Investigation of muscle synergies and their consistency among fresh fruit bunches manual harvesters in a real-life oil palm industry

Abstract

Oil palm industry still relies on manual harvesting, a physicality-reliant task that was found related to the occurrence of musculoskeletal disorders (MSDs) among the harvesters. Through experience, common muscle synergies could be found among healthy subjects, which could be useful for screening any possible musculoskeletal disorders. This study investigated and confirmed the consistency of the muscle synergies used by healthy, well-trained harvesters during a real-life fresh fruit bunches (FFB) manual harvesting task with eight enrolled subjects. The subjects' muscle synergies during the manual harvesting were investigated from seven upper limb muscles in an outdoor environment. Our results demonstrated that the harvesters consistently used three muscle synergies to perform the manual harvesting task, dedicated to different upper body parts (neck, upper arm, and lower back). The consistent number of synergies was accompanied by high intra- and inter-subject similarities (similarity index >0.7) found in the contribution of muscle in the synergies (weighting coefficient). On the other hand, the alteration in activation timing (SI < 0.6) in the harvesting movement was presumed to be related to the adaptation to environmental constraints, which were also observed in other relevant studies. The result, therefore, confirmed consistent muscle synergies among the oil palm harvesters even in an uncontrolled outdoor environment, providing a reference that brings benefits to the knowledge in the screening of musculoskeletal disorders among the harvesters. Relevance to industryThe paper presents an investigation of muscle synergies and their consistency among healthy, well-trained manual fresh fruit bunches (FFB) oil palm harvesters in an outdoor environment. The result, together with the presented methodologies, provide a reference that can be used in screening musculoskeletal disorders among harvesters in the industry.