شناسایی ارگونومیک و ارزیابی بیومکانیکی استراتژی های کارگری و اعتبارسنجی خود در یک وضعیت آموزش: خلاصه ای از پژوهش

Our goal was to evidence the role of workers in the search for safer manual handling strategies. Different strategies used by expert and novice workers, such as footwork (positioning/displacement), box manoeuvres (handgrips and load tilting) and posture were ergonomically identified. They were biomechanically evaluated to shed light on their potential for safe handling by reducing back loadings, back asymmetries and mechanical work requirements. The experts’ strategies were validated in a training situation and evaluated by two independent studies among novice workers. The first, a control study, showed that free practice did not lead to safer handling practices. The second, a training situation based on observing contrasted performances of experts and novices for footwork, box manoeuvres and back posture, when combined with practice and the search for optimal solutions, prompted the novices to adopt new ways of manoeuvring boxes and positioning themselves that appear safer for back efforts, asymmetries, and mechanical work. These elements should be included in educational programs for safe handling. Relevance The observation of contrasted strategies of expert and novice workers using an ergonomic approach, supplemented by biomechanical evaluations of these strategies, is a key factor in designing training programs for safe handling.

Training in safe handling techniques is recommended as a way to reduce risk factors in the working environment. However, training programs have not so far led to substantial reductions in musculoskeletal problems, especially back injuries, perhaps owing to inadequate training methods (St-Vincent et al., 1989) and their inadaptability to a variety of tasks, workplaces and workers (Sedgwick and Gormley, 1998). A broad consensus of opinions favours the promotion of sound mechanical principles; however, they do not appear to be easily applicable to the range and complexity of manual handling situations. Integrating theory with practice and evidence-based practice have been identified as potential influences on the effectiveness of manual handling education (Gray and White, 2004). Two potential solutions could be to design more valid biomechanical experiments for handling tasks and to develop training programs based on expert workers’ knowledge of their jobs. Biomechanical analyses have several drawbacks as to the validity of experimental tasks. In fact, to improve data reliability, researchers often control workers’ performance in a way that may alter its validity—e.g., restrictions of feet displacements on small force plates, use of handles on experimental boxes (when field studies have shown they are seldom utilized) or limiting analyses to lifting in a single plane (sagittal). Training methods may also be called into question, especially teaching techniques that focus on specific instructions such as leg lift (squat) rather than back lift (stoop), weight distribution on both legs (Nygård et al., 1998), straighter trunk postures (Nussbaum and Torres, 2001) or use of a back lordosis (Schenk et al., 1996). Even if these elements are acquired, their long-term effect in reducing back injuries may be limited. An investigation into the performances of workers themselves is one way to remedy these shortcomings, the assumption being that expert workers are best qualified to provide key elements for safer handling strategies. This study has three specific objectives: To ergonomically identify the different strategies used by expert and novice workers (Section 2); to biomechanically evaluate these strategies for their safety potential (Section 3), and to validate experts’ strategies in a training situation by determining whether novices could learn them and thus improve safety conditions (Section 4).

Ergonomic analyses enabled us to identify strategies that are typical to experts and novices, especially footwork, load manoeuvres (tilting/handgrips), and body posture. Biomechanical evaluations indicated that experts’ strategies presented a potential for safety in terms of reducing back loadings and asymmetries, and mechanical work: (1) Footwork analyses showed the importance of feet mobility (feet pivoting) to avoid trunk asymmetries and, conversely, the detrimental effects of keeping the feet in fixed positions when handling. Comparisons of experts’ and novices’ typical footwork strategies showed the experts’ strategies were advantageous for mechanical work, especially in reducing load transfer duration and trajectory. (2) Box manoeuvres (tilts/handgrips) affected mechanical work, by reducing load transfer duration and trajectory and minimizing knee flexion. (3) Body posture is an influential factor in both cases: (a) a fixed feet strategy when reaching the load out of the sagittal plane led to trunk asymmetries, unless special care was taken to reduce torsion, by keeping the shoulders parallel to the ground; (b) typical experts’ postures such as reduced knee flexion or shoulders parallel to the ground when combined with load tilting, had a positive impact on mechanical work, back loadings and asymmetries. A training situation for novices based on the observation of expert and novice workers for footwork, load manoeuvres and body posture showed that novices were able to alter their strategies to more closely resemble the experts’ and were able to improve, by reducing back loadings and mechanical work, thus validating the experts’ strategies. This comparative approach to training programs opens up a new avenue of research whose potential has been confirmed.