Biomechanics

2 ● Bones, Cartilage:Structural members ● Flesh:Volumes, masses ● Joints:Bearing surfaces, articulations ● Joint Linings:Lubricants ● Muscles:Motors, dampers, locks ● Tendons:Cables ● Tissue:Load-bearing surfaces, springs

3 Significance ● Safety ● Productivity / Performance ● Comfort

4 Biomechanical - Dangers ● Bones, Cartilage:Breakage, deterioration ● Flesh:Cuts, abrasion ● Joints: Inflammation, deterioration ● Muscles:Fatigue, tearing ● Tendons: Tendonitis ● Tissue:Inflammation, other damage

5 General Postural Requirements 1.Weight of body segments transmitted with minimal strain 2.Forces to external objects counteracted

6 General Postural Recommendations ● Provide for postural changes ● Sitting preferable to standing – exceptions: large hand forces, body movement ● Provide comfortable chair

7 Manual Material Handling and Low Back Pain

8 Skeletal System Source (Left): Wikimedia Commons, accessed 19 Jan 10. Source (Right): Wikimedia Commons, accessed 19 Jan 10.

9 Vertebral Column/Spine Source (Left): Wikimedia Commons, accessed 19 Jan 10. Source (Right): Konz & Johnson, Work Design, 6 th edition.

10 Vertebrae, Side-View Source (Right): Wikimedia Commons, accessed 19 Jan 10.

11 Vertebrae/Disk, Oblique View Source: Wikimedia Commons, accessed 19 Jan 10.

12 Vertebra Cross-Section (cervical vertebra) Source: Wikimedia Commons, accessed 19 Jan 10.

13 Manual Material Handling Recommendations (1) ● Lifting Method: squat vs. stoop vs. free style ● Job Design: – reduce manual materials handling (MMH) – decrease weight – use 2 or more people where possible – Push or pull vs. lift & carry – minimize carrying distance – stacking height < shoulder height

14 Manual Material Handling Recommendations (2) ● Job Design (continued): – heavy objects at knuckle height – reduce lifting frequency – provide rest periods – use job rotation – provide handles ● Worker Selection ● Training ● Supports and Braces???

15 NIOSH Lifting Equation: Background ● Created by OSHA, 1970 ● Purpose: – Rank alternatives – Identify and correct problems – Not to rate absolute risk ● Goals – Biomechanical: ≤ 350 kg on L5-S1 – Physiological: ≤ 9.5 kcal/min

16 NIOSH Lifting Equation: Does Not Apply If ● > 1-2 steps ● One-handed lifting ● Seated/kneeling ● Restricted workspace ● Hot/cold/contaminated objects ● Unexpected events (e.g., slips, falls) ● Unstable load ● Carrying, pushing, pulling ● Using tools (e.g., wheelbarrow) ● Slippery floor ● Unfavorable environment (e.g., hot, cold)

17 NIOSH Lifting Equation RWL = LC × HM × VM × DM × FM × AM × CM ● LC = Load constant ● HM = Horizontal multiplier ● VM = Vertical multiplier ● DM = Distance multiplier ● FM = Frequency multiplier ● AM = Asymmetry multiplier ● CM = Coupling multiplier

18 Multiplier Formulas ● Horizontal multiplier HM = BIL / H – BIL = Body interference limit – H = Horizontal location – Large HM (small H) better (load close to body) ● Vertical multiplier VM = 1 – VC × | V – KH | – VC = Vertical constant = in. – V = Vertical location – KH = Knuckle height (for typical lifter = 30 in.) – Large VM (V close to KH) better (load closer to optimal lifting height)

19 Multiplier Formulas (cont.) ● Distance multiplier DM =.82 + DC / D – DC = Distance constant = 1.8 in. – D = Vertical travel distance

20 Multiplier Formulas (cont.) ● Frequency multiplier ● Lifting frequency = mean number of lifts in a 15-minute period ● Lifting duration /session in hours may be: – Short =.001 h to ≤ 1 h with recovery time of ≥ 1.2 × duration – Moderate = >1 h ≤ 2 h with recovery time of ≥.3 × duration – Long = >2 h but ≤ 8 h

21 Multiplier Formulas (cont.) ● Asymmetry multiplier AM = 1 – × A – A = Angle of symmetry (≤ 135°) – 30% penalty for 90° angle ● Coupling multiplier – See Table 11.3 ● Depends on: – Height of initial and final hand–container coupling – Whether coupling is good, fair, or poor

22 NIOSH Lifting Equation Example 1 from Waters et al (1994)

23 Job Analysis Parameters ● Object weight – L = 40 lbs. ● Hand location – Origin ● H = 18 in. ● V = 15 in. – Destination ● H = 10 in. ● V = 36 in. ● Vertical Distance – D = 21 in. ● Asymmetry – Origin: A = 45° – Destination: A = 45° ● Frequency – 1 – 12 times/shift – F < 0.2 lifts/min. ● Duration – < 1 hour ● Object Coupling – C = Fair

24 “Significant control of the object is not required at the destination so the RWL is computed only at the origin.”

