Correlated EMG Oscillations between Antagonists during Cocontraction in Men

Anti-phase cocontraction practice attenuates in-phase low-frequency oscillations between antagonistic muscles as assessed with