Smart Sensing Chairs for Sitting Posture Detection, Classification, and Monitoring: A Comprehensive Review.

Incorrect sitting posture, characterized by asymmetrical or uneven positioning of the body, often leads to spinal misalignment and muscle tone imbalance. The prolonged maintenance of such postures can adversely impact well-being and contribute to the development of spinal deformities and musculoskeletal disorders. In response, smart sensing chairs equipped with cutting-edge sensor technologies have been introduced as a viable solution for the real-time detection, classification, and monitoring of sitting postures, aiming to mitigate the risk of musculoskeletal disorders and promote overall health. This comprehensive literature review evaluates the current body of research on smart sensing chairs, with a specific focus on the strategies used for posture detection and classification and the effectiveness of different sensor technologies. A meticulous search across MDPI, IEEE, Google Scholar, Scopus, and PubMed databases yielded 39 pertinent studies that utilized non-invasive methods for posture monitoring. The analysis revealed that Force Sensing Resistors (FSRs) are the predominant sensors utilized for posture detection, whereas Convolutional Neural Networks (CNNs) and Artificial Neural Networks (ANNs) are the leading machine learning models for posture classification. However, it was observed that CNNs and ANNs do not outperform traditional statistical models in terms of classification accuracy due to the constrained size and lack of diversity within training datasets. These datasets often fail to comprehensively represent the array of human body shapes and musculoskeletal configurations. Moreover, this review identifies a significant gap in the evaluation of user feedback mechanisms, essential for alerting users to their sitting posture and facilitating corrective adjustments.

Biomechanical repercussion of sitting posture on lumbar intervertebral discs: A systematic review.

BACKGROUND: The static sitting position contributes to increased pressure on the lumbar intervertebral disc, which can lead to dehydration and decreased disc height. OBJECTIVE: To systematically investigate the of sitting posture on degeneration of the lumbar intervertebral disc. MATERIALS AND METHODS: One researcher carried out a systematic literature search of articles with no language or time limits. Studies from 2006 to 2018 were found. The searches in all databases were carried out on January 28, 2022, using the following databases: Pubmed, Scopus, Embase, Cochrane, and Physiotherapy Evidence Database (PEDro) databases, and for the grey literature: Google scholar, CAPES Thesis and Dissertation Bank, and Open Grey. The acronym PECOS was used to formulate the question focus of this study: P (population) - male and female subjects; E (exposure) - sitting posture; C (comparison) - other posture or sitting posture in different periods; O (outcomes) - height and degeneration of the lumbar intervertebral disc(s), imaging exam; and S (study) - cross-sectional and case control. RESULTS: The risk of bias was in its moderate totality in its outcome: height and degeneration of the lumbar intervertebral disc(s) - imaging. Of the four selected studies, three found a decrease in the height of the disc(s) in sitting posture. CONCLUSION: The individual data from the manuscripts suggest that the sitting posture causes a reduction in the height of the lumbar intervertebral disc. It was also concluded that there is a need for new primary studies with a more in-depth design and sample size.

Improving wheelchair user sitting posture to alleviate lumbar fatigue: a study utilizing sEMG and pressure sensors.

Background: The wheelchair is a widely used rehabilitation device, which is indispensable for people with limited mobility. In the process of using a wheelchair, they often face the situation of sitting for a long time, which is easy to cause fatigue of the waist muscles of the user. Therefore, this paper hopes to provide more scientific guidance and suggestions for the daily use of wheelchairs by studying the relationship between the development of muscle fatigue and sitting posture. Methods: First, we collected surface Electromyography (sEMG) of human vertical spine muscle and analyzed it in the frequency domain. The obtained Mean Power Frequency (MPF) was used as the dependent variable. Then, the pose information of the human body, including the percentage of pressure points, span, and center of mass as independent variables, was collected by the array of thin film pressure sensors, and analyzed by a multivariate nonlinear regression model. Results: When the centroid row coordinate of the cushion pressure point is about 16(range, 7.7-16.9), the cushion pressure area percentage is about 80%(range, 70.8%-89.7%), and the cushion pressure span range is about 27(range, 25-31), the backrest pressure point centroid row coordinate is about 15(range, 9.1-18.2), the backrest pressure area percentage is about 35%(range, 11.8%-38.7%), and the backrest pressure span range is about 16(range, 9-22). At this time, the MPF value of the subjects decreased by a small percentage, and the fatigue development of the muscles was slower. In addition, the pressure area percentage at the seat cushion is a more sensitive independent variable, too large or too small pressure area percentage will easily cause lumbar muscle fatigue. Conclusion: The results show that people should sit in the middle and back of the seat cushion when riding the wheelchair, so that the Angle of the hip joint can be in a natural state, and the thigh should fully contact the seat cushion to avoid the weight of the body concentrated on the buttocks; The back should be fully in contact with the back of the wheelchair to reduce the burden on the waist, and the spine posture can be adjusted appropriately according to personal habits, but it is necessary to avoid maintaining a chest sitting position for a long time, which will cause the lumbar spine to be in an unnatural physiological Angle and easily lead to fatigue of the waist muscles.

