Normative database of response surface method for human trunk extension in isometric mode.

Recent studies show that asymmetric movements are important Low Back Disorders risk factors. Measuring the trunk strength and identifying the coupling effects in different postures can provide an objective tool to assess one's task capacity. This paper estimates the maximum performance capacity for isometric trunk extension and accompanying torques. Thirty males performed maximum voluntary isometric extension in 33 trunk postures on Sharif Lumbar Isometric Strength Tester device. Corresponding moments and angular positions were collected. Second-order full response surface models (RSM) were exploited to formulate the relationship between strengths and three trunk angles. The results of correlation coefficient, percent of standard estimation error and lack of fit reflected the adequacy of models. In conclusion, the main torque was the extension, but at the same time lateral bending and rotation torques were observed. For predicting these three torques in a specific posture and injury prevention, the second order RSM is a useful tool. The presented models can be used in the fields of ergonomics, occupational biomechanics and sport.

Effects of tool grip span, workpiece orientation, moving direction, and working height on two-handed torque strength and subjective measures.

BACKGROUND: Using both hands is regularly needed for force/torque exertions in many activities, especially when using hand tools. OBJECTIVE: To investigate the effects of tool grip span, workpiece orientation, moving direction, and working height on two-handed wrist U/R deviation torque strength, usability, comfort, and discomfort while using locking pliers. METHODS: Participants (n = 22) took part in an experimental study which evaluated the effects of tool grip span (4.5-6.5 cm), workpiece orientation (transverse/sagittal), moving direction (clockwise (CW)/counterclockwise (CCW)), and working height (shoulder/elbow/knuckle) on two-handed wrist U/R deviation torque, (dis)comfort, and usability while using locking pliers. RESULTS: The results showed no significant effect of tool grip span on wrist U/R deviation torque strength, but the locking pliers with 4.5 cm handle grip span led to more comfort and better usability. The two-handed wrist U/R deviation torque strengths were significantly higher in sagittal plane than in transverse plane, and in CW direction than in CCW direction. The highest values of two-handed wrist U/R deviation torque strength in sagittal and transverse planes were exerted in knuckle and elbow heights, respectively. CONCLUSION: The findings can be used to develop guidelines and recommendations with regard to daily and occupational activities which require the use of both hands for force exertion with manual hand tools.

T-shaped handle set-up: effects of handle diameter, between-handle distance, workpiece orientation, working height, and exertion direction on two-handed torque strength, usability, comfort, and discomfort.

The use of both hands is often required for force/torque exertions, particularly when using hand tools. This study investigated the effects of handle diameter (3-5 cm), between-handle distance (0.5-1.5 shoulder span (SS), workpiece orientation (horizontal/frontal), working height (shoulder/elbow/knuckle), and exertion direction (clockwise/counter-clockwise) on maximum two-handed torque strength, usability and comfort/discomfort while using T-shaped handles. Participants (n = 20) performed 36 experimental conditions. The handle diameter had no significant main effect on torque strength. The 3 cm diameter handle was associated with better usability and comfort compared to other options. Higher torque values were recorded with between-handle distance of 1.0 and 1.5 SS, in frontal plane, in shoulder and knuckle heights, and in counter-clockwise direction. The between-handle distance of 1.0 SS had better comfort and higher usability than other conditions. Interactions between the between-handle distance and working height, between-handle distance and workpiece orientation, and workpiece orientation and working height were also significant.Practitioner summary: Effects of handle diameter, between-handle distance, workpiece orientation, working height, and exertion direction on torque exertions, and subjective measures when using T-shaped handles were evaluated. Higher levels of strength were measured with between-handle distance of 1.0-1.5 shoulder span, and in frontal plane, in shoulder/knuckle heights, and in counter-clockwise direction.

Effects of handle characteristics of manual hand tools on maximal torque exertions: a literature review.

