STRAIN
MUSCULOSKELETAL Disorders and discomfort associated with stress to one or more of the components of the musculoskeletal system (MS). MAIN COMPONENTS OF THE MS: bones muscles ligaments tendons nerves biological and mechanical system.
MUSCULOSKELETAL SYSTEM
Bones internal framework Muscles generate force and movement Ligaments connect bones Tendons connect muscles to bone
CAUSES OF MUSCULOSKELETAL DISCOMFORT
Musculoskeletal System = biological and mechanical system biomechanical wear and tear physiological stress due to muscle fatigue: inadequate nourishment or accumulation of waste products cumulative trauma: continued exposure
MUSCLE FATIGUE
Not enough time for recovery Oxygen deficit Lactic acid build up Waste build up / no nourishment
MUSCULAR EFFORT
DYNAMIC EFFORT:
characterized by a rhythmic alternation between contraction and relaxation of muscles. the muscle acts as a pump to the blood circulation. the muscle is continuously supplied with sugar and oxygen, while at the same time waste products are removed.
STATIC EFFORT:
characterized by a prolonged state of contraction which usually implies a postural stance or constrained postures. the muscle is not relaxed, but tense. the blood vessels are compressed by the internal tension of muscle tissue, so that blood no longer flows through the muscle. the muscle does not receive sugar or oxygen from the blood, and waste products are not being removed.
STATIC AND DYNAMIC MUSCULAR EFFORT
Blood needed Blood flow Blood needed Blood flow Blood needed Blood flow
Resting
Dynamic effort
Static effort
EXAMPLE COMBINED OF STATIC AND DYNAMIC EFFORTS
keyboard operations:
The shoulders and arms do mainly static work: holding the hands in typing position. The fingers perform dynamic work: operating the keys.
STATIC EFFORT
Static work can be sustained for several hours without symptoms of fatigue if the exerted force does not exceed about 8% of the maximum force of the involved muscles. Constrained postures are certainly the most frequent form of static muscular work. The main cause of constrained postures in VDT work is the restriction of space for physical activities.
STATIONARY NATURE OF COMPUTER WORK
Computer workers remain seated for long periods in fixed postures. FIXED POSTURES:
sitting erect leaning forward at a desk holding the arms outstretched to manipulate a keyboard bending the neck
LOCALIZED FATIGUE AND MUSCULOSKELETAL TROUBLES
If the static load is repeated daily over a long period, aches will appear in the limbs and may involv...