Isometric Exertions Research Articles

There is no bilateral deficit of torque and rate of torque development of knee extensors during isometric exertion when measured by two independent isokinetic machines

There is no bilateral deficit of torque and rate of torque development of knee extensors during isometric exertion when measured by two independent isokinetic machines

Nutritional Ergogenic Aids in Combat Sports: A Systematic Review and Meta-Analysis.

Nutritional ergogenic aids (NEAs) are substances included within the group of sports supplements. Although they are widely consumed by athletes, evidence-based analysis is required to support training outcomes or competitive performance in specific disciplines. Combat sports have a predominant use of anaerobic metabolism as a source of energy, reaching peak exertion or sustained effort for very short periods of time. In this context, the use of certain NEAs could help athletes to improve their performance in those specific combat skills (i.e., the number of attacks, throws and hits; jump height; and grip strength, among others) as well as in general physical aspects (time to exhaustion [TTE], power, fatigue perception, heart rate, use of anaerobic metabolism, etc.). Medline/PubMed, Scopus and EBSCO were searched from their inception to May 2022 for randomised controlled trials (RCTs). Out of 677 articles found, 55 met the predefined inclusion criteria. Among all the studied NEAs, caffeine (5–10 mg/kg) showed strong evidence for its use in combat sports to enhance the use of glycolytic pathways for energy production during high-intensity actions due to a greater production of and tolerance to blood lactate levels. In this regard, abilities including the number of attacks, reaction time, handgrip strength, power and TTE, among others, were improved. Buffering supplements such as sodium bicarbonate, sodium citrate and beta-alanine may have a promising role in high and intermittent exertion during combat, but more studies are needed in grappling combat sports to confirm their efficacy during sustained isometric exertion. Other NEAs, including creatine, beetroot juice or glycerol, need further investigation to strengthen the evidence for performance enhancement in combat sports. Caffeine is the only NEA that has shown strong evidence for performance enhancement in combat sports.

Abstract 10757: Patient-Reported Quality of Life Outcomes in Hypertrophic Cardiomyopathy Patients

Background: Few studies have systematically assessed quality of life (QOL) in hypertrophic cardiomyopathy (HCM) patients not meeting the septal reduction therapy (SRT) threshold, but require avoiding isometric exertion and weightlifting. We prospectively studied a newly developed QOL instrument to examine the associations between patient characteristics and self-reported QOL scores in HCM patients not anticipated to undergo SRT for at least 6 months. Methods: A single-center, prospective sample of 51 adult HCM patients (54±14 years, mean interventricular septum thickness = 1.7±0.4cm, 65% with left ventricular outflow tract (LVOT) obstruction, mean provokable LVOT gradient 65±42 mmHg, 59% men) completed a baseline 70-item QOL instrument, adapted from validated QOL questionnaires. All patients signed informed consent. Results: Mean self-reported QOL scores (on a 5-point Likert scale with higher scores indicating higher QOL) were as follows: physical function (3.5±1), depression (3.7±1), anxiety (3.6±1), post-traumatic stress disorder (PTSD) (3.7±1), social function (4.1±1), spiritual acceptance of diagnosis (3.8±1), self-efficacy (4±1), and resilience (4±1). Men vs. women reported higher physical function (3.9±1 vs. 2.9±1), less depression (4±1 vs. 3.3±1), less anxiety (3.8±1 vs. 3.3±1), and higher social function (4.3±0.7 vs. 3.8±1) (all p<0.05). Patients with obstructive HCM reported lower physical function scores (3.3±0.8) vs. non-obstructive HCM (3.8±0.8), p=0.03. Symptomatic patients reported lower physical function (3.2±0.8 vs. 4.3±0.5), social function (3.8±0.8 vs. 4.5±0.6) and worse depression (3.5±0.7 vs. 4.3±0.6), anxiety (3.4±0.8 vs. 4.1±0.7) and PTSD (3.5±0.8 vs. 4.3±0.9) scores (all p<0.01). Presence of an implantable cardioverter defibrillator (ICD) was associated with lower vs. higher physical (2.9±0.4 vs. 3.5±1) and social function (3.6±1 vs. 4.1±1) (all p<0.05). Conclusion: In HCM patients not requiring SRT, higher physical function scores were significantly associated with a better self-perceived overall health. Being a woman, having LVOT obstruction, presence of a defibrillator and presence of symptoms was significantly associated with worse perceived physical and social function.

