Force Exertion Research Articles

Research on the Mechanics Principle of 100-Meter Running

Fascinated by “superpowers” all over time, people are increasingly attracted by speed, a form of superpowers, which can be seen from the “flash” in movies or “locomotive” in American TV series. Given such obsession with the pursuit of speed, this paper selects the 100-meter race that reflects the speed of human beings as the research topic. This research analyzes the most basic movement of humans, that is, running. Firstly, with humans regarded as particles, 100-meter running is divided into stages of start, acceleration, maintenance, and sprint in this paper. By analyzing the speed, acceleration, reaction time, stride length, stride frequency, and other indicators of top athletes represented by Bolt in different stages, MATLAB simulation is conducted for comparison and summary. Secondly, with humans regarded as non-particles for analysis, simulation research is implemented on the landing mode of feet, the force exertion mode of arms, and some leg muscles combined with torque. Finally, this paper carried out experiments to understand the laws of particle motion mechanics in 100-meter running as well as figure out how various stride frequencies and arm swings affect running speed, in addition to analyzing the influence of resistance on running posture. Theoretically and experimentally exploring the principles of running mechanics, this paper initiates a detailed discussion of the influencing factors and their improvement from an innovative perspective, so as to put forward suggestions for teenagers to optimize their running performance.

Single-Belt Versus Split-Belt: Intelligent Treadmill Control via Microphase Gait Capture for Poststroke Rehabilitation.

Stroke is the leading long-term disability and causes a significant financial burden associated with rehabilitation. In poststroke rehabilitation, individuals with hemiparesis have a specialized demand for coordinated movement between the paretic and the nonparetic legs. The split-belt treadmill can effectively facilitate the paretic leg by slowing down the belt speed for that leg while the patient is walking on a split-belt treadmill. Although studies have found that split-belt treadmills can produce better gait recovery outcomes than traditional single-belt treadmills, the high cost of split-belt treadmills is a significant barrier to stroke rehabilitation in clinics. In this article, we design an AI-based system for the single-belt treadmill to make it act like a split-belt by adjusting the belt speed instantaneously according to the patient's microgait phases. This system only requires a low-cost RGB camera to capture human gait patterns. A novel microgait classification pipeline model is used to detect gait phases in real time. The pipeline is based on self-supervised learning that can calibrate the anchor video with the real-time video. We then use a ResNet-LSTM module to handle temporal information and increase accuracy. A real-time filtering algorithm is used to smoothen the treadmill control. We have tested the developed system with 34 healthy individuals and four stroke patients. The results show that our system is able to detect the gait microphase accurately and requires less human annotation in training, compared to the ResNet50 classifier. Our system "Splicer" is boosted by AI modules and performs comparably as a split-belt system, in terms of timely varying left/right foot speed, creating a hemiparetic gait in healthy individuals, and promoting paretic side symmetry in force exertion for stroke patients. This innovative design can potentially provide cost-effective rehabilitation treatment for hemiparetic patients.

Time-varying changes in median nerve deformation and position in response to quantified pinch and grip forces.

The ability of the median nerve (MN) to adapt in response to altered carpal tunnel conditions is important to mitigate compressive stress on the nerve. We assessed changes in MN deformation and position throughout the entire time course of hand force exertions. Fourteen right-handed participants ramped up force from 0% to 50% of maximal voluntary force (MVF) before ramping force back down in three different hand force exertion tasks (pulp pinch, chuck pinch, power grip). Pinch and grip forces were measured with a digital dynamometer, which were time synchronized with transverse carpal tunnel images obtained via ultrasound. Ultrasound images were extracted in 10% increments between 0% and 50% MVF while ramping force up (loading phase) and down (unloading phase). MN deformation and position relative to the flexor digitorum superficialis tendon of the long finger were assessed in concert. During loading, the nerve became more circular while displacing dorsally and ulnarly. These changes primarily occurred at the beginning of the hand force exertions while ramping force up from 0% to 20%, with very little change between 20% and 50% MVF. Interestingly, deformation and position changes during loading were not completely reversed during unloading while ramping force down. These findings indicate an initial reorganization of carpal tunnel structures. Mirrored changes in nerve deformation and position may also reflect strain-related characteristics of adjoining subsynovial connective tissue. Regardless, time-varying changes in nerve deformation and position appear to be an important accommodative mechanism in the healthy carpal tunnel in response to gripping and pinching tasks.

