Occupational Biomechanics

Presentasi berjudul: "Occupational Biomechanics"— Transcript presentasi:

1 Occupational Biomechanics
Hardianto Iridiastadi

2 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)

3 Guiding philosophy Job Demand Individual Capacity

4 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).

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

6 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%

7 Components of the MS System

8 Anatomy and Biomechanics
MECHANICAL PROPERTIES PERFORMANCE FAILURE LIMITS

9 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

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

11 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

12 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)

13 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

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

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

16 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 = -1.64 Dari distribusi normal: z =  0.95 Artinya, 95% dari populasi mempunyai kekuatan otot ≥ 15.4 Nm

17 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

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

19 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

20 Manual Material Handling

21 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

22 The Vertebrae

23

24 Disc Herniation

25 Disc Degeneration

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

27 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

28 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

29 Acuan Posisi

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

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

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

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

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

35 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) ≤

36 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

37 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

38 Calculations HMStart = (25/13) = 1 HMEnd = (25/41.5) = 0.60
VMS = (1-(0.003| |) = 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

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

40 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

41 Teknik Pengangkatan Manual

42 Typical Manual Handling Tasks
Survey > tasks in 2442 industrial locations in the US Nilai median (Ciriello and Snook, IJIE, 1999, pp ): Lift/lower mass = 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 ( lifts):

43 Questions?