Surface EMG Analysis on Pre-Activation and Co-Contraction of Knee and Ankle Joint in Brush-Knee Twist-Step / 医用生物力学

Objective To analyze muscle pre-activation and surface electromyography (sEMG) characteristics of knee and ankle joints of long-term Tai Chi practitioners during brush-knee twist-step and normal walking, and explore the neuromuscular control strategies of Tai Chi to prevent falls. Methods Vicon motion capture system, Kistler force plate, and Noraxon sEMG system were synchronously used to collect the EMG signals of the rectus femoris, biceps femoris, tibialis anterior muscle, lateral head of gastrocnemius and body posture information during brush-knee twist-step and normal walking. The pre-activation and co-contraction of knee and ankle joints were calculated by integrated EMG of the rectus femoris/biceps femoris, tibial anterior/lateral gastrocnemius muscles. Results Compared with normal walking, the average time of brush-knee twist-step in four phases was significantly increased. There was a significant difference in the percentage of time in four phases. The knee joint co-contraction level and pre-activation level decreased, and the ankle joint co-contraction level and pre-activation level increased. Conclusions Long-term Tai Chi exercises may increase the activation level of the muscles around knee joints and enhance the synergy in muscle groups to help stabilize the joint. The results provide references for rehabilitation assessment and training of neuromuscular control disorders.

Comparison of Muscle Activation and Co-Contraction Patterns for Trunk Muscles During Four-Point Hand-Knee and Hand-Foot Kneeling Positions / 医用生物力学

Objective To analyze the similarities and differences between four-point hand-knee position and hand-foot kneeling positions in trunk muscle activation and co-contraction, explore the possibility of hand-foot kneeling position as core stabilization exercises, so as to provide suggestions for actual training.Methods Nineteen healthy volunteers randomly performed exercises of four-point hand-knee position (4 motions) and hand-foot kneeling position (3 motions), while surface electromyography (sEMG) signals were collected from bilateral rectus abdominis, external oblique, erector spine, and multifidus muscles. The average sEMG and muscle co-contraction index (CCI) based on the sEMG signals were analyzed and compared.Results Significant differences were found in the sEMG and CCI within and between the two positions. Under four-point hand-knee position with the right hand and left leg lifting, the activation of all muscles was higher than that in the starting position. In four-point hand-knee position with the left leg lifting, the activation of ipsilateral multifidus muscle was significantly higher than that in hand-foot kneeling position. The activation degree of external oblique muscle and rectus abdominis was higher in hand-foot kneeling position with right hand lifting. A total of 28 muscle matching methods were obtained by pair-to-pair matching of 8 muscles. The starting posture in four-point hand-knee position fluctuated the least, indicating that the spine was the most stable, while the index of other exercises fluctuated in a larger range.Conclusions The possibility of hand-foot kneeling position as core stabilization exercises was proved from two aspects, namely, muscle activation and CCI. The hand-foot kneeling position and four-point hand-knee position can be used for strengthening abdominal muscles and back muscles, respectively. The four-point hand-knee position with contralateral upper and lower limbs lift is a more advanced exercise for trunk muscles, but sports injuries should be avoided.

Movement pattern and sEMG characteristics of upper limb muscles during one-finger pushing manipulation operation with different forces / 医用生物力学

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.

AGING EFFECTS ON CO-CONTRACTION OF ANKLE MUSCLES DURING VOLUNTARY SWAY TASK / 体力科学

The aim of this study was to compare co-contraction of ankle muscles between older and young adults performing a voluntary sway task, and identify any relationships between co-contraction, balance ability and muscular strength. The task involved displacement of the center of mass backwards and forwards continually during upright stance under three amplitude conditions, large, small and preferred, with sway speeds of slow, medium and fast. The participants comprised 17 older (64.1±2.9 years) and 14 young (21.3±3.3 years) women. Electromyographic recordings were obtained from the tibialis anterior and the medial gastrocnemius muscles during task performance to calculate the co-contraction index (CCI) and evaluate the relative level of co-contraction of antagonist muscle. Additional measurements were obtained from balance tests including body sway tests, functional reach, gait tests, and the EquiTest (Neurocom), and also muscular strength of plantar flexion and dorsiflexion. The CCI was highest under large sway amplitude, but did not differ among sway speeds. The CCI was higher in the older group (23%) than in the young group (15%). Multiple regression analysis revealed that the CCI correlated with body sway in the EquiTest and functional reach, and dorsiflexion strength. Therefore, this study suggested that co-contraction of ankle muscles increased with aging and related to not only static and dynamic balance abilities, but also ankle dorsiflexor strength.

