Occupational Biomechanics Hardianto Iridiastadi

Motivation Physical activities in many occupational settings Dynamics, requiring large muscle groups, large forces Statics, involving smaller muscles, minimal forces MS problems Prevalent (epidemiology data) Costly (individual, organization, society) Resulting in poor performance and productivity Job requirements Individual variations Regulations (e.g., ADA, EOE)

Guiding philosophy Job Demand Individual Capacity

Definitions Biomechanics : Kinetics: aspek gaya dan momen Kinematics: aspek gerakan tubuh (motion) Aplikasi: rehabilitasi medik, olahraga, ergonomi Occupational Biomechanics is a sub-discipline within the general field of biomechanics which studies the physical interaction of workers with their tools, machines and materials so as to enhance workers performance while minimize the risk of musculoskeletal injury. Biomechanics uses the laws of physics and engineering mechanics to describe the motions of various body segments (kinematics) and understand the effects of forces and moments acting on the body (kinetics).

Definitions “mechanical behavior of the musculoskeletal (MS) system and component tissues when performing physical work” Objectives Minimize MS problems Improve performance

Cost $$$ ? www.libertymutual.com Event: %: (Billions) 2002- 2003    %:  (Billions)  2002- 2003  1999- 2003  Overexertion  26.4%  $13.4  -0.03%  15.1%  Falls on the Same Level     13.7%    $6.9   10.4%  32.3%  Bodily Reaction    10.2%    $5.1    -4.7%  20.3%  Falls to Lower Level      9.0%    $4.6    -1.9%    8.8%  Struck by Object    8.5%    $4.3    -3.4%  12.2%  Repetitive Motion    5.9%    $3.0     3.4%   -2.2%  Highway Incidents    5.8%   12.8%    9.2%  Struck Against Object    4.4%    $2.2    -6.1%    5.2%  Caught in or Compressed by      3.9%    $2.0     1.4%  12.9%  Assaults & Violent Acts    0.8%    $0.4    -9.9%   -8.5%  All other   11.3%    $5.8     Total   100%   $50.8     0.7%  11.4% www.libertymutual.com

Components of the MS System

Anatomy and Biomechanics MECHANICAL PROPERTIES PERFORMANCE FAILURE LIMITS

Model for Injury Pathogenesis - mechanical loads simple categories: force, distance, time complex categories: e.g. intensity, power, work, duration, frequency, variability mental loads information EXPOSURE RESPONSE EFFECT INDIVIDUAL FACTORS: inherited trainable modified by response and effect primary mechanical strain acute physiological changes secondary local in cells and tissues health promoting training well being coping detrimental injuries atrophy -From Sejersted and Vøllestad (1993) Progress in Fibromyalgia and Myofascial Pain

Applied Biomechanics Biomechanics of human body Compare mechanical demands vs. joint/muscle strength Manual handling evaluations Ergonomic assessments

Biomechanical Model - Simple Unknown: Elbow reactive force Elbow moment Asumsi: No motion No out-of-plane forces (Flatland) Known anthropometry (segment sizes and weights) Known forces and directions Known postures 1 muscle Known muscle geometry No muscle antagonism (e.g. triceps) Others Dari: Chaffin and Andersson (1991) Occupational Biomechanics

Example Akan dihitung: Force pada otot Biceps (FB) ELBOW COM HAND Akan dihitung: Force pada otot Biceps (FB) Force pada elbow (FE) External elbow moment (ME)

Steps required Free Body Diagram Hitung external moment(s) pada sendi (joint) Hitung net internal moment(s) Hitung external force(s) pada sendi Hitung net internal force(s) Evaluasi

Example - solution SME = 0 ME = MLA + MH = (WLA x maLA) + (FH x maH) ME = (-10 x 0.17) + (-180 x 0.35) = -64.7 Nm ME = -ME ME = (FJT x maJT) + (FB x maB) FB = 1294 N (up) External moment Internal moment

Solution (lanjutan) SFE = 0 FE = WLA + FH = -10 + (-180)= -190 N (down) FE = - FE FE = FJT + FB FJT = 190 - 1294 = -1104 N (down) Kesimpulan, untuk menahan sebuah benda 18 kg dibutuhkan force (bicep) ~1300 N dan dihasilkan force ~1100 N pada sendi elbow

Evaluasi Populasi Jika momen pada elbow (ME)= 15.4 Nm, berapa persen populasi yang diprediksi bisa menahan beban ini (asumsi: untuk waktu yang singkat)? Mis: m = 40 Nm; s = 15 Nm z = (y - µ)/σ = (15.4 - 40)/15 = -1.64 Dari distribusi normal: z = -1.64  0.95 Artinya, 95% dari populasi mempunyai kekuatan otot ≥ 15.4 Nm

Ergonomic Controls Strategi perbaikan kerja Kurangi D (Demand) Forces: berat beban Moment arms: jarak beban ke tubuh, postur, layout kerja Tingkatkan C (Capacity) Seleksi pekerja Hindari dampak beban kerja untuk sendi tubuh yang relatif lemah/ kritis

