically found relationship. It is suggested that this approximation of the planar spring-mass dynamics may serve as an analytical tool for application in robotics and further research on legged locomotion.

Animals↗

PubMed2004

Human leg design: optimal axial alignment under constraints.

Alignment of joints with respect to the leg axis reduces the moment arm of external forces and therefore joint torques. Moreover, it affects the gearing of muscle forces and displacements. Thus, it influences tissue stress, cost of support and locomotion, and stability. Assuming that alignment is of general advantage we propose a mathematical criterion quantifying the axial alignment using the static torque equilibrium of a three-segment leg. Using this criterion derived from joint torque minimisation we asked for optimal leg designs (segment lengths and joint angles) at varied leg lengths. The trivial "straight is best" solution is excluded and the configuration space is restricted by geometrical constraints such as the ground contact. For different total leg lengths we could identify different optimal segment length combinations and appropriately adjusted joint angles. The extended human leg configuration characterised by a short foot and a combination of unequal ankle and knee angles emerges as a global optimum from our analysis. For crouched configurations allowing for larger leg extensions an angle symmetrical 1:1:1 segment length combination is best. The plantigrade optimum is enforced by the requirement of the distal segment (foot) being shorter than the opposite outer segment (thigh), as well as by the ground contact constraint. Different (e.g. digitigrade) geometries might be of advantage in different biological contexts with different constraints. The fact that small mammals use a crouched equal segment design implies that other locomotor requirements such as stability, strain rates, and acceleration distance per step might dominate.

Biomechanical Phenomena↗

PubMed2003

Positive force feedback in bouncing gaits?

During bouncing gaits (running, hopping, trotting), passive compliant structures (e.g. tendons, ligaments) store and release part of the stride energy. Here, active muscles must provide the required force to withstand the developing tendon strain and to compensate for the inevitable energy losses. This requires an appropriate control of muscle activation. In this study, for hopping, the potential involvement of afferent information from muscle receptors (muscle spindles, Golgi tendon organs) is investigated using a two-segment leg model with one extensor muscle. It is found that: (i) positive feedbacks of muscle-fibre length and muscle force can result in periodic bouncing; (ii) positive force feedback (F+) stabilizes bouncing patterns within a large range of stride energies (maximum hopping height of 16.3 cm, almost twofold higher than the length feedback); and (iii) when employing this reflex scheme, for moderate hopping heights (up to 8.8 cm), an overall elastic leg behaviour is predicted (hopping frequency of 1.4-3 Hz, leg stiffness of 9-27 kN m(-1)). Furthermore, F+ could stabilize running. It is suggested that, during the stance phase of bouncing tasks, the reflex-generated motor control based on feedbacks might be an efficient and reliable alternative to central motor commands.

Biomechanical Phenomena↗

PubMed2003

Stabilizing function of antagonistic neuromusculoskeletal systems: an analytical investigation.

Under normal conditions human walking or running consists of stable cyclic movements. Minor perturbances such as a stone or a pothole do not disrupt the cycle, and the system returns to its prescribed trajectory. We investigated whether a pair of antagonistic muscles is able to stabilize the movement without neuronal feedback. The human is represented by a model consisting of a massless two-segment linkage system (leg) topped by a point mass. Both the extensor and flexor muscles are described by a Hill-type muscle model. Conditions for stability are calculated analytically based on the Ljapunov Theory and the results are illustrated by numerical examples. The activation functions of both the extensor and flexor muscles can be calculated for a prescribed trajectory to maintain the self-stabilizing ability of such a system. Experimental evidence supports the prediction. Our investigation shows that a moving center of rotation of the kneejoint, a biarticular flexor muscle group, the force-velocity relation, and the ascending limb of the force-length relation improves the self-stabilizing ability of human movement.

Electromyography↗

PubMed2002

A movement criterion for running.

The adjustment of the leg during running was addressed using a spring-mass model with a fixed landing angle of attack. The objective was to obtain periodic movement patterns. Spring-like running was monitored by a one-dimensional stride-to-stride mapping of the apex height to identify mechanically stable fixed points. We found that for certain angles of attack, the system becomes self-stabilized if the leg stiffness was properly adjusted and a minimum running speed was exceeded. At a given speed, running techniques fulfilling a stable movement pattern are characterized by an almost constant maximum leg force. With increasing speed, the leg adjustment becomes less critical. The techniques predicted for stable running are in agreement with experimental studies. Mechanically self-stabilized running requires a spring-like leg operation, a minimum running speed and a proper adjustment of leg stiffness and angle of attack. These conditions can be considered as a movement criterion for running.

Accidental Falls↗

PubMed2002

Joint stiffness of the ankle and the knee in running.

The spring-mass model is a valid fundament to understand global dynamics of fast legged locomotion under gravity. The underlying concept of elasticity, implying leg stiffness as a crucial parameter, is also found on lower motor control levels, i.e. in muscle-reflex and muscle-tendon systems. Therefore, it seems reasonable that global leg stiffness emerges from local elasticity established by appropriate joint torques. A recently published model of an elastically operating, segmented leg predicts that proper adjustment of joint elasticities to the leg geometry and initial conditions of ground contact provides internal leg stability. Another recent study suggests that in turn the leg segmentation and the initial conditions may be a consequence of metabolic and bone stress constraints. In this study, the theoretical predictions were verified experimentally with respect to initial conditions and elastic joint characteristics in human running. Kinematics and kinetics were measured and the joint torques were estimated by inverse dynamics. Stiffnesses and elastic nonlinearities describing the resulting joint characteristics were extracted from parameter fits. Our results clearly support the theoretical predictions: the knee joint is always stiffer and more extended than the ankle joint. Moreover, the knee torque characteristic on the average shows the higher nonlinearity. According to literature, the leg geometry is a consequence of metabolic and material stress limitations. Adapted to this given geometry, the initial joint angle conditions in fast locomotion are a compromise between metabolic and control effort minimisation. Based on this adaptation, an appropriate joint stiffness ratio between ankle and knee passively safeguards the internal leg stability. The identified joint nonlinearities contribute to the linearisation of the leg spring.

Adult↗