RESUMO
Angles of the shoulder joint are usually defined in each of the sagittal, coronal, and horizontal planes passing through the center of the shoulder joint. One of the problems with this method is the difficulty of describing some positions of the shoulder joint such as the anterolaterally elevated position. In 2005, the International Society of Biomechanics proposed a recommendation on definitions of joint coordinate systems including the shoulder based on Euler/Cardan angles, which have often been used for the purpose of research on shoulder joint movement in daily activities. With this definition, however, it still remains impossible to define the angle of axial rotation in the hanging down position. Also, Codman's paradox, the phenomenon where the rotation angle of the shoulder changes after motions without axial rotation of the arm, remains unsolved. To solve these problems, a new method to define the angle of shoulder axial rotation, the non-singular method, has been proposed. This review describes the history and the problems of the methods used to define shoulder angles, and presents this new method of definition.
RESUMO
We have developed a method for estimating the depth and intensity of muscular unit represented as equivalent current dipoles by the inverse analysis of surface electromyograms (EMGs) . In this study, the validity of the locations of current dipoles estimated through the inverse analysis was verified by animal experiments. Surface motor unit action potentials (MUAPs) were recorded from the gastrocnemius muscle activated by electrical stimulation at the ventral root of lumbar spinal cord (L4 or L5) of rats. After recording the surface MUAPs for the inverse analysis and glycogen depletion of active muscle fibers by repeated electrical stimulation, periodic acid-Schiff (PAS) staining was used to determine the position of muscle fibers belonging to an active single motor unit. In the results of the inverse analysis, the values of ‘goodness of fit’ between measured and calculated MUAP were 71%, 79% and 85%. Estimated depths of current dipoles ranged from 1.8 mm to 5.9 mm. The locations estimated through the inverse analysis were more medial and shallower than the actual distribution of active muscle fibers determined by PAS staining. These errors were probably caused by the effects of the boundary in the model, the relationship between the measurement area and the location of an active motor unit, and the artifacts such as deformation of the muscle during dissection and freezing.
RESUMO
The purpose of this study was to noninvasively extract information about the size and muscle fiber density of muscular units through the inverse analysis of surface electromyograms. Surface motor unit action potentials (MUAPs) were recorded with a multi-channel electrode array arranged along the circumference direction of the biceps brachii. The depth and intensity of equivalent current dipoles were estimated through the inverse analysis of surface MUAPs. The simulation of inverse analysis of surface potentials generated by the muscular unit models showed that the relationship between the depth and the intensity depends on the muscular unit size and muscle fiber density.<BR>In the simulation, we systematically varied the model parameters including distance from the skin, radius, and fiber density and used the inverse analysis to estimate the depth and intensity of current dipoles. And, our method to estimate the radius and fiber density of muscular units using estimated depth and intensity is demonstrated. Mean values (± SD) estimated from the surface MUAPs were 3.0±1.8mm for depth and 13.8±32.0nAm for intensity. The estimated distance ranged from slightly less than 1 mm to slightly more than 2 mm. The estimated radius ranged from 1.8 to 4.6 mm and fiber density from 0.7 to 5.4 fibers/mm<SUP>2</SUP>.
RESUMO
We evaluated motor unit (MU) fatigue in the first dorsal interosseous muscle (FDI) using the collision principle. Eight healthy men exerted 70% (short-duration fatigue task: SDF task) and 30% (long-duration fatigue task: LDF task) maximum voluntary contraction of isometric abductions in the left FDI until exhausted. Before and after voluntary contractions, the ulnar nerve was stimulated at the wrist and elbow with supramaximal intensity, and a pair of M-waves was obtained. Fatiguerelated changes were studied in mean power frequency (MPF), averaged rectified value (ARV) calculated from surface EMG, and motor nerve conduction velocity (MCV) and distribution of motor nerve conduction velocity (DMCV) calculated from M-waves. The MPF of voluntary EMG decreased, whereas ARV increased significantly during SDF and LDF tasks, indicating fatigue had developed in the FDI. Endurance was significantly shorter in the SDF task than in the LDF task (p<0.01), whereas differences between tasks were not seen in MPF and ARV changes. Tasks did not affect MCV, but lower components in DMCV increased for both tasks. Increased lower components were larger in the LDF task than in the SDF task. The shift in DMCV indicated that fatigued MUs stopped activity and enduring MUs, which had lower axon conduction velocity, were activated selectively. These results suggest that the collision principle is applicable in evaluating motor unit fatigability.
