• PNF and Movement
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• v.14 no.1
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• pp.49-52
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• 2016

Purpose: The purpose of the present study was to examine the effects of the area of the base of support formed by the human body on the maximal voluntary isometric contraction of upper limb muscles. Methods: The study was conducted with 20 normal adults. To identify changes in the base of support, the maximal voluntary isometric contraction of the biceps muscle was measured in a standing position, a sitting position, and a lying position for each subject. The sizes of the base of support formed in the standing, sitting, and lying positions were set to 1, 2, and 3 respectively, based on the sizes, to analyze the correlations. The maximal voluntary isometric contraction of the biceps muscle was measured using surface electromyograms (EMGs) (Noraxon DTS, Germany). Results: The results showed negative correlations in which, as the size of the base of support increased, the maximal voluntary isometric contraction of the biceps muscle decreased. Conclusion: Changes in the base of support of the body affect the maximal voluntary isometric contraction of the upper limbs. Therefore, when resistance exercises are applied for muscle strengthening, the positions should be changed considering the changes in muscle activity according to those positions. In addition, when EMGs are used to measure the maximal voluntary isometric contraction, the measurements should be conducted in the same positions, considering muscle activity that changes according to the base of support and positions, for data quantification.

• PNF and Movement
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• v.14 no.1
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• pp.59-65
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• 2016

Purpose: The purpose of this study was to review articles in order to establish optimal contraction intensity and duration in the performance of relaxation techniques for maximal increase in range of motion. Methods: The Cochrane, EBSCO, Embase, Medline, ProQuest, PubMed, ScienceDirect, and Scopus databases were used to search articles from 1990 to January 2016. The search terms were "contract relax," "hold relax," "muscle energy technique (MET)," and "proprioceptive neuromuscular facilitation (PNF) stretching." Only experimental human studies (randomized controlled trials) that compared the effects of varying intensity and duration of isometric contraction were included. Non-English language and unpublished studies were excluded. Results: A total of 2,156 articles were initially identified, with only five eventually meeting the inclusion and exclusion criteria. Three studies compared the effects of varying intensity in isometric contraction and two studies compared the effects of varying duration in isometric contraction with regard to range of motion (ROM). Two articles suggested that submaximal voluntary isometric contraction was more effective than maximum voluntary isometric contraction (MVIC) in the improvement of ROM. One article showed that a longer contraction time led to greater increases in ROM. Conclusion: Submaximal voluntary isometric contraction was recommended during contract-relax exercises in healthy people. Lack of evidence makes it difficult to suggest the optimal duration of isometric contraction during relaxation techniques. For future research, high-quality evidence will be needed to establish the optimal contraction intensity for maximum improvement of ROM.

• Journal of the Korean Academy of Clinical Electrophysiology
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• v.3 no.1
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• pp.1-12
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• 2005

This study aimed at examining the maximal isometric contraction caused by voluntary exercise and at comparing its aspects of decrease and restoration in their different repeated application, as to the quadriceps muscles of thigh in the subjects composed of patients with spastic hemiplegia and normal adults. Using isokinetic exercise analyser(Biodex Medical Systems Inc., Biodex System 3PRO, U.S.A.), experiment was conducted as to the normal group composed of fifteen adults and the patient group composed of fifteen patients with spastic hemiplegia. As to each group, MVIC(maximal voluntary isometric contraction) of the quadriceps muscle of thigh caused by voluntary exercise and the aspects of decrease and restoration of the isometric contraction were examined with the method to induce isometric exercise, and their SDI(strength decrement index) and SRI(strength recovery index) were also calculated. The results can be summarized as follows: 1. As for decrease of maximal isometric contraction, both groups showed slow decrease in voluntary exercise, but the normal group showed rapid decrease later phase. 2. As for SDI, no significant differences could be observed in comparison between groups. 3. As for restoration of maximal isometric contraction, both groups showed slow restoration in voluntary exercise, but the normal group showed rapid restoration early phase. 4. As for SRI, comparison between groups showed significant differences in voluntary exercise. These results lead us to the conclusions that spastic muscle is characterized by slow decrease and restoration of MVIC in comparison with normal muscle in voluntary exercise.

