Musculoskeletal disorders of the upper limb. Work and individual risk factors

Objective: To relate functional capacities, work strains and upper limb musculoskeletal disorders (ulMSD) to define the content of a work analysis which allows an effective ulMSD prevention strategy.
Methods: A study was conducted in 3 factories with 90 full time female workers 39.6 y, 160 cm, 23,7 kg/m² of mean age, height and bmi respectively. Functional capacities (upper limbs and trunk strengths, cardiorespiratory fitness) and work strains (observed, perceived and measured) are assessed. Work subjective evaluation was based on Borg CR10 scale recorded at 7 body locations 5 times a shift. Electromyography (EMG) of the right and left finger flexors and goniometry (P&Giles) of the right and left wrist were recorded on 34 workers (> 10 in each factory) during 2 to 4 periods of 10 to 20 min. Health status were recorded through clinical general health questionnaires and ulMSD classification in 3 levels (never, once or light, disabling with or without sickness absence and therapeutics) and 3 anatomical locations (distal, proximal, not specific) and laterality (one side, 2 sides with predominance, equal on both sides).
Results: The study main conclusions are: I) individual functional characteristics of the workers are poorly related to ulMSD. Indeed, strength levels or fitness or perceived health are poor predictors of ulMSD. In our results, only ulMSD without clear location are more frequent in the strongest workers; II) simple methods of work analysis by observation completed by workers subjective assessment allow task strain classifications in accordance with those obtained by electromyography and goniometers. Indeed, the contact count is highly related to movement speed and frequency computed from the goniometers. In this field study it is difficult to distinguish the respective effects of movement speed and applied force on the EMG level; III) these simple tools can detect the most strained body parts and the corresponding ulMSD locations. Shoulder is the most frequent complain location but causes the less sickness absenteeism; and IV) surprisingly in between the large number of parameters investigated the most predictive of ulMSD is a question of the Taylor index relative to the possibility to take rest when needed.
Conclusions: The results of the present study confirm the low value of what is currently considered as functional capacities and that imbalance between work demands and these basic capacities is not a major determinant of ulMSD occurrence. Work observation allows a satisfactory classification of strains but is not efficient when an accurate quantification of biomechanical strains of the work activity is needed. But in association with subjective evaluations at different body parts, in our study, it allows to determine the most risky tasks and the most exposed body parts. At last, a large field of research remains open in the definition and validation of what is so called functional capacities.