13.1 Purpose, scope, and basis of the analysis

Ergoniza Intelligent Load Lifting mode assesses manual-handling tasks in which a person raises or lowers a load between an origin and a destination. It analyzes a task defined by its geometric, temporal, and operating conditions rather than an isolated posture.

The analysis is based on the Revised NIOSH Lifting Equation79F¹. Its main result is the Recommended Weight Limit (RWL), a reference weight for the conditions studied. It must not be interpreted as an individual limit guaranteeing the absence of injury. The RWL is used to calculate the Lifting Index (LI), which expresses the ratio between the actual load weight and the RWL:

LI = L / RWL

Equation 55

where L is the load weight.

NIOSH recommends an LI of 1 or less. A value above 1 indicates that the load exceeds the Recommended Weight Limit for the analyzed conditions and that the task should be reviewed. The index is a relative estimate of physical demand; it does not express an individual's probability of injury or mean that a task with LI ≤ 1 is risk-free.

The RWL is calculated using Equation 56, which starts from a Load Constant (LC) and applies several multipliers related to lifting characteristics. These factors include the horizontal distance of the load from the body, vertical height, vertical travel distance between origin and destination, lifting asymmetry, handling frequency, task duration, and coupling quality.

RWL = LC · HM · VM · DM · AM · FM · CM

Equation 56

In this expression, LC is the Load Constant; HM, the Horizontal Multiplier; VM, the Vertical Multiplier; DM, the Distance Multiplier for vertical travel; AM, the Asymmetry Multiplier; FM, the Frequency Multiplier accounting for frequency, duration, and recovery; and CM, the Coupling Multiplier. All multipliers have a maximum value of 1 and reduce the RWL as conditions depart from the reference conditions.

Ergoniza Intelligent obtains the geometric parameters and calculates results for both the origin and destination. However, the destination contributes to the task result only when significant control of the load is required at that point. When such control exists, the program compares both endpoints and adopts the less favorable condition. Otherwise, the task result is determined from the origin, although destination data and results are retained to describe and review the movement. Significant control exists when the load must be regrasped, held, stabilized, guided, or positioned precisely at the destination.

The Revised NIOSH Lifting Equation is not a general assessment of pushing, pulling, carrying, seated or kneeling lifting, very rapid movements, unstable loads, or other forms of handling outside its scope. Ergoniza Intelligent also includes extensions that are not part of the conventional formulation, such as anthropometric adjustment, one-handed handling, and a configurable Load Constant. These extensions must be considered when interpreting the results.