• Journal of the Ergonomics Society of Korea
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• v.20 no.2
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• pp.71-82
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• 2001

Twisting posture in lifting tasks has been identified as a risk factor of low back pain. However, it has been usually estimated in terms of compressive stress or muscular activity. Thus, this study was conducted to predict the influence on muscular fatigue during lifting simulation. Fifteen young and healthy subjects were recruited and performed isometric trunk exertions during upright standing, two-level flexions and five-level asymmetric twisting conditions. EMG signals from five primary trunk muscles in right part of body were collected during 20sec for 45 different lifting conditions. RMS(root mean square) and MPF(mean power frequency) parameters were used to analyze the EMG signals. Twisting postures were significant in right erector spinae(ERSR), right latissimus dorsi(LATR), right internal oblique(INOR) for muscular activities. Especially, when trunk was $30^{\circ}$ CCW twisting posture. ERSR and INOR activities increased respectively by 11% and 3%. Regarding the trunk muscle fatigue, we found that MPF shifts in twisting posture increased 2.3 and 2.6 times for ERSR and INOR muscles respectively. Therefore, It is probable for workers to suffer from low back disorders when they were exposed to a extreme twisting posture during prolonged lifting. This study suggests NIOSH(National Institute for Occupational Safety and Health) lifting equation needs the time-duration multiplier in addition to asymmetric multiplier.

• Journal of the Ergonomics Society of Korea
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• v.32 no.3
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• pp.273-278
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• 2013

Objective: This study aims to analyze and evaluate fatigue in upper trapezius muscles of adults when inputting text on a smart phone, thereby examining the risk of cumulative trauma disorders in the musculoskeletal system of the upper extremity. Method: Forty-five healthy adults were divided equally into three groups: a smartphone group, a notebook group, and a desktop group. A surface electromyogram was placed on the upper trapezius muscle of each participant, after which they inputted text for ten minutes within an ergonomic setting; their side posture was recorded on video and analyzed. Results: The spectral edge frequency values for the smartphone group, as recorded from the upper right trapezius muscles on the surface electromyogram, showed a significant decrease(p<.05). Regarding the RULA, all three groups had results indicating "action level 2". Conclusion: All three groups had results indicating "action level 2" according to the RULA, which means that additional research on the posture of the participants while performing tasks is necessary, and their posture needs to be corrected. In particular, the smartphone group has the highest levels of fatigue in the upper trapezius muscles, suggesting that the task of inputting text on a smartphone is a high risk for causing cumulative trauma disorders.

• Journal of International Academy of Physical Therapy Research
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• v.4 no.1
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• pp.516-522
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• 2013

The purpose of this study is to analysis of muscle fatigue in the upper trapezius and splenius capitis muscles according to therapy table height variation. The subjects were consisted of 15 healthy adults(10 males, 5 females) who had no medical history of neurological and musculoskeletal problems. In experiment, wireless electrode EMG system was measured for each the upper trapezius and splenius capitis muscles during the treatment performed on table. the differences in the muscle fatigue was compared for 4 types of table height(-6cm, -3cm, 0, +3cm from elbow in $90^{\circ}$ flexion position). Muscle fatigue according to therapy table height were significant difference except for left upper trapezius. And muscle fatigue of right upper trapezius and splenius capitis showed significant decrease in +3cm table height compared to -6cm table height(p<.05). Muscle fatigue of right upper trapezius and splenius capitis were the highest in -6cm table height, but those were the lowest in +3cm table height. This study propose to change therapy table height higher than +3cm from elbow in $90^{\circ}$ flexion position, if you hope to reduce muscle fatigue.

• International Journal of Contents
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• v.10 no.3
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• pp.90-95
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• 2014

The purpose of this study was to analyze the changes in muscle fatigue by using electromyography (EMG) measurements of the median frequency of shoulder muscles of patients who underwent rotator cuff repair, and to provide basic data for efficient exercise methods during rehabilitation after the repair. In the study, 24 male and 8 female patients who underwent rotator cuff repair performed continuous passive shoulder joint motion for 3 weeks and the median frequency of their shoulder muscles before and after the repair were compared using measurements by EMG. The infraspinatus, supraspinatus, and serratus anterior muscles showed significant differences in the changes in the median frequency before and after the repair. Significant differences were also found in the median frequency of the three muscles both before and after the repair. Additionally, the middle deltoid muscle had a lower median frequency than the supraspinatus muscle before the repair and the infraspinatus muscle had a lower median frequency than the middle deltoid muscle after the repair. It is expected that these results will serve as important data in developing rehabilitation exercise programs for the infraspinatus, supraspinatus, and serratus anterior muscles by compensating the middle deltoid muscle with the lowest muscle fatigue after the rotator cuff repair erase.

• Physical Therapy Korea
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• v.28 no.3
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• pp.215-226
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• 2021

Background: Robot-assisted gait training (RAGT) is an effective method for walking rehabilitation. Additionally, the body weight support (BWS) system reduces muscle fatigue while walking. However, no previous studies have investigated the effects of RAGT with BWS on isokinetic strength of quadriceps and hamstring muscles. Objects: The purpose of this study was to investigate the effects of torque, work, and power on the quadriceps and hamstring muscles during RAGT, using the BWS of three conditions in healthy subjects. The three different BWS conditions were BWS 50%, BWS 20%, and full weight bearing (FWB). Methods: Eleven healthy subjects (7 males and 4 females) participated in this study. The Walkbot_S was used to cause fatigue of the quadriceps and hamstring muscles and the Biodex Systems 4 Pro was used to measure the isokinetic torque, work, and power of them. After RAGT trials of each of the three conditions, the subjects performed isokinetic concentric knee flexion and extension, five at an angular velocity of 60°/s and fifteen at an angular velocity of 180°/s. One-way repeated analysis of variance was used to determine significant differences in all the variables. The least significant difference test was used for post-hoc analysis. Results: On both sides, there were significant differences in peak torque (PT) of knee extension and flexion between the three BWS conditions at an angular velocity of 60°/s and 180°/s conditions. A post-hoc comparison revealed that the PT in the BWS 50% was significantly greater than in the BWS 20% and the FWB and the PT in the BWS 20% was significantly greater than in the FWB. Conclusion: The results of this study suggest that the lower BWS during RAGT seems to lower the isokinetic torque, work, and power of the quadriceps and hamstring muscles because of the muscle fatigue increase.

