• 한국운동역학회지
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• 제16권3호
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• pp.75-83
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• 2006

The purpose of this study was to investigate steady-state force depression following active muscle shortening in human tibialis anterior muscle during voluntary contractions. Subjects (n = 7; age $24{\sim}39$ years; 7 males) performed isometric reference contractions and isometric-shortening-isometric contractions, using maximal voluntary effort. Force depression was assessed by comparing the steady-state isometric torque produced following active muscle shortening with the purely isometric reference torque obtained at the corresponding joint angle. In order to test for effects of the shortening conditions on the steady-state force depression, the speed of shortening were changed systematically in a random order but balanced design. Ankle dorsiflexion torque and joint angle were continuously measured using a dynamometer. During voluntary contractions, muscle activation of the tibialis anterior and the medical gastrocnemius was recorded using surface electromyography. Force depression during voluntary contractions, with a constant level of muscle activation, was 12 %, on average over all subjects. Force depression was independent of the speeds of shortening ($13.8{\pm}2.9%$, $10.3{\pm}2.6%$ for 15 and 45 deg/sec over 15 deg of shortening, respectively). The results of this study suggest that steady-state force depression is a basic property of voluntarily-contracting human skeletal muscle and has functional implication to human movements.

• 한국전문물리치료학회지
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• 제23권2호
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• pp.75-83
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• 2016

Background: Several studies have discussed diverse exercise methods considered to be useful for the selective contraction of the vastus medialis oblique (VMO) muscle for the treatment of patellofemoral pain syndrome. Some studies have reported that exercise methods, including hip adduction, in closed kinetic chain exercises are more effective in terms of the muscle activation of the VMO and the timing of the muscle's initial contraction. We focused on isometric contraction during a closed kinetic chain exercise with hip adduction. Objects: The purpose of this study was to examine muscle activation in the VMO and the vastus lateralis (VL) and the onset time difference between their initial contractions via closed kinetic chain isometric quadriceps femoris exercises including hip adduction. Methods: In total, 36 healthy subjects adopted two hip positions during isometric contraction of the quadriceps femoris in a closed kinetic chain exercise (hip neutral and hip adduction position). Statistical analyses were conducted using a paired t-test (${\alpha}=.05$). Results: Isometric contraction of the quadriceps femoris in a closed kinetic chain exercise caused a greater increase in VMO muscle activity in the hip adduction position [$52.68{\pm}22.21$ percentage of maximal voluntary isometric contraction (%MVIC)]than the hip neutral position ($43.43{\pm}19.85%MVIC$). The onset time difference (VL-VMO) decreased more in the hip adduction position ($-82.14{\pm}34.2ms$) than the hip neutral position ($73.94{\pm}2.94ms$). Conclusion: We recommend this exercise as a clinically useful therapeutic method for patients with patellofemoral pain syndrome due to weakening of the VMO muscle and lateral inclination of the patella.

• 대한인간공학회지
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• 제21권2호
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• pp.25-33
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• 2002

The purpose of study is to investigate the relationship between the trunk muscle fatigue and recovery time during repetitive extension by using a surface electromyogram(EMG). Ten healthy subjects particioated in a simulated lifting task with five levels of recovery time and three levels of sub-maximal contraction. EMG signals of the L1(Lumbar 1st Vertebrae) and L3(Lumbar 3rd Vertebrae) level of the erector spinae muscle were recorded. and analyzed in terms of MPF(mean power frequency) parameter to quantify the level of muscle fatigue. It was found that MPF significantly (p<0.05) decreased during repetitive extension task at 50% and 75% sub-maximal contractions. Then it took minutes for the trunk muscle to recover from fatigue during 50% sub-maximal contraction. and it took five minutes during 75% sub-maximal contraction. and it took five minutes during 75% sub-maximal contraction. The recovery time estimated by the maximum force needs to be re-evaluated for the trunk muscle to fully recover from fatigue. In conclusion. the work/rest cycle needs to be studied based upon the information of muscle fatigue in order to prevent workers from musculoskeletal injuries during repetitive lifting task.

