Occupational Biomechanics

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: aspekgayadanmomen • Kinematics: aspekgerakantubuh (motion) • Aplikasi: rehabilitasimedik, 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.

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

7. Components of the MS System

8. Anatomy and Biomechanics ANATOMY MECHANICAL PROPERTIES PERFORMANCE FAILURE LIMITS

9. - mechanical loads - primary - health promoting - simple categories: - mechanical strain - training force, distance, time - acute physiological - well being - complex categories: changes - coping e.g. intensity, power, work, duration, - secondary - detrimental frequency, variability - local in cells and - injuries tissues - atrophy - mental loads - information EXPOSURE RESPONSE EFFECT INDIVIDUAL FACTORS: - inherited - trainable - modified by response and effect Model for Injury Pathogenesis -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 Dari: Chaffin and Andersson (1991) Occupational Biomechanics

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

13. Steps required • Free Body Diagram • Hitung external moment(s) padasendi (joint) • Hitung net internal moment(s) • Hitung external force(s) padasendi • 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) = -64.7 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 = -10 + (-180)= -190 N (down) FE = - FE FE = FJT + FB FJT = 190 - 1294 = -1104 N (down) • Kesimpulan, untukmenahansebuahbenda 18 kg dibutuhkan force (bicep) ~1300 N dandihasilkan force ~1100 N padasendi 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= (15.4 - 40)/15 = -1.64 Dari distribusi normal: z = -1.64  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. F c.o.m F compression M = external muscle moment F shear a F BW q=90-a F Load Analisis Biomekanika 6 cm M internal M external q=90-a FL5/S1 = FBW + Load

20. Manual Material Handling

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

22. The Vertebrae

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

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. AcuanPosisi

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

31. Pengali Vertikal • VM = (1-(0.003|V-75|)) • V = jarakvertikal (cm) V V

32. Distance Multiplier (DM) • DM = (0.82 +(4.5/D)) • D = jarakperpindahanvertikal (cm)

33. Asymmetry Multiplier (AM) • AM = (1-(0.0032|A|)) • A = sudutasimetri

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

35. ≤ 1 hour ≤ 2 hour ≤ 8 hour Frequency initial load lifts/min V<75 V≥75 V<75 V≥75 V<75 V≥75 height 0.2 1.00 1.00 0.95 0.95 0.85 0.85 0.5 0.97 0.97 0.92 0.92 0.81 0.81 1 0.94 0.94 0.88 0.88 0.75 0.75 2 0.91 0.91 0.84 0.84 0.65 0.65 3 0.88 0.88 0.79 0.79 0.55 0.55 4 0.84 0.84 0.72 0.72 0.45 0.45 5 0.80 0.80 0.60 0.60 0.35 0.35 6 0.75 0.75 0.50 0.50 0.27 0.27 7 0.70 0.70 0.42 0.42 0.22 0.22 8 0.60 0.60 0.35 0.35 0.18 0.18 9 0.52 0.52 0.30 0.30 0.00 0.15 10 0.45 0.45 0.26 0.26 0.00 0.13 11 0.41 0.41 0.00 0.23 0.00 0.00 12 0.37 0.37 0.00 0.21 0.00 0.00 13 0.00 0.34 0.00 0.00 0.00 0.00 14 0.00 0.31 0.00 0.00 0.00 0.00 15 0.00 0.28 0.00 0.00 0.00 0.00 >15 0.00 0.00 0.00 0.00 0.00 0.00 Frequency Multiplier (FM) (cm) ≤

36. RWL Analysis • Lift Index = (BebanAktual)/RWL • 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|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

39. 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 Jikaberatbebanaktual yang diangkat 22.68 kg: LI = Bebanaktual / RWL = 22.68 / 10.26 = 2.21 Kesimpulan?

40. Ergonomic Controls • Engineering • Perbaiki cara kerja & sistem kerja • Mesin • alat bantu • metode baru • Administrative • Work scheduling • Work rotation • Worker selection

41. Teknik Pengangkatan Manual

42. 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):

43. Questions?