Study on Neural Co-activation during Human Upper Limb Muscle Fatigue Based on Surface Electromyography / 中国运动医学杂志

Objectives To observe the co-activation phenomenon during exercise fatigue induced by the proximal muscles on the upper limbs.Methods Sixteen undergraduates not majoring in sports participated in this study,and their left arms were chosen as the observed arms and right arms were selected as the weighted arms.The weighted arm was alternatively in the state of relaxation without any load and fatigue after bending and extending elbow joints to uphold a 5 kg dumbbell.However,the observed arm kept weighing a 4 kg dumbbell with 90 degrees elbow flexion until the muscles were exhausted.The surface electromyography of biceps brachii and triceps brachii of the observed arms was measured using the ME6000.And the integrated surface electromyography (IEMG),root of mean square (RMS),mean power frequency (MPF)and median frequency (MF)were further analyzed.Results The IEMG and RMS of biceps brachii and triceps brachii of the observed arms increased gradually after the exercise began (P＜0.05)regardless of in the relaxed state or in the in the state of weighing a 5 kg dumbbell for the weighted arm,but in the state of weighting a 5 kg dumbbell the IEMG and RMS increased more significantly (P＜0.01),Meanwhile the electrical activities of the triceps brachii as an antagonistic muscle were intensively inhibited.The changes of MPF and MF of biceps brachii in the observed arms were more significant in the state of exercise fatigue than in the relaxed state (P＜0.01),but without such an impact on the triceps brachii.Conclusions The fatigue in one arm can trigger contingent changes in sEMG time domain and frequency domain indexes of its contralateral parallel muscles,suggesting that sEMG changes of upper limb proximal muscles have the co-activation effect.

Patterns of Frequency Domain Indexes of Surface Electronic Signals of Adolescent Idiopathic Scoliosis Patients' Paraspinal Muscles / 中国康复理论与实践

@#Objective To investigate the patterns of frequency domain indexes of surface electronic signals of adolescent idiopathic scoliosis (AIS) patients' paraspinal muscles by using surface electromyographic (sEMG) techniques .Methods 25 AIS patients enrolled, 7 males, 18 females, ages range from 11 to 21 years old. All of the enrolled patients undertook the Biering Sorensen test(BST) and the object-lifting test, a Finland made type ME3000P sEMG instrument was applied to record the electronic activities of paraspinal muscles(convex /concave) of all subjects, and the frequency domain indexes: median frequency(MF）,mean power frequency(MPF）, zero crossing rate(ZCR）were analyzed.Results The wave amplitudes and scales of paraspinal muscles electronic frequency domain indexes(MF, MPF, ZCR) were lower than the other tested positions when recorded at the zone of apex vertebrae, and MFslope, MPFslope and ZCRslope all showed a linear degressive tendency as the exercise time was extended.Conclusion Paraspinal muscles at the zone of apex vertebrae have low fatigue durabilities and more likely to be exhausted. sEMG ought to be one of the objective examinations used to evaluate the differences of electronic activities of paraspinal muscles(convex /concave) of AIS patients, and may have a promising value in clinical practice.

Evaluation of voluntary muscle activation and tolerance for fatigue using twitch interpolation technique / 体力科学

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.