A computer vision approach for classifying isometric grip force exertion levels

Exposure to high and/or repetitive force exertions can lead to musculoskeletal injuries. However, measuring worker force exertion levels is challenging, and existing techniques can be intrusive, interfere with human–machine interface, and/or limited by subjectivity. In this work, computer vision techniques are developed to detect isometric grip exertions using facial videos and wearable photoplethysmogram. Eighteen participants (19–24 years) performed isometric grip exertions at varying levels of maximum voluntary contraction. Novel features that predict forces were identified and extracted from video and photoplethysmogram data. Two experiments with two (High/Low) and three (0%MVC/50%MVC/100%MVC) labels were performed to classify exertions. The Deep Neural Network classifier performed the best with 96% and 87% accuracy for two- and three-level classifications, respectively. This approach was robust to leave subjects out during cross-validation (86% accuracy when 3-subjects were left out) and robust to noise (i.e. 89% accuracy for correctly classifying talking activities as low force exertions). Practitioner summary: Forceful exertions are contributing factors to musculoskeletal injuries, yet it remains difficult to measure in work environments. This paper presents an approach to estimate force exertion levels, which is less distracting to workers, easier to implement by practitioners, and could potentially be used in a wide variety of workplaces. Abbreviations: MSD: musculoskeletal disorders; ACGIH: American Conference of Governmental Industrial Hygienists; HAL: hand activity level; MVC: maximum voluntary contraction; PPG: photoplethysmogram; DNN: deep neural networks; LOSO: leave-one-subject-out; ROC: receiver operating characteristic; AUC: area under curve

The effects of repetitive bouts of a fatiguing exertion (with breaks) on the slope of EMG measures of localized muscle fatigue

Decreases in the median frequency of the power spectrum and increases in amplitude measures of an electromyographic signal have been used to assess localized muscle fatigue. How these responses are affected by repetitive bouts of exertions - separated by rest breaks - is not well understood. It was hypothesized that repetitive bouts of a fatiguing, isometric exertion, separated by periods of rest, would have cumulative effects (across bouts) on the slope of these EMG-based variables, with an expectation of a steeper rate of decline in the median frequency and a steeper rate of increase in amplitude measures in subsequent bouts. To test these hypotheses, 24 participants performed four bouts of an isometric (15% MVC) elbow flexion exertion. Each exertion lasted for four minutes and then a 15-minute break was provided between bouts. Surface electromyography was used to capture the activity of the biceps brachii at twenty-second intervals during the exertions. The median frequency and average rectified value were calculated, as were the slopes of these variables within each of the four-minute bouts. Contrary to the original hypotheses, the results showed that there were no statistically significant differences in the slopes of these EMG-based measures across bouts. One direction for future work is to explore different combinations of work-rest durations to refine this response while another may be to explore alternate EMG-based measures of muscular fatigue that may be more sensitive to this cumulative effect.

Effect of Handwheel Diameter and Orientation on Torque Production Capabilities

OCCUPATIONAL APPLICATIONSIn this study, we determined that the torque production capabilities are maximized using larger handwheel diameters (as large as 70 cm) in a horizontal orientation (0°). When using a 70 vs. 35 cm handwheel, torque production capabilities increased by 89.7%. Larger handwheels may allow operators to work at lower percentages of their maximum physical capacities, helping to reduce their risks of injuries. Handwheels at a slanted orientation (45°) reduced torque production capabilities, and therefore should be avoided in handwheel design. Our results also indicated that torque production capabilities may be considerably lower than both existing standards and the actual torque demands experienced in practice. Recommended torque limits are proposed, and cumulative distributions of the collected torque data are presented, which may serve future standard developers in defining appropriate torque limits for the health and well-being of valve operators.TECHNICAL ABSTRACT Background: Handwheels are prevalent across numerous industries for regulating the flow of material within a valve. There are, however, no well-established design guidelines for handwheels, which can be found in different diameter sizes and orientations, and often require forces beyond an operator’s physical capacity. Purpose: The purposes of this study were to: (1) determine the effects of handwheel diameter and orientation on torque production capabilities; (2) propose recommended torque limits (RTL) to accommodate operator physical strength; and (3) explore gender differences in torque production capabilities. Methods: Sixty college students (gender balanced) participated in this study. Four handwheel diameters were examined (35, 45, 60, and 70 cm), each at three different orientation angles (0, 45, and 90° from horizontal). In each diameter-orientation combination, participants performed maximal isometric torque exertions on the handwheels. Cumulative distributions of capabilities were determined, and RTLs were derived based on the 25th percentile torque strength of females. Results: As diameter increased, torque production capabilities also increased. The 0° orientation was associated with the highest torques for all handwheel diameters. The 45° orientation was associated with the lowest torques, especially at the larger diameters. Female participants had approximately half (45–51%) the torque production capabilities of male participants. The proposed RTLs ranged between 26.4 and 57.6 Nm, depending on the diameter and orientation of the handwheel. Conclusions: To maximize torque production capacity, a large diameter handwheel – as large as 70 cm – in a horizontal orientation (0°) is recommended. Handwheels in a 45° orientation should be avoided because this reduces torque production capabilities. RTLs are proposed to accommodate the torque capacity of a general population.

