Anatomy and Biomechanics for Occupational Ergonomics IE 665

Anatomical sites important for occupational ergonomics Spine – Occupational back pain Upper extremity – CTDs in neck, shoulder and wrist Lower extremity – pain foot and ankle

Lordosis Kyphosis Spinal curves Spinal shrinkage and Disc nutrition No pain sensation in load bearing bodies Micro-trauma of discs and cumulative load Disc degeneration

Clavicle Scapula Humerus Radius Ulna Carpals Metacarpals Phalanges

Rotor cuff syndrome Tendonitis Bursitis Frozen shoulder

Ball and socket – Shoulder, Hip Hinge – Elbow, Knee Pivot – Between ulna and radius Fixed - Skull Bursa A small, flat, fluid filled sack protects ligaments from friction with bones Bursitis – inflamed bursa

All body segment is subjected to gravitational force When CG of a body segment is vertically aligned with a joint – joint tension or compression = weight of the body segment Due to postural changes, CG of the body segment moves away from the joint’s vertical alignment. This creates a moment around the joint. M = Force*Moment arm (perpendicular distance from the joint axis). This moment due to gravitational force is countered internally by the muscles to maintain the posture. To maintain the posture  R    M R   Moment due to external forces M M = Moment due to internal muscle forces

Head-neck – 7% of BW =0.07*150 = 10.5 lb Ratio of moment arm = 2:1 Muscle force = 21 lb Joint compressive force = 31.5 lb M MRMR

Body weight = 200 lb R = Upper body wt = 200*0.65= 130 lb F=back muscle tension at (L5/S1) ? Spine compression at (L5/S1) ? For straight back: R*2=F*2 or, F = 130 lb Total L5/S1 compression = R+F = 260 lb For bent back: R*8=F*2, F= 130*8/2 = 520 lb Total L5/S1 compression R+F = = 650 lb L5/S1 joint compression increased by 2.5 times and back muscle tension increased by 4 times from leaning forward F R 2” 8”