Biomedical subjects

L Lindbeck

Publications and source records attributed to L Lindbeck.

7 recordsLinked to original sources

PubMed1998

Method and performance: two elements of work technique.

In the present study work technique was viewed in two basic elements: the method of carrying out a work task and the individual performance of the work task. The aim was to investigate how eight selected kinematic, kinetic, electromyographic and psychophysical variables can characterize the two elements of work technique. Twelve female subjects lifted a box using two methods, back and leg lifts, and two different simulated performances, fast and slow lifts. Motions, ground reaction forces, muscle activity in the lower back and perceived exertion were measured. A dynamic biomechanical model was applied. The trunk angular displacement and velocity clearly separated the lift methods. The trunk angular velocities and accelerations, the L5/S1 moments and the EMG variables were closely related to the performances. The work technique varied between the subjects to a greater extent than the individual variability over repetitions of a lift task. A larger inter-individual variability for kinematic variables was mostly shown in leg lifts compared with back lifts. The EMG patterns displayed differences in muscle activation that were not revealed by the kinematic or kinetic patterns. The results imply that separate variables should be used for descriptions of work methods and task performances; for method descriptions ranges of motion seem to be appropriate, for performance descriptions displacement time derivatives and load variables seem to be more useful. Moreover, the inter-individual differences suggest that work technique should be evaluated on an individual level.

Adult↗

PubMed1991

Inertial effects from single body segments in dynamic analysis of lifting.

Biomechanical calculations of loads on the locomotor system in lifting tasks are often based on static models. Several investigators have shown, though, that in a dynamic act like lifting, inertial effects are not generally negligible. A complete dynamic analysis includes the calculation of linear and angular accelerations of body segments and is rather complicated to carry out. So it was of interest to find out whether the contribution of single body segments to the dynamic effects of the whole body might be negligible. Ten male subjects lifted a 12.8 kg box using two different techniques and two speeds. Ground reactions and body segment movements were recorded and reaction forces and net moments at different joints were calculated with static, dynamic and 'semidynamic' methods. The latter method incorporated the ground reaction forces as measured from a force plate but was otherwise equal to the static method. The results from semidynamic analyses agreed well with those from complete dynamic analyses for the ankle, knee, hip, and L5/S1 joints. For example, the semidynamically calculated peak moments at L5/S1 differed on average less than 3% from the dynamically calculated values. The contributions of the lower extremities and the pelvis to the dynamic effects of the whole body seemed to be quite small. The less complicated semidynamic method offers a good alternative to a fully dynamic analysis for estimations of peak moments in the lower back, at least for the studied lifting techniques.

Adult↗

PubMed1987

Analysis of the asymmetrically loaded spine by means of a continuum beam model.

A continuum beam model of the human spine, proposed by Hjalmars (Proceedings of the Fourth International Conference on Continuum Models of Discrete Systems, 1981), and earlier used by the present author as a tool for the analysis of mild functional scoliosis, is here used for the study of a spine, asymmetrically loaded in the frontal plane. In order to validate the theoretical predictions of the model, preliminary experiments are carried out, which show that the model fairly well describes the lateral curvatures that occur when, for various loading conditions, the spine is adjusted into a muscle-relaxed state of equilibrium. Values of the flexural rigidity estimated from the experiments are found to be in reasonable agreement with values, estimated from earlier observations on dead material, reported in the literature. The experiments also indicate that the model may be developed to a tool for estimations of the effective flexural rigidity of the spine in vivo.

Adult↗

PubMed1985

Analysis of functional scoliosis by means of an anisotropic beam model of the human spine.

An upright, muscle-relaxed human spine, suffering from a mild functional scoliosis, caused by a small difference in leg length, is modeled as an anisotropic, elastic beam. The lower end of the beam is built-in in a fixed body, i.e., the laterally tilted pelvis. The upper end is rigidly attached to a rigid body, i.e., the supported upper part of the trunk, which is supposed to move freely in the frontal plane. It is shown that the characteristic scoliotic curvature of the spine, observed on an X-ray picture, can be reproduced by means of buckling analysis of the beam model, using realistic values of geometric and loading parameters and a properly chosen bending stiffness, which is found to be in reasonable agreement with earlier experimental findings. The analysis also shows that the muscle-relaxed upright equilibrium position of the spine is mechanically unstable.

Biomechanical Phenomena↗

PubMed1983

Impulse and moment of impulse in the leg joints by impact from kicking.

In a previous paper we have given a theoretical analysis of the impulsive motion of the leg, modeled as a double pendulum. This analysis made it possible to estimate the impulsive reactions in the knee joint as a function of the measured initial and final velocities of the leg, when an impact was given to the lower leg, e.g., by means of a kick. This estimation was made under the assumption that no impulsive moments occur in the hip and the knee joints, i.e., that no muscles were stretched during the time of impact. In the present paper it is shown how such impulsive moments, should they occur, can be determined by means of an additional measurement, i.e., of the velocity of the ball after the impact. The results from a series of experiments are reported, showing that such impulsive moments in the joints occur in an appreciable number of the kicks, especially in the hip joint, indicating that muscles, acting on this joint, are prestressed during the impact.

Adult↗

PubMed1978

Dynamic load in the human knee joint during voluntary active impact to the lower leg.

The aim of the study was to get an insight into the nature of the dynamic load in a joint caused by impacts of physiological magnitude to the distal part of an extremity of normal, live human subjects. A method was developed for the calculation of two components of the impulse reaction (parallel and perpendicular to the lower leg) as a measure of the dynamic load in the knee. A theoretical model regarding the lower limb as a double pendulum was chosen and equations developed. Five subjects were studied during kicking situations and the components of the impulse reaction were calculated. With a normal kicking motion pattern the direction of the components of the impulse reaction in the knee joint caused by the impact to the lower leg are usually distal and anterior. The impulse reaction thus tends to cause a traction of the lower leg from the thigh and an anterior displacement of the proximal part of the lower leg in relation to the distal part of the thigh. Anatomical structures which can prevent this displacement are discussed.

Biomechanical Phenomena↗

PubMed1978

Knee muscular moment, tendon tension force and EMG during a vigorous movement in man.

With injuries to the components of the extensor apparatus of the knee as a background, it is interesting to investigate the magnitude of forces acting on these components, i.e. m. quadriceps femoris, the quadriceps tendon, patella, lig. patellae and tuberositas tibiae, during a vigorous but physiological movement. By means of the dynamic laws of mechanics the muscular moment of force with respect to the bilateral knee axis during kicking was calculated in 6 normal subjects. It was found that the maximum extending muscular moment in the knee occurs very early in the movement, when the initial flexion changes into extension, and thus long before the ball is hit. The peak of quadriceps EMG activity coincides with maximum moment. The EMG peak of the antagonistically acting hamstrings comes later, nearer to when the ball is struck. The greatest extending muscular moment obtained during the swing phase of kicking was surprisingly high, 260 Nm, corresponding to a tension force in the patellar tendon of 5200 N or about 7 times body weight. These values are discussed in relation to tendon strength.

Adult↗