Strength, endurance and fatigue response of rotator cuff muscles during isometric exertions

Among the shoulder musculoskeletal disorders (MSDs), rotator cuff disorders are prevalent and known to substantially limit an individual's strength and ability to work. Despite the frequency and cost of rotator cuff injuries, very little research has been done on understanding the load response relationship of rotator cuff muscles. Therefore, this study was aimed at evaluating the strength, endurance and fatigue response of rotator cuff muscles. As a first step, strengths of Supraspinatus, Infraspinatus, and Teres Minor were measured for ten healthy male participants using muscle specific Maximum Voluntary Contractions (MVC). Then, endurance time and surface Electromyography (EMG) data were recorded during 15%, 30%, 45%, and 60% MVC exertions. Infraspinatus exhibited the highest strength followed by Teres Minor and Supraspinatus. Despite the strength differences, small variations were observed in the endurance time between the muscles. The effect of %MVC exertions on endurance time, average muscle activity and muscle fatigue were statistically significant. Median frequency decreased and muscle activation increased with an increase in force exertion levels; however, the changes observed for an increase in the exertion level from 15% to 30% MVC were much higher than the changes observed for an increase in the exertion level from 45% to 60% MVC. Relevance to industryResults of this study indicate that the rotator cuff muscles have different strengths but exhibit very similar endurance and fatigue behavior. These findings can assist ergonomic practitioners with the design and/or evaluation of workplace upper extremity exertions to reduce/manage stress on the rotator cuff muscles and shoulder.

Triggering of Acute Coronary Occlusion by Episodes of Vigorous Physical Exertion

There is increasing recognition that heavy exertion can occasionally trigger an acute myocardial infarction (MI), although some uncertainties exist regarding the link. The primary aim of this study was to compare the relative risk (RR) of MI following vigorous exertion between those with confirmed coronary occlusion and those with a non-occluded culprit artery on acute angiography. Secondary aims were to determine if the risk of coronary occlusion is modified by the type of exercise (dynamic or isometric resistance), the frequency of regular exertion or whether the exertion was emotionally charged. Seven hundred sixty-two (762) participants with MI (410 with coronary occlusion TIMI 0,1), and 352 (46%) with a non-occluded culprit artery (TIMI 2,3) completed a questionnaire within 4days of admission, detailing episodes of physical exertion in the 28hours prior to symptom onset and the usual frequency of such exertion. Exertion exposures within 1hour prior to symptom onset were compared to subjects' usual yearly exposure, with case-crossover methodology. The RR of symptom onset following heavy physical exertion level ≥6 (exertion scale 1-8), was higher in those with TIMI 0,1 compared to those with TIMI 2,3 flow (RR 6.30, 95% CI 4.70-8.50 vs 3.93, 2.89-5.30). The increased risk of coronary occlusion following vigorous exertion was observed following both dynamic exertion and isometric resistance, and did not differ between exertion types. The highest risk of coronary occlusion following exertion was observed in those who were sedentary (regular vigorous exertion <1day weekly) (RR=77, 95% CI 46-132), whereas in those who frequently perform regular vigorous physical exertion (>4days weekly), the RR of symptom onset during exertion was significantly lower, RR 2.3 (95% CI 1.5-3.6). There was no significant difference in relative risk based on whether the exertion was reported as emotionally charged. The relative risk that heavy exertion will trigger a non-fatal MI with an occluded artery is greater than for a non-occluded culprit artery. Both dynamic and isometric exertion increase the relative risk of event, while exposure to regular vigorous exertion reduces the relative risk.