Comparison of energy expenditure of individuals with Duchenne muscular dystrophy in the sitting posture on the ground and in water.

Duchenne Muscular Dystrophy (DMD) is one of the most frequent childhood dystrophies, affecting cardiopulmonary functions and walking ability. One of the main symptoms is fatigue, which is caused by altered muscle metabolism related to energy expenditure (EE). Aquatic physiotherapy is a therapeutic modality that facilitates the maintenance of this posture because of immersion on the body. This cross-sectional observational study aimed to compare the EE on the ground and water of individuals with DMD through oxygen consumption in the maintenance of sitting posture. The individuals were in a sitting position on the ground and in the water for 20 min for the assessments. The variables peripheral oxygen saturation, heart rate, maximum expiratory pressure, maximum inspiratory pressure, forced vital capacity, respiratory quotient (RQ), and oxygen consumption per kilogram of body weight (VO2 /kg) were compared, adopting a significance of 5 %. No difference was found between medians and quartiles of RQ when comparing the two environments. The same was observed for VO2 /Kg values on the ground and in water. The data from this study demonstrate that the EE of individuals with DMD did not change when maintaining a sitting posture on the ground and in water.

Intelligent systems for sitting posture monitoring and anomaly detection: an overview.

The number of people who need to use wheelchair for proper mobility is increasing. The integration of technology into these devices enables the simultaneous and objective assessment of posture, while also facilitating the concurrent monitoring of the functional status of wheelchair users. In this way, both the health personnel and the user can be provided with relevant information for the recovery process. This information can be used to carry out an early adaptation of the rehabilitation of patients, thus allowing to prevent further musculoskeletal problems, as well as risk situations such as ulcers or falls. Thus, a higher quality of life is promoted in affected individuals. As a result, this paper presents an orderly and organized analysis of the existing postural diagnosis systems for detecting sitting anomalies in the literature. This analysis can be divided into two parts that compose such postural diagnosis: on the one hand, the monitoring devices necessary for the collection of postural data and, on the other hand, the techniques used for anomaly detection. These anomaly detection techniques will be explained under two different approaches: the traditional generalized approach followed to date by most works, where anomalies are treated as incorrect postures, and a new individualized approach treating anomalies as changes with respect to the normal sitting pattern. In this way, the advantages, limitations and opportunities of the different techniques are analyzed. The main contribution of this overview paper is to synthesize and organize information, identify trends, and provide a comprehensive understanding of sitting posture diagnosis systems, offering researchers an accessible resource for navigating the current state of knowledge of this particular field.

Influence of Spinal Sagittal Alignment in Sitting Posture on the Swallowing Speed of Older Adult Women: A Cross-Sectional Study.