• 대한임상전기생리학회지
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• 제2권2호
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• pp.1-12
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• 2004

The purpose of this study was to determine the effect of muscle fatigue by neuromuscular electrical stimulation(NMES). Using Biodex System 3PRO(Biodex Medical Systems Inc, USA), experiment was conducted as to the normal group(I) composed of fifteen adults and the patient group(II) composed of fifteen patients with spastic hemiplegia. As to each group, maximal tolerated intensity(MTI) and maximal tolerated isometric contraction(MTIC) in electric currents yielded by low rate(20 pps) and high rate(100 pps) neuromuscular electrical stimulation and the aspects of decrease and restoration of the isometric contraction were examined, and their strength decrement index(SDI) and strength recovery index(SRI) were also calculated. 1. As for MTI in NMES, the MTI of the group II was higher than that of the group I in both low rate and high rate NMES. In comparison within group, MTI of group II was significantly higher in high rate NMES rather than in low rate NMES(p<0.05). 2. In comparison of MTIC between groups, the group I showed higher in both low rate and high rate NMES. In comparison within group, MTIC of group II was significantly higher in high rate NMES rather than in low rate NMES(p<0.01). 3. As for SDI, both groups showed highest SDI in high rate NMES, but no significant differences could be observed. 4. As for SRI, both groups showed significantly low SRI in low rate NMES(p<0.01, p<0.05), and comparison between groups showed no significant differences could be observed. These result lead us to the conclusion that muscle fatigue was influenced by frequency, high rate NMES was lower at SDI and higher at SRI on compare to low rate NMES, therefor, a further studies concerning electrical stimulation should consider differences each frequency in response to treatment.

• 대한물리치료과학회지
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• 제28권2호
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• pp.19-29
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• 2021

Background: The purpose of this study was to investigate the effects of pulsed-ultrasound intervention and continued-ultrasound on the MVIC (maximal voluntary isometric contraction) and active ROM (range of motion) recovery of before EIMD (exercise-induced muscle damage). Design: Randomized controlled trial. Methods: Thirty subjects who are student in their 20s at a university participated in this study, these subjects were assigned into three groups, a control group (n=10), experiment group I (n=10) and experiment group II (n=10). The subjects in experimental group were intervened by pulsed-ultrasound and continued-ultrasound, while ones on control group weren't by any intervention after induced EIMD. Results: First, In comparison of the MVIC, in the among group comparison, the MVIC of continued-ultrasound group was significantly larger than those of other groups (p<.005). Second, In the among group comparison, the active extension angle of continued-ultrasound group was significantly smaller than those of other groups (p<.005). Third, In the among group comparison, the active flexion angle of continued-ultrasound group was significantly lager than those of other groups (p<.05). Conclusion: The above results revealed that the continued-ultrasound intervention before an exercise had a significantly improve of muscle function after EIMD. Therefore we can consider the continued ultrasound as a considerable intervention method to prevent or reduce an exercise injury.

• 대한임상전기생리학회지
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• 제2권1호
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• pp.49-57
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• 2004

The purpose of this study was to determine the effect of muscle contraction torque and muscle fatigue by low-frequency PC. In this article, We would like to experiment on electrical stimulation, determine optimal forms of stimulation setting. We used normal fourteen subjects(seven women, seven men) without neuromuscular disease and all subjects participated in the 3 session. Torque was measured using a computerized Kin-Com dynamometer for MVIC, MIC, Fatigue tests. The following results were obtained; 1. Torque of man were significantly higher than women in the MIC test(p<.05). 2. Torque of women, man were significantly decreased in the Fatigue test(p<.001). Between woman and man groups were significant difference(p<.05). These results lead us to the conclusion that muscle fatigue was influenced by PC, fatigue of women was higher than man. Therefore, A further studies concerning the electrical stimulation should consider differences between sexes in response to treatment and could enhance the development of the most effective treatment regimens.

• 한국운동역학회지
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• 제15권3호
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• pp.51-59
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• 2005

To examine the influence of aging on the mechanism of muscle fatigue, we compared the magnitude of central and peripheral fatigue in young and old women before, during and after a sustained submaximaI isometric contraction of elbow flexor muscles. Twelve women (6 young. $20.7{\pm}1.2$ years and 6 old, $68.8{\pm}29$ years) performed a contraction at 20% of maximal voluntary contraction (MVC) torque with their non-dominant arm. The old women were weaker than the young women, however their endurance time for the 20% contraction was longer compared with the young women ($1822{\pm}444$ vs. $1061{\pm}678$ sec, P <. 05). Both groups had a similar reduction in voluntary activation ratio (VA) during and after the fatiguing contraction. However, the old women showed much greater variability in VA before and after the contraction ($91.61{\pm}4.54%$ and $76.70{\pm}19.55\;%$ range of $79{\sim}99$ to $87{\sim}99%$ respectively) compared with the young women ($95.71{\pm}1.86\;%$ and $83.46{\pm}7.57\;%$ range of $39{\sim}75$ to $69{\sim}90%$, respectively). Furthermore, the EMG activity of the elbow flexor muscles and triceps brachii was greater for the old women compared with the young women throughout the fatiguing contraction, indicating different activation strategies with age. Indices of peripheral fatigue including twitch properties, showed that fatigue within the muscle was more rapid for the young women compared with the old women. These results suggest that although old women are weaker than young women, they have greater endurance due to mechanisms within muscle. Furthermore, old women showed great variability in their ability to optimally activate all muscle fiber compared with young women for an isometric contraction.

