13.2 Defining lifting tasks, general parameters, and anthropometric adjustment

In Load Lifting mode, the analysis is organized around one or more lifting tasks. An analysis can contain from one to forty tasks. Each task represents an operation performed under a specific set of conditions. If the same activity includes lifts with different weights, frequencies, positions, couplings, or handling methods, they must be entered as separate tasks.

The main panel shows the tasks created and the results for each one (Figure 66). From this panel, users can select the active task, view its results, and access its configuration options.

The general lifting settings are shared by all tasks in the analysis. They include temporal organization, the load constant, and anthropometric adjustment. Changing any of these parameters recalculates every task and every temporal block.

NIOSH tasks must be distinguished from temporal periods. A task describes a specific lifting condition. A period indicates how long the task profile is performed before recovery. The number of periods does not change the number of tasks, and the number of tasks does not determine the number of periods.

Ergoniza Intelligent uses a shared profile: all periods contain the same tasks at the same frequencies. Durations and recovery times can vary between periods, but a different set of tasks or frequencies cannot be assigned to each period.

Temporal organization can be entered in three ways (Figure 67):

• One lifting period: represents a continuous activity with a single duration and does not require a subsequent recovery time.

• Regular pattern of periods: represents several periods of equal duration separated by equal recovery times. Users enter the duration of each period, the number of periods, and the recovery time between periods.

• Custom sequence of periods: allows periods with different durations and recovery times to be defined and arranged. The recovery time entered after a period occurs before the next period; the last period does not require a subsequent recovery time.

Ergoniza Intelligent uses recovery times to determine whether periods are evaluated independently or must be combined into the same evaluation block. At each boundary between periods, the available recovery time, RT, is compared with the lifting time accumulated in the block, WT. If the recovery meets the applicable requirement, the block ends and the next period starts a new block. Otherwise, the recovery is considered insufficient to separate the periods, and their lifting times are accumulated.

When insufficient recovery requires periods to be combined, the duration category is determined from the lifting time accumulated in the resulting block. Once the long-duration category has been reached, the Revised NIOSH Lifting Equation assumes ordinary industrial rest allowances and does not establish an RT/WT ratio that would allow subsequent periods in the same block to be separated again.

For short-duration blocks, with up to 60 minutes of accumulated lifting time, recovery must be at least equal to the lifting time; that is, RT/WT ≥ 1.0. For moderate-duration blocks, with more than 60 and up to 120 minutes of lifting, RT/WT must be ≥ 0.3. Blocks lasting more than 120 and up to 480 minutes are classified as long duration and are evaluated assuming ordinary industrial rest allowances. NIOSH does not provide weight limits for more than eight hours of lifting.

The temporal summary shows total lifting time, total recovery time, total elapsed time, and the resulting evaluation blocks. Total elapsed time is the sum of lifting time and recovery times in the sequence.

All evaluable blocks are calculated and compared. The LI is compared in a single-task analysis, and the CLI is compared in a multitask analysis. The block with the most unfavorable index is identified as the governing block. If several blocks reach the same maximum value, all of them share this status. Indices from different blocks are neither added nor averaged.

Ergoniza Intelligent considers the temporal organization non-evaluable when a block accumulates more than eight hours of lifting or when the total elapsed time of the sequence, including recovery times, exceeds eight hours. In that case, no valid overall NIOSH result is presented and no governing block can be identified.

Figure 66: Main Load Lifting mode panel.

The load constant, LC, is the initial value to which the six multipliers are applied. The conventional NIOSH formulation uses 23 kg. Ergoniza Intelligent allows values from 20 to 30 kg to be selected, but any value other than 23 kg modifies the standard method and should only be used when there is an explicit methodological justification.

When several tasks are present, the program calculates the RWL and LI for each one and also obtains a Composite Lifting Index (CLI) for the task profile in each required duration category. This index is neither the mean nor the maximum of the individual indices: it incorporates the effect of the cumulative frequencies of the different tasks using the procedure described in Section 13.5. The overall result corresponds to the block with the most unfavorable composite index.

The Revised NIOSH Lifting Equation uses standard geometric references: an optimal vertical height of 75 cm, a maximum height of 175 cm, and horizontal limits of 25 and 63 cm. These references do not vary with the dimensions of the person being assessed. When anthropometric adjustment is enabled, Ergoniza Intelligent replaces these references with values derived from the model's dimensions.

Specifically, the system adapts the vertical lifting reference, the maximum height considered, and the horizontal limits used in the calculation based on the worker's anthropometry. This change can affect several equation multipliers, particularly those related to the load's horizontal distance, vertical height, vertical travel distance, frequency, and coupling quality.

This option introduces an adaptation of the conventional application of the NIOSH equation80F¹. Therefore, when anthropometric adjustment is enabled, the results should not be interpreted as a strictly standard application of the method, but as an estimate adjusted to the body dimensions of the person being analyzed. This option may be useful when assessing how a worker's anthropometric characteristics may influence actual lifting conditions.