Thoracolumbar kyphosis in sitting posture is associated with forward head posture and may adversely affect swallowing function. However, few studies have investigated the effect of spinal alignment in the sitting posture on the swallowing function of older adults. This cross-sectional study aimed to investigate whether spinal alignment in the sitting posture influences the swallowing function of older adult women. Overall, 18 older adult women (mean age, 69.78 ± 3.66 years) without dysphagia were enrolled. Participants were positioned in two sitting postures, namely, comfortable sitting (CS) and thoracic upright sitting (TUS). In each sitting posture, the kyphosis index (using a flexicurve), sagittal angles (head, cervical, shoulder, and pelvic angles; using a digital camera), and cervical range of motion (ROM) were evaluated. Swallowing speed (100-mL water swallowing test), maximum tongue pressure (MTP), and oral diadochokinesis (ODK) were also evaluated. Compared with TUS, CS showed a greater kyphosis index, anterior head translation, and posterior pelvic tilt. CS had greater flexion (p < 0.001) and less extension (p < 0.001) of cervical ROM than TUS. Swallowing speed was significantly decreased in CS compared with TUS (p = 0.008). MTP and ODK were not significantly different between CS and TUS. Thus, changes in sitting posture with spinal alignment may affect swallowing speed. Consequently, adjustments to reduce sitting postural kyphosis in older adult women may improve swallowing speed.

Spinal Cord Epidural Stimulation Improves Lower Spine Sitting Posture Following Severe Cervical Spinal Cord Injury.

Cervical spinal cord injury (SCI) leads to impaired trunk motor control, negatively impacting the performance of activities of daily living in the affected individuals. Improved trunk control with better sitting posture has been previously observed due to neuromuscular electrical stimulation and transcutaneous spinal stimulation, while improved postural stability has been observed with spinal cord epidural stimulation (scES). Hence, we studied how trunk-specific scES impacts sitting independence and posture. Fourteen individuals with chronic, severe cervical SCI with an implanted neurostimulator performed a 5-min tall-sit task without and with trunk-specific scES. Spine posture was assessed by placing markers on five spine levels and evaluating vertical spine inclination angles. Duration of trunk manual assistance was used to assess independence along with the number of independence changes and average independence score across those changes. With scES, the sacrum-L1 inclination and number of independence changes tended to decrease by 1.64 ± 3.16° (p = 0.07; Cohen's d = 0.53) and 9.86 ± 16.8 (p = 0.047; Cohen's d = 0.59), respectively. Additionally, for the participants who had poor sitting independence without scES, level of independence tended to increase by 12.91% [0%, 31.52%] (p = 0.38; Cohen's d = 0.96) when scES was present. Hence, trunk-specific scES promoted improvements in lower spine posture and lower levels of trunk assistance.

Effect of sitting posture with and without sole-ground contact on chewing stability and masticatory performance.

PURPOSE: To verify the effect of sitting posture with and without sole-ground contact on chewing stability and masticatory performance. METHODS: Thirty healthy subjects were evaluated. The Conformat was used to analyze the center of sitting pressure (COSP), and the three-dimensional motion analysis system was used to analyze changes in head and trunk postures while subjects remained in a sitting position with and without sole-ground contact. The parameters of masticatory performance and movement were calculated as follows. For evaluating masticatory performance, the amount of glucose extraction (AGE) during chewing of a gummy jelly was measured. For evaluating masticatory movements, the movement of the mandibular incisal point was recorded using the Motion Visi-Trainer V1, and parameters of the stabilities of movement path and rhythm were calculated. RESULTS: Head and trunk sway values and the displacement of COSP were significantly smaller with sole-ground contact than those without sole-ground contact. The masticatory movement path with sole-ground contact showed less variation in the opening distance and more stable movement path compared to those without sole-ground contact. The AGE was significantly greater with sole-ground contact than that without sole-ground contact. CONCLUSION: Sitting posture with and without sole-ground contact affects chewing stability and masticatory performance.

An Automated Sitting Posture Recognition System Utilizing Pressure Sensors.

Prolonged sitting with poor posture can lead to various health problems, including upper back pain, lower back pain, and cervical pain. Maintaining proper sitting posture is crucial for individuals while working or studying. Existing pressure sensor-based systems have been proposed to recognize sitting postures, but their accuracy ranges from 80% to 90%, leaving room for improvement. In this study, we developed a sitting posture recognition system called SPRS. We identified key areas on the chair surface that capture essential characteristics of sitting postures and employed diverse machine learning technologies to recognize ten common sitting postures. To evaluate the accuracy and usability of SPRS, we conducted a ten-minute sitting session with arbitrary postures involving 20 volunteers. The experimental results demonstrated that SPRS achieved an impressive accuracy rate of up to 99.1% in recognizing sitting postures. Additionally, we performed a usability survey using two standard questionnaires, the System Usability Scale (SUS) and the Questionnaire for User Interface Satisfaction (QUIS). The analysis of survey results indicated that SPRS is user-friendly, easy to use, and responsive.

