| BACKGROUNDThe trunk bears body balance, load-bearing and other important function, and the core muscle plays an important role in maintaining the stability of the spine. The spinal stabilization system is conceptualized as consisting of three subsystems. The passive musculoskeletal subsystem includes vertebrae, facet articulations, spinal ligaments, intervertebral discs and joint capsules, as well as the passive mechanical properties of the muscles. The active musculoskeletal subsystem consists of the muscles and tendons surrounding the spinal column. The the neural and feedback subsystem consists of the various force and motion transducers, located in ligaments, tendons, and muscles, and the control centers. These passive, active, and neural control subsystems, although conceptually separate, are functionally interdependent. Rotation of the trunk is a common activity of daily living, and was associated with over60%of all back injuries. The torque producing behavior of the spine with increasing velocity of rotation and corresponding EMG is not known. Furthermore, the rate of muscle activity and relationship between torque and EMG in active trunk rotation is not known. This information will be helpful in designing human activities with consideration of the maximal voluntary contraction capabilities in an effort to avoid injury to the back. The current study was designed to address the foregoing issues and could provide a theoretical reference for the different stages of the scientific strength training in the rehabilitation process.Core stability refers in a sporting environment as the ability to control the position and motion of the trunk over the pelvis to allow optimum production, transfer and control of force and motion to the terminal segment in integrated athletic activities. The concept of core muscle raised from the first study of core stability. It can be divided into two groups according to their function and property. First group for the deep musculature that provides intersegmental lumbar vertebral control, such as the multifidi; muscles that increase intra-abdominal pressure to increase lumbar stability and maintain and lumbar area in the neutral zone, such as the transversus abdominis, diaphragm, and pelvic floor, was also known as the local stabilizing muscles. Under the precise neural control, these muscles have been the first line of defense in order to maintain a stable lumbar. The second group for superficial core muscles, were also known as the global stabilizing muscles that control trunk movement and provide co-contraction during activities such as walking and lifting, such as the latissimus dorsi, the rectus abdominis, internal oblique, external oblique, erector spinae, quadratus lumborum and hip muscles, its main function is to control the direction of movement of the spine, and generates a larger operation torque, in order to against the external load applied to the trunk and maintain the posture of the spine, so this second line of defense is to maintain the stabilization of the spine.Isokinetic dynamometer is recognized as the most authoritative strength evaluation method. The term ’isokinetics’ is defined as the dynamic muscular contraction when the velocity of movement is controlled and maintained constant by a special device. It could get the torque curve and multiple parameters that reflecting muscle function, such as torque, torque acceleration energy, power, ratio, work, used to evaluate the stability and strength of the trunk, through computer processing and real-time recording the torque change during movement. Isokinetic provides a new technical method to evaluate the core muscle function. EMG signals is the muscle force source and superposition varieties of muscle motor unit action potential in time and space, reflecting the neuromuscular functional status, and has a wide range of applications. Surface EMG is a noninvasive and has a broad application prospect, coming from human skin through surface electrodes recorded the neuromuscular activity of biological electrical signals, measuring in the participants’ actual movement, providing electronic information of the target muscle, reflecting coordination, muscle activation patterns, fatigue and muscle contraction strength. sEMG is the increasingly sophisticated method to evaluate the core muscle function in recent years. With the development of science and technology, the neuromuscular characteristics of muscle contraction has been started to understand more comprehensively by combining the isokinetic technology with sEMG in application.In recent years, domestic and foreign researchers made the isokinetic and sEMG technology applied in various fields synchronously, to understand more comprehensively on the neuromuscular characteristics. Although there was some study reported on character of related parameters in isokinetic contraction, but it focused on the knee joint injury; there is few reported on isokinetic flexion-extension movement, but isokinetic axial rotation movement has not yet been reported. Therefore, this study explore isokinetic combined with sEMG technology to evaluate core muscle function, and compare related parameters difference in maximum contraction and muscle power efficiency during different velocities; to study the effect of different speed loads within the same ROM on the left or right rotation muscle strength and EMG parameters level, further understanding the neuromuscular characteristics of trunk under different velocities; to provide the theoretical basis and clinical foundation for isokinetic testing and the combination of surface EMG.Objective1. To explore the correlation between the isometric and isokinetic muscle strength of the core muscles during axial rotation.2. To compare the differences of relevant parameters and muscle work efficiency during different angular velocity isokinetic axial rotation.3. To study the effect of different speed loads within the same ROM on the left or right rotation muscle strength and EMG parameters level, further understanding the neuromuscular characteristics of trunk under different velocities.4. To provide the theoretical basis and clinical foundation for isokinetic testing and the combination of surface EMG.MethodsSubjects:The sujects of this study were randomly selected healthy population.38subjects from March2011to December2012in the Department of Rehabilitation, Nanfang Hospital, Southern Medical University, including student, accompany, staff and so on. Inclusive criteria:(1) age20to50years old, male;②weight50-80kg;③No spine, lower limb surgery and trauma history;④No isokinetic contraindications (such as severe high blood pressure, heart disease, the