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Objective:To observe any dependence of anticipatory postural adjustment (APA) on the difficulty of fine upper limb tasks and to document any effect of reticulospinal tract (RST) facilitation on APAs during such tasks.Methods:The study′s bivariate mixed design involved 4 different tasks and 3 different priming states. Thirteen healthy, male, right-handed subjects were recruited. They were asked to complete the 4 tasks of reaching, grasping a cup, pinching a card using the thumb or using the little finger, respectively for 10 times 1 in response to two different starting cues delivered through an earphone. Half of the trials with each task were initiated with 114dB white noise to startle and activate the reticulospinal tract (RST), while the others were activated with 80dB beeps as a control. Electromyographic signals were recorded from the bilateral sternocleidomastoid (SCM), lower trapezius (LT), latissimus dorsi (LD), lumbar erector spinae and right anterior deltoid muscles and also from the right flexor and extensor carpi radialis muscles (ECR/FCR). In the subsequent processing the electromyographic time domain and frequency domain indicators were converted into a pre-motor reaction time, a time to muscle peak contraction, an activation latency, and APA or compensatory postural adjustment (CPA) amplitude of the tested muscles. These were compared among the different tasks and stimuli. In addition, the 114dB test tasks were classified as two different priming status as SCM + and SCM - according to whether the sternocleidomastoid muscle (SCM) was activated in advance. Results:After RST activation the pre-motor reaction time and the time to peak contraction of all of the muscles were significantly shortened in all of the tasks. The deltoid muscle reaction times in the SCM + , SCM - and control states were (106.89±43.78)ms, (136.78±48.74)ms and (168.60±73.17)ms, respectively, and those differences are significant. The APA amplitudes of the contralateral LT and ipsilateral LD were significantly greater than normal, but the timing of muscle activation onset and the APA/CPA amplitudes of the ECR/FCR were not affected. The latency in the anticipatory muscle activation of the ECR in the little finger grip task was significantly shorter than that in reaching. Conclusions:The extensor carpi radialis show task-specific early activation in fine tasks of the upper limbs with different difficulties. RST activation can lead to early starting of expected actions, accelerate muscle contraction and increase APA amplitude of some trunk muscles, but it has no significant effect on APA/CPA amplitudes in the forearm muscles.
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Objective To explore the effect of acute endurance exercise on the balance control,maximum contraction of the back extensor and the anticipatory postural adjustments(APAs) and compensatory postural adjustments (CPAs) of the lumbar vertebra.Methods Seventeen male students from a police college participated in this study voluntarily.Three tests were performed right before and after the 10000 meters run:the single foot standing test with eyes closed,maximum contraction test of the back extensor and arm-rising test.The maximum voluntary contraction (MVC) of the back extensor and the time of standing with eyes closed were collected.The sEMG activities of lumbar erector spinae(LES) and Lumbar multifidus(LMF) as lumbar stable muscles were recorded.The pre-activation time and integrated EMG of APAs and CPAs were calculated.Results Before and after the 10000 meters run,no significant difference was observed in MVC,but the time of single foot standing decreased significantly.On the condition of the internal postural perturbation,the LES was activated significantly earlier and the APAs IEMG of LMF decreased significantly after the run,but no significant difference was observed in the pre-activation time of LMF and APAs IEMG of LES.The CPAs IEMG of LES and LMF both decreased significantly after the run.Conclusions The acute endurance exercise of 10000 meters run does not cause fatigue of lumbar stable muscles,but it has an effect on the performance of body balance control.It has effects on the postural control strategies of the central nerve system in response to the internal sudden postural perturbation,resulting in the earlier pre-activation of LES to compensate the decreased activation magnitude of LMF.
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PURPOSE: This study was to identify the anticipatory postural adjustment (APA) mechanism which is represented by the onset time of trunk muscles and the displacement of the center of pressure (COP) according to the different base of support (BOS) during upper extremity movement. METHODS: Thirty healthy subjects (14 males, 16 females) participated in this study. The movement was performed for 10 trials during each of various BOS (shoulder - width double leg stance, narrow base double leg stance, tandem stance, non-dominant single leg stance) at the 1.2 Hz frequency. Electromyography was used to measure muscle onset time and biorescue was used to measure characteristics of the displacement of COP. Surface bipolar electrodes were applied over the right deltoid anterior, right latissimus dorsi, both rectus abdominis, both internal oblique and both erector spinae. The data were analyzed by repeated one-way ANOVA and Duncan's post hoc test. RESULTS: The study has revealed following. There were significant differences with muscle onset time in each BOS (p<0.01). There were significant differences in characteristics of the COP in each BOS (p<0.01). CONCLUSION: The study found that the more narrowed the basis requires the more rapid anticipatory postural control in contralateral postural muscle when the upper extremity movement is performed.