Model 2: Low-Back Dari Chaffin and Andersson (1991) Occupational Biomechanics

Analisis Biomekanika FL5/S1 = FBW + Load F F M a q=90-a M F F q=90-a M = external moment c.o.m F Load BW q=90-a a F muscle 6 cm F shear M internal M external F compression q=90-a FL5/S1 = FBW + Load

Manual Material Handling

Masalah Overexertion sebagai sumber biaya MSDs terbesar Back injury Penyebab utama: lifting Back injury 20% dari total kelainan MSDs 30% dari total biaya kompensasi Total biaya $ ~30 billion per tahun

The Vertebrae

Disc Herniation

Disc Degeneration

Solusi Ergonomik Evaluasi penanganan material Perancangan baru sistem penanganan material Training Pemilihan karyawan

NIOSH Guides untuk Manual Lifting Acuan pengangkatan beban secara manual Beban maksimum 23 kg Asumsi Fokus pada L5/S1 vertebral joint Batas compressive force = 3400 N Keterbatasan NIOSH Lembaga riset dan edukasi Mengembangkan standard dan petunjuk keselamatan kerja

Recommended Weight Limit (RWL) RWL = C x 6 multipliers C = konstanta = 23 kg Multipliers: horizontal location (HM) vertical location (VM) vertical travel distance (DM) asymmetry (AM) frequency (FM) coupling (CM) Multipliers ≤ 1 RWL = 23 kg  HM  VM  DM  AM  FM  CM

Acuan Posisi

Horizontal Multiplier (HM) HM = (25/H) H = jarak horizontal (cm) H H

Pengali Vertikal VM = (1-(0.003|V-75|)) V = jarak vertikal (cm) V V

Distance Multiplier (DM) DM = (0.82 +(4.5/D)) D = jarak perpindahan vertikal (cm)

Asymmetry Multiplier (AM) AM = (1-(0.0032|A|)) A = sudut asimetri

Coupling Multiplier (CM) Lihat Tabel V<75 cm V≥75 cm 1.0 .95 .90 Good Fair Poor Coupling Initial load height

Frequency Multiplier (FM) V<75 V≥75 0.85 Frequency lifts/min 0.95 1.00 0.2 ≤ 1 hour ≤ 2 hour ≤ 8 hour 0.81 0.92 0.97 0.5 0.75 0.88 0.94 1 0.65 0.84 0.91 2 0.55 0.79 3 0.45 0.72 4 0.35 0.60 0.80 5 0.27 0.50 6 0.22 0.42 0.70 7 0.18 8 0.00 0.15 0.30 0.52 9 0.13 0.26 10 0.23 0.41 11 0.21 0.37 12 0.34 13 0.31 14 0.28 15 >15 initial load height (cm) ≤

RWL Analysis Lift Index = (Beban Aktual)/RWL LI < 1 OK Interpretasi: LI < 1 OK LI > 1 may have increased risk LI > 3 likely have increased risk

Contoh Awal Akhir H = 13.0 cm H = 41.5 cm V = 13.5 cm V = 89.0 cm A = 0 deg A = 0 deg D = 75.5 cm; F = 1/min; Pegangan = Fair

Calculations HMStart = (25/13) = 1 HMEnd = (25/41.5) = 0.60 VMS = (1-(0.003|13.5-75|) = 0.82 VME = (1-(0.003|89-75|) = 0.96 DM = (0.82+(4.5/75.5)) = 0.88 AMS = AME = (1-(0.0032)(0)) = 1 CMS = [Fair, V<75] = 0.95 CME = [Fair, V≥75] = 1 FM = [1/min, ≤2h, V<75] = 0.88

RWL and LI calculations RWLAwal = 23 kg x 1 x 0.82 x 0.88 x 1 x 0.95 x 0.88 = 13.87 kg RWLAkhir = 23 kg x 0.6 x 0.96 x 0.88 x 1 x 1 x 0.88 = 10.26 kg Jika berat beban aktual yang diangkat 22.68 kg: LI = Beban aktual / RWL = 22.68 / 10.26 = 2.21 Kesimpulan?

Ergonomic Controls Engineering Administrative Perbaiki cara kerja & sistem kerja Mesin alat bantu metode baru Administrative Work scheduling Work rotation Worker selection Get the load close to the body! Lowering lebih baik dari lifting Hindari twisting Pegangan (handles) Gunakan alat bantu atau helper

Teknik Pengangkatan Manual

Typical Manual Handling Tasks Survey > 25.000 tasks in 2442 industrial locations in the US Nilai median (Ciriello and Snook, IJIE, 1999, pp. 379-388): Lift/lower mass = 19 - 20 kg One lift/lower every 3 and 2 minutes Hand distance from front of body = 22 cm Initial push and pull forces = 177 and 222 N One push/pull every 30 and 23 minutes Carry mass, distance, and frequency = 20 kg, 2.3 m, and every 2.6 min Distribusi berat beban (10.000 lifts):

Questions?