Investigating change of discomfort during repetitive force exertion though an exoskeleton cuff

This article investigates discomfort development for forces exerted repetitively and for extended durations through a rigid cuff.Three force patterns, chosen to mimic exoskeleton use, were applied to the thigh of 15 healthy participants for 30 min. Changes in perceived comfort and skin effects were recorded.Discomfort was detected at normal forces ranging from 40 to >230 N. Repetitive force application triggered discomfort after a median of 4.1 min (normal force only) and 5.4 min (normal and shear force) respectively. Discomfort increased over time but the repetitive force applications did generally not result in pain and there were no significant differences between repetitive loading patterns.Exoskeleton design and use should be informed by comfort thresholds specific to prolonged repetitive loading. Large interindividual differences in perception of discomfort limit the possibilities for generally applicable comfort thresholds. Further research is needed to investigate how patient groups perceive such repetitive loading.

Hierarchically manufactured chiral plasmonic nanostructures with gigantic chirality for polarized emission and information encryption

Chiral metamaterials have received significant attention due to their strong chiroptical interactions with electromagnetic waves of incident light. However, the fabrication of large-area, hierarchically manufactured chiral plasmonic structures with high dissymmetry factors (g-factors) over a wide spectral range remains the key barrier to practical applications. Here we report a facile yet efficient method to fabricate hierarchical chiral nanostructures over a large area (>11.7 × 11.7 cm2) and with high g-factors (up to 0.07 in the visible region) by imparting extrinsic chirality to nanostructured polymer substrates through the simple exertion of mechanical force. We also demonstrate the application of our approach in the polarized emission of quantum dots and information encryption, including chiral quick response codes and anti-counterfeiting. This study thus paves the way for the rational design and fabrication of large-area chiral nanostructures and for their application in quantum communications and security-enhanced optical communications.

Effect of extension of the ulnar fingers on force control and muscle activity of the hand during a precision pinch.

Some individuals extend the three ulnar fingers when performing a precision pinch. The aim of the present study was to investigate the mechanisms and effect of the extension of the ulnar fingers during a pinch. When performing a pulp pinch task with the ulnar fingers in two positions (extension and flexion), 27 participants maintained 5% of their maximum force. The mean pinch force, force variability and time taken to reach the targeted force (reaching time) were calculated. Muscle activity was simultaneously measured, using surface electromyography, for nine muscles: the flexor pollicis brevis; abductor pollicis brevis; flexor pollicis longus; first lumbrical; first dorsal interosseous; flexor digitorum superficialis of the index finger; extensor indicis; and extensor digitorum of the index and ring fingers. No significant differences in the mean pinch force or force variability were found. However, the reaching time was significantly shorter (approximately 20% reduction) in the extension position and the activities in the flexor pollicis brevis, first lumbrical, extensor indicis and extensor digitorum of the ring finger were significantly higher. These findings suggest that extending the ulnar fingers during pinching enhances the activity of key muscles involved in the movement and allows for more rapid force exertion.

Prevalence of work-related musculoskeletal disorders and associated factors among University of Zimbabwe Faculty of Medicine and Health Sciences non-academic workers: a cross-sectional study