Ergonomics in online education of medical undergraduates: A challenge to post-COVID transformation in educational activities.

BACKGROUND: Practicing incorrect postures in online and virtual education during the COVID-19 pandemic can cause significant study-related musculoskeletal problems among students. OBJECTIVE: This study evaluated the knowledge, attitude, and practice of sitting posture and computer ergonomics and study-related musculoskeletal problems in undergraduates who followed online education during the pandemic. METHODS: A cross-sectional online survey among a cohort of Sri Lankan medical undergraduates was conducted using a structured questionnaire with 56 multiple-choice or Yes/No type questions. RESULTS: Of the 410 participants, over 85% (n = 362) knew the correct posture to sit on the chair type that they frequently used for studies. However, the majority (n = 378,92.20%) practised incorrect sitting postures in which leaning forward (n = 319,77.80%) was the most common suboptimal posture. Knowledge (n = 161,40%) and practice (n = 167,40.73%) on taking frequent breaks were poor among the majority. Their knowledge on computer ergonomics was good (>80%, n = 304) except for the recommended eye-to-screen distance (n = 129,31.46%). Importantly, ∼50% (n = 206) did not practise the recommended eye-to-screen distance. Use of non-adjustable chairs with no armrests (n = 346,84.39%) and smartphones (n = 354,86.34%) were identified as the main factors which hindered correct practices. Study-related pain/discomfort reported by the majority (n = 241,58.78%) is potentially due to suboptimal ergonomics. Their attitude toward learning and practicing correct ergonomics in home workstations was good (n = 383,93.41%). CONCLUSION: Poor practice of posture and computer ergonomics, despite the good knowledge and attitude is possibly due to the suboptimal work environments. Introducing simple practical measures to facilitate ergonomically appropriate work environments is mandatory in virtual education to prevent study-related musculoskeletal problems.

Highly Sensitive Fabric Sensors Based on Scale-like Wool Fiber for Multifunctional Health Monitoring.

Highly sensitive, multifunctional, and comfortable fabric sensors with splendid electrical properties for precise detection of human physiological health parameters have attractive prospects in next-generation wearable flexible devices. However, it remains a non-ignorable challenge to construct a multifunctional fabric sensor to meet the requirements of compact structure, high sensitivity, fast response, excellent stability, and air permeability. Here, a wool felt@MXene fabric sensor (WF@MFS) prepared by felting large quantities of wool coated with MXene is reported for measuring multiple physiological parameters in a noninvasive manner. With the high conductivity and outstanding mechanical properties of MXene and the special scale-like surface structure of the wool fiber, the sensor exhibits remarkable sensing performance such as high pressure sensitivity (80.79 kPa-1), fast response (40 ms), low detection limit (12 Pa), and strong stability (>12,500 cycles). Furthermore, to avoid direct contact between MXene and the human body, the WF@MFS is encapsulated in pure wool without MXene, thereby enabling the fabricated sensor to be tightly integrated into a variety of clothing for monitoring different physiological signals and information about human activities. More importantly, we develop an intelligent cushion with a square and panda pattern and an intelligent neckerchief in the form of arrays based on the WF@MFS, which can intuitively observe the real-time force distribution of the thigh and cervical spine by means of machine learning when a human body sits in different postures. The sensor proposed in this work demonstrates the great ability to prevent cardiovascular disease and the related diseases caused by improper sitting postures in advance, paving a promising path for future wearable smart fabric electronics.

Effects of physical activity breaks during prolonged sitting on vascular and executive function-A randomised cross-over trial.

