Abstract:
Exoskeletons are wearable, mechanical structures supporting the musculoskeletal system (e.g., in physical work) by generating torques which act on the human body. Recently, they have been introduced as a new prevention approach for work-related musculoskeletal disorders (WMSDs), receiving growing interest in various occupational areas and in research. However, their effectiveness on musculoskeletal health has not been proven, and possible negative effects impacting the musculoskeletal system have not been sufficiently investigated. Therefore, the aim of this doctoral thesis was to investigate the effects of using back-support exoskeletons (BSEs) on physical stress and strain during industrial tasks. Herein, the back, as the main target area, and other unsupported areas (e.g., the legs, shoulders, abdomen) are focused.
The thesis begins with a systematic review with several meta-analyses (Bär et al., 2021) outlining the effects of occupational exoskeletons on biomechanical, physiological, and subjectively perceived stress and strain. The meta-analyses revealed that using a BSE can potentially reduce the acute stress or strain in the back area during industrial tasks. Negative side-effects were not identified by the analyses for the BSEs, but occur occasionally. However, there is still not enough research on this aspect. Overall, research following high methodological standards and evaluating various health-relevant aspects is thoroughly lacking.
In response to the findings of Bär et al. (2021), an exploratory laboratory experiment was conducted to determine the influence of the commercially available passive BSE Laevo® V2.56 on physical stress and strain during simulated industrial tasks. Specifically, we investigated the effects of using the device on muscle activity in various body areas, spine and lower limb postures, and heart rate, focusing on a sorting task holding a static forward bent posture (including different trunk orientations; Bär et al., 2022a), and on a dynamic lifting task (including different lifting styles and trunk orientations; Luger et al., 2021b). Finally, Bär et al. (2022b) presents the exoskeleton’s effects on vertical and horizontal (anteroposterior) tibiofemoral joint forces during the static and the dynamic work tasks.
In Bär et al. (2022a) and Luger et al. (2021b) we found that using the Laevo® in simulated industrial tasks resulted in only minor, reductions of the back extensor muscle activity (the erector spinae), but moderate support for hip extension (the biceps femoris). Meanwhile, minor changes in spinal posture and muscle activity in unsupported body areas occurred, and hip and knee flexion moderately increased. Thereby, the individual task executions (lifting style, trunk orientation) influenced the effects. Heart rate slightly decreased when using the Laevo® across all task executions (Bär et al., 2022a; Luger et al., 2021b). The vertical tibiofemoral joint forces generally increased with using the Laevo® without interacting with the task executions, while the device’s effects on the horizonal (anteroposterior) tibiofemoral joint forces varied across the individual experimental conditions (Bär et al., 2022b).
This research shows that using a BSE may support either the back or hip extension and reduce acute stress or strain in target areas. However, changes of only single parameters (e.g., muscle activity) without monitoring associated musculoskeletal structures and functions (e.g., joint postures and forces) may prevent correct interpretations behind possible changes. Furthermore, negative side-effects may occur when using a BSE, which are insufficiently examined or not yet identified. The detection and further exclusion of negative side-effects is essential for the safe application of occupational exoskeletons. Various other factors may also codetermine any effects (either desired or undesired) associated with the use of occupational BSEs, e.g., individual work tasks and executions, mechanical characteristics of the device, and human individualities. Therefore, implementations of occupational exoskeletons at work should be preceded by individual assessments of the devices, with particular consideration of the various influencing factors. Overall, definitive conclusions in relation to musculoskeletal health is still beyond this dissertation and the current literature. Randomized controlled intervention studies in the field are critical for detecting long-term effects related to WMSD risk. They must include a well-thought selection and combination of various outcome parameters and body areas (e.g., relate various interacting stress and strain parameters, and include several interrelated musculoskeletal structures) and consider adherence to high methodological quality standards.
assitive device
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