BackgroundWork-related musculoskeletal disorders most commonly contribute to years lived with disability among workers. Heavy physical work, static work posture, awkward posture, force exertion, lifting and repetitive movements increase the risk of developing work-related musculoskeletal disorders.ObjectivesThe aim of the study was to determine the prevalence of work-related musculoskeletal disorders and associated factors among non-academic workers at the University of Zimbabwe Faculty of Medicine and Health Sciences. Non-academic workers included security personnel, catering staff, drivers, library staff, clerical staff, technicians and janitorial staff.Methods and materialsThe study used a cross-sectional analytical design. One hundred and eight non-academic workers at the University of Zimbabwe Faculty of Medicine and Health Sciences were sampled through proportional stratified sampling in January 2021. An adapted Nordic Musculoskeletal Questionnaire capturing socio-demographics and ergonomic risk factors was used to gather data. SPSS v24 was used for data analysis including frequencies, tests of association and multivariate logistic regression.ResultsOne hundred non-academic workers from the University of Zimbabwe Faculty of Medicine and Health Sciences responded. The 3-month and 12-month prevalences of work-related musculoskeletal disorders were highest in the lower back (n = 72, 72% and n = 75, 75%) and wrists/hands (n = 60, 60% and n = 69, 69%) respectively. Sociodemographic factors such as age (p = 0.002), gender (p < 0.001), educational level (p = 0.008) and worker category (p < 0.001) were associated with increased work-related musculoskeletal disorders, while work experience (p = 0.002) was associated with a decreased prevalence of back pain and discomfort. Females (AOR = 55.90; 95% CI [3.84, 814.54]), security personnel (AOR = 39.53, 95% CI [1.57, 996.00]), catering staff (AOR = 91.3295% CI [2.24, 3724.78]) and those who attained bachelor’s degrees (AOR = 73.25, 95% CI [1.46, 3682.39]), higher national diplomas (AOR = 93.49, 95% CI [1.28, 6848.04]) and national diplomas (AOR = 52.22; 95% CI [1.09, 2510.73]) had higher odds of experiencing WMSDs. Increased working experience was protective against experiencing lower back pain (AOR = 0.84; 95% CI [0.74, 0.95]).Discussion and conclusionThe prevalence of work-related musculoskeletal disorders was high among the participants. This was influenced by the nature of work as well as cultural factors.RecommendationsOccupational therapists and physiotherapists need to design focused ameliorative and health promotive interventions targeting at-risk populations in universities. Employers should consider developing wellness programs for workers and promoting healthy working environments.

Effects of postural threat on the scaling of anticipatory postural adjustments in young and older adults.

The ability to scale anticipatory postural adjustments (APAs) according to the predicted size of the upcoming movement is reduced with aging. While age-related changes in central set may be one reason for this effect, an individual's emotional state might also contribute to changes in anticipatory postural control. Therefore, the purpose of this study was to determine whether an altered emotional state, as elicited through postural threat, alters the scaling of APAs during a handle pull movement in young and older adults. It was hypothesized that the presence of postural threat would lead to more homogenous APAs (i.e., less scaling of APAs) across a range of pulling forces. Young (n = 23) and older adults (n = 16) stood on top of a force plate that was mounted to a motorized platform. From this position, participants performed a series of handle pull trials without (no threat) or with (threat) the possibility of receiving a postural perturbation in the form of an unpredictable surface translation. Handle pulls were performed at force levels between 50 and 90% of maximum force. For each trial, the magnitude and timing of the APA were quantified from center of pressure (COP) recordings as well as electromyographic (EMG) activity of the soleus and medial gastrocnemius. The scaling of APAs with respect to force exertion was then determined through regression analyses and by comparing APAs during pulls of lower versus higher force. As evidenced by their smaller slope of the regression line between various dependent measures (i.e., COP velocity, soleus EMG onset latency, and soleus EMG amplitude) and the pulled forces, older adults demonstrated less scaling of APAs than the young. However, increases in arousal, anxiety and fear of falling due to postural threat, only minimally altered the scaling of APAs. Regardless of age, the slope of the regressions for none of the measures were affected by threat while only the soleus and medial gastrocnemius EMG onsets demonstrated significant force × threat interaction effects. These results suggest that the decreased ability to scale APAs with aging is unlikely to be due to changes in emotional state.

