10.7.1 Limitations in single-posture analysis

Calculating joint moments and reaction forces estimates the biomechanical demand required to maintain a posture and balance the applied loads. However, a low joint moment does not necessarily mean that the posture is acceptable or that the joint is free from mechanical loading.

Figure 50 shows an example of this difference. In posture A, load P and the weight of the body segments have appreciable moment arms relative to the wrist, elbow, and shoulder. The corresponding muscle groups must generate internal moments to maintain equilibrium, so the analysis clearly identifies the resulting biomechanical demand.

In posture B, the line of action of the external load is approximately aligned with the arm segments. Its moment arm relative to the joints is consequently small, and the joint moments produced by that load may be low. However, the load may still transmit compressive or tensile forces through the joints, and the posture may require muscular stabilization. In addition, the weight of the body segments themselves may continue to generate moments if their centers of mass are not aligned with the joints.

Keeping the arm raised above the head may also be unfavorable because of deviation from a comfortable functional posture, reduced range-of-motion margin, compression or tension in certain tissues, and the demand created by maintaining the posture for a prolonged period. These effects may be relevant even when the calculated joint moments are low.

Similarly, a joint may be close to its functional limits even when the required moment is low. In these situations, risk does not necessarily result from a high contraction of the primary muscle groups, but from the postural configuration, loading of passive structures, or reduction in the available range-of-motion margin.

The indicators used by Ergoniza Intelligent also have specific limitations. % Recommended Joint Capacity compares the required moment with the Base Maximum Moment, customized according to the worker's characteristics and the temporal conditions declared for the action, but does not account for every musculoskeletal risk mechanism. % Maximum Recommended Exertion incorporates weighting based on the prevalence of musculoskeletal disorders by body region, but should be interpreted as a preventive-priority index rather than an individual estimate of susceptibility or injury probability. % Unprotected Population is based on population capacity distributions and does not replace assessment of the specific worker's characteristics.

For these reasons, posture assessment should not be based exclusively on joint-exertion limits. Ergoniza Intelligent supplements force and moment analysis with postural-risk assessment and other evaluation procedures. This combination can detect unfavorable situations even when the posture geometry produces low joint moments.