• Journal of the Korean Society for Precision Engineering
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• v.26 no.3
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• pp.129-136
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• 2009

The estimation of muscle force is important to understand the roles of the muscles. The static optimization method can be used to figure out the individual muscle forces. However, muscle forces during the movement including muscle co-contraction cannot be considered by the static optimization. In this study, a hybrid static optimization method was introduced to find the well-matched muscle forces with EMG signals under muscle co-contraction conditions. To validate the developed algorithm, the 3D motion analysis and its corresponding inverse dynamics using the musculoskeletal modeling software (SIMM) were performed on heel-rise movements. Results showed that the developed algorithm could estimate the acceptable muscle forces during heel-rise movement. These results imply that a hybrid numerical approach is very useful to obtain the reasonable muscle forces under muscle co-contraction conditions.

• Journal of Biomedical Engineering Research
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• v.29 no.1
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• pp.8-16
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• 2008

The aim of this study was to evaluate the motor recovery in 4 chronic hemiparetic patients with Fugl-Meyer (FM) and EMG characteristics before and after the training program. The training was performed at 1hr/day, 5days/week during 6 weeks in 4 chronic stroke patients. Electromyographic activities of the affected hand were recorded during isometric wrist flexion/ extension movements. In all patients, FM was significantly improved after the 6-week training. Onset/offset delay of muscle contraction significantly decreased in the affected wrist after the training. The co-contraction ratio of flexor/extensor muscles decreased significantly. Also, onset/offset delay of muscle contraction and co-contraction ratio correlates significantly with upper limb motor impairment and motor recovery. This EMG technique allows an objective evaluation of changes in muscle activity in post-stroke patients, providing easily measurable, quantitative indices of muscle characteristics.

• Journal of the Korean Society of Physical Medicine
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• v.14 no.2
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• pp.21-28
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• 2019

PURPOSE: This study was conducted to compare different standing postures with the use of standing aids for lumbar spine posture and muscle activity, and to identify the most desirable standing posture. METHODS: The lumbopelvic angle was assessed based on static radiographic measurement on the sagittal plane. Lumbar lordosis, lumbosacral lordosis, and the intervertebral joint angle at L1/L5 and L5/S1 were measured using radiography in three standing postures (standing on level ground, standing with one foot on a platform, and standing on a sloped surface). In addition, muscle activity was measured using surface electromyography to examine the co-contraction of the lumbar and hip muscles. RESULTS: Lumbar lordosis, lumbosacral lordosis, and L5/S1 intervertebral joint flexion occurred with one foot on the platform. No significant differences were found between standing on a sloped surface and standing on level ground. However, muscle co-contraction was reduced with the use of standing aids. CONCLUSION: This study demonstrated that standing with a foot on a platform induced lumbar lordosis, but that there was no significant difference between standing on a sloped surface and standing on level ground. However, muscle co-contraction was reduced with the use of standing aids. Based on the motor control pattern as a predictor of LBP, the use of standing aids would help workers during prolonged standing.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.246-249
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• 2004

The purpose of this study was to investigate the characteristics between EMG timing of muscle contraction and motor impairment in chronic hemiplegic stroke patients. Delay time and co-contraction of 4 patients who had stroke less than 3 years were measured during isometric wrist flexion and extension along the 3 seconds beep signal. Onset and offset of muscle contraction were significantly delayed on the more affected sides than control sides. Offset was significantly delayed than the onset on the affected sides in wrist flexion. Also, recruitment of antagonist was larger than agonist on the affected sides. Co-contraction ratio on the affected side was significantly smaller than control sides in wrist flexion. In affected sides, Fugl-Meyer motor assessment(FMA) shows the correlation of onset delay in wrist flexion and extension. However, co-contraction ratio correlated with FMA in wrist flexion. EMG assessment is likely to be useful outcome measure and provide insights into mechanism for motor recovery in stroke patients.