Forestry professionals’ perspectives on exoskeletons (wearable assistive technology) to improve worker safety and health

ABSTRACT Exoskeletons have been recognized as an effective ergonomic control to reduce physical risk factors, including forceful exertions and awkward postures that are common in manual timber felling. However, no evidence exists to date that offers industry perspectives, important facilitators, and potential barriers for adopting exoskeletons in the forest industry. Therefore, this study aimed to quantify biomechanical stress of timber fellers and assess forestry professionals’ awareness and acceptance of exoskeletons. We measured working postures using wearable sensors during manual timber felling [N = 10] to suggest appropriate and beneficial exoskeleton types for timber fellers. We examined forestry professionals’ awareness and acceptance of exoskeletons and identified perceived barriers and risks using a questionnaire [N = 22]. This study revealed that the forestry professionals expressed considerable interest and acceptance level in exoskeleton use. The important factors influencing the adoption of exoskeletons identified in this study were weight, comfort, simplicity/portability, practicality (usable and easy to use), and easy maintenance. The results also identified timber felling, cutting/sawing, and mechanic work as potential forestry tasks that may benefit most from the exoskeleton use. The wearable sensor data showed that manual timber felling posed substantial torso bending and upper-arm elevation. Given the awkward posture and high prevalence of musculoskeletal pain in the back and upper-arms, this study suggests that back-support and upper-limb support exoskeletons may be suitable to the forest industry. This study provides important insights for future studies investigating the feasibility, readiness, and effectiveness of exoskeletons to be applied to the forest industry.

Developing prototypes of the assistant opener of packaging for consumer accessibility

The purpose of this research was to focus on the design of packaging openers for consumer access to the contents. The packaging opener was created to make opening easier and safer. In this study, online questionnaires were used to investigate the problems and solutions of user experiences when opening packaging. According to the findings, a major issue among the responding participants is that they should have a strong hand force. However, the hand force not only had enough energy to open the packaging, but it was also unable to open the closure at the specified location. When participants encountered opening problems, they preferred to use an assistant tool rather than ask for assistance. The risk of packaging materials, scissors, knives, and wrist and finger twisting occurred during opening packaging. According to the respondents' experiences, the four functions of the packaging opener were integrated together for the corrugated box, ring-pull a can, lug cap closure, and flexible packaging. As a result, the newly designed packaging opener required less opening force, a safer hold, and optimized hand ergonomics. The attractive configuration and comfortable grip were also important factors to consider when designing the packaging openers in this study. Opener prototypes were modelled using SolidWorks and were formed by a 3D printer. The FSUDE system was employed to evaluate the functions, safety, usability, design, and engineering of all prototypes. Based on the results of this study, form, dimension, surface, friction, and grip posture were factors affecting torque force exertion, slitting and cutting force, and openability of consumers.

Shoulder Tendinopathies and Occupational Biomechanical Overload: A Critical Appraisal of Available Evidence.

The aim of this study is to evaluate the association between occupational exposure to biomechanical risk factors and shoulder tendinopathies. We updated recent systematic reviews about specific shoulder disorders and work-related risk factors. MEDLINE was searched up to September 2022. Studies satisfying the following criteria were included: i) the diagnosis was based on physical examination plus imaging data (when available), and ii) the exposure assessment was based on video analysis and/or directly measured. Five studies met the inclusion criteria: three cross-sectional studies identified from published systematic reviews and two cohort studies retrieved from the update. Two studies investigated shoulder tendinitis, one supraspinatus tendinitis, and the other two rotator cuff syndrome. The diagnosis was based on physical examination, not supported by imaging techniques for all the included studies. In four out of five studies, the exposure was assessed by experienced ergonomists with the support of video recordings. In two studies, the exposure assessment was further supplemented by force gauge measurements or direct measurements of upper arm elevation. Only the combined exposure of working with arms above shoulder level with forceful hand exertion appears to be associated with rotator cuff syndrome: i) a cohort study reported an HR=1.11 (95%CI 1.01-1.22) for each unit increase in forceful repetition rate when the upper arm is flexed ≥45° for ≥29% of the working time; and ii) a cross-sectional study showed an OR=2.43 (95%CI 1.04-5.68) for the combination of upper arm flexion ≥45° for more than 15% of the time with a duty cycle of forceful exertions more than 9% of the time. There is moderate evidence of a causal association between shoulder tendinopathy and combined exposures of working above shoulder level with forceful hand exertion. The evidence is insufficient for any single biomechanical exposure on its own. High-quality cohort studies with direct exposure measures and objective diagnostic criteria are needed. The occupational origin of shoulder tendinopathies is still an open question that must be properly answered.

