PubMed Health⌕ Search

Biomedical subjects

H Hatze

Publications and source records attributed to H Hatze.

At least 19 recordsLinked to original sources
PubMed2002

Fundamental issues, recent advances, and future directions in myodynamics.

A state-of-the-art report is presented on recent progress in selected areas of myodynamics, but also on problems that severely hamper the further development of the discipline. Significant advances have been made in elucidating the force-producing interaction between actin and the myosin-S1-subunit, including the localization of the most probable molecular site of power stroke initiation. Concerning the architecture of the myostructures, strong experimental evidence has accumulated for numerous intra-, inter-, and extramuscular pathways for lateral force transmission in addition to the serial sarcomere-to-sarcomere myotendinous path. It is shown that contemporary muscle models are inadequate in most respects and lag far behind the requirements an appropriate myodynamic model should fulfil. A similar comment applies to the current approaches designed to solve the myoskeletal indeterminacy problem. These formulations neglect myodynamic properties and do not allow for the implementation of biologically realistic objective functions. The solutions currently obtained are highly unsatisfactory. New research directions to rectify these situations are suggested, also with regard to the identification of subject-specific myodynamic parameters.

Adenosine Triphosphate↗
PubMed2001

An efficient simulation method for discrete-value controlled large-scale neuromyoskeletal system models.

An efficient Euler-Adams hybrid integration scheme for simulating on the computer discrete-value controlled large-scale neuromyoskeletal system models is presented. If, as discussed in the model, the differential equations describing the recruitment and excitation dynamics of the muscular subsystem are independent of the corresponding contraction-dynamical state variables, they can be integrated separately over certain time intervals by a modified Euler routine that handles discontinuous right-hand sides efficiently. The resulting myostates can then be stored and used as continuous input values for the subsequent integration by an Adams predictor-corrector algorithm of the remaining contraction-dynamical and skeletomechanical state differential equations. With such an Euler-Adams hybrid integration routine one avoids the detrimental effects and efficiency losses associated with frequent stop-restart cycles of otherwise efficient Adams-type algorithms, which cycles are forced by discontinuities on the right-hand side of the myostate equations. In the example presented, a reduction in the execution time by a factor of about 5 could be achieved by implementing the proposed technique.

Algorithms↗
PubMed2000

The inverse dynamics problem of neuromuscular control.

The myoskeletal inverse dynamics problem and the myocybernetic control inverse problem were investigated with respect to their ill-posedness. The first problem consists of finding from observed experimental motion and reaction force data the resultant muscle moments that generated the observed motion, while the second aims at finding the corresponding neural controls. It is shown that both problems belong to the class of incorrectly posed (ill-posed) problems that, by definition, do not possess unique solutions. To illustrate this point, results of a forward dynamics simulation of a comprehensive neuromusculoskeletal model of the human body are presented. These results demonstrate that fairly chaotic neural control perturbations have very little influence on the resulting motion trajectory, at least in the present example. While a regularization procedure may be applied to solve successfully the myoskeletal inverse dynamics problem, the myocybernetic control inverse problem is unsolvable. The latter fact has the important implication that, based on the somatosensory inputs it receives, the pars intermedia in the cerebellum is not able to control individual motor unit stimulation rates and recruitment patterns but only whole muscles by means of a single compound signal. The latter signal is identified as the "common drive." Presumably at the spinal level, special neural circuits are used to decompose the common drive signal into motor unit recruitment patterns and stimulation rates that are specific for a given mode of contraction and probably obey certain optimality principles.

Computer Simulation↗
PubMed1997

A three-dimensional multivariate model of passive human joint torques and articular boundaries.

OBJECTIVE: The development of a novel three-dimensional mathematical model of passive human joint torques that is of practical use, takes into account the complex non-linear interactions that exist between the moments generated by the various passive structures spanning the joint in question, and is applicable to all types of articular joints. DESIGN: Mathematical model validated by practical implementation. BACKGROUND: Previous models of passive human joint torques were predominantly one-dimensional and did not take into account the interactions of the various structural components. METHODS: Mathematical modelling is used in conjunction with repeated passive torque experiments on the right elbow joint of a healthy 29-year-old male. On the basis of the experimentally observed torque-angle data, the full set of articular model parameters characterizing the two-dimensional passive elastic torque function of the subject's right elbow joint could be determined. RESULTS: In addition to the passive elastic torque functions, the two-dimensional contour of the elbow joint's articular boundaries was also obtained. CONCLUSIONS: The present model is especially useful for assessing certain pathological conditions in any body joint investigated, and in addition is best suited for the inclusion in large-scale dynamic simulation models of the human neuromusculoskeletal system.

