Ergonomic Considerations BID 220 T. Ask

Ergonomics is …. Ergonomics is the application of scientific information concerning humans to the design of objects, systems and environment for human use.

1948 vs 1955 Post WWII Ergonomics

Ouch Approximately 100,000 keystrokes per day as a keyboardist. 125,000 back injuries due to improver lifting each year.

Acronyms Muscular-Skeletal Disorders (MSD) Blanket term for injury of soft tissues of the upper extremity (fingers through upper arm), shoulders and neck, low back, and lower extremity (hips through toes) that is primarily caused or exacerbated by workplace risk factors. E.g. tendonitis. Type of MSD: Repetitive strain injury (RSI) aka: repetitive stress injury, repetitive motion injuries, repetitive motion disorder (RMD), cumulative trauma disorder (CT) Disorders caused by repeated exertions of body. E.g. carpal tunnel syndrome CTS: Carpal Tunnel Syndrome LBP: Lower Back Pain

Key Principles Keep body in neutral position People have different dimensions Reduce repetitive motions Recognize strength and dexterity are reduced with reach.

Wrist Orientation Avoid overexertion of connective tissues (muscles, tendons, tendon sheaths) in wrist. Avoid compression of the median nerve in the carpal tunnel. Use natural grasp Angle of 60-70 degrees Figure 4.2

Strength Psychophysical assessments: judgments based on personal perception of strenuousness. Helpful adjunct to static tests

Nerve Injuries Carpal Tunnel Syndrome: Thoracic Outlet Syndrome: Compression of median nerve in carpal tunnel. Thoracic Outlet Syndrome: Brachial plexus compression arising from poor head position or slumped posture. Radial Tunnel Syndrome: Compressed radial nerve at outside of elbow arising from wrist and finger extensions. Cubital Tunnel Syndrome: Ulnar nerve compression inside of the elbow arising from bending of elbow.

Tendonitis Tendons attach muscle to bone. Overuse causes inflammation – tendonitis. Tennis and Golfers elbow.

Basic Ergonomic Principles Joint position should be neutral, typically midpoint of their range of motion. Work should be done by larges appropriate muscle groups. Allow movement of worker to adopt different safe positions/postures.

Summary Work directly in front and close to body. Upper arms close to body, elbows 90-100 degrees Hand angle 60-70 degrees. Limit movement to 15 degrees. Avoid wrist pronation (palm down) and supination (palm up) when lifting. Reduce static posture. Moving enhances circulation. Feet flat on floor. Use larges joints and muscles for task. Minimize shear of vertebrae disks.

Neutral Position No pronation (rotation) of forearms

Spinal Anatomy 33 vertebrae stabilized by ligaments Protects spinal cord Axial strength Facet joints allow movement Intervertebral disk is shock absorber

Spinal Anatomy

Ligaments are important! Spines vertebrae are held together by ligaments. Ligaments critical in keeping vertebrae in place, especially during spinal flexion.

Tendons Muscles attached by tendons.

Herniated Disk can pinch spinal nerve.

Other Disc Problems

Back Ergonomics Best zone for lifting is between your shoulders and waist. Stretch back. Avoid repetitive back motion. Avoid prolonged static posture. Avoid awkward postures and motions. Avoid overhung weight lifts. Back operates at 10:1 ratio. 10 lb lift with 105 lb torso = 1,1150 lbs on back

http://www. youtube. com/watch http://www.youtube.com/watch?v=SwNF_foFfAQ&feature=related lumbar review

Foot Anatomy

BID 110 Industrial Design T. Ask Ergonomics BID 110 Industrial Design T. Ask

1. Keep people in neutral position 2. People are different dimensions

Ergonomics is …. Ergonomics is the application of scientific information concerning humans to the design of objects, systems and environment for human use.

1948 vs 1955 Post WWII Ergonomics

Neutral Position No pronation (rotation) of forearms

Neutral Position

Carpal Tunnel Syndrome (CTS)

Carpal Tunnel Syndrome

Nerves are compressed when your wrist is forced into an unnatural posture (such as typing on a straight keyboard) or by direct pressure on the median nerve from hard, sharp edges of work surfaces or tools. Surrounding the median nerve are the tendon sheaths (tubular sacs lined with a thin layer of tissue and a layer of oily lubricating fluid). Continued pressure and tendon activity on the tunnel can cause inflammation, which puts pressure on the nerve, and eventually results in nerve damage or CTS.

Workplace risk factors include Hands held in fixed positions over prolonged periods (e.g., installing overhead electrical wiring). Repeated wrist and finger flexion (e.g., operating a hand tool). Light, highly repetitive wrist and finger movements (e.g., typing or data entry). Repeated flexion or hyperextension (wrist and hand bent backwards) of the wrist (e.g., painting).

Prolonged strenuous use of the hands (e.g., molding materials). Repeated pinching or grasping (e.g., inspecting materials). Vibration, particularly that associated with power tools. Bending the wrist toward the little finger (e.g., typing). Acceleration and velocity of dynamic motions (e.g., scanning items in a checkout line).

Summary Factors Vibration Repetitive Motion Excess force High local stress Awkward Postures Temperature

Repetitive or Awkward Motions Workers who perform repeated (unsupported) lifting, turning, or moving motions within a work cycle have an increased susceptibility to LBP (lower back pain). Awkward postures that can contribute to LBP are caused by poor workstation layout and/or equipment design. Poor chair design with inadequate lower back support can also contribute to LBP, especially when performing tasks that require prolonged sitting.

Anthropometry Anthropometry =body measurements such as body size, shape and strength. It is used to ensure that products fit and suit as many users as possible.

Anthropometry

Kinesiology is the scientific study of human movement.

Pelvic tilt measurement

normal/swayback/flatback

56

58

Forceful Exertion Forceful exertions increase stress on the muscles, tendons, joints, and spine. The following factors can contribute to LBP: Object weight. Load Distribution (e.g., shifting or bulky loads require more force exertion). Object friction (e.g., slippery objects require more force).

High Local Stress

Tendons enter your wrist through a U-shaped cluster of eight bones Across the "top" of the wrist is a tough, strong ligament (similar to a tendon, but linking two bones together at a joint). This ligament forms the arch of the carpal bones, or the "roof" of the carpal tunnel.