Gauging force by tapping tendons

Muscles are the actuators that drive human movement. However, despite many decades of work, we still cannot readily assess the forces that muscles transmit during human movement. Direct measurements of muscle–tendon loads are invasive and modeling approaches require many assumptions. Here, we introduce a non-invasive approach to assess tendon loads by tracking vibrational behavior. We first show that the speed of shear wave propagation in tendon increases with the square root of axial stress. We then introduce a remarkably simple shear wave tensiometer that uses micron-scale taps and skin-mounted accelerometers to track tendon wave speeds in vivo. Tendon wave speeds are shown to modulate in phase with active joint torques during isometric exertions, walking, and running. The capacity to non-invasively assess muscle–tendon loading can provide new insights into the motor control and biomechanics underlying movement, and could lead to enhanced clinical treatment of musculoskeletal injuries and diseases.

Electromyographic investigation of anterior and posterior regions of supraspinatus: a novel approach based on anatomical insights

Supraspinatus is composed of anterior and posterior regions that are distinct. To date, the relative electromyographic (EMG) activity of these regions during different tasks has not been investigated. This work, thus, evaluated activity of the anterior and posterior regions of supraspinatus during isometric actions in different postures. Data were analyzed from 11 healthy participants. Fine-wire electrodes were inserted into the anterior and posterior regions of supraspinatus. EMG activity was recorded during isometric abduction and external rotation exertions against 5% of body weight resistance. Three postures for abduction (30°, 60°, and 90° of humeral abduction, scapular plane) and two for external rotation (0° and 90° humeral abduction) were tested. Each participant’s data were normalized to the peak root mean square (RMS) values for the corresponding region. The RMS of the anterior region was divided by that of the posterior to calculate muscle activation ratios. Non-parametric statistics were used for analyses. The median ratio was lower during external rotation at 90° abduction compared to abduction at 30° (P = 0.003). These results suggest that the two regions of supraspinatus are functionally distinct during isometric tasks. The posterior region may play a more dominant role in postures with higher degrees of abduction and during external rotation exertions.

An Exploratory Electromyography-Based Coactivation Index for the Cervical Spine.

Objective Develop a coactivation index for the neck and test its effectiveness with complex dynamic head motions. Background Studies describing coactivation for the cervical spine are sparse in the literature. Of those in existence, they were either limited to a priori definitions of agonist/antagonist activity that limited the testing to sagittal and lateral planes or consisted of isometric exertions. Multiplanar movements would allow for a more realistic understanding of naturalistic movements in the cervical spine and propensity for neck pain. However, a gap in the literature exists in which a method to describe coactivation during complex dynamic motions does not exist for the cervical spine. Methods An electromyography-based coactivation index was developed for the cervical spine based on previously tested methodology used on the lumbar spine without a high-end model and tested using a series of different postures and speeds. Results Complex motions involving twisting (i.e., flexion and twisting) and higher speed had higher magnitudes of coactivation than uniplanar motions in the sagittal or lateral plane, which was expected. The coupled motion of flexion and twisting showed four to five times higher coactivation than uniplanar (sagittal or lateral) movements. Conclusion The coactivation index developed accommodates multiplanar, naturalistic movements. Testing of the index showed that motions requiring higher degrees of head control had higher effort due to coactivation, which was expected. Application Overall, this coactivation index may be utilized to understand the neuromuscular effort of various tasks in the cervical spine.

