11. Biomechanics of Work

THE MUSCULOSKELETAL SYSTEM

Bones and Connective Tissues

Synovial Joint Fibrous Joint Cartilaginous Joint

Muscles

Muscles

BIOMECHANICAL MODELS

Single-Segment Planar Static Model (Q) Suppose a person is holding a load of 20-kg mass with hands in front of his body and his forearm are horizontal. The load is equally balanced the two hands W = mg = 20kg*9.8m/sec = 196N Won-each-hand = 98N ∑ Felbow = 0 - 16N – 98N + Relbow = 0 Relbow = 114N ∑ Melbow = 0 - 16N(0.18m) – 98N(0.36m) + Melbow = 0 Melbow = 38.16N-m shoulder 30° HW: What are the reactive force and moment at shoulder? BW = 78Kg Upper arm = 0.028BW distance from shoulder to elbow = 33cm center of mass = 15 cm from the shoulder elbow

LOW-BACK PROBLEM

Low-Back Biomechanics of Lifting Clockwise rotational moment: Mload-to-torso (L5/S1) = Wload*h + Wtorso*b Counterclockwise rotational moment: Mback-muscle = Fback-muscle * 5(N-cm) ∑ ML5/S1 = 0 Fmuscle * 5 = Wload*h + Wtorso*b Fmuscle = Wload*h/5 + Wtorso*b/5 If h=40cm and b=20cm then Fmuscle = 8*Wload + 4*Wtorso Torso weight = 350N, Load = 300N (about 30kg) then Fmuscle = 3,800N Normal range of strength capability of the erector spinal muscle is 2,200 to 5,500N Compression force on L5/S1 (ignoring the abdominal force, fa) ∑ F L5/S1 = 0 Fcompression = Wload*cosα + Wtorso*cosα + Fmuscle Suppose α = 55°, torso weight 350N, load = 450N Fcompression = 450*cos 55° + 350*cos 55° + 5000 = 258 + 200 + 5000 = 5458N

Seated Work and Chair Design

Seated Work and Chair Design

아우디 생산직 파트에 보급된 제품. 가볍고(무게 2.5kg 정도) 어디서나 앉아 쉴 수 있도록 만들어졌음.

UPPER-EXTREMITY CUMULATIVE TRAUMA DISORDERS

Common Forms of CTD Tendon-Related CTD Neuritis Ischemia Bursitis

Causes and Prevention of CTDs Common Forms of CTD CTDs of the Finger CTDs of the Hand and Wrist CTDs at the Elbow CTDs at the Shoulder Causes and Prevention of CTDs

Hand-Tool Design Do not bend the wrist. Shape tool handles to assist grip.

Hand-Tool Design Provide adequate grip span. Provide finger and gloves clearances