outer periphery vascular diseases, respiratory diseases, etc.).Rejective criteria:①previous chronic low back pain, especially in patients with lumbar disc herniation, whether or exacerbation;②appears in discomfort of the lower back or lower extremity radiating pain during test, or in the above symptoms within2days after the test.Record general information:age, gender, height, weight, occupation, BMI, etc. Experimental procedure:All subjects were completed in speciallized room with the temperature22to26℃, and placed in the Isomed2000Torso Rotation isokinetic dynamometer (D&R, Hemau, Germany) in a seated position with90°of hip and knee flexion. The subjects’ feet were secured in straps to a platform that could be adjusted to produce a consistent hip and knee position. A90°arc of total rotation was set using range of motion stops (45°of right and left rotation). In the current study, three angular velocities were chosen for isokinetic testing, that is,30,60and120°/s. Prior to formal testing, all subjects attended the familiarization session so that they may gain some knowledge of the equipment and testing procedure, thus minimizing the learning effect. Afterwards, Isometric maximum voluntary contraction continues5s at the neutral position,each subject underwent5maximal repetitions at30°/s,10maximal repetitions at60°/s and 15maximal repetitions at120°/s. A60s rest period was used between sets. During the testing protocol, consistent verbal commands and visual feedback were given. All subjects were also instructed to exert maximal effort throughout the whole range of motion. The whole procedure was operated by a well-trained examiner.The surface EMG activities of three pairs of trunk muscles (latissimus dorsi, LD; external oblique, EO; and internal oblique,IO) were recorded using a portable EMG system (ME6000; Mega Electronics Ltd., Finland). Surface Ag/AgCl electrodes (Ag-AgCl, Shenfeng, ShangHai, China) were selected at an interelectrode distance of30mm. The positions to place surface electrodes were determined by palpation of each muscle belly. For details, the electrodes for LD were placed at T12level and along a line connecting the most superior point of the posterior axillary fold and the S2spinous process. The T12level was selected so as to avoid the pressure of the thoracic pad on the electrode. For EO, electrodes were placed just below the rib cage and along a line connecting the most inferior point of the costal margin and the contralateral pubic tubercle. For IO, electrodes were placed1cm medial to the anterior superior iliac spine (ASIS) and beneath a line joining both ASISs. The area surrounding each electrode site was shaved using a disposable razor and disinfected by rubbing the area with alcohol-soaked cotton wool.Record indicators and data processing:Peak Torque (N*m), Time at peak torque (ms), Angle at peak torque (°), PT/BW, Work (J), power (W), and the raw EMG, using MegaWin2.4software further analyzed to obtain the corresponding RMS.STATISTICAL METHODSAll statistical analyses were conducted using SPSS software (SPSS Inc., Chicago, IL). One-way ANOVA was used to compare trunk rotation torque, work, power as well as angle at peak torque (APT) among different velocities. RMS values were compared using two-way ANOVA with repeated measures (muscle×angular velocity). Bonferroni’s post hoc analysis was conducted if the ANOVA showed statistically significant main effects or interaction effects. All data were presented as mean±standard deviations. Statistical significance was set as p<0.05. RESULTS1. Trunk rotation muscle strength between isometric and isokinetic testing showed a significant positive correlation (P<0.01). The established regression equation was y=22.330+0.937x in the left rotation and y=32.752+0.847x in the right rotation. Isometric strength was between30°/s and120°/s isokinetic strength; the left to right rotation moment ratio was close to1:1during isometric at the neutral position, with the speed increasing,the ratio decreased and was0.9618at120°/s. During isokinetic concentric movement, the maximal work was no statistical difference among the different speeds; while power increased with the velocity increasing and showed significantly statistical difference. Angle at PT was showed differences among different velocities; during left rotation,30°/s at-24.81°,6°/s at-31.12°,120°/s at-17.69°; during right rotation30°/s at24.85°,60°/s at31.88°,120°/s at19.00°.2. In isokinetic concentric rotational movement, the maximum RMS value was showed in the contralateral external oblique at30°/s. With increasing movement speed, RMS value decreased, and there was the significantly statistical difference among different velocities (P<0.01), in different muscle (P<0.01), and the interaction effect between speed and muscle (P<0.01). The antagonistic muscles to agonistic muscles ratio increased with the speed increasing, no statistically difference.Conclusions1. During isokinetic concentric movement, the core muscle strength decreased with increasing angular velocity. Isometric strength was between30°/s and120°/s isokinetic strength; the left to right rotation moment ratio was close to1:1during isometric at the neutral position, with the speed increasing,the ratio decreased and was0.9618at120°/s. During isokinetic concentric movement, the maxmial work was no statistical difference among the different speeds; while power increased with the velocity increasing and showed significantly statistical difference. Angle at PT was showed differences among different velocities.2. EMG results showed that the contralateral external oblique, ipsilateral latissimus dorsi and abdominal oblique were responsible for trunk rotation, especially the external oblique muscles. RMS values decreased with the velocity increasing and core muscle had co-activitation phenomenon in isokinetic axial rotation at different angular velocity, which more obvious in fast motion, in order to counteract the active muscle excessive rotation of the trunk, and thereby maintain the stabilizing of trunk.3. Isokinetic exercise acted as one method in improving and increasing muscle strength during resistance training. In the early stages of rehabilitation, we could choose the rapid isokinetic exercise to promote the work efficiency of the muscle, and in strengthening stage, slow speed isokinetic exercise to progress isokinetic training as well as the stage assessment.4. The isokinetic combined with surface EMG technology may have a more comprehensive evaluation the subjects’muscle function and be able to provide the basic data, so that the result of this theory is used in clinical rehabilitation. |
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