Assessment of Muscle Coordination Changes Caused by the Use of an Occupational Passive Lumbar Exoskeleton in Laboratory Conditions.

The introduction of exoskeletons in industry has focused on improving worker safety. Exoskeletons have the objective of decreasing the risk of injury or fatigue when performing physically demanding tasks. Exoskeletons' effect on the muscles is one of the most common focuses of their assessment. The present study aimed to analyze the muscle interactions generated during load-handling tasks in laboratory conditions with and without a passive lumbar exoskeleton. The electromyographic data of the muscles involved in the task were recorded from twelve participants performing load-handling tasks. The correlation coefficient, coherence coefficient, mutual information, and multivariate sample entropy were calculated to determine if there were significant differences in muscle interactions between the two test conditions. The results showed that muscle coordination was affected by the use of the exoskeleton. In some cases, the exoskeleton prevented changes in muscle coordination throughout the execution of the task, suggesting a more stable strategy. Additionally, according to the directed Granger causality, a trend of increasing bottom-up activation was found throughout the task when the participant was not using the exoskeleton. Among the different variables analyzed for coordination, the most sensitive to changes was the multivariate sample entropy.

Assessment of a Passive Lumbar Exoskeleton in Material Manual Handling Tasks under Laboratory Conditions.

Manual material handling tasks in industry cause work-related musculoskeletal disorders. Exoskeletons are being introduced to reduce the risk of musculoskeletal injuries. This study investigated the effect of using a passive lumbar exoskeleton in terms of moderate ergonomic risk. Eight participants were monitored by electromyogram (EMG) and motion capture (MoCap) while performing tasks with and without the lumbar exoskeleton. The results showed a significant reduction in the root mean square (VRMS) for all muscles tracked: erector spinae (8%), semitendinosus (14%), gluteus (5%), and quadriceps (10.2%). The classic fatigue parameters showed a significant reduction in the case of the semitendinosus: 1.7% zero-crossing rate, 0.9% mean frequency, and 1.12% median frequency. In addition, the logarithm of the normalized Dimitrov's index showed reductions of 11.5, 8, and 14% in erector spinae, semitendinosus, and gluteus, respectively. The calculation of range of motion in the relevant joints demonstrated significant differences, but in almost all cases, the differences were smaller than 10%. The findings of the study indicate that the passive exoskeleton reduces muscle activity and introduces some changes of strategies for motion. Thus, EMG and MoCap appear to be appropriate measurements for designing an exoskeleton assessment procedure.

Ergonomics assessment of passive upper-limb exoskeletons in an automotive assembly plant.

Over the years, the industry's interest in using external support devices, such as exoskeletons, is increasing. They are introduced as a new technique for improving the conditions of workers and for reducing the risk of musculoskeletal injuries. An investigation of muscle activity, Jonsson's (Jonsson, 1982) ergonomic acceptance ranges, and shoulder range of motion was conducted with a sample of 12 workers using an upper extremity exoskeleton in an automotive assembly line. The operators performed continuous cycles of dynamic overhead work consisting of the assembly of the car body at the underside of the car making use of pneumatic screwdrivers. The EMGs (anterior part of deltoid, trapezius, latissimus dorsi and erector spinae) were measured for the muscle activity analysis on the one hand, and for the ergonomics study on the other hand. The latter consisted of an approach based on Jonsson's work, that establishes acceptance thresholds of cumulative percentage of maximum voluntary contraction of muscle activity (%MVC) in a work cycle. The joint angles motion capture was carried out by measuring the angles of the neck, back, and arms joints. All measurements were performed during experimental sessions with and without an exoskeleton. The key findings show reductions of 34% and 18% of the deltoid and the trapezius muscular activities, respectively, which in turn could lead to a reduction of discomfort and fatigue. The erector spinae and latissimus dorsi muscles were not significantly affected by exoskeleton. The values of muscular activity were also represented over Jonsson's acceptance areas. Referring to the posture, some differences were found in the range of movement of back, neck, and arms owing to the use of the exoskeleton; however, the differences were smaller than 5% in all cases.