Prevalence and Pattern of Musculoskeletal Disorder in Panteka Mechanic Village, Kaduna

Musculoskeletal disorders (MSDs) are illnesses that make working people disabled and generate significant economic loss worldwide. Automobile mechanics are at risk of injury at the onset of MSDs due to repetitive tasks, uncomfortable posture, and heavy lifting of objects. The frequency and pattern of work-related musculoskeletal disorders among auto mechanics in Panteka Village, Kaduna State, are investigated in this study. Using a version of the standard Nordic Musculoskeletal questionnaire, a quatitative method was used to gather data on the prevalence pattern of musculoskeletal illnesses at Panteka Village. To analyze the data obtained, purposive sampling method was employed. The study found that there was a high prevalence of MSDs among auto mechanics in Panteka village, with rates of 90% (Neck), 92.3% (shoulder), 56.4% (knee) and over 70% prevalence of MSD for lower and upper back. The results of relationship between age of respondents, years spent as a mechanic and prevalence of the musculoskeletal disorders showed no significant relationship. However, there was a significant relationship between the respondent's section of mechanic activities ie the nature of their job and MSD. These are primarily the result of poor ergonomics and insufficient rest periods at their workshop. Also, manual handling of heavy loads, repetitive tasks and force exertion were the identified factors. Ergonomic and MSD awareness among workers should be increased through training. In addition, govermnents should investigate more in other to reduce or eliminate risk factors leading to musculoskeletal disorders. Members of the Panteka village committee can use the research's findings to enhance the working environment for mechanics. Therefore, Mechanics will need to be educated more on risk factors associated with MSDs.

On deformable object handling: multi-tool end-effector for robotized manipulation and layup of fabrics and composites

Over the past decades, robotic automation has expanded in numerous industrial sectors; however, manufacturing operations involving the manipulation of non-rigid products are mostly preserved manual. The dynamic distortion of flexible objects underlines limitations in robot cognition and dexterity. Inspired by the gaps in composites industry automation, this paper presents a novel multifunctional robot end-effector for the robotic automation of composites layup. Aiming a holistic confrontation of layup challenges, the proposed end-effector incorporates tools for (a) the manipulation of sheet materials, like composite fabrics of variable dimensions; (b) the grasping of core materials, like foam blocks; (c) the handling of peripheral tools; (d) the exertion of fitting forces; and (e) the application of resin in diverse mold geometry cavities. The meticulous design of the end-effector’s configuration allows for consistent and collision-free tool usage with no excess robot tool changes, granting even higher productivity and efficiency. The enhancement in robot dexterity and proficiency for layup operations is validated within an automotive case, where semi-automation is intended for the improvement in overall workstation’s efficiency, quality, ergonomics, and well-being.

Modular Soft Robotic Actuators from Flexible Perforated Sheets

Soft robotic actuators can be designed to achieve complex and tailored motions while simultaneously leveraging their compliance to interact with complex and often delicate environments. Mechanical metamaterials reveal a route to customizable deformations, force exertion, and mechanical energy efficiency attainable by careful arrangement of local geometric features. Herein, modular soft robotic actuators are developed from soft elastomers and flexible thermoplastic sheets of various unit cell designs. The efforts are focused on center‐symmetric perforated sheets, which are formed into flexible cylindrical skins that surround the soft inflatable actuators. The results demonstrate the influence of perforation geometry on the spatial stiffness of the reinforcement structure and the proposed actuators’ response through several investigations. It is demonstrated that the free‐boundary displacement, maximal force exertion, and mechanical energy efficiency of extensile actuators are dependent on a change of deformation mode in the mesostructure. The spatial stiffness concept is extended to develop soft robotic actuators that can bend, twist, and perform hybrid motions, such as simultaneous bending and twisting. Multisegment soft robotic arms are also developed from the aforementioned actuators. Investigations in this study provide a step toward the development of highly customizable and programmable soft robotic actuators for various applications.

