Approaches to Standing, Sitting, and lying DR. FATIMA ZEHRA (Physical Therapist) School of Physiotherapy, IPMR Dow University of Health Sciences

Biomechanics of Standing Muscles extending from the neck to the ankle are continually active to prevent collapse of the skeleton  Postural Muscles. Postural muscles tends to spontaneous functional or even anatomical shortening. This manifests itself in a higher muscle tone Postural muscles have an inhibiting effect on their phasic partners (inhibition of an antagonist muscle by the agonist). With insufficient variety in muscle use, postural muscles can be activated disproportionately, which leads to inhibition and weakening of postural muscles. This process can lead to an imbalance between groups of muscles, resulting in poor posture with loss of mobility and increase of joint load.

Biomechanics of Standing Any deviation from the anatomical posture generates increased tension in soft tissue and increased loading on the skeletal structures. Standing in shoes in general means standing on uneven ground because a heel of elastic rubber has a certain height for shock absorption and because at the ball of the foot, the sole must be thin to give good flexibility. It is better to look at the inclination of the foot, and not at the height of the heel, because the inclination determines the degree to which a person loads the forefoot. With any given heel height, the inclination of the foot depends on the length of the foot.

With a certain heel height, the angle of inclination of the smaller foot is greater than that of the larger foot. In practice, however, it is often the smallest women who wear the highest heels. In this figure, the angle is 40°. Recommended angles are 10° to 14°, which translates to heel heights of 3 to cm maximum.

Biomechanics of Sitting It is possible to predict whether a chair is comfortable or not. independent of the size of the person. Evaluation of design criteria on the basis of biomechanical aspects demonstrates the poor design of such furniture's. Body posture is highly influenced by the form of a chair. A good sitting posture is characterized by minimal muscle effort which is produced with proper support by arm rests, back rest, seat, and foot rest. Nonetheless, the first law of good sitting is the ability to change posture regularly (Case Study 17-1).

Assignment Assess her sitting posture. Assess her workplace conditions in detail. What possible adjustments would we make to help her?

Biomechanics of Lying A bed is a body support surface on which prolonged and complete rest must be found. It is a combination of a mattress, a mattress carrier, and a bed frame or bedstead or spread-out mat on the floor. There are three types of mattresses can be distinguished:  Polyether  Foam rubber  Internally sprung.

Biomechanics of Lying A good bed should (1) adapt to body curvatures (2) remain flat, (3) have a pleasant spring action (4) have good ventilation (5) not be too warm or too cold Aspects I to 3 concern body support that evenly spreads the pressure on protruding (bony) parts, gives a straight spine when lying on the side, and gives a natural S-shape to the spine in the supine posture. Lying on a horizontal surface is special because each body part receives separate support with minimal pressure on skin, and underlying tissues and joints can be kept in a relaxed position. The result must be that for static equilibrium, muscle action is superfluous.

For support of the head, a pillow is needed. The thickness of the pillow is related to the curvature of the spine: the more curved (especially in older people), the thicker the pillow. If the pillow is too thin, the head must be tilted backward. A pillow that is too thick is inconvenient because it causes a bend in the cervical spine. This bend can also occur when the pillow is hard. Pillows must be pliable to also support the neck.

Applied Biomechanics The design of human tools should include knowledge of biomechanics and its effect on humans. Use and adaptation of supports, including rests, back rests, and adjustable desks or beds, help to decrease the load on musculoskeletal structures. The most important factor to reducing load on the lumbar spine during lifting is to keep the load close to the body. For engineering purposes, the is to reduce the lever arm of the object.

Reference Read Basic Biomechanics Chapter 17: Engineering Approaches to Standing, Sitting, and lying - Chris J. Snijders