25 Multiplier Calculations ● Horizontal multiplier HM = BIL / H = 10/18 = 0.56 ● Vertical multiplier VM = 1 – VC × | V – KH | = 1 – |15 – 30| = 1 – (15) = 0.89 ● Distance multiplier DM = DC / D = / 21 = 0.91 ● Frequency multiplier FM = 1.0 (from Table 15.9) ● Asymmetry multiplier AM = 1 – × A = 1 – (45) = 0.86 ● Coupling multiplier CM = 0.95 (from Table 15.10)

26 Final Calculations RWL = LC × HM × VM × DM × FM × AM × CM = 51 x 0.56 x 0.89 x 0.91 x 1.0 x 0.86 x 0.95 = 18.9 lb. LI = load weight / RWL = 40 / 18.9 = 2.1

27 Applications Manual For the Revised NIOSH Lifting Equation

Biomechanics and Hand Tools

29 Upper Extremity Source: Wikimedia Commons, accessed 19 Jan 10. Notes: Skeleton is facing observer. Skeleton's left hand (on observer's right) is supinated (palm toward observer). Skeleton's right hand (on observer's left) is pronated (back toward observer).

30 Shoulder Source: Wikimedia Commons, accessed 19 Jan 10.

31 Wrist Palmar/Volar (palm-side) View Dorsal (back-side) View Source (Left): Wikimedia Commons, accessed 19 Jan 10. Source (Right): Wikimedia Commons, accessed 19 Jan 10.

32 Wrist Cross-Section Source: Wikimedia Commons, accessed 19 Jan 10.

33 Cumulative Trauma Disorders Associated With Hand Tool Use ● tendonitis – irritation & swelling of tendons ● tenosynovitis – inflammation of tendons & sheaths ● carpal tunnel syndrome – compression of median nerve caused by swelling ● trigger finger – finger cannot be extended ● vibration-induced white finger – loss of circulation, numbness caused by vibration

34 Risk Factors and Prevention

35 Risk Factors Considerations ● More factors means more risk. ● Reduced factors means reduced risk. ● Presence of factor(s) does not imply CTD. ● Critical levels of exposure not known.

36 Rapid Upper Limb Assessment (RULA) Technique

Hand Tool Guidelines

38 Provide the Proper Grip ● Thickness – power grip: 38 mm - 50 mm diameter – precision grip: > 6 mm diameter. ● Shape (perpendicular to axis of tool) – rotation undesirable: provide tab – rotation OK: round ● Shape (parallel to axis) – change in shape ● reduces movement ● permits greater force ● can act as shield

39 Provide the Proper Grip Surface ● Compressible – reduced slippage – reduced vibration ● Nonconductive – resistance to heat/cold – resistance to electric shock/electrocution ● Smooth – reduced compression, trauma

40 Consider Angles: Forearm, Grip, Tool ● Reduced repetition – use both hands – use feet ● Keep wrist in neutral position – change worker/work position – change tool (angled handles) – provide splints ● Reduce force – amount – duration – use large muscle groups (e.g., by trigger strip)

41 Design Tools to be Used By Either Hand Preferred hand –about 6% greater strength –greater dexterity Benefits of either-hand-usability –everyone can use (about 10% left-handed) –non-preferred hand can be used when preferred hand busy when preferred hand resting

42 Reduce Vibration ● Vibration-isolated handles ● Vibration-absorbing gloves ● Breaks (e.g., 10 min/hr) ● Support tool ● Keep hands warm & dry ● Minimize handgrip force

43 Use Motor Power ● Economical ● Extended capability

44 Examples - Knives Source: Intercodev, last accessed 19 May 04http://

45 Knife with upright handle Source: Intercodev, last accessed 19 May 04http://

46 Knife with upright handle Source: Intercodev, last accessed 19 May 04http://

47 Ergonomic Pliers Source: Wiha Quality Tools, last accessed 16 Nov 09

48 Wire Stripping Pliers Source: MichaelHoligan.com, last accessed 19 May 04

49 Scissors Source: Intercodev, last accessed 19 May 04

50 Scissors Source: Intercodev, last accessed 19 May 04

51 Handles Source: Intercodev, last accessed 19 May 04

52 Ratchet Screwdriver Source: Lara Specialty Tools, last accessed 19 May 04http://

53 Ratchet Screwdriver Source: Pro’sKit, New Product Release …, last accessed 19 May 04

54 Hammers Source: ContractorsTools.com, last accessed 19 May 04

55 Coiled-Handle Hammer Source:NIOSH/Ergonomic Interventions in Ship Building/Coiled Hammer Handle, last accessed 19 May 04

56 Ergonomic Hand Tools Links ● humantech Vendorweb – ● NIOSH Guide –