An Exploration of the Effects of Cycle Time and Force Variations on Muscle Fatigue during Submaximal Intermittent Isometric Exertions

This study investigated the effects of two intermittent task parameters on muscle fatigue, namely cycle time and force level variation. Of particular interest was whether a constant low-level underlying force would contribute to fatigue. Twelve students participated in four experimental conditions, each lasting 8 minutes. Participants repeatedly performed intermittent isometric exertions of biceps brachii at two cycle times (5 or 10 seconds), and two force levels, varying either between 0% and 50%max isometric force or between 10% and 40%max force. These parameters and a duty cycle of 0.5 ensured a mean force exertion of 25%max for all conditions. Muscle fatigue was inferred from local Ratings of Perceived Exertion (RPE), maximum force and EMG(RMS). Significant (p&lt;0.05) increases in RPE and EMG(RMS), and reductions in maximum force overtime indicate fatigue development during all conditions. Conditions with force levels varying between 10% and 40%max force showed significantly greater RPE and EMG(RMS) recordings, but only marginal reductions in maximum force (p=0.350), compared to conditions with force varying between 0% and 50%max force. Cycle time did not significantly influence fatigue development since no significant changes occurred for RPE, maximum force or EMG(RMS). These results show accelerated fatigue development under conditions with a constant underlying force, despite the lower maximum exertion level, and irrespective of cycle time. Work involving intermittent static force exertions should thus include periods of complete relaxation between exertions to prevent the early onset of muscle fatigue.Keywords: Muscle fatigue, submaximal isometric exertions, intermittent tasks, cycle time, constant underlying force.

Optimized maximum voluntary exertion protocol for normalizing shoulder muscle activity

Muscle activity is typically normalized to maximal activation from isometric maximum voluntary exertions (MVE) in posture and direction specific exertions for each muscle. This is challenging for the shoulder complex due to the large number of muscles. The objective of this investigation was to compare maximum shoulder muscle activity elicited from a multi-muscle MVE test protocol versus individual muscle MVE tests and determine their reliability. Ten healthy males had muscle activity recorded from 12 trunk and upper extremity muscles while performing 3 repetitions of 12 individual and 4 multi-muscle MVEs. Peak surface EMG (sEMG) amplitudes were compared using paired sample t-tests between the two protocols for each muscle. Individual muscle test maximum sEMG amplitudes differed significantly from the multi-muscle test protocol in 3 of 12 muscles (p < 0.05). In muscles that did not attain statistical significance, maximum amplitude differences of 6–15% were found. There was high reliability (Interclass Correlation Coefficient, ICC = 0.831–0.986) and no significant differences between the second and third repetitions of the protocol. Since differences of 6–15% could have functional significance, 8 MVE tests (3 multi-muscle, 5 individual muscle) were selected for future use. Using two repetitions of the reduced MVE protocol will reduce time, risk of pain and injury during experiments.

Multi-directional strength and perceived discomfort of shoulder complex

BACKGROUND: The shoulder complex possesses sufficient strength to exert forces in multiple directions. Little is known about the maximum strength and perceived discomfort while performing multidirectional force exertions using shoulder complex. In this study, maximum strengths and perceived discomf ort was studied for the exertions performed in the six anatomical directions. METHODS: Eight healthy, right-hand dominant, male participants were recruited for the research. A custom-build device was used to measure shoulder strength at Maximum Voluntary Contraction (MVC). The MVC strength was measured in the six anatomical directions: 1) anterior (+X), 2) superior (+Y), 3) lateral (+Z), 4) posterior (-X), 5) inferior (-Y), and 6) medial (-Z). In addition, isometric exertions were performed in the six anatomical directions at 20 N, 40 N, and 60 N force levels and the ratings of perceived discomfort were used to quantify the workload placed on the shoulder. RESULTS: The highest MVC strength was observed in the -Y, +X directions, followed by -X, -Z directions. The lowest MVC strength was observed in the +Y, +Z directions. High discomfort was perceived while performing isometric exertions in +Z and -Z directions. Low discomfort was perceived while performing isometric exertions in +X and -X directions. CONCLUSION: The results of this study conclude that the MVC strength and perceived discomfort for the shoulder complex is direction dependent. The exertions performed in the mediolateral direction impose higher workload on the shoulder complex compared to the other directions.

Investigation of the Differential Contributions of Superficial and Deep Muscles on Cervical Spinal Loads with Changing Head Postures.

