ABSTRACT
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.
ABSTRACT
Objective To observe the surface electromyography (sEMG) characteristics of upper limbs during one-finger pushing manipulation under different operating forces, so as to find out the muscle coordination movement pattern for key operating technology. Methods sEMG data of performing one-finger pushing manipulation by the expert, skilled and novice groups were collected. The manipulation force was divided into three different types, namely mild, moderate and severe. The continuous, stable data were adopted for analysis on Myo-Research software. Results Significant differences were found in the upper limb muscle integrated electromyography (iEMG) values (P0.05), with the flexor carpi ulnaris, deltoid, wrist flexors and extensors ranking the top three of iEMG ratio. The expert and skilled groups had the same core muscles in the same movement pattern during their manipulation operation, while the novice group had different core muscles under different forces. There were significant differences in co-contraction ratio among the expert, skilled and novice groups (P<0.01). The novice and expert groups had the highest and lowest co-contraction ratio, respectively, and the co-contraction ratio was gradually decreased with force increasing. During 6-minute manipulation operation, deltoid median frequency(MF) slope of the expert group was declined more slowly than that in the other two groups (P<0.05), which indicated that the expert group were better at resisting to fatigue. Conclusions The expert and skilled groups have the same sEMG characteristics during one-finger pushing manipulation operation with the same core muscles. The movement pattern of upper limb muscles is of regularity. The iEMG ratio, MF slope and co-contraction ratio can be used as reference standard for evaluating the durability, and homogeneity of the manipulation operation and normalization of force application.