10.3.9 Final result and ergonomic interpretation

The result of the calculation is a cumulative exertion load for each joint, biomechanical channel, and functional muscle group. This dimensionless quantity represents the state of cumulative exposure produced by the temporal doses generated during the activity, after accounting for the continuous partial recovery described in the preceding sections.

When cumulative load is expressed as a percentage, a value of 100% corresponds to the preventive threshold defined by the model. Values above 100% indicate that this threshold has been exceeded under the analyzed conditions. The threshold does not represent an exact physiological boundary or necessarily imply that fatigue or injury has occurred; rather, it identifies a situation requiring particular attention during the ergonomic assessment.

When the Calculate Max. Recommended Exertion (%) control in the Epidemiological Priority Adjustment section of the Biomechanical Analysis Settings dialog is enabled, Ergoniza Intelligent multiplies the base cumulative load by the weighting factor for the body region. The displayed percentage and its comparison with the 100% threshold therefore incorporate the selected epidemiological priority. This adjustment is described in Section 10.1.1.1.1.

Load is kept separate for each joint, biomechanical channel, and functional muscle group. To obtain the summary value for a biomechanical channel, Ergoniza Intelligent selects the greatest cumulative load among the muscle groups associated with its directions of action. Similarly, the overall value displayed for a joint corresponds to the channel with the greatest cumulative load. Loads from antagonist muscle groups or different biomechanical channels are therefore not added together.

The result should be interpreted in disaggregated form. A high value at a joint identifies the anatomical region subject to the greatest exposure, while the biomechanical channel and functional muscle group identify more precisely the type of exertion that generated it. For example, a high cumulative load in shoulder abduction does not have the same interpretation as a high load in flexion, extension, or rotation. Likewise, a high load in the wrist extensors represents a different exposure from that generated by the flexors or the groups associated with radial and ulnar deviation.

The result should not be confused with instantaneous relative exertion. A channel may show high exertion at a particular time yet maintain a moderate cumulative load if the exposure is brief or sufficient recovery periods are available. Conversely, moderate instantaneous exertions may produce a high cumulative load when sustained for a prolonged period or repeated frequently without sufficient recovery.

Cumulative exertion load therefore distinguishes situations that cannot be adequately differentiated by analyzing a single posture or by using the maximum exertion value reached. Two activities may have the same maximum instantaneous exertion in a given channel yet produce different cumulative loads if they differ in exposure duration, number of repetitions, time distribution of exertions, or rest duration. This characteristic is particularly relevant in cyclic or intermittent tasks.

From an ergonomic perspective, the results identify the joints, biomechanical channels, and functional muscle groups that concentrate the greatest temporal exposure. This information can be used to compare design alternatives, modify load distribution, reduce the duration of particular phases, introduce rest periods, redistribute exertions between the two sides of the body, or prevent the same muscle group from being engaged repeatedly without sufficient recovery.

When several channels have high values, the complete exposure pattern should be analyzed. The load may be concentrated in a single body region or distributed among several joints and muscle groups. In the first case, preventive measures should focus primarily on reducing demand in the affected channel. In the second, a broader review of task organization, movement sequence, work height, load location, or repetition frequency may be necessary.

Figure 48 shows a specific posture within a repeated activity. The active instantaneous indicator appears at the top of the Exertion panel. Its name depends on the controls selected in the Biomechanical Analysis Settings dialog:

• % Maximum Recommended Exertion is displayed when Calculate Max. Recommended Exertion (%) is enabled.

• % Recommended Joint Capacity is displayed when the preceding control is disabled and Include Cumulative Exertion Load in Recommended Exertion (%) remains enabled.

• % Maximum Isometric Capacity Used is displayed when both controls are disabled.

The value corresponds to the represented time.

When the 3CC-r model is involved, the recommended moment used as a reference may reflect the previous exertion and recovery history of the muscle group. However, this instantaneous indicator differs from the cumulative exertion load displayed at the bottom of the panel and calculated using the temporal-dose procedure described in this section.

Cumulative exertion load is displayed at the bottom of the panel. In the example, repetition 10 has been selected and a one-minute rest has been set between repetitions. The result displayed during that repetition therefore incorporates the effect of the base cycle, the nine previous repetitions, and the partial recovery occurring during the rest periods. The same posture may consequently have different cumulative loads depending on whether it appears in the first repetition or after several work cycles.

Consequently, cumulative exertion load should be interpreted as a relative, preventive, and comparative indicator of temporal biomechanical exposure. It is not a direct measurement of individual physiological fatigue or a probability of injury. Its value lies in showing how intensity, duration, repetition, and partial recovery interact, and in helping the ergonomist identify where and how exposure can be reduced.