The present study was conducted to review the literature on the effects of handle characteristics of manual hand tools including handle diameter, shape and material on forearm supination/pronation, wrist flexion/extension and wrist ulnar/radial deviation torque strengths to assist ergonomists and designers in developing guidelines to improve workstations and hand tool designs. Twenty-seven papers meeting the inclusion criteria were reviewed. The study provides different points that can be applied to improve the design of hand tools with an emphasis on handle diameter, shape and material, and highlights various methodological issues including interactions among variables affecting maximum torque strength, posture, torque exertion using one or two hands, torque exertions in multiple anatomical axes, using gloves, upper extremity anthropometry and test protocols, which should be considered in future research.

Objective assessment of spasticity by pendulum test: a systematic review on methods of implementation and outcome measures.

BACKGROUND: Instrumented pendulum test is an objective and repeatable biomechanical method of assessment for spasticity. However, multitude of sensor technologies and plenty of suggested outcome measures, confuse those interested in implementing this method in practice. Lack of a standard agreement on the definition of experimental setup and outcome measures adds to this ambiguity and causes the results of one study not to be directly attainable by a group that uses a different setup. In this systematic review of studies, we aim to reduce the confusion by providing pros and cons of the available choices, and also by standardizing the definitions. METHODS: A literature search was conducted for the period of 1950 to the end of 2019 on PubMed, Science Direct, Google Scholar and IEEE explore; with keywords of "pendulum test" and "Spasticity". RESULTS: Twenty-eight studies with instrumented pendulum test for assessment of spasticity met the inclusion criteria. All the suggested methods of implementation were compared and advantages and disadvantages were provided for each sensor technology. An exhaustive list categorized outcome measures in three groups of angle-based, angular velocity-based, and angular acceleration-based measures with all different names and definitions. CONCLUSIONS: With the aim of providing standardized methodology with replicable and comparable results, sources of dissimilarity and ambiguity among research strategies were found and explained with the help of graphical representation of pendulum movement stages and corresponding parameters on the angular waveforms. We hope using the provided tables simplify the choices when implementing pendulum test for spasticity evaluation, improve the consistency when reporting the results, and disambiguate inconsistency in the literature.

Effects of human stature and muscle strength on the standing strategies: A computational biomechanical study.

It has been hypothesized that the muscular efforts exerted during standing may be altered by changes in personal factors, such as the body stature and muscular strength. The goal of this work was to assess the contribution of leg muscles using a biomechanical model in different physical conditions and various initial postures. An optimized inverse dynamics model was employed to find the maximum muscular effort in 23,040 postures. The simulation results showed that mid-range knee flexion could help the healthy and strong individuals maintain balance, but those with weaker muscle strength required more knee flexion. Individuals of weak muscular constitution as well as those with tall stature are at the highest risk of imbalance/falling. The number of imbalanced postures due to deficits in the calf and hamstring muscles was reduced by 7.5 times by strengthening the whole body musculature. The calf and the hamstring muscles play a key role in balance regardless of stature.

Myoelectric Activity of Individual Lumbar Erector Spinae Muscles Variation by Differing Seat Pan Depth.

BACKGROUND: The chair influences the position of the user in relation to his or her devices. Prolonged static sitting is a frequently mentioned risk factor for low back pain. Seat design, thus, plays an important role in the study of human sitting. Quantitative information is needed on what happens to body when one sits in chairs with different seat depth. OBJECTIVE: To determine the myoelectric activity (EMG) of individual lumbar erector spinae muscles after sitting in chairs with different seat pan depth. METHODS: EMG recordings were taken using surface electrodes placed on the lumbar erector spine muscles of 25 normal, volunteer subjects. EMG recordings for muscle activity were made while the study participants were in a comfortable position and performed the required tasks. The experiments investigated with 3 seat depths according to the 5th, 50th and 95th percentiles of the buttock popliteal length. The recorded EMG data were normalized to the maximal voluntary contraction. The mean EMG recording was calculated for each of the 3 chairs tested. A mixed model was used to assess the differences among the situations. RESULTS: A significant (p<0.05) difference was observed between the mean EMG recordings for the 3 tested seat pan depths. EMG activity was higher in seats with the 5th and 95th percentiles compared with that for the seat with 50th percentile of buttock popliteal length depth. CONCLUSION: The seat pan depth used during a comfortable position has a significant effect on the level of myoelectric activity in the lumbar erector spinal muscles. The finding of this study may contribute to our understanding of the biomechanics of sitting.

