13.5 Analysis results: Recommended Weight Limit, Lifting Index, and Composite Lifting Index

Once the task parameters have been defined, Ergoniza Intelligent calculates the main lifting-analysis results. These results are displayed in the Load Lifting panel, as shown in Figure 65.

A key result is the Recommended Weight Limit (RWL). This value is a reference limit for the specific task conditions and duration category being evaluated. It should not be interpreted as an individual maximum weight or a guarantee that injury will not occur. To obtain it, the system starts with the load constant and applies the multipliers defined by the Revised NIOSH Lifting Equation (Equation 56).

The RWL is used to calculate the Lifting Index (LI), defined as the ratio of the actual load weight to the Recommended Weight Limit (Equation 55). A value of LI ≤ 1 indicates that the actual weight does not exceed the calculated RWL. If LI > 1, the load exceeds the recommendation for the conditions considered and the task should be reviewed. The index should be interpreted as a relative indicator of physical demand, not as a prediction of injury for an individual.

The index must be interpreted by considering all task conditions. A high LI may be due to the load weight, but it may also result from excessive horizontal distance, an unfavorable origin or destination height, high frequency, prolonged duration, marked asymmetry, or poor coupling quality. The multipliers should therefore also be reviewed to identify which conditions are penalizing the lift.

When the analysis contains several tasks, the system also calculates the Composite Lifting Index (CLI) defined by the NIOSH methodology. To obtain it, tasks are ordered from highest to lowest individual index. The most demanding task contributes its full LI, and the remaining tasks contribute the incremental demand produced as their frequencies are progressively added to the cumulative frequency.

The complete task profile is evaluated for every duration category present in the temporal blocks. The same task can therefore have different FM, RWL, and LI values when evaluated as part of a short-, moderate-, or long-duration block. The CLI can also change in a multitask analysis.

All evaluation blocks are compared. In a single-task analysis, the governing block is the one with the most unfavorable LI. In a multitask analysis, it is the one with the most unfavorable CLI. If several blocks reach the same maximum value, all of them are governing blocks. The overall assessment result is the index of the governing block. Results from the other blocks provide context about the activity's temporal progression, but they are neither added to nor averaged with the governing result.

When a block accumulates more than eight hours of lifting or the total elapsed time of the sequence exceeds eight hours, the temporal organization is considered non-evaluable. In that case, Ergoniza Intelligent does not present a valid overall LI or CLI and does not identify a governing block.

Ergoniza Intelligent allows these results to be used not only to assess the existing task but also to explore redesign alternatives. By changing the load position, reducing horizontal distance, improving coupling, decreasing frequency, limiting duration, or adjusting the weight handled, the evaluator can see how the RWL and Lifting Index change.