• 한국전문물리치료학회지
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• 제28권2호
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• pp.93-100
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• 2021

Background: Lateral epicondylitis (LE) is the most common chronic musculoskeletal conditions of the upper extremity with pain and wrist extension disability. The tendon which is most affected is the extensor carpi radialis brevis (ECRB). Previous study evaluated the effect of taping technique on patient with LE, but no study investigated the changes of electromyography (EMG) on ECRB when using dynamic taping (DT) technique. Objects: The aim of this study was to investigate the effect of DT technique using dynamic tape on muscle activity of ECRB during wrist isometric extension, isotonic extension and flexion. Methods: Twenty-one healthy subjects volunteered to participate in this study. Subjects were instructed to perform wrist isometric extension, isotonic extension and flexion without and with DT on origin area of ECRB. Wrist isometric extension was performed at 75%, 50% and 25% (%maximal voluntary contraction force), respectively, based on maximum contraction force. Isotonic extension and flexion test used dumbbell. EMG data was collected from ECRB. Results: EMG of ECRB were statistically significant decrease in wrist isotonic extension after DT (p < 0.05). Significant increase in wrist isometric extension during 25% and 50% force task (p < 0.05). Conclusion: This study applied DT technique to suppress the wrist extensor muscles in 21 healthy adults in their twenties. Change in muscle activity was compared in the ECRB muscle during wrist isometric extension, isotonic extension and flexion task. Based on the results of this study, the DT technique applied to the wrist and forearm area can reduce the load on the wrist extensors when the wrist performs various movements during daily life movements or repetitive tasks, and by using these effects, excessive stress is applied to tennis elbow patients.

• The Journal of Korean Physical Therapy
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• 제18권3호
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• pp.37-45
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• 2006

Purpose: This study analyzed changes in spinal neuron and action potential of motor unit depending on voluntary contraction on spinal neuron adaptation. Methods: It selected 80 university students in their twenties and divided into experimental groups of 25% MVIC (I), 50% MVIC (II), 75% MVIC (III) and 100% MVIC (IV) depending on maximum voluntary isometric contraction (MVIC) and performed isometric exercise of plantar flexor muscle to each experimental group with given contraction for 20 times. It measured Mmax, H/Mmax, Hmax latency, V/Mmax, V wave latency before and after exercise, compared method and volume of contraction. Results: H/Mmax ratio showed significant difference in comparison among groups (p<0.01) and there was difference in I and IV groups. V/Mmax ratio showed significant difference in comparison among experimental groups (p<0.05) and there was difference in I and IV groups. When voluntary contraction level was maximum, changes were greatest. However, no significantly difference was to Mmax, H latency and V wave latency. Conclusion: These results suggest that amplitude changes of voluntary contraction level, spinal neuron and supra-spinal neuron had a dose connection that the more contraction level, the better central activation seem to decrease highly for a short time.

• The Journal of Korean Physical Therapy
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• 제19권3호
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• pp.11-17
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• 2007

Purpose: The purpose of this study were to analyze fatigue patterns of the rectus femoris muscle by isometric contraction. Methods: Twenty healthy subjects(10 male, 10 female) participated in this study. Maximal voluntary isometric contraction(MVIC) was measured by the dynamometer. Muscle activity was recorded from the rectus femoris muscle. During the experiment, the subject was seated in the chair. The measured items, median frequency(MDF) and root mean square (RMS), were collected from the surface EMG. All data were analyzed using repeated measures ANOVA. Results: There was significant difference of MVIC between male and female. Endurance time was significant difference by the level of MVIC but no significant in the main effect(sex) and interaction effect. The MDF and fatigue index were significant differences in the interaction effect. The RMS was not significant difference in both of main and interaction effect. The muscle fatigue patterns of female was greater than male after 60% MVIC. Conclusion: This study showed that sex differences of muscle fatigue were started from 60% MVIC.