The effect of a passive exoskeleton on trunk co-activation during liftings at different risk levels

Abstract

The new Industry 4.0 scenarios offer opportunity for both the prevention of biomechanical overload risks and the implementation of extra return-to-work initiatives for people with disabilities. Wearable assistive devices (e.g., an industrial exoskeleton) can help to lower the risk of acquiring work-related musculoskeletal diseases (WMSDs) caused by manual material handling (MMH) tasks, among other things [1]. The most prevalent and expensive musculoskeletal diseases are WLBDs, which are primarily caused by manual lifting jobs [1]. This study aims to investigate the influence of TRUExo, a passive exoskeleton for the trunk composed of a textile and a mechanical component for energy restitution, on trunk coactivation in lifting activities at various risk levels (more details cannot currently be described because the device is under patent). Twelve healthy volunteers (age: 36.33±7.66 years; BMI: 22.34±2.21 kg/m2; 6 females and 6 males) completed the lifting tasks designed using the revised NIOSH lifting equation, [2], at progressively increasing lifting indexes (from 1 to 3). The tasks were performed with and without the TRUExo exoskeleton, and the activity of the erector spinae longissimus (RESL) and rectus abdominis superior (RAS) was recorded bilaterally using a 16-channel Wi-Fi transmission surface electromyograph (Mini Wave Infinity, Cometa, Milan, Italy) system at a sampling rate of 2000 Hz. Before beginning the lifting tasks, participants completed three repetitions of a specific exercise to record the isometric maximal voluntary contractions (iMVCs) for the muscles under investigation. Then, after sEMG processing and normalization respect to iMVC values, we computed the time-varying multi-muscle co-activation function (TMCf), [3]. Our findings reveal that the mean TMCf of all patients is lower with the passive exoskeleton than without it at each LI. The mean of the TMCf reduces significantly with LI when wearing the exoskeleton, according to two-way repeated-measures ANOVA and post-hoc analysis (Fig. 1B). The results reveal that the TMCf increases in relation to the risk levels both with and without the exoskeleton, but the TMCf is lower at each LI when the subject wears the exoskeleton ( Fig. 1 , B). These findings could lend credence to the notion that a passive exoskeleton worn during a working activity could alleviate biomechanical load and, as a result, lower the likelihood of WMSD occurrence. Furthermore, our findings highlight the TMCf's sensitivity to differentiate different risk levels even when wearing an exoskeleton, implying that it might be used as an operational tool to assess biomechanical risk in situations where traditional approaches (e.g., NIOSH's method) cannot be used.