Cable-Driven Haptic Interface With Movable Bases Achieving Maximum Workspace and Isotropic Force Exertion.

Haptic interactions play an essential role in education to enhance learning efficiency; however, haptic information for virtual educational content remains lacking. This paper proposes a planar cable-driven haptic interface with movable bases that can display isotropic force feedback with maximum workspace extension on a commercial screen display. A generalized kinematic and static analysis of the cable-driven mechanism is derived by considering movable pulleys. Based on the analyses, a system including movable bases is designed and controlled to maximize the workspace subject to isotropic force exertion for the target screen area. The proposed system is evaluated experimentally as a haptic interface represented by the workspace, isotropic force-feedback range, bandwidth, Z-width, and user experiment. The results indicate that the proposed system can maximize workspace to the target rectangular area and exert isotropic force up to 94.0% of the theoretical computed one within the workspace.

TMEM123 a key player in immune surveillance of colorectal cancer.

Colorectal cancer (CRC) is a leading cause of cancer-associated death. In the tumor site, the interplay between effector immune cells and cancer cells determines the balance between tumor elimination or outgrowth. We discovered that the protein TMEM123 is over-expressed in tumour-infiltrating CD4 and CD8 T lymphocytes and it contributes to their effector phenotype. The presence of infiltrating TMEM123+ CD8+ T cells is associated with better overall and metastasis-free survival. TMEM123 localizes in the protrusions of infiltrating T cells, it contributes to lymphocyte migration and cytoskeleton organization. TMEM123 silencing modulates the underlying signaling pathways dependent on the cytoskeletal regulator WASP and the Arp2/3 actin nucleation complex, which are required for synaptic force exertion. Using tumoroid-lymphocyte co-culture assays, we found that lymphocytes form clusters through TMEM123, anchoring to cancer cells and contributing to their killing. We propose an active role for TMEM123 in the anti-cancer activity of T cells within tumour microenvironment.

Compensation strategy of shoulder synergist muscles is not stereotypical in patients with rotator cuff repair.

Rotator cuff tear is a common shoulder injury that causes shoulder dysfunction and pain. Although surgical repair is the primary treatment for rotator cuff tear, it is well recognized that impaired force exertion of muscles connecting to the involved tendon and subsequent complemental change in the force exertion of synergist muscles persist even after repair. This study aimed to identify the compensation strategy of shoulder abductors by examining how synergist muscles respond to supraspinatus(SSP) muscle force deficit in patients with rotator cuff repair. Muscle shear modulus, an index of muscle force, was assessed for SSP, infraspinatus, upper trapezius, and middle deltoid muscles in repaired and contralateral control shoulders of 15 patients with unilateral tendon repair of the SSP muscle using ultrasound shear wave elastography while the patients passively or actively held their arm in shoulder abduction. In the repaired shoulder, the shear modulus of the SSP muscle declined, whereas that of other synergist muscles did not differ relative to that of the control. To find the association between the affected SSP and each of the synergist muscles, a regression analysis was used to assess the shear moduli at the population level. However, no association was observed between them. At the individual level, there was a tendency of variation among patients with regard to a specific muscle whose shear modulus complementarily increased. These results suggest that the compensation strategy for SSP muscle force deficit varies among individuals, being nonstereotypical in patients with rotator cuff injury.

Muscle coordination patterns in regulation of medial gastrocnemius activation during walking