• The Journal of Korean Physical Therapy
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• v.18 no.3
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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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• v.24 no.2
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• pp.127-133
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• 2012

Purpose: This study aims to examine the power changes in eletrocenphalogram (EEG) detected from the tibialis anterior muscle, during repetitive contraction exercise in normal female adults. Methods: The subjects of this study were 24 normal adult females, with no musculoskeletal or nervous system disorders. The 24 female subjects were divided into two groups: 12 subjects comprised a voluntary stimulation training group, and the other 12 subjects comprised an electrical stimulation training group. A total of thirty contractions were made repetitively by each woman, with maximal voluntary contraction exercise for six seconds, and a resting time of three seconds. During the experiment, their EEG was measured at eight positions. The eight positions were Fpz, Fz, Cz, CPz, C3, C4, P3, and P4, in accordance with the international 10~20 system. Results: The relative alpha power and beta power showed no statistically significant differences between the two groups. But the relative gamma power of the CPz, C3, C4, P3, and P4 areas showed statistically significant differences between the two groups (p<0.05). The relative theta power of the C4 area showed statistically significant differences between the two groups (p<0.05). Conclusion: Our findings show that tibialis anterior muscle contraction by electrical stimulation and by voluntary repeated contraction differentially affected brain activation. In particular, the CPz, C3, C4, P3 positions of relative gamma power showed brain activation in voluntary contraction. The C4 position of relative theta power showed different brain activation between the two groups.

• PNF and Movement
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• v.1 no.1
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• pp.19-25
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• 2003

Objectives: The purpose of this article is to summarize the effect of stretch stimulus on muscle contraction facilitation. Methods : Some studies of the stretch reflex. ${\gamma}-motor$ system, and the effect of stretch stimulus on muscle activation were reviewed. Results : To facilitate muscle contraction, before the movement is started, the prime mover is in stretched position. The patient must be instructed to occur voluntary muscle contraction after quick stretching. It elicits the functional stretch reflex to produce a more powerful and functional contraction. The intensity of muscle contraction depends on two ways. One is firing rate of ${\alpha}-motor$ neuron by sensory information from the periphery induced in stretched position and stretch reflex. The other is excitation level of the cortical motor area and the corresponding motor neurons. Conclusions: To activate central nervous system and to increase firing rate of ${\alpha}-motor$ neuron. the therapist should apply quick stretch for the patient with stretched position and the patient should make voluntary muscle contraction.

• Korean Journal of Applied Biomechanics
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• v.16 no.3
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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.

• Journal of Korean Physical Therapy Science
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• v.2 no.3
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• pp.587-598
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• 1995

The purpose of this study was to test the microcurrent electrical neuromuscular stimulation on muscle soreness, serum creatine kinase levels and force deficits evident following a high-intensity eccentric exercise bout. 10 volunteer male subjects were randomly assigned to a treatment group or to a control group. Exercise consisted of high-intensity eccentric contractions of the elbow flexors. Resistance was reduced as subjects fatigued, until they reached exhaustion. Muscle soreness rating was determined using a visual analog scale. Serum creatine kinase levels were analyzed using a blood sample. Force deficits were determined by measures of maximal voluntary isometric contraction at $90^{\circ}$ of elbow flexion on a Orthotron II dynamometer. Muscle soreness rating, serum creatine kinase levels and maximal voluntary isometric contraction were determined at the before exercise and again at 24 and 48 hours postexericse. Treatments were applied immediately following exercise. The control group subjects rested following their exercise bout. Statistical analysis showed significant increases in muscle soreness rating and significant decreases in maximal voluntary isometric contraction when the before exercise was compared with 24 and 48 hour measures(p<0.01). No significant effects were observed between groups in muscle soreness rating and maximal voluntary isometric contraction(p>0.05). Highly significants differences in serum creatine kinase levels were found using on Analysis of variance(ANOVA) repeated measures between groups for each time cycles(p<0.001). This modality may have benefits when used early stage in the muscle damage.

• Korean Journal of Applied Biomechanics
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• v.15 no.3
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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.

• Journal of International Academy of Physical Therapy Research
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• v.3 no.2
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• pp.422-428
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• 2012

The present study purposed to examine the effects of transcutaneous electrical nerve stimulation, self-stretching and functional massage on the recovery of muscle contraction force for muscle fatigue caused by sustained isotonic contraction. The subjects of this study were 45 healthy students. They were divided into transcutaneous electrical nerve stimulation group(n=15), self-stretching group(n=15) and functional massage group(n=15), and using Primus RS. We observed the pattern of changes in maximal voluntary isometric contraction force(MVIC) after causing muscle fatigue in quadriceps femoris muscle through sustained isotonic contraction. Maximal voluntary isometric contraction force(MVIC) were greatly increased after transcutaneous electrical nerve stimulation, self-stretching and functional massage. In the comparison of recovery rate of muscle contraction force for muscle fatigue caused by sustained isotonic contraction among the treatment groups, it did not show any significant differences. However, it showed that each treatment may be effective in recovery of muscle fatigue caused by sustained isotonic contraction.