Cervical spinal loads are predominately influenced by activities of cervical muscles. However, the coordination between deep and superficial muscles and their influence on the spinal loads is not well understood. This study aims to document the changes of cervical spinal loads and the differential contributions of superficial and deep muscles with varying head postures. Electromyography (EMG) of cervical muscles from seventeen healthy adults were measured during maximal isometric exertions for lateral flexion (at 10°, 20° and terminal position) as well as flexion/extension (at 10°, 20°, 30°, and terminal position) neck postures. An EMG-assisted optimization approach was used to estimate the muscle forces and subsequent spinal loads. The results showed that compressive and anterior-posterior shear loads increased significantly with neck flexion. In particular, deep muscle forces increased significantly with increasing flexion. It was also determined that in all different static head postures, the deep muscle forces were greater than those of the superficial muscle forces, however, such pattern was reversed during peak efforts where greater superficial muscle forces were identified with increasing angle of inclination. In summary, the identification of significantly increased spinal loads associated with increased deep muscle activation during flexion postures, implies higher risks in predisposing the neck to occupationally related disorders. The results also explicitly supported that deep muscles play a greater role in maintaining stable head postures where superficial muscles are responsible for peak exertions and reinforcing the spinal stability at terminal head postures. This study provided quantitative data of normal cervical spinal loads and revealed motor control strategies in coordinating the superficial and deep muscles during physical tasks.

Isometric Thumb Exertion Induces B Cell and T Cell Lymphocytosis in Trained and Untrained Males: Physical Aptitude Determines Response Profiles

Purpose: The present study examined the effect of low-dose thumb exertion on lymphocyte subpopulation trafficking. The potential role of blood lactate in mediating lymphocyte redistribution was also investigated. Methods: 27 male participants (18 weightlifting-trained; 9 untrained) were separated into 3 groups of 9 (Weightlifting and Untrained Experimental: WL EXP , UT EXP ; Weightlifting Placebo: WL PLA ). WL EXP and UT EXP performed 4x60 second isometric thumb intervals separated by 60 second rest intervals in a single-blinded placebo-controlled study. Participants were assessed over a 60 minute post-intervention recovery period for pain, blood lactate and lymphocyte subpopulation counts. Results: WL PLA did not change for any measured variable (p>0.05). The two experimentalgroups increased significantly (p 0.05). No differences in cell count were seen for CD56+/CD16+ lymphocytes across time for any group (p>0.05). UT EXP showed an early significant increase (20 min post-intervention) in CD4+CD3+ (20.78%, p 0.05). Conversely, WL EXP group showed no early increase followed by a delayed increase in cell count evident at the final time-point; CD4+CD3+ (19.06%, p<0.01), CD8+CD3+ (11.46%, p=0.033) and CD19+ (28.87%, p<0.01). Blood lactate was not correlated with lymphocyte counts. Conclusions: Physical aptitude and not cellular energy demand influences the lymphocyte response to resistance-exercise. Keywords: B-Lymphocytes; Exercise; Lactic Acid; Lymphocytosis; Resistance Training; T-Lymphocytes

The Influence of Hand Location and Force Direction on Shoulder Muscular Activity in Females During Nonsagittal Multidirectional Overhead Exertions.

We examined interactions of overhead work location and direction of force application on shoulder muscular activity. Overhead work tasks are common occupational stressors. Previous research has quantified influences of overhead work spatial placement and different force application directions but typically separately or exclusively for tasks done in the median plane. Twenty female participants exerted 40 N of force in six directions (forward/backward, upward/downward, left/right) 150 cm off the floor while seated. An asymmetric pattern of 14 work locations spaced 15 cm centered directly overhead were evaluated. Force direction and work location strongly influenced mean muscle activity (F = 559, p < .01). Interaction effects existed between force direction and hand location in the transverse plane (F = 21, p < .01), with increases as high as 49% in normalized mean muscle activity. Backward exertions produced the highest mean overall muscle activity across hand force directions, exceeding 30% maximum voluntary isometric exertion (MVE) across work locations, with higher activation of anterior deltoid, biceps, infraspinatus, supraspinatus, and upper and lower trapezius. Downward exertions had the lowest mean overall activity, with <10% MVE across work locations. Altered (up to 47%) muscular activity occurred as exertions moved laterally from the origin, and increasingly forward hand positions generally yielded decreased mean overall activity for most force directions. This study provides previously unavailable submaximal shoulder muscular activity data for a wide range of overhead tasks. As such, it enables novel work design considerations that include modifying existing overhead elements to reduce or redistribute associated muscular demands.