Three-dimensional finite element analysis of the pelvic organ prolapse: A parametric biomechanical modeling.

AIMS: To evaluate the role of soft tissue and ligaments damage and level of pelvic muscles activation versus intra-abdominal pressure, on pelvic organ prolapse. METHODS: This was a computational modeling based on the finite element analysis. Three pelvic muscles, four pelvic ligaments, and three organs (urethra, vagina, and rectum) were simulated. The model was subjected to total 41 472 analysis cases including three intra-abdominal pressures, two damaging levels for the ligaments, three damaging levels for the muscles, and four intentional levels of activation for muscles. RESULTS: Increased intra-abdominal pressures caused significant statistical increase of the pelvic organ prolapse (P = 0.000) up to 10 mm downward. Ligaments' defect had no statistically-significant effect on prolapse of the organs (P = 0.981 for rectum, P = 0.423 for urethra, and P = 0.752 for vagina). Damage in the pelvic floor muscles and low intentional level of activation also deteriorated the prolapse (P = 0.000). CONCLUSION: Increase of the intra-abdominal pressure (IAP) as may be existed during pregnancy or physical activity increased the organ prolapse. Damages of the ligaments caused less effects on the prolapse. Loss of the passive properties of the muscles which is probable after delivery or aging moderately deteriorated the prolapse disorder. However, activation of the pelvic floor muscles prevented the prolapse. Different recruitments of the muscles, specifically the pubococcygeus (PCM), could compensate the possible defects in other tissues. Targeted pelvic floor muscle training (PFMT) could also be effective in older adults due to considerable role of the pelvic muscles' intentional activation.

Initial balance in human standing postures: Roles of the joint mechanisms.

The static initial postures of standing before applying perturbations may affect the maintenance of postural balance. The goal of this article was to find the stable set of postures and then determine the roles of joint mechanisms. The set of posture was defined in a biomechanical model based on three joint angles of the lower limbs. Optimized inverse dynamics method was used to solve for muscle forces in a precise model of the human musculoskeletal system posed in 4096 static sets of posture using AnyBody software. Results showed that the overall body muscular activity in standing is reduced by knee flexion. Moderate knee angles between 20° and 60° provided safer postures against possible perturbations because of higher collaboration levels of the joint mechanisms. About 36% of the overall postural infeasibilities were attributed to the inability of the ankle muscles to more sustain the exerted loads. Although the roles of the joint mechanisms were closely dependent on the postures, there was no direct relation between the joint kinematics and activation levels of their supporting muscles. Lower extremity muscle groups collaborate to maintain the balance in a considerable number of static postures.

The effect of saddle height and saddle position changes from pedal on muscles and joints behaviors in ergometer: A parametric study.

The physical activities such as pedaling can affect the lower limb muscles strength and rehabilitation. Improper pedaling can cause injury. In this study, we would investigate the effects of saddle place (saddle position and saddle height) on the behavior of muscles and joints. Moreover, we would try to reveal the relationship between the muscles activity (Act) and the joints reaction forces (F) and saddle position and saddle height. To this end, the pedaling conditions are obtained from the biomechanical model of the human movement system presented in AnyBody software. The variations in 12 muscles Act and total, normal and shear F of ankle, knee and hip joints are studied for the various saddle places in the pedaling feasible range. The relationships of those muscles Act and joints F are predicted by the response surface method. The results indicate that the muscles and the joints behavior changes for various saddle position and saddle height. The maximum and the minimum of the total response are acquired in the ankle and hip joints, respectively. In contrast to the ankle and hip joints, the knee shear response is greater than the normal response. The predictive models of the muscles Act and the joints F (the regression coefficients (R2) are 0.60-0.95 and 0.76-0.97, respectively) indicate their nonlinear behavior with saddle position and saddle height variations. Studying the muscles and joints behavior in different pedaling condition can be helpful for the suitable saddle placement in order for rehabilitation, muscles soreness reduction, and joints disorder treatment.