• Proceedings of the ESK Conference
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• 1997.04a
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• pp.10-16
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• 1997

The ride comfort is one of the most important indices which decide the quality of automotive seats. A subjective evaluation is the general method for comfort evaluation of automotive seats. But the subjective evaluation assess the individual sensibility using questionnaire. Therefore, a need to develop methodologies to obtain objective measurements of the fatigue evaluation is evident. In an effort to monitor muscle activity during driving electromyography (EMG) was employed. In an experimental setting the subjective evaluation was conducted using questionnaire under the static conditions (8 subjects) and the fatigue was induced in muscles using EMG under the dynamic conditions (2 drivers). The resultant EMG signals were then sampled for three different muscles. In test involving 2 subjects of similar size and build, utilizing four different automotive seats, test results support the use of EMG to quantify muscular fatigue as a viable means of objective evaluation for the different automotive seats.

• Proceedings of the KIEE Conference
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• 1998.07b
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• pp.611-613
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• 1998

A structure of musculotendon model with a fatigue profile is investigated. The Hill-type musculotendon model can predicts the decline in muscle force for a given fatigue profile. It consists of nonlinear activation and contraction dynamics based on the physiological concepts. It is normalized for generalization to deal with the various muscles. Muscle force generated by continuous tetanic electrical monophasic pulsewidth modulation stimulation is decreased in time. A fatigue profile is expressed by a function of intramuscular acidification and applied to the relationship between muscle force and shortening velocity in contraction dynamics. The results of computer simulation are well matched with data in a literature which are isometrically performed for knee extension muscles. Also change in optimal fiber length has an effect only on muscle time, constant not on the steady-state tetanic force.

• Journal of the Ergonomics Society of Korea
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• v.24 no.4
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• pp.55-62
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• 2005

This study examined the effect of ergonomic heel rest that was designed for drivers who have physical handicap in the low leg muscles or have to drive prolonged hours with frequent foot pedaling. An experiment was designed to test the ergonomic heel rest with traditional foot pedal. Forty subjects participated in the experiment. Electromyography(EMG) was used to monitor the muscle activity and fatigue of right leg, and Electro-goniometer was used to measure the ranges of motions of the knee and ankle. A simulator of driver's seat was built for the experiment and the heel rest was installed on it. In order to examine the low muscle activity and range of motion, subjects used the foot pedal for 15 minutes repetitively for each experimental condition. Another 15 minutes test without the heel rest was also performed for comparison. The Root Mean Square(RMS) and Mean Power Frequency(MPF) Shift were used to quantify the level of muscle activity and local muscle fatigue. In results, statistically significant decreases of muscle activity and fatigue were found in all the low leg muscles. The range of motion of the knee and ankle joint also decreased when the heel rest was used. The mechanism of the heel rest effect was discussed in this study. This type of heel rest can be applied to real driving situation after ensuring the safety, or overcoming the psychological discomfort possibly due to unfamiliarity.

• Journal of Biosystems Engineering
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• v.29 no.6 s.107
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• pp.531-538
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• 2004

This study examined the muscle fatigue of the erector spinae according to box size during lifting activity. Ten healthy adult man participated in the experiment for lifting the boxes 10 times with 0.2 lift/s frequency. Bilateral surface EMG (Electomyogtamphy) recordings were made regarding M. (Muscle) Longissimus, M. Iliocostal and M, Multifidus activity throughout lifting working. The median frequency in back muscle fatigue was investigated using power spectral analysis of surface EMG. When the box larger than shoulder width was lifted, the muscle fatigue of M, Multifidus was shown larger than one of the other muscles. Accordingly, the result far M. Multifidus can be applied in optimizing design parameter of box. Also, the standard of box width for box makers have to be below about 420 mm, being average shoulder width of adult male.

• Journal of Oral Medicine and Pain
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• v.17 no.1
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• pp.41-50
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• 1992

The authors performed a experimental study to evaluate the effects of masticatory muscle fatigue on tooth contact and masticatory muscle activity in 26 normal healthy women. The experimental masticatory muscle fatigue was induced by unilateral biting of 5kg force on mandibular first molar. The results were as follows : 1. The initial symptom related to muscle fatigue pain appeared in 85.19 seconds of isometric contraction and the endurance time of isometric contraction was 203.15 seconds. 2. The pain occurred more frequently in masseter region than in temporal region. In masseter pain the incidence was almost equal between both sides, whereas the temporal pain was more in contralateral side. 3. The spontaneity and the symmetry of tooth contact during maximum clenching were reduced after isometric unilateral biting. 4. After induction of experimental muscle fatigue, the EMG activities of masseter muscles of both sides and ipsilateral temporal muscle showed the tendency of decreasing activities. 5. The asymmetry indicies of masseter and temporal muscles were reduced after isometric bilateral biting.