The Rapid Upper Limb Assessment of McAtamney and Corlett (1993) assigns scores to the posture of the upper arm, lower arm, wrist, neck, trunk and legs from angle bands, adjusts them for muscle use and for force or load, and combines them through tables into a grand score from 1 to 7 with four action levels. The Rapid Entire Body Assessment of Hignett and McAtamney (2000) follows the same logic for whole-body tasks and adds terms for coupling and activity. For static postures the standard ISO 11226 gives acceptable angle ranges with holding times (ISO, 2000), and for lifting the revised NIOSH equation computes a recommended weight limit from the geometry and frequency of the lift (Waters et al., 1993).

These methods were designed for the eye. An observer selects a posture judged to be the worst or the most frequent and classifies it. Reviews have pointed out the consequences: the result depends on which moment is chosen, angles near a band boundary are classified inconsistently, and duration and repetition are captured crudely (Li and Buckle, 1999). A systematic evaluation of observational methods by Takala et al. (2010) found that evidence on their validity and repeatability was uneven and that no single method suited all purposes.

An inertial measurement unit contains a three-axis gyroscope and accelerometer, usually with a magnetometer. A fusion algorithm combines the three signals into an estimate of the unit's orientation in space: the gyroscope follows fast movement, gravity corrects inclination, and the magnetic field corrects heading. The principles and error sources are reviewed by Sabatini (2011), and a widely used computationally light filter is that of Madgwick et al. (2011). With a unit on each body segment and a calibration that relates unit axes to anatomical axes, joint angles follow from the relative orientation of adjacent segments. Comparison with optoelectronic systems has shown close agreement for whole-body movement in the laboratory, with larger differences in some axes and in long or complex tasks (Robert-Lachaine et al., 2017).

The step from joint angles to risk scores has also been demonstrated. Vignais et al. (2013) computed RULA scores continuously from inertial sensors and goniometers and returned them to the worker in real time. The idea is therefore established. The contribution attempted here is a protocol that makes the many small decisions explicit.

The analyst defines the workstation, the task and its cycle, the product variants to be covered, and the scoring method: RULA for seated or standing work dominated by the upper limbs, REBA where the whole body moves or loads are handled. Workers are told what will be recorded, why, and who will see the results, and they take part only with written consent, which they may withdraw. Where the work forms part of research, the principles of the Declaration of Helsinki apply (World Medical Association, 2013). Movement recordings are personal data. In the European Union their processing falls under the General Data Protection Regulation (European Union, 2016), and comparable rules exist elsewhere. The protocol requires that data be stored under a code, that results be reported for the workstation and not for the individual, and that the recordings not be used to appraise performance. Worker representatives should be consulted before the first recording.

For upper-body scoring, units are placed on the pelvis, the sternum, the head, both upper arms, both forearms and both hands; for whole-body scoring, the thighs and shanks are added. Units are fixed with straps over or under work clothing so that they neither slip nor hinder the task, and protective equipment is worn as usual. Calibration follows the manufacturer's procedure, typically a neutral standing pose held for a few seconds and sometimes a set of prescribed movements. Joint angles are defined according to the recommendations of the International Society of Biomechanics for the upper limb (Wu et al., 2005). Because steel structures, motors and tools distort the local magnetic field, the analyst checks the field at the workstation before recording and, if it is disturbed, uses a fusion mode that does not rely on the magnetometer and shortens the recording blocks.

The worker performs the normal job at the normal pace. Enough consecutive cycles are recorded to cover the variants and the natural variation between cycles, after a settling period in which the worker becomes used to the sensors. A video is recorded in synchrony, with consent, to identify task elements and to supply what sensors cannot. The neutral pose is repeated at the end of each block, so that drift can be detected by comparing the first and last poses. Loads handled, forces exerted, the quality of grip, and any support of the arms or body are noted by the analyst, using a scale or force gauge where practicable.

Processing produces, for each sample, the angles that the scoring method needs: trunk flexion, side bending and twist; neck flexion, side bending and twist; upper-arm elevation and abduction; elbow flexion; forearm rotation; wrist flexion and deviation; and for REBA, knee flexion. Samples in which a unit lost its signal are marked and excluded, not interpolated across long gaps. Inclination angles, which depend on gravity, are more trustworthy than rotations about the vertical, which depend on the magnetometer or on integration of the gyroscope (Sabatini, 2011). The record states which angles are of the less reliable kind.

The angle bands and tables of the chosen method are applied to every sample, with the observed load, coupling and muscle-use terms held constant within each task element. Table 1 lists the inputs of the two methods and the source the protocol assigns to each. Three summaries are then computed for the cycle: the proportion of time spent at each action level, the highest score sustained for a stated minimum duration, and the time-weighted mean. The first is the primary result. To prevent flicker between adjacent bands from inflating the count of posture changes, a small tolerance is applied at each boundary before a change of band is registered. The muscle-use term, which in the original methods depends on whether a posture is held or repeated, is derived from the angle signals themselves by rule and reported with the rule used.

A report under the protocol contains the task description, the sensor set and placement, the calibration procedure, the fusion mode, the result of the magnetic check, the share of excluded samples per segment, the drift between first and last neutral poses, the observed inputs with their sources, and the three summaries. Results are presented beside the task elements identified from the video, so that the reader can see which part of the job produces the high scores. That link, more than the score itself, is what a redesign needs.