Background and objectives: Functional electrical stimulation (FES) has shown good results in improving static and dynamic sitting balance in persons with spinal cord injuries. There is limited information about how regular surface FES combined with therapeutic exercise (TE) affect dynamic sitting balance and muscle tone. The objective of this study was to evaluate the effectiveness of a six-week physical therapy program consisting of FES and TE on muscle tone and sitting balance in persons with spinal cord injury (SCI). It was also important to explore the relationship between muscle tone and dynamic sitting balance. The third objective was to assess the change of characteristics over a six month period, when no intervention was carried out. Material and methods: Five men with SCI were alternately allocated to two study groups: SCI_FES+TE and SCI_TE. Eight healthy control group participants were recruited to collect reference data. SCI participants’ intervention lasted for six weeks in their homes. SCI_FES+TE conducted exercises with FES applied on erector spinae (ES) and rectus abdominis (RA) muscles. SCI_TE conducted exercises only. Muscle oscillation frequency (MOF; characterizing muscle tone) and limits of stability (LOS; characterizing sitting balance) were measured. A crossover study design was used. The time between the initial intervention and the crossover was seven months (ClinicalTrials registration ID NCT03517787). Results: MOF in SCI_FES+TE increased by 6.0% for ES and 6.1% for RA muscles. LOS of flexion increased 30.1% in SCI_FES+TE. Increase in lateral directions was similar for both study groups. Moderate to high negative correlation was found between MOF and LOS. After seven months, MOF of ES decreased 0.8%, MOF or RA decreased 1.4%, LOS of flexion decreased 31.9%, and LOS of lateral flexion to the left decreased 46.4%. Conclusions: The six-week therapy program combining FES and TE increased trunk muscle tone and dynamic sitting balance in flexion more than TE alone. Higher antagonist muscle tone negatively affects dynamic sitting balance and center of pressure (COP) trajectory distance in various directions. After seven months, a slight decline in trunk muscles tone values and an extensive decrease in sitting balance values were noticed.

The purpose of this study was to analyse subjective self-evaluation of musculoskeletal discomfort conducted by female production assembly workers. Thirty-seven female assembly workers aged 20-54 years participated in this study, whereas 35 of them were right-handed. Discomfort in neck, shoulder, upper back, upper arm, low back, forearm, wrist, hips, thigh, knees, lower legs and heels was subjectively evaluated by Cornell Musculoskeletal Discomfort Questionnaire. The results indicated that female assembly workers felt most work-related discomfort in the neck (44%), lower back (19.7%) and in the right wrist (15%). Discomfort was less pronounced in the right knee (0.01%), left upper arm (0.04%) and left hip buttocks (0.1%). In conclusion, this study indicated that subjective discomfort sensed by female production assembly workers was higher in the neck, lower back, right shoulder and the right wrist. According to the study results, further research is needed on the relationship between musculoskeletal discomfort and its influence on the quality of assembly work.

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Objective: The aim of this study was to evaluate the ergonomic benefits of an angle grinder with a rotatable main handle in a cutting task. Background: Angle grinder manufacturers rarely address ergonomic features in their advertisements, and if they do, the benefits are expressed in a qualitative manner. Meanwhile, quantitative information about the effects of the device on the worker is required to make informed decisions during tool selection and cumulative trauma prevention. Method: Eleven maintenance workers and metalworkers used an angle grinder to cut a horizontal steel rod using three wrist postures. Only one of the postures was exclusively available in the case of a rotatable main handle. The postural effect was evaluated objectively with electromyography and a force-sensing-resistor-based force glove. Subjective ratings about discomfort and control were obtained with a visual analog scale. Results: The subjective ratings favor the near-neutral wrist posture. The forearm muscles’ electromyographic activities were similar across the postures. Forces on the hand–handle interface were concentrated on the intermediate phalanges. If the device is operated without gloves, the forces on the intermediate phalanges may exceed the discomfort pressure threshold regardless of wrist posture. Conclusion: In the cutting task, the subjective measures favor the posture with a near-neutral wrist, which is a feature of the rotatable main handle. The objective measures did not allow one to prefer one posture to another. Application: The findings give insight into the impact of wrist posture on muscle activity, forces on the hand–handle interface, and discomfort. This is useful information for the person responsible for tool selection.

For decades, surface electromyography (sEMG) has been one of the essential methods of Human Factors and Ergonomics. Although capturing sEMG data is relatively easy, proper interpretation of acquired data is possible only with sufficient background in electrophysiology, muscle mechanics and muscle functions. As the last decade has made biosignal acquisition more accessible, the current overview discusses the intrinsic properties of contemporary low-cost sEMG acquisition systems and proposes applications of sEMG for Human Factors and Ergonomics.