Key points
- The Revised NIOSH Lifting Equation (RNLE) calculates the risk for back injuries from two-handed lifting tasks.
- The RNLE Applications Manual can help you understand how to use the RNLE for preventing musculoskeletal injuries from lifting tasks.
The Revised NIOSH Lifting Equation (RNLE)
The Revised Lifting Equation (RNLE) is a tool to calculate risk for work-related musculoskeletal disorders (WMSDs). The equation can be used to calculate both single and multiple manual lifting tasks. Using the equation can reduce the incidence of low back injuries in workers.
NIOSH created the RNLE because many workers are responsible for manually lifting and moving objects on the job. These workers are in numerous occupations and industries. Exposure to repetitive lifting puts workers at risk for developing WMSDs. Understanding how much workers can safely lift is important to preventing those injuries.
Key benefits of using the RNLE
The RNLE helps employers make informed decisions about mitigating potential hazards to their workers' musculoskeletal health. The RNLE benefits employers and safety professionals by:
- Providing guidelines for designing safe lifting tasks
- Serving as a risk assessment tool
- Helping raise workers' awareness about their job tasks
- Collecting quantitative lifting data for research
How to use the RNLE
Guidelines
Key variables
The equation has users input specific measurements, including:
- Weight of the object being lifted
- Horizontal Location of the hands away from the mid-point between the ankles
- Vertical Location of the hands above the floor
- Vertical Travel Distance of the hands between the origin and destination of the lift
- Asymmetry Angle of how far the object is displaced from the front of the body
- Frequency of the lifting task
- Duration of all lifting tasks and rest time in an 8-hour workday
- Coupling quality of gripping or grasping the object while lifting
Details from these variables are calculated to provide a Recommended Weight Limit (RWL). The RWL is the principal output of the RNLE.
Interpreting results
The RWL is the recommended weight that most workers can lift during a work shift without the risk of a WMSD. Common WMSDs that workers could develop include low back pain.
The equation provides a Lifting Index (LI), the relative estimate of the physical stress associated with a single manual lifting task. Jobs that require multiple lifting tasks can use the equation to calculate the Composite Lifting Index (CLI). The C which is a calculation of the collective demands from different lifting tasks.
NIOSH recommends using the LI or CLI to interpret results in estimating risk from lifting.
- NIOSH recommends that the LI or CLI be equal to or lower than 1.0.
- Learn more about the relationship between the LI and some WMSDs.
- Use the Elements of Ergonomics Programs to reduce risk.
- Fox B., Lu M., Occhipinti E. and Jaeger M.: Understanding outcome metrics of the revised NIOSH lifting equation. Applied Ergonomics 81 (2019) doi.org/10.1016/j.apergo.2019.102897