RESUMO
The purpose of this study was to examine the effects of short-term immobilization on the maximum voluntary contraction (MVC) force. The first dorsal interosseus (FDI) of 10 healthy male adults was immobilized for 1 week using casting tape. Atrophy of the muscle was estimated from a cross sectional view of magnetic resonance images (MRI) . To clarify the factors of a peripheral neuromuscular system contributing to the change in the MVC force, twitch force at rest was measured. The contribution of central factors was estimated from a voluntary activation (VA) index, which was obtained by the twitch interpolation method.<BR>The MRI showed no significant changes in the cross sectional area. The MVC force declined after immobilization (p<0.01), and recovered after 1 week from the termination of immobilization (p<0.01) . Both the twitch force at rest and the VA at MVC declined after immobilization (p<0.01), and recovered after 1 week (p<0.05) .<BR>The results indicate that the temporary decline of the MVC force was not accompanied by atrophy of the muscle. Furthermore the decline of the MVC was caused both by the deterioration of peripheral and central functions in the neuromuscular system. Possible factors in the peripheral and central neuromuscular systems affected by the immobilization were discussed.
RESUMO
We studied the mechanism for slowing surface electromyography (EMG) during fatiguing contraction using superimposed M-wave analysis. Seven healthy male subjects exerted 60% maximum voluntary contraction of isometric abductions in the left first dorsal interosseous muscle (FDI) until exhaustion. Simultaneously with voluntary contractions, the ulnar nerve was electrically stimulated at supramaximal intensity, and volitional EMG and superimposed M-waves were obtained. We examined the behavior of muscle fiber conduction velocity (MFCV) and median frequency (MDF) for both EMG, with the following results:<BR>1) MFCV calculated from volitional EMG of FDI was about 6 m/s during 60% MVC.<BR>2) The waveform of voluntary EMG detected from FDI slowed in all subjects during fatiguing contraction at 60% MVC, indicating fatigue had developed in the muscle.<BR>3) As fatigue progressed, the waveform of the superimposed M-wave tended to decrease in amplitude and increase in duration.<BR>4) As fatigue progressed, MDF and MFCV in volitional EMG decreased significantly (p<0.04) . The rate of change was larger in MDF than in MFCV (p<0.01) .<BR>5) As fatigue progressed, MDF and MFCV in the superimposed M-wave decreased significantly (p<0.01) . The rate of change was larger in NIDF than in MFCV (p<0.05) .<BR>These results suggested that MFCV and other peripheral factors affected the slowing of volitional EMG. Elongation of the depolarization zone in muscle fiber is proposed as a peripheral factor.
RESUMO
The purpose of this study is to examine the validity of muscle fatigue evaluation using maximum voluntary torque (MVT), and to identify the dependence of individual's tolerance for fatigue on the capacity to exert MVT. In 14 young male subjects (10 regular exercisers and 4 sedentary), MVT was measured during isometric knee extension, and voluntary activation (VA), which reflects motor unit activation, was evaluated using the twitch interpolation technique. In addition, the maximum endurance time (ET) was measured, and behavior of the mean power frequency (MPF) and the average rectified value (ARV) of surface EMGs from the vastus lateralis muscle were analyzed during constant force isometric contractions of 60% MVT (short-duration fatigue task; SDF task) and 20% MVT (long-duration fatigue task; LDF task) . Correlations were examined among these five variables.<BR>The results were as follows:<BR>1) Subjects were divided into a high voluntary activation group (HVA group) and a low voluntary activation group (LVA group) . Four sedentary subjects were included in the latter group.<BR>2) MVT was significantly larger in the HVA group than in the LVA group (p<0.01) . A significant positive correlation (r=0.72) was found between MVT and VA (p<0.01) .<BR>3) A significant negative correlation (r=-0.71) was found between MVT and endurance time (ET) for the LDF task (p<0.01) . The ET was significantly longer in the LVA group than in the HVA group (p<0.01) .<BR>4) The MPF of voluntary EMG decreased consistently, as ARV increased during isometric contraction in both tasks (p<0.01), indicating the development of fatigue in the muscle. The final change of MPF relative to the initial value was significantly greater in the SDF task than in the LDF task (p<0.05) .<BR>5) A significant correlation (r=-0.83) was seen between the relative change in MPF and ARV in the SDF task (p<0.01) .<BR>6) For the SDF task, the final change of MPF and ARV relative to the initial value was significantly greater in the LVA group than in the HVA group (p<0.05) .<BR>These results indicate that tolerance for local muscle fatigue usually evaluated as maximum endurance time, may depend on individual differences in VA, the VA, in turn, depending on adapta-tion to exercise, and that there appears to exist a corresponding adaptative strategy of the neuromuscular system during fatiguing contractions. Usefulness of our procedure using the twitch interpolation technique in evaluating muscle fatigue was also suggested.