10.3 Cumulative exertion load in multiple-posture analysis

When the activity being analyzed consists of a sequence of postures, exertion assessment cannot be based solely on the maximum instantaneous value reached at a joint or on the maximum voluntary contraction percentage recommended for an isolated posture. For a task performed over time, the intensity and duration of joint moments, their repetition, alternation between functional muscle groups, and the partial recovery that may occur during periods of lower demand or inactivity must also be considered.

For this reason, Ergoniza Intelligent incorporates a procedure for calculating cumulative exertion load in posture sequences. Its purpose is to estimate, for each joint and biomechanical channel, the cumulative exposure resulting from the time course of relative exertion. Unlike single-posture analysis, in which the Base Maximum Moment is determined from the duration or repetitiveness conditions defined by the user, multiple-posture analysis processes the complete time course of the activity.

At each time interval, the program calculates the relative exertion intensity, transforms it into a temporal dose, and integrates it while accounting for partial recovery. Doses are kept separate by joint, biomechanical channel, and functional muscle group, so that exertions corresponding to antagonist groups are not added as though they constituted the same muscular exposure.

The result should be interpreted as a cumulative exertion load or cumulative biomechanical dose. It does not represent the instantaneous maximum voluntary contraction percentage, a direct probability of injury, or an individual physiological measurement of muscle fatigue. The following sections describe the basis of the procedure, its calculation stages, and the criteria used to interpret its results.