1. NIOSH Lifting Equation submitted by William A. Groves
C.6.b

2. Introduction
NIOSH first developed a lifting equation in 1981 to aid in evaluating lifting demands
Original equation was widely used by occupational health practitioners since it provided an empirical method for estimating a weight limit for different manual lifting tasks
Useful for identifying lifting tasks that posed a risk for developing low back pain
Limited to sagittal plane lifting tasks – no asymmetry or rotation out of longitudinal plane

3. Introduction
A revised lifting equation was developed and initially presented in 1991
Documentation and an application manual were subsequently developed and released in
Based on more recent research
Provided methods for evaluating asymmetrical lifting tasks, and lifts of objects with less than optimal coupling between object and worker’s hands

4. Introduction
NIOSH Lifting Equation represents only one tool in a comprehensive effort to prevent work-related low back pain and disability
Lifting is only one of the causes of low back pain
Psychosocial factors, medical treatment, and job demands can also play an important role

5. Criteria Used in Developing Equation
Physiological
limit energy expenditure (3.5 Kcal/min)
Biomechanical
limit compression on L5/S1 disc (770 lb)
Psychophysical
75% of female population capable of lift
Epidemiological
consider risk to “fit” and “susceptible” populations

6. NIOSH Lifting Equation Limitations
Does NOT apply to:
Lifting/lowering with one hand
Lifting/lowering for over 8 hrs
Lifting/lowering while seated or kneeling
Lifting/lowering in a restricted work space
Lifting/lowering unstable object
Lifting/lowering while carrying, pushing, or pulling

7. NIOSH Lifting Equation Limitations (cont)
Does NOT apply to:
Lifting/lowering with wheelbarrows or shovels
Lifting/lowering with high speed motion (faster than 30 in./sec)
Lifting/lowering with poor foot/floor coupling (< 0.4 coefficient of friction)
Lifting/lowering in an unfavorable environment (high or low temperature / humidity)

8. Required Input Load weight Horizontal distance from load to low back
Vertical location of load at beginning and end of lift
Degrees from midline where load is located at beginning and end of lift
Frequency of lifting in lifts per minute
The duration of the task
The quality of any handles or hand-holds

9. Revised Lifting Equation
The revised equation for calculating the recommended weight limit (RWL) is a multiplicative model that incorporates weighting factors (multipliers) corresponding to six task variables:
RWL = LC x (HM x VM x DM x AM x FM x CM)
Load Constant Weighting Factors
(maximum weight for ideal lift)

10. NIOSH Equation Multipliers1) 2) 3) 4) 5) 6)

11. Task Variables

12. Task Variables

15. Frequency Multiplier

16. Coupling Multiplier

17. Coupling Multiplier Decision Tree

18. Procedure
Measure horizontal distance (H1) and vertical distance (V1) at the origin of lift
Estimate asymmetry at origin (A1)
Measure horizontal distance (H2) and vertical distance (V2) at the destination of lift
Estimate asymmetry at destination (A2)
Select hand-hold category (good, fair, or poor)
Count the number of lifts in a given time frame, and convert to lifts per minute
Select the duration of the task: 1 hr, 2 hr, or 8 hr

20. Multipliers < 1.0 indicate non-optimal conditions for that task variable
Table 8 outlines design strategies for each task variable to improve the lift geometry (adjust multiplier toward value of 1.0)

21. Lifting Index (LI)

22. Example Problem 1

24. Example Problem 1

26. Example 1

27. Example 1

28. Review Questions (Answers on the next slide)
1. The maximum load that should be lifted according to the revised NIOSH equation is ?
a. 23 lbs
b. 43 lbs
c. 37 lbs
d. 51 lbs
2. The maximum value for any of the six task multipliers is ?
a. 100
b. 1
c. -1
d. 10
3. Which of the following design techniques would not be used to decrease the lifting index (LI) ?
a. increase lift frequency
b. reduce lift duration
c. bring load closer to worker
d. reduce vertical distance between origin and destination
4. The coupling type for an optimally sized container, with non-optimal handles, that allow for 90o finger flex would be ?
a. optimal
b. good
c. fair
d. poor

29. Answers to the Review Questions
1. The maximum load that should be lifted according to the revised NIOSH equation is ?
d. 51 lbs
2. The maximum value for the six task multipliers is ?
b. 1
3. Which of the following design techniques would not be used to decrease the lifting index (LI) ?
a. increase lift frequency
4. The coupling type for an optimally sized container, with non-optimal handles, that allow for 90o finger flex would be ?
c. fair

30. References
Applications Manual for the Revised NIOSH Lifting Equation; T.R. Waters, V. Putz-Anderson, and A. Garg, DHHS (NIOSH) Publication No
Waters, T.R.; Putz-Anderson, V.; Garg, A.; and Fine, L.J. Revised NIOSH Equation for the Design and Evaluation of Manual Lifting Tasks, Ergonomics, 1993, Vol 36(7),