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Humans , Male , Electrodes , Electromyography , Healthy Volunteers , Leg , Muscles , Rectus Abdominis , Superficial Back Muscles , Upper ExtremityABSTRACT
Objective To explore the effects of tilted seat surface on front protraction of upper limb and postural adjustment while sitting in children with spastic cerebral palsy. Methods From 2010 to 2014, 15 children with spastic cerebral palsy (patients group) and 15 healthy children (control group) were recruited. They were asked to reach forward sitting on the tilted seat surface with different degrees (-15°, 0°, 15° ) to test the reaction time and movement time. The contraction times of rectus abdominis and back extensors were recorded and ana-lyzed. Results The reaction time and movement time were shorter, and the contraction rates of rectus abdominis and back extensors were lower in the degree with-15° than with 0° and 15° (P0.05), and the movement time was longer in the patients group than in the control group (P<0.001). The contraction rates were higher in the patients group than in the control group. Conclusion Anterior tilted seat surface may improve the front protraction function of upper limb and the postural adjustment in children with cerebral palsy.
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Objective To develop a new visual feedback postural adjusting ability assessing system, and to study its application value. Methods Pressure sensor was used to determine the changes of the body weight center by tracing the pressure variation of the soles and heels, then eight target points in different directions were added into the software interface to enable the subject move his body weight center to the target point intentionally, finally the system was evaluated by loading on back.Results Program design was performed for the testing system. It's proved that posture adjusting ability might decrease with 20% load on back or the body leaning backwards. Conclusion The newly developed visual feedback postural adjusting ability testing system can be used to research standing balance function.
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The purpose of the present study was to determine whetehr differences exist between nine experimental conditions mixing 10°, 40°and 70°of hip joint angles with knee joint angles, when thirteen subjects performed the same response task. In the experiment 1, each subject was asked to stand on the inside two of the four mat switches (500×700 mm) and keep the assigned joint angles during a second of preparatory period. After the period, each subject was asked to respond with a step out on either the right or the left outside mat switch as quickly as possible. Then the data was collected analyzing the whole body choice response time (RESPONSE TIME) defined as the interval time from the signal to respond with step out, the whole body choice reaction time (REACTION TIME) defined as the interval time from the signal to reaction with lifting the leg for responding to the step out, and the movement time (MOVEMENT TIME) defined as the interval time subtracting RESPONSE TIME from REACTION TIME. Moreover, in the experiment 2, the data was collected and analyzed from the onset time of various forces from the two force platforms on which each subject stood instead of the mat switch and EMG which was led from the right side of m. rectus femoris, m, biceps femoris, m. gastrocnemius, m. tibialis anterior and the left side of m. quardriceps femoris, during performance of the response task. The results were as follows:<BR>1. The subjects' posture with each 70°flexion of the hip and the knee joint revealed the shortest RESPONSE TIME, because of the shortened MOVEMNT TIME, compared with the other posture. Conversely, the posture with 70° flexion of the knee joint showed an expanded REACTION TIME.<BR>2. The knee joint angle was an important factor effecting both REACTION TIME and MOVEMENT TIME, rather than the hip joint angle for the task of the experiment, since flexion of the knee joint expanded the REACTION TIME, but shortened the MOVEMENT TIME.<BR>3. The result of the force platform measurements indicated that the posture with each 70°flexion of the hip and the knee joint was shorter than that with each 10°flexion of them at the onset time of the first reaction force after the reaction signal, and that the order of response for the task was beginning at the leg for responding, followed by the other leg for keeping stability.<BR>4. Conclusive evidence for a shortened RESPONSE TIME was found in the facilitation of the central nervous system, which revealed the preliminary muscle activity and the stabilizing of the posture.