Biomechanics (original) (raw)
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Practical demonstrations of ergonomic principles
2011
Awkward posture. Deviation from the natural or-neutral‖ position of a body part. A neutral position places minimal stress on the body part. Awkward postures typically include reaching overhead or behind the head; twisting at the waist; bending the torso forward, backward, or to the side; squatting; kneeling; and bending the wrist. Cumulative injury (overuse injury). Cumulative injuries develop from repeated loading of body tissues over time. Such injuries include overuse sprains/strains, herniated discs, tendonitis, and carpal tunnel syndrome. Disorder. A medical condition that occurs when a body part fails to function properly. Ergonomics. The science of fitting workplace conditions and job demands to the capabilities of workers, and designing and arranging items in the workplace for efficiency and safety. Fatigue failure. The weakening or breakdown of material subjected to stress, especially a repeated series of stresses. Force. The amount of physical effort a person uses to perform a task. Inline grip. A hand tool with a straight handle that is parallel with the direction of the applied energy. Moment (torque). The tendency to produce motion about an axis. Moment arm. The perpendicular distance between an applied force and the axis of rotation. For muscles, this is the perpendicular distance between the line of action of the muscle and the center of rotation at the joint. Musculoskeletal disorders (MSDs). Illnesses and injuries that affect one or more parts of the soft tissue and bones in the body. The parts of the musculoskeletal system are bones, muscles, tendons, ligaments, cartilage, and their associated nerves and blood vessels. Neutral body posture. The resting position of body parts. Pinch grip. A grasp in which one presses the thumb against the fingers of the hand and does not involve the palm. Pistol grip. A tool handle that resembles the handle of a pistol and is typically used when the tool axis must be elevated and horizontal or below waist height and vertical. Power grip. A grasp where the hand wraps completely around a handle, with the handle running parallel to the knuckles and protruding on either side.
Examination of biomechanical principles in a patient handling task
International Journal of Industrial Ergonomics, 1988
Handling patients in bed using a pique (a waterproof padded sheet placed under the patient) with, in particular, the activity of pulling and turning the patient, is associated with a high incidence of risks for th e spine. Six female subjects, not experienced with the task, were evaluated for spinal loadings at the L5 / S1 joint, for selected muscular activities in the trunk and shoulders and for work-energy factors. Films, force platforms and EMG recordings supplied the data; dynamic segmental analyses were performed to calculate reaction forces at L5 / S1, and a planar single-muscle equivalent was used to estimate internal loads. Three treatments were administered which allowed comparisons to be made for two hand grip positions on th e pique (close to th e patient vs. a 15 em distance) and two movement
Physicists recognize four fundamental forces. In the order of their relative strength from weakest to strongest they are: gravitational, electrical, weak nuclear, and strong nuclear. Only the gravitational and electrical forces are of importance in our study of the forces affecting the human body. The electrical force is important at the molecular and cellular levels, e.g., affecting the binding together of our bones and controlling the contraction of our muscles. The gravitational force, though very much weaker than the electrical force by a factor of 10 39 , is important as a result of the relatively large mass of the human body (at least as compared to its constituent parts, the cells). 3.1 How Forces Affect the Body We are aware of forces on the body such as the force involved when we bump into objects. We are usually unaware of important forces inside the body, for example, the muscular forces that cause the blood to circulate and the lungs to take in air. A more subtle example is the force that determines if a particular atom or molecule will stay at a given place 37
Physiological Methods to Solve the Force-Sharing Problem in Biomechanics
Multibody Dynamics, 2008
The determination of individual muscle forces has many applications including the assessment of muscle coordination and internal loads on joints and bones, useful, for instance, for the design of endoprostheses. Because muscle forces cannot be directly measured without invasive techniques, they are often estimated from joint moments by means of optimization procedures that search for a unique solution among the infinite solutions for the muscle forces that generate the same joint moments. The conventional approach to solve this problem, the static optimization, is computationally efficient but neglects the dynamics involved in muscle force generation and requires the use of an instantaneous cost function, leading often to unrealistic estimations of muscle forces. An alternative is using dynamic optimization associated with a motion tracking, which is, however, computationally very costly. Other alternative approaches recently proposed in the literature are briefly reviewed and two new approaches are proposed to overcome the limitations of static optimization delivering more realistic estimations of muscle forces while being computationally less expensive than dynamic optimization.
Medicine & Science in Sports & Exercise, 2008
During locomotion and exercise, bone is subjected to forces induced by gravitational loading and muscle loading. The inherent link between these modes of loading has confounded emergence of either one as the principal anabolic or anticatabolic signal in bone. A paradigm has emerged in the literature stipulating that muscle loading is the larger of the two, and therefore, bone morphology is predominantly determined by muscle loads. In spite of the intuitive appeal of a muscle-bone unit tuned to the magnitude of contractile forces, little evidence exists for the relatively few, large-magnitude muscle contractions arising during daily activities to dominate the mechanosensory input of bone. Moreover, a review of the literature raises several inconsistencies in this paradigm and indicates that the alternative-gravitational loading-can have a significant role in determining bone mass and morphology. Certainly, the relative contribution of each type of loading will depend on the specific activity, the location of the bone within the skeleton, and whether the bone is weight-bearing or not. Most likely, a more comprehensive paradigm for explaining sensitivity of bone to loading will have to include not only large-magnitude gravitational and muscle loads, but also other factors such as high-frequency, low-magnitude signals generated by the muscles during postural adjustments.