Objectives: High sedentary behaviour is associated with adverse effects on central vascular function and cognitive function. Although interventions to mitigate the adverse effects of workplace sitting are intriguing, evidence of the efficacy of such interventions remains lacking. This randomised cross-over trial was aimed at exploring the effectiveness of prolonged sitting, with or without physical activity breaks, on central, peripheral vascular and cognitive function in adults. Methods: Twenty one healthy adults completed 4 h of simulated work conditions in three experimental visits: (1) uninterrupted sitting (SIT); (2) sitting interrupted by 3 min of walking every hour (LIT); and (3) sitting interrupted by 3 min of stair climbing every hour (MIT). Carotid (CA) and superficial femoral artery (SFA) diameter, velocity, shear rate and blood flow were measured with Duplex ultrasound at 50 MHz at three time points (hours 0, 2 and 4), and executive function was assessed with the computer based Eriksen Flanker task every hour. Results: The decreases in reaction time (-30.59%) and accuracy (-10.56%) during SIT conditions were statistically significant, and less of a decrease was observed under LIT and MIT conditions. No significant differences in CA and SFA function were observed with LIT and MIT interventions. Conclusion: Physical activity breaks of varying intensity during prolonged sitting improve reaction time. However, the vascular benefits of physical activity breaks should be confirmed in the future through long term studies in natural environment.

A multidimensional sensory evaluation model to investigate the (dis)comfort of body parts in a supine sitting position during a lunch break.

Employees who work long hours frequently complain of muscle fatigue caused by prolonged sitting. As a result, products that assist them when resting in a chair in a reclining position, in order to relieve fatigue and improve comfort are required. To ensure that the new product works as intended, a usability test based on prototyping must be developed. The research process was divided into three stages: firstly, the development of the perception assessment questionnaire; secondly, a validated factor analysis (CFA) was conducted on the perception assessment data of 26 subjects and the measurement model was fitted to verify the reliability and validity of the questionnaire; finally, the sEMG technique was used to verify the comfort level of 21 subjects. Based on usability experiments and an exploration of human factor relationships, this study develops a prototype testing model, which focuses on the comfort perception of body parts, as a means of promoting innovation in the design and manufacturing industry.

Adaptation and clinical application of assistive device chair for bedside sitting in acute stroke phase: two case reports.

PURPOSE: This report presents the adaptation of an assistive device chair for bedside sitting and its application in two patients with trunk control impairment in the acute stroke phase. MATERIALS AND METHODS: The device was built with polyvinylchloride (PVC) pipes and designed by a team of mechanical engineers and physiotherapists to maintain a prolonged sitting position with less demand from therapists. To test the device, two patients were followed up during the acute phase of stroke. Both patients underwent an early mobilization program (30 min, twice a day, for three days) with an assistive device chair for bedside sitting. Patients were evaluated using the National Institutes of Health Stroke Scale (NIHSS), Trunk Impairment Scale (TIS), and International Classification of Functioning, Disability, and Health (ICF) checklist (b: body function; d: activity and participation). RESULTS: The adaptations generated the following equipment: 1) foldable, 2) three levels of backrest inclination, and 3) a safety anterior support or an activity table. Both patients showed clinical improvement after the intervention period, with NIHSS score reduction, TIS improvement, and greater functionality and independence on the ICF framework. CONCLUSION: The equipment with adaptations seems to be functional, easy to handle, and can potentially contribute to clinical and functional improvements in patients with trunk control deficits after stroke.

The assistive device chair has a low manufacturing cost, and allow an easy handling and storageThe assistive device chair has been adapted to facilitate sitting posture;The assistive device chair can be used as an auxiliary tool in early mobilizations protocols and contemporary rehabilitation approaches;The early mobilization protocol associated with the assistive device chair can generate clinical improvements in acute stroke.The mobilization protocol associated with the assistive device chair can promote improvement in International Classification of Functioning, Disability, and Health domains in acute stroke.

Development of Infant Sitting Postural Control in Three Groups of Infants at Various Risk Levels for Autism Spectrum Disorder.

The purpose of this study was to examine the development of sitting postural control among two groups of infants at elevated risk for autism spectrum disorders (ASD) and a group of infants at typical risk for ASD and its association with cognitive, language and communication skills at a later age. We visited infants in their home environment from the onset of sitting until sitting independence and at 12 and 18 months of age. We collected data on sitting posture (center of pressure), through a portable force platform, as well as communication, cognitive and social behavior assessments at various time points. Our results showed that postural control differences at the onset of sitting, were present among the groups of infants but there were no statistically significant differences among the groups in the development of sitting posture. In addition, there were statistically significant communication differences among the groups and mostly the change in sample entropy in the anterior/posterior direction (posture measure) was significantly correlated with other skills at a later age. This study highlights the importance of investigating multiple at-risk groups to identify unique developmental pathways that may lead to an ASD diagnosis.

