PubMed · 10518298
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M T Cibulka. 1999. Classifying sacroiliac dysfunction.. https://doi.org/10.2519/jospt.1999.29.9.556
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The purpose of this study was to explore how the muscles which control postural body segments are activated during bilateral isometric ramp pushes exerted with the upper limbs by seated subjects. The paradigm under study presents the advantage that the subject is in a quasi-static posture, and since upper limbs are stretched out, the dynamic phenomena, which might occur, can only originate from the rest of the body, which means from the postural chain. A dynamometer was used to measure the horizontal force, Fx, exerted on the bar, and a custom-designed force-plate was used to measure global reaction forces (Rx) and displacement of the centre of pressure (Xp) along the antero-posterior axis. Electromyograms (EMGs) were picked up by bipolar surface electrodes from 14 muscles crossing the lower limb, pelvis, trunk and upper limb joints. It was shown that transient push efforts require monotonous EMG increase in postural as well as in focal muscles. The EMG sequence starts with the postural muscles and ends with the focal ones. The postural EMG sequence is anticipatory. It is concluded that the EMG sequence is programmed according to the task parameters, and that its role is to counteract in advance the perturbing effect of the effort, in order to allow the effort to be performed efficiently. It is suggested that excitation between the postural muscles is distributed according to their biomechanical role in relation to the supports.
During the course of a criminal trial, an investigating pathologist is commonly asked how much force was required to produce an injury. This subjective opinion is based on the pathologist's previous experience of dealing with wounds inflicted with similar weapons. However, in the case of stab wounds inflicted by broken glass, it is unlikely that two glass fragments would be physically similar. In the case studied, two theories were examined: that a wound resulted from a thrown glass fragment or that it had been caused as a stab injury by the glass held in the bare hand. The investigation involved quantifying the energy required for human tissue penetration, comparison of sharpness, a biomechanical analysis of throwing actions and testing of the hypothesis that if the glass shard were used as a stabbing implement it would result in a cut to the hand.The investigation utilised a scientific methodology that reduced the need for speculative (though informed) opinion from the pathologist by producing quantitative results.
During maturation of the red blood cell (RBC) from the nucleated normoblast stage to the mature biconcave discocyte, both the structure and mechanical properties of the cell undergo radical changes. The development of the mechanical stability of the membrane reflects underlying changes in the organization of membrane-associated cytoskeletal proteins, and so provides an assessment of the time course of the development of membrane structural organization. Membrane stability in maturing erythrocytes was assessed by measuring forces required to form thin, tubular, lipid strands (tethers) from the surfaces of mononuclear cells obtained from fresh human marrow samples, marrow reticulocytes, circulating reticulocytes, and mature erythrocytes. Cells were biotinylated and manipulated with a micropipette to form an adhesive contact with a glass microcantilever, which gave a measure of the tethering force. The cell was withdrawn at controlled velocity and aspiration pressure to form a tether from the cell surface. The mean force required to form tethers from marrow reticulocytes and normoblasts was 27 +/- 9 pN, compared to 54 +/- 14 pN for mature cells. The energy of dissociation of the bilayer from the underlying skeleton increases 4-fold between the marrow reticulocyte stage and the mature cell, demonstrating that the mechanical stability of the membrane is not completely established until the very last stages of RBC maturation.