Effects of postural and cognitive difficulty levels on the standing of healthy young males on an unstable platform.

Standing on an unstable platform requires continuous effort of the neuro­musculoskeletal system. The aim of the present study is to evaluate the ability to remain standing on an unstable platform at different levels of postural and cognitive difficulty. Healthy young males stood in the sagittal plane on an unstable platform supported by a pair of springs with modifiable stiffness. The balance test also assessed different levels of vision and cognitive function. Linear and nonlinear metrics of standing, based on motion captured kinematic data, were assessed to analyze the stability of standing. Results showed that vision plays a significant role in maintaining balance in terms of linear metrics. Elimination of visual feedback changed the direction of body sway and increased standing instability. Placement of low stiffness springs led to unstable standing. The cognitive dual task, however, had no effect on the stability metrics and merely could be revealed in the simplest test condition. Standing on an unstable platform was closely related to visual feedback and decreasing the spring stiffness significantly reduced stability. The roles of cognitive involvement were subdued by increasing the postural difficulty in standing on an unstable platform.

Effects of visual and cognitive interference on joint contributions in perturbed standing: a temporal and spectral analysis.

Postural balance requires using joint strategies which may be changed from normal conditions by interfering with the sensory information. The goal of the present study was to quantitatively evaluate the role of the joint mechanisms during perturbed stance. Visual and cognitive interference was imposed to sixteen healthy young males under rotational toes-down or up perturbations. Power spectral analysis was employed to distinguish the joint contribution and their in- or out-phase co-works. Results showed that addition of cognitive loads reduce the stability by increasing the center of mass (CoM) power to three times greater. Besides the CoM, the knee and hip powers were also significantly enhanced by the cognitive loads (p < .004), but the ankle was not influenced by cognition involvement (p > .05). Elimination of the vision had lower effect on the time and spectral functions of the knee and hip while the ankle rotations were increased due to the lack of visual feedback (p = .001). The toes-down perturbations resulted in more prominent contribution of the knee while the toes-up evoked the hip joint to keep the balance more than the other joints. Addition of the cognitive loads hindered the reactions of the joint mechanisms and vision caused more conservative responses of the joints.

A new algorithm for ECG interference removal from single channel EMG recording.

This paper presents a new method to remove electrocardiogram (ECG) interference from electromyogram (EMG). This interference occurs during the EMG acquisition from trunk muscles. The proposed algorithm employs progressive image denoising (PID) algorithm and ensembles empirical mode decomposition (EEMD) to remove this type of interference. PID is a very recent method that is being used for denoising digital images mixed with white Gaussian noise. It detects white Gaussian noise by deterministic annealing. To the best of our knowledge, PID has never been used before, in the case of EMG and ECG separation or in other 1D signal denoising applications. We have used it according to this fact that amplitude of the EMG signal can be modeled as white Gaussian noise using a filter with time-variant properties. The proposed algorithm has been compared to the other well-known methods such as HPF, EEMD-ICA, Wavelet-ICA and PID. The results show that the proposed algorithm outperforms the others, on the basis of three evaluation criteria used in this paper: Normalized mean square error, Signal to noise ratio and Pearson correlation.

The relationship between RMS electromyography and thickness change in the skeletal muscles.

The knowledge of muscle function may affect prescribing medications and physical treatments. Recently, ultrasound and electromyography (EMG) have been used to assess the skeletal muscles activity. The relationship between these methods has been reported in numerous articles qualitatively. In this paper, the relationship between EMG root-mean-square (RMS) and ultrasound data of muscle thickness has been investigated using Response Surface Methodology in the muscles separately and together and predictive models reported. Results show that to assess the relationship between the changes of thickness and activity (EMG) in muscles, we can use quadratic model for the rectus femoris, tibialis anterior, transverse abdominal, biceps brachii and brachialis muscles (R2=0.624-0.891) and linear model for the internal and external oblique abdominal, lumbar multifidus and deep cervical flexor muscles (R2=0.348-0.767). Due to the high correlation coefficient for the equations in the bulky muscles, it seems that the correlation between EMG RMS and ultrasound data of muscle thickness on the bulky muscles is higher than the flat muscles. This relationship may depend more on the type of activity than the type of muscle.