Effect of Spinal Sagittal Alignment in Sitting Posture on Swallowing Function in Healthy Adult Women: A Cross-Sectional Study.

Swallowing function is both directly and indirectly related to postures, such as head and cervical angle and body position. However, the effects of different sitting postures on oropharyngeal swallowing have not been investigated. This study aimed to investigate whether the change in thoracolumbar alignment affected the oropharyngeal swallowing. A total of 58 healthy adult women (mean age 22.2 ± 1.67 years) without dysphagia were enrolled in this cross-sectional study. Participants were positioned in three sitting postures: comfortable sitting (CS), thoracic upright sitting (TUS), and slump sitting (SS). In each sitting posture, the kyphosis index (using a flexicurve), head and cervical angles (using a digital camera), swallowing speed (100-ml water swallowing test), and oral and articulatory function [by maximum tongue pressure (MTP) and oral diadochokinesis (ODK)] were evaluated. SS showed the largest kyphosis index and was associated with a greater anterior translation of the head. Swallowing speed was significantly decreased in SS compared with CS (p = 0.002) and TUS (p = 0.020) and ODK was significantly decreased in SS compared with other postures, for both /ta/ (p = 0.004) and /ka/ (p < 0.001) syllables. Further, MTP tended to decrease in SS compared with TUS (p = 0.064). Our results suggest that changes in sitting posture with different thoracolumbar alignments affect swallowing speed and oral and articulatory function. Consequently, adjustments to reduce sitting postural kyphosis may improve swallowing speed and oral and articulatory function.

Predictors of Musculoskeletal Pain among Primary School Students Using Smartphones in Nakhon Si Thammarat, Thailand.

School-age children increasingly use smartphones to conduct their learning activities; increasing reports of disorders related to smartphone use exist, including visual-related symptoms, stress, and musculoskeletal pain. This study aimed to examine risk factors for musculoskeletal pain among primary school students using smartphones. A cross-sectional study was conducted with 233 school-aged children in Nakhon Si Thammarat, Thailand. Data collection used a questionnaire for musculoskeletal symptoms using the Nordic Musculoskeletal Questionnaire with ISO 11,226:2000. Through Chi-square, t-test, and logistic regression analysis, factors independently associated with musculoskeletal pain were determined. An important factor in the development of musculoskeletal pain was the prolonged use of smartphones for longer than 60 min, particularly among children aged 6-9 years old. In regards to musculoskeletal pain, almost 53% of the students used their smartphones while lying down. Posing in a prone position while using a smartphone was 7.37 times more dangerous than sitting. The laying position tilts numerous organs at varying angles, especially the upper arm. The risk of musculoskeletal complaints must be reduced by educating parents, children, and the relevant government organizations about safe smartphone usage. The mentioned factors may be used to anticipate the onset of musculoskeletal pain caused by smartphone use in young children.

A hybrid approach to product prototype usability testing based on surface EMG images and convolutional neural network classification.

OBJECTIVE: It is common for employees to complain of muscle fatigue when resting in a reclined position in an office chair. To investigate the physical factors that influence resting comfort in a supine position, a newly designed product was used as the basis for creating a prototype experiment and testing its efficacy in use. Subjective questionnaires were combined with surface EMG measurements and deep learning algorithms were used to identify body part comfort to create a hybrid approach to product usability testing. METHODS: To facilitate the use of sEMG-based CNNs in human factors engineering, a subjective user assessment was first conducted using a combination of body mapping and an impact comfort scale to the screen which body parts have a significant impact effect on comfort when using the prototype. A control group (no used) and an experimental group (used) were then created and the body parts with the most significant effects were measured using sEMG methods. After pre-processing the sEMG signal, sMEG feature maps were obtained by mean power frequency (MPF) and linear regression was used to analyze the comforting effect. Finally, a CNN model is constructed and the sMEG feature maps are trained and tested. RESULTS: The results of the experiment showed that the user's subjective assessment showed that 10 body parts had a significant effect on comfort, with the right and left sides of the neck having the highest effect on comfort (4.78). sEMG measurements were then performed on the sternocleidomastoid (SCM) of the left and right neck. Linear analysis of the measurements showed that the control group had higher SCM fatigue than the experimental group, which could also indicate that the experimental group had better comfort. The final CNN model was able to accurately classify the four datasets with an accuracy of 0.99. CONCLUSION: The results of the study show that the method is effective for the study of physical comfort in the supine sitting position and that it can be used to validate the comfort of similar products and to design iterations of the prototype.