• The Korean Journal of Physiology and Pharmacology
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• v.4 no.6
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• pp.479-486
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• 2000

The aim of this study was to clarify the mechanism of the inhibitory action of carbon monoxide (CO) on contraction, by measuring cytosolic $Ca^{2+}$ level $([Ca^{2+}]_i)$ and ionic currents in guinea-pig ileum. CO (10%) inhibited 40 mM KCl-induced contraction and this effect was blocked by ODQ $(1\;{\mu}M),$ a soluble guanylyl cyclase (sGC) inhibitor. CO inhibited the 40 mM KCl-induced contraction without changing $[Ca^{2+}]_i.$ Cumulative addition of KCl induced a graded increase in $[Ca^{2+}]_i$ and muscle tension. In the presence of CO, cumulative addition of KCl induced smaller contraction than in the absence of CO. On the other hand, the increase in $[Ca^{2+}]_i$ induced by cumulative addition of KCl was only slightly decreased in the presence of CO, and the $[Ca^{2+}]_i-tension$ relationship shifted downwards. Using the patch clamp technique with a holding potential of -60 mV, we found that CO had little effect on the peak Ba currents $(I_{Ba})$ when voltage was stepped from -60 mV to 0 mV. In addition, CO showed no effect on the depolarization-activated outward $K^+$ currents in the all potential ranges. We conclude that CO inhibits smooth muscle contraction mainly by decreasing the $Ca^{2+}$ sensitivity of contractile elements via a cGMP-dependent pathway, not by involving L-type $Ca^{2+}$ and outward-potassium currents in guinea-pig ileum.

• Journal of the Korean Society of Physical Medicine
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• v.7 no.3
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• pp.275-282
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• 2012

Purpose : Bridge exercise has been commonly used in clinical rehabilitation settings to improve trunk control, and hip adductor muscles were a related muscle that may affect trunk muscle activation. The aim of this study was to investigate whether the co-contraction of hip adductor muscles may affect trunk muscle activation during bridge exercises. Methods : Thirty-eight healthy young subjects (19 men and 19 women) performed bridge exercises (with and without hip adduction movement). Surface electromyography (EMG) data were collected from the dominant-side internal oblique (IO), rectus abdominis (RA), multifidus (MF) and erect spine (ES) during bridge exercises to compare trunk muscles activation patterns. Result : The EMG activities of IO and RA appeared to be significantly higher during bridge exercise with hip adductor co-contraction than during bridge exercise alone (p<.01), but there were no significant differences in those of MF and ES. Furthermore, there were significant differences in the IO:RA EMG ratio during bridge exercise with hip adductor co-contraction (p<.05). Conclusion : These findings suggest that integration of hip adduction during bridge exercise may be beneficial in increasing deep muscles' activity for trunk stabilization.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.7
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• pp.805-810
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• 2012

Determining of the exercise intensity is very important in terms of induction of low fatigue during exercise. Little information is available on the contraction level of the trunk muscles during whole body tilts with and without axial rotation. This study was to investigate the difference muscle activation level according to axial rotation. Twenty subjects were participated. The muscle activities of the five trunk muscles were bilaterally measured at eight axial rotation angles with 12 tilt angles along $15^{\circ}$ intervals. The results showed that tilt with $45^{\circ}$ axial rotation was more balanced in the same tilt angle and was maintained approximately level of 40% MVC at over $60^{\circ}$ tilt angle with respect to co-contraction of abdominal and back muscle. Lumbar stabilization exercise using whole body tilts would be more effective with axial rotation than without axial rotation in terms of muscle co-contraction.