The ankle plantar flexion in the late stance phase is referred to as the ankle push-off. When the ankle push-off force is enhanced, compensatory adjustments occur in the adjacent phases. The muscle control that achieves these compensatory movements remains unknown, although they are expected to be coordinately regulated across multiple muscles and phases. Muscle synergy is used as a quantification technique for muscle coordination, and this analysis enables the comparison of synchronized activity between multiple muscles. Therefore, this study aimed to elucidate the tuning of muscle synergies in muscle activation adjustment of push-off. It is hypothesized that muscle activation adjustment of push-off is performed in the muscle synergy related to ankle push-off and in the muscle synergy that activates during the adjacent push-off phase. Eleven healthy men participated, and participants manipulated the activity of the medial gastrocnemius during walking through visual feedback. Two conditions were compared as experimental conditions: increasing the muscle activity to 1.6 times that during normal walking (High) and matching it with that during normal walking (Normal). Twelve muscle activities in the trunk and lower limb and kinematic data were recorded. Muscle synergies were extracted by the non-negative matrix factorization. No significant difference was observed in the number of synergies (High: 3.5 ± 0.8, Normal: 3.7 ± 0.9, p = 0.21) and muscle synergy activation timing and duration between the High and Normal conditions (p > 0.27). However, significant differences were observed in the peak muscle activity during the late stance phase of the rectus femoris (RF), biceps femoris (BF) between conditions (RF at High: 0.32 ± 0.21, RF at Normal: 0.45 ± 0.17, p = 0.02; BF at High: 0.16 ± 0.01, BF at Normal: 0.08 ± 0.06 p = 0.02). Although the quantification of force exertion has not been conducted, the modulation of RF and BF activation could have occurred due to the attempts to help knee flexion. Muscle synergies during normal walking are therefore maintained, and slight adjustments in the amplitude of muscle activity occurred for each muscle.

Non-Surgical Lower-Limb Rehabilitation Enhances Quadriceps Strength in Inpatients with Hip Fracture: A Study on Force Capacity and Fatigue

Measuring muscle fatigue and resistance to fatigue is a topical theme in many clinical research studies. Multi-domain approaches, including electromyography (EMG), are employed to measure fatigue in rehabilitation contexts. In particular, spectral features, such as the reduction in the median frequency, are accepted biomarkers to detect muscle fatigue conditions. However, applications of fatigue detection in clinical scenarios are still limited and with margin for improvement. One of the potential applications of such methodology in clinics concerns the evaluation of the rehabilitation after hip fracture. In this work, 20 inpatients, in the acute phase after hip fracture surgery and with lower limb weakness, performed isometric contractions with their healthy lower limb (quadriceps muscle) and their resistance to fatigue before and after 2 weeks of rehabilitation program was measured. Multi-channel EMG and Maximum Voluntary Contractions (MVC, force) were recorded on five muscle heads. We found that, after performing the same number of repetitions (repetitions pre-treatment: 19.7 ± 1.34; repetitions post-treatment: 19.9 ± 0.36; p = 0.223), MVC improved (MVC pre-treatment: 278 ± 112 N; MVC post-treatment: 322 ± 88 N; p = 0.015) after rehabilitation for most of the patients and fatigue did not change. These results suggest that higher force exertion was performed after rehabilitation, with the same level of fatigue (fatigued muscles pre-treatment: 1.40 ± 1.70; fatigued muscles post-treatment: 1.15 ± 1.59; p = 0.175) after. Results are discussed addressing the potential of multifactorial instrumental assessments for describing patients’ status and provide data for clinical decision making.

EEG Source Localization during an Arm Isometric Force Exertion Task at Different Levels of Perceived Exertion.

Neuroergonomics is an emerging science that focuses on the human brain's performance during physical work. The advent of portable neurophysiological methods, including electroencephalography (EEG), has enabled measurements of real-time brain activity during physical tasks without restricting body movements. However, the EEG signatures of different levels of physical exertion activity involving the musculoskeletal system remain poorly understood. This study investigated the EEG source localization activity induced by predefined force exertion levels during an isometric arm force exertion task in healthy female participants for the alpha and beta frequency bands. Exact low-resolution electromagnetic tomography (eLORETA) was used to localize the current source densities (CSDs) in 84 anatomical brain regions of interest. The maximum CSDs for extremely hard force exertion levels for the alpha frequency were localized in Brodmann area (BA) 6, whereas CSDs associated with other exertion levels were localized in BA 8. The maximum CSDs for extremely hard force exertion levels for beta were localized in BA 5, whereas CSDs associated with other exertion levels were localized in BA 7. These findings extend the current understanding of the neurophysiological basis of physical exertion with various force levels and suggest that specific brain regions are involved in generating the sensation of force exertion. To our knowledge, this is the first study localizing EEG activity among various predefined force exertion levels during an isometric arm exertion task in healthy female participants.