Hip joint torques in type II diabetes with and without neuropathy.

BACKGROUND: Patients with diabetes and peripheral neuropathy demonstrate significantly reduced peak torques at the peripheral joints. OBJECTIVES: The aim of this study was to assess isometric and concentric peak torques of the hip joint in people with type II diabetes with and without peripheral neuropathy in comparison with healthy participants. METHODS: 27 patients with type II diabetes including 15 patients without peripheral neuropathy, 12 patients with diabetes and peripheral neuropathy and 15 healthy people participated. Isometric and concentric peak torques of hip flexion, extension, adduction and abduction of the non-dominant leg were measured by motorized dynamometer. RESULTS: Peak and average peak concentric torques of the hip extension and abduction in patients with diabetes and peripheral neuropathy were lower than those patients with diabetes and control group. Angle of extension peak torque was significantly greater in patients with diabetes and peripheral neuropathy compared with other groups. Angle of flexion peak torque was lower in the patients with diabetes and peripheral neuropathy. CONCLUSIONS: Torque related parameters in patients with type II diabetes with or without peripheral neuropathy, are different from healthy subjects. As a result, patients with diabetes especially with peripheral neuropathy are more susceptible of injury and disability in lower limbs.

Influence of unstable footwear on lower leg muscle activity, volume change and subjective discomfort during prolonged standing.

PURPOSE: The present study was an attempt to investigate the effect of unstable footwear on lower leg muscle activity, volume change and subjective discomfort during prolonged standing. METHODS: Ten healthy subjects were recruited to stand for 2 h in three footwear conditions: barefoot, flat-bottomed shoe and unstable shoe. During standing, lower leg discomfort and EMG activity of medial gastrocnemius (MG) and tibialis anterior (TA) muscles were continuously monitored. Changes in lower leg volume over standing time also were measured. RESULTS: Lower leg discomfort rating reduced significantly while subjects standing on unstable shoe compared to the flat-bottomed shoe and barefoot condition. For lower leg volume, less changes also were observed with unstable shoe. The activity level and variation of right MG muscle was greater with unstable shoe compared to the other footwear conditions; however regarding the left MG muscle, significant difference was found between unstable shoe and flat-bottomed shoe only for activity level. Furthermore no significant differences were observed for the activity level and variation of TA muscles (right/left) among all footwear conditions. CONCLUSIONS: The findings suggested that prolonged standing with unstable footwear produces changes in lower leg muscles activity and leads to less volume changes. Perceived discomfort also was lower for this type of footwear and this might mean that unstable footwear can be used as ergonomic solution for employees whose work requires prolonged standing.

Anti-fatigue mats, low back pain, and electromyography: An interventional study.

OBJECTIVES: Increasing bilateral gluteus medius co-activation has been identified as one of the most important factors in developing low back pain due to prolonged standing in healthy people. This study aims to investigate the impact of an anti-fatigue mat on the bilateral gluteus medius co-activation pattern and to report the low back pain subjectively in 2 different standing positions on the normal rigid surface and on the anti-fatigue mat. MATERIAL AND METHODS: While carrying out an easy simulated profession, 16 participants who had no low back pain background were requested to stand for 2 h in each position, with and without using the anti-fatigue floor mat, respectively. At the beginning of standing process and at every 15 min until the time of 120 min lapses, electric activities for the bilateral gluteus medius co-activation and subjective pain level in low back area were collected by the surface electromyogeraphy (EMG) and the visual analogue scale (VAS), respectively in each position. RESULTS: The obtained findings revealed that the anti-fatigue mat significantly decreased subjective pain level in low back area among 15 participants (p < 0.05). However, there was objectively no significant difference in the bilateral gluteus medius co-activation pattern among the participants between the position 1 and the position 2 (p > 0.05). The findings obtained under this study related to the impact of the anti-fatigue mat upon the low back pain based on the increase of > 10 mm on the VAS threshold, which showed that this intervention had no significant impact upon decreasing the number of patients suffering from the low back pain and also minimizing the bilateral gluteus medius co-activation in both pain developer groups (p > 0.05). However, 73% of the participants preferred to apply it. CONCLUSIONS: It seems that the anti-fatigue mat may be useful in reducing the low back pain although it objectively didn't significantly change the gluteus medius co-activation pattern related to the low back pain.