• The Korean Journal of Physiology
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• v.1 no.1
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• pp.67-72
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• 1967

Present paper is attempted to introduce the phenomenon of 'after contraction' in isolated cardiac-muscle. Papillary muscles were removed from cat right ventricle and were used as a preparation. The muscle strip was Placed in tissue bath which is kept in steady temperature of around $25^{\circ}C$ and was perfuced by Tyrode solution, saturated with 95% $O_2$ and 5% $CO_2.$ under the condition of high calcium (8.2-10.0 mM/l), low sodium (72.4-70.0 mM/l) perfusion with the administration of epinephrine (1-2 mg/l) into tile tissue bath normally triggered muscle contraction was followed by oscillatory, repetitive contractions - after contraction. The phenomenon of after contraction was augumented by decrease in tissue bath temperature and by increase in number of preceding beats and in driving rate. Authors were able to maintain the phenomenon in prominent and steady state giving proper experimental conditions such as fixed bath temperature (ranged from $22^{\circ}C\;to\;27^{\circ}C$), suitable driving rate (20 per minute in average) and perfusion of high calcium, loll sodium and 1-2 mg/l of epinephrine. In some preparations, the strength of after contraction (second contraction) reached up-to 80% of normally triggered contraction and five repetitive contractions were observed as largest number of after contractions. Intracellular action potential measured in the muscle which was beating regulary showing steady after contraction revealed no oscillating after potential in most parts of the muscle but in few cases oscillating changes of after potentials were detectable. In electrogram of the muscle preparation recorded by means of contact electrode prominent, oscillating after potentials were observable when the recorder was set at highest sensitivity. It still is not clear that whether after contraction is the phenomenon which corresponds to those changes in action potential, oscillating after potential, of the muscle preparation. Possible mechanism of the phenomenon of after contraction relating with after potential changes was proposed. Detailed results obtained from further studies on after contraction and concrete discussion on the phenomenon will be reported by authors.

• Physical Therapy Korea
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• v.12 no.1
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• pp.91-99
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• 2005

We assessed whether the use of a symmetrical upper limb motion trainer in daily repetitive training for a 6-week period reduced spasticity and improved motor function in three chronic hemiparetic patients. Upper limb motor impairment and disability were measured by the Fugl-Meyer Assessment (FMA), Modified Ashworth Scale (MAS) and Manual Muscle Test (MMT), respectively. The electromyography (EMG) of the affected hand was recorded during isometric wrist flexion and extension. In all patients, FMA and MMT scores were significantly improved after the 6-week training. However, MAS scores of the affected wrist spasticity did not change considerably. Onset and Offset delays in muscle contraction significantly decreased in the affected wrist. The co-contraction ratio of flexor and extensor muscles significantly increased after the 6-week training. Onset and offset delays of the muscle contraction and co-contraction ratio correlated significantly with the patients' FMA. This study showed that repetitive, symmetric movement training can improve upper limb motor functions and abilities in chronic hemiparetic patients. Also, the EMG assessment of motor response is likely to provide insights into mechanisms and treatment strategies for motor recovery in chronic hemiparetic patients.

• Korean Journal of Applied Biomechanics
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• v.28 no.1
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• pp.37-43
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• 2018

Objective: The aim of this study was to analyze muscle activation of the lower extremities as a function of changes of the center of pressure (CoP) of the foot during squats in order to provide quantitative information to trainers who would like to teach correct movements for developing muscles. Method: Ten men with over three years of weight training experience participated in this study (age: $26.1{\pm}0.8yrs$, height: $171.2{\pm}3.9cm$, body mass: $71.1{\pm}5.7kg$, 60%RM: $84{\pm}9kg$, career: $4.0{\pm}0.7yrs$). The participants were instructed to perform a squat in each of 3 conditions, with different CoP's (the front, middle, and rear of the foot). Results: The position of the CoP showed significant differences according to instructions in both the eccentric and concentric contraction phases (p < .05). The range of movement of the hip and ankle joints showed significant differences corresponding to changes of the CoP position (p < .05). The rectus femoris and gluteus maximus muscle showed significant differences for different CoP positions only in the concentric contraction phase, while the gastrocnemius and anterior tibialis were significantly different in both the concentric and eccentric contraction phase (p < .05). Conclusion: When the target muscle of squat training is the gastrocnemius, the CoP should be located in the front of the foot for effective muscle training. When the target muscles of squat training are the gluteus maximus and quadriceps femoris, the CoP should be located on the rear of the foot.