Journal Article↗
PubMed1995

The extended transentropy function as a useful quantifier of human motion variability.

A new concept is presented for quantifying the variability of iterated human motions and other recurrent biological phenomena. The concept is based on the idea of interpreting the variations occurring in repeatedly executed stereotyped motions as particular realizations of a regular stochastic process with superimposed but infrequently occurring chaotic excursions. Under these premises, the extended transentropy of such a process turns out to be a dimensionless and appropriate quantifier of motion variability. Extended transentropy functions can be used to monitor variability changes during motion execution. The practical applicability and usefulness of the new method is demonstrated by means of an example from gymnastics (the kip on the horizontal bar). Major areas of future applications are expected to be gait analysis, all sports movements, and the objective evaluation of the success rates of certain medical treatment procedures for specific movement disorders.

Gymnastics↗
PubMed1992

The effectiveness of grip bands in reducing racquet vibration transfer and slipping.

The effectiveness of cushion grip bands in reducing impact shock and vibration transfer, and slipping in tennis racquets has been investigated. The results also apply, in principle, to badminton and squash racquets, and to golf clubs. An artificial arm (manusimulator) replicating the structure and all the important properties of the real human arm (shoulder, upper- and forearm, hand, soft tissue- and muscle simulators, etc.) was used together with a standard tennis racquet for the investigation. Laser beams were employed for precision adjustment of the spatial racquet position and the ball impact location. The impact velocity was standardized at 20 m.s-1 +/- 1.2%, while the impact point was located 32.5 +/- 2 mm distal to the sweet spot (the nodal point of the fundamental transverse vibration mode) on the racquet long axis. The grip circumference for the 26 different grip bands tested was controlled at 116 +/- 1 mm (grip size 5), and the adjustable manusimulator grip pressure was kept at preset values. Impact shock and post-impact racquet vibrations were determined by manusimulator-accelerometry, while slipping resistance was measured by friction methods. The major finding was that cushion grip bands do statistically significant (at P = 0.05) reduce impact shock and vibration transfer in tennis racquets, albeit to varying degrees depending on the brand. At present, there is no clear indication whether these reductions are, in fact, biologically relevant. Very large differences were found to exist between the various grip band types as regards the reduction of slipping.

Humans↗
PubMed1988

High-precision three-dimensional photogrammetric calibration and object space reconstruction using a modified DLT-approach.

Two modified DLT algorithms are presented that improve the accuracy of three-dimensional object space reconstruction by almost an order of magnitude when compared with conventional methods. The improvement in the linear modified DLT (MDLT) algorithm is achieved by satisfying certain orthogonality conditions in the form of a non-linear constraint, thereby effectively eliminating a redundant DLT parameter. In the non-linear MDLT algorithm, the improvement and computational stability results from the appropriate elimination of implicit variables from one side of the approximating relations and the corresponding reformulation of the objective function to be minimized. The highest reconstruction accuracy of 0.733 mm rms mean error was obtained with the non-linear MDLT algorithm. This corresponds to a spatial resolution of about one part in 2860 or 0.035% overall accuracy. The accuracy obtainable with the linear MDLT was found to be slightly less and about 0.041% (0.833 mm rms mean error).

Algorithms↗
PubMed1981

Analysis of stretch responses of a myocybernetic model muscle fibre.

The characteristics of the response to stretch of a muscle fibre are investigated using a validated model of skeletal muscle. It is found that the model correctly predicts all the peculiar features of the stretch response: the initial rapid force rise; the subsequent slower rise; the slow decay of the force upon termination of the elongation; and the dependence of these phenomena upon stretching velocity and muscle length. The hypothesis explaining these phenomena is discussed in detail.

Computers↗
PubMed1981

Estimation of myodynamic parameter values from observations on isometrically contracting muscle groups.

A new method is presented which makes it possible to estimate from a series of experimental observations of isometric maximum-effort muscle torque, a set of myodynamic parameter values for each of a number of muscles contributing collectively to the total torque output. The parameters that can be estimated are: the individual maximum isometric forces; the spreads of the length-tension curves; the relative maximum isometric tendon extensions; and the optimum muscle lengths; most of which parameters could not be estimated previously. The method is described for both penniform and fusiform muscles, and is demonstrated using the human triceps muscle as an example. The values obtained by this method are in general agreement with comparable values obtained by in vitro methods.

Adult↗