Contribution of co-contraction to arm impedance in the free planar movement / 医用生物力学

Objective Impedance control plays an important role in stability.This paper intends to explore such mechanism through modeling human reaching movement.Method Implemented with revised model,we ap-ply optimal control theory to neuro-muscle-skeleton model to calculate the stiffness ellipses.Result Com-pared with the original model and experimental figures,the model we proposed could overcome the shortage of monotonous changing of the original one and fit the data better.Conclusions So that this paper concludes that co-contraction contributes to impedance control even during free upper limb planar movement.

Contribution of co-contraction to arm impedance in the free planar movement / 医用生物力学

Objective Impedance control plays an important role in stability.This paper intends to explore such mechanism through modeling human reaching movement.Method Implemented with revised model,we ap-ply optimal control theory to neuro-muscle-skeleton model to calculate the stiffness ellipses.Result Com-pared with the original model and experimental figures,the model we proposed could overcome the shortage of monotonous changing of the original one and fit the data better.Conclusions So that this paper concludes that co-contraction contributes to impedance control even during free upper limb planar movement.

Contribution of co-contraction to arm impedance in the free planar movement / 医用生物力学

Objective Impedance control plays an important role in stability.This paper intends to explore such mechanism through modeling human reaching movement.Method Implemented with revised model,we ap-ply optimal control theory to neuro-muscle-skeleton model to calculate the stiffness ellipses.Result Com-pared with the original model and experimental figures,the model we proposed could overcome the shortage of monotonous changing of the original one and fit the data better.Conclusions So that this paper concludes that co-contraction contributes to impedance control even during free upper limb planar movement.

Effect of Dynamic Contractions on sEMG Co-contraction Ratio Taken from Antagonist Muscles of Knee Joint in Stroke Patients at Convalescence Stage / 中国康复理论与实践

@#Objective To observe the influence of dynamic contractions on the sEMG co-contraction ratio taken from the antagonist muscles of the knee joint of stroke patients.Methods 11 stroke patients and 14 healthy subjects were measured the dynamic contractions in both knee flexion and extension with the surface electromyography(sEMG).Results There was no significant differences of the median frequency(MF),mean power frequency(MPF),average EMG(AEMG)and the sEMG co-contraction ratio within the stroke patients and the healthy(P>0.05).There was no significant difference of the MF between the patients compared with the healthy(P>0.05),but the sEMG co-contraction ratio of the MPF increased significantly and that of AEMG decreased significantly(P<0.01).Conclusion The MPF,AEMG and the sEMG co-contraction ratio taken from the stoke patients may reflect the characters of the low limb muscle and the MF may not.

Changes in the Cutaneous Reflex During Co-contraction of the Antagonist Muscles in the Lower Limb / 体力科学

Task-dependent changes in the cutaneous reflex in the upper and lower leg muscles were examined in normal human subjects (n=11) . After instruction, the subjects were asked to selectively contract agonist muscles (SC task) and to co-contract antagonistic muscles (CC task) for the ankle or knee joint while standing. The cutaneous reflex was elicited by applying non-noxious electrical stimulation to the superficial peroneal nerve at the ankle joint (200 Hz, 5 pulses) . The EMG signal was rectified, averaged (n=10), cumulatively summated up to 150ms after the end of the stimulation artifact, and then divided by the time interval for the summation (ACRE<SUB>150</SUB>) . A strong inhibitory effect was determined at a latency of 50 ms and was followed by a facilitatory effect after the electrical stimulation during the SC task in all muscles. In contrast, it was found that the early inhibition and the later facilitation tended to be decreased and increased during the cc task, respectively. A linear regression analysis between the ACRE<SUB>150</SUB> and the background EMG revealed that the regression slopes were significantly decreased during CC task except for the tibialis anterior (TA) and biceps femoris. The reflex ratio (ACRE<SUB>150</SUB>/background EMG) was also negative for the SC task in all muscles tested, but was significantly reduced or showed a positive value for the CC task. These results suggest that the brain may control the cutaneous reflex pathways to enhance the facilitatory effects of the thigh and ankle extensor muscles during the CC task. This reflex action during the CC task may serve to prevent an undesirable fall in the center of gravity in response to a sudden tactile sensation to the dorsal surface of the foot.

A Dynamic EMG Study on Co-contraction of Quadriceps and Hamstrings in Spastic Hemiplegic Gait / 中国康复理论与实践

@#The purpose of this study was to propose a co-contraction profile(CCP)to assess co-con-traction of agonist and antagonist muscles about the knee in spastic hemiplegic gait.Surface EMG wasrecorded from quadriceps and hamstrings of 9 ablet-bodied subjects and 6 spastic hemiplegic subjects follow-ing stroke.Results showed that CCPs were high during weight bearing both in able-bodied subject walkingand in subjects with spastic hemiplegia. However, they were higher in most part of stance phase and lateswing phase in spastic hemiplegics compared to able-bodied subjects (P<0.05).The study concluded thatco-contraction profiles provide descriptive information on the sources of variation in co-contraction,particu-larly in co-contraction in assessment of spastic hemiparetic subjects following stroke.