Similarity of different lifting techniques in trunk muscular synergies.

Lifting is known to be a major reason for musculoskeletal injuries. In this way, lifting has a crucial effect on human musculoskeletal system and intensity of this impact depends slightly on the selection of techniques. Underlying mechanisms by which trunk muscles are executed during performing lifting are central to biomechanical study of lifting techniques. In the current study, the trunk muscular control mechanisms of lifting are investigated using the synergetic control analysis. Non-negative matrix factorization has been used to extract trunk muscles synergies from their activities - which are computed by a previously validated musculoskeletal model - during different lifting techniques aimed to investigate motor control strategies. Three lifting techniques are considered; stoop, squat and semi-squat. Three synergies account for variety among muscle activation of trunk muscles with related VAF (Variability Account For) of over 95%. Trunk muscle synergy weightings and related time-varying coefficients are calculated for each kind of lifting techniques considering three synergies. Paired correlation coefficients between muscle synergies are all greater than 0.91 (P < 0.05) suggesting that trunk muscle synergies are similar for examined techniques in spite of their kinematic diversity. This similarity can be a result of their common ultimate goal. The acquired results also elucidate the mechanisms of muscle activation patterns that can be exploited in future studies and ergonomic interventions.

Musculoskeletal modeling and simulation of three various Sit-to-Stand strategies: An evaluation of the biomechanical effects of the chair-rise strategy modification.

BACKGROUND: The human chair-rise ability reduces according to various factors such as; Age, Incidents, diseases and etc. The Sit-to-Stand (STS) movement strategy modification is a way chosen to compensate the STS inabilities. OBJECTIVE: Musculoskeletal evaluation of the effects of standing up strategy modification is beneficial for correct selection. The aim of this study is to compute, compare, and classify the biomechanical effects of each STS movement strategy. METHODS: A full-body human who stands up from seat with three various strategies are modeled and simulated with commercial musculoskeletal simulation software, AnyBody (Anybody Technology, Aalborg, Denmark). A specific algorithm is employed to compute time-histories of the reaction forces between body and seat. RESULTS: Time-histories of joint moments, joint loads and muscles forces are computed and compared between strategies. Two statistical analyses (Pearson product-moment correlation and paired-samples t-test) are also employed to compare the effects of strategy modification in various aspects. The major finding is that the body joints and muscles reactions to strategy modification are different or even antithetical to each other. CONCLUSION: A table is derived which depicts the sequences of the body joints and muscles affected from strategy modification from the most to the least. This table could be practical for therapists, physicians, and rehabilitation devices experts.

Validation of a musculoskeletal model of lifting and its application for biomechanical evaluation of lifting techniques.

BACKGROUND: Lifting methods, including standing stance and techniques have wide effects on spine loading and stability. Previous studies explored lifting techniques in many biomechanical terms and documented changes in muscular and postural response of body as a function of techniques .However, the impact of standing stance and lifting technique on human musculoskeletal had not been investigated concurrently. METHODS: A whole body musculoskeletal model of lifting had been built in order to evaluate standing stance impact on muscle activation patterns and spine loading during each distinctive lifting technique. Verified model had been used in different stances width during squat, stoop and semi-squat lifting for examining the effect of standing stance on each lifting technique. RESULTS: The model muscle's activity was validated by experimental muscle EMGs resulting in Pearson's coefficients of greater than 0.8. Results from analytical analyses show that the effect of stance width on biomechanical parameters consists in the lifting technique, depending on what kind of standing stance was used. CONCLUSIONS: Standing stance in each distinctive lifting technique exhibit positive and negative aspects and it can't be recommended either one as being better in terms of biomechanical parameters.