Postural strategies among office workers during a prolonged sitting bout.

Sedentary behavior has increased steadily over prior decades, primarily due to increased computer use at work and at home. The total sedentary time per day has been associated with increased risk of cardiometabolic diseases; increased sitting time at work has been associated with musculoskeletal discomfort particularly in the low back. Office workers spend many hours sitting, thus efforts to increase movement through changes of posture (sit to stand) or moving while sitting have been proposed as ways to mitigate the negative effects of prolonged sitting. Yet, few studies have investigated differences in the movement patterns of office workers while sitting performing their actual work. Therefore, the aim of this study was to characterize movement patterns during a prolonged sitting bout and to determine their association with musculoskeletal pain. Twenty-eight office workers participated in this field study that used a pressure sensitive mat to quantify seat pan pressure (4 regions) and trunk sway parameters over a 2-hour bout of computer work. Data were stratified by breakers who stood up at least once within the 2-hour test and prolongers who remained sitting throughout the test. Overall, there was a decreasing trend in trunk sway parameters (mean COP position, sway path, sway area, sway velocity, maximum displacement, and in-chair movements) over time (p < 0.05), with significant changes in sitting strategies. There were significant differences in trunk sway parameters and perceived musculoskeletal discomfort between breakers and prolongers with breakers having more consistent movement while sitting over the prolonged sitting bout (p < 0.05) and lower discomfort ratings. This may indicate that interrupting prolonged bouts of sitting with short periods of standing can maintain sitting movement patterns and reduce the development of musculoskeletal discomfort. Trunk sway monitoring and promoting periodic standing may be useful tools for maintaining in chair movements that may reduce or prevent the onset of musculoskeletal discomfort during prolonged sitting.

An Empirical and Subjective Model of Upper Extremity Fatigue Under Hypogravity.

In the context of extra-terrestrial missions, the effects of hypogravity (0 < G < 1) on the human body can reduce the well-being of the crew, cause musculoskeletal problems and affect their ability to perform tasks, especially during long-term missions. To date, studies of the effects of hypogravity on human movement are limited to experiments on the lower limbs. Here, we extend the knowledge base to the upper limbs, by conducting experiments to evaluate the effect of hypogravity on upper limb physical fatigue and mental workload in participants. Our hypothesis was that hypogravity would both increase participant productivity, by reducing overall physical fatigue expressed in Endurance Time, and reduce mental workload. Task Intensity-Endurance time curves are developed especially in seated positions, while performing static, dynamic, repetitive tasks. This experiment involved 32 healthy participants without chronic problems of the musculoskeletal system aged 33.59 ± 8.16 years. Using the collected data, fatigue models were constructed for tasks of varying Intensity. In addition, all participants completed the NASA - Task Load Index subjective mental workload assessment, which revealed the level of subjective workload when executing different tasks. We found two trends in the empirical fatigue models associated with the difference between the strength capabilities of males and females. The first is a significant positive (p = 0.002) relation between Endurance time and gravity level (⅙ G Moon, ⅓ G Mars, 1G) with negative coefficient for males and females for a static task. And there is marginal relation (p < 0.1) between overall mental workload and gravity level with a positive coefficient for males and females for the same task. The same trend was observed for dynamic and repetitive tasks. We concluded that the Task Intensity-Endurance Time model, adapted to hypogravity in combination with subjective mental assessment, is useful to human fatigue investigation. The combination of these methods used for ergonomic analysis and digital human modeling, could improve worker productivity. Finally, this study may help prepare astronauts for long-term missions on the Moon and Mars and improve our understanding of how we can prevent musculoskeletal disorders caused by hazardous manual handling under such extreme environments.