Effect of Handwheel Height and Angle on Operators' Torque Production Capabilities

OCCUPATIONAL APPLICATIONSFrom investigating the maximum isometric torque exertions of participants on a handwheel set at different heights and angles, it was determined that torque production capability is greatest when the handwheel is set overhead at 45° and is lowest when overhead at 0°. The mean torque production capacity of the participants was substantially lower than the torque demands in the field and in existing standards. Therefore, maximum recommended torque that accommodates the strength of most of the male population was determined for each handwheel height and angle investigated. The findings of this study may be useful for forming guidelines for handwheel-valve system designs, such as in standardizing the height and angle of a handwheel and defining a maximum recommended torque for handwheel-valve systems.TECHNICAL ABSTRACT Background: Handwheel-valve operation is a common task in many workplaces, including power, chemical, water, and oil industries. Handwheels of various angles and heights are common in a typical plant. The torque required to turn a handwheel differs from one valve to another, and there are no well-established torque standards derived specifically from operators' capabilities. Purpose: The purpose of this research was (1) to determine the effects of handwheel height and angle on torque production and (2) to propose maximum recommended torque limits for valve systems. Methods: Sixty male and female college students participated. Handwheel heights included knee, elbow, shoulder, and overhead levels, while handwheel angles included 0°, 45°, and 90°. At each height–angle combination, maximum isometric torque exertions on a handwheel were measured. These data were used to compute maximum recommended torque limits using the 25th percentile torque strength values of the female participants. Results: The mean maximum torque exertions ranged from 51.6 Nm (overhead at 0°) to 74.9 Nm (overhead at 45°). The height–angle and height–gender interaction effects were statistically significant. Male participants produced significantly greater torques (88.1 Nm) than the female participants (44.7 Nm). The 25th percentile torque strength values ranged between 25.2 and 38.9 Nm, depending on the height and angle of the handwheel. Conclusions: The relationship between torque production and handwheel height depends on the handwheel angle and vice versa. Overall, torque production was greatest when the handwheel was at shoulder or overhead levels, at either 45° or 90°, and lowest when overhead at 0°. The mean torque production capacity of the participants was substantially lower than torque demands in the field and even existing standards (about 40% lower). Maximum recommended torque limits for handwheels that would accommodate most of the male population's strength are proposed.

Identifying and classifying force-generation strategies for one-hand isometric force exertion tasks with bracing availability

Obstructions within a task environment provide opportunities for people to brace themselves with the non-task hand, thigh, or other body part. Previous research has shown that bracing can increase one-hand isometric force-exertion capability in standing tasks. The current laboratory study examined the patterns of force on the bracing surfaces as a function of task and human characteristics. Twenty-two men and women exerted static forces with their right hands. Bracing opportunities were provided at the thigh, contralateral hand, or both. Using the task hand force as a reference, bracing forces were decomposed into opposing and non-opposing components and normalised relative to task hand force magnitude. Five distinct patterns of bracing force, termed force-generation strategies (FGSs), emerged.

The effect of chronic low back pain on trunk accuracy in a multidirectional isometric tracking task.

A cross-sectional study to quantify trunk motor control during multidirectional isometric tracking tasks. To investigate the effect of chronic low back pain (LBP) on trunk neuromuscular performance while participants performed isometric exertions of trunk muscles to track targets in different angles with various magnitudes. Tracking tasks especially in multidirectional activities are among the common research methods to quantify human motor control in different conditions. However, little information is available on trunk motor control during these tasks. There is no study investigating trunk accuracy during multidirectional isometric tracking tasks in patients with LBP. Twelve patients with chronic LBP and 16 asymptomatic participants performed isometric target tracking tasks in 12 different directions with varying magnitude, from 0% to 80% of individual maximum voluntary exertion, in upright standing posture. The tracking system included a moving target object that moved on a straight line in a predefined angle with the rate of 6% maximum voluntary exertion/s. Trunk accuracy was quantified by computing constant error and variable error during each trial. A mixed model repeated measure analysis of variance was conducted to assess statistical analysis. Patients with chronic LBP track the target object with higher error compared with healthy controls across almost all of the target angles (P < 0.01). Trunk accuracy decreased significantly in higher level of exertions (P < 0.01). The results provided additional evidence of a change in trunk control strategies in patients with chronic LBP. Decreased accuracy of trunk during isometric tracking tasks especially in higher levels of asymmetric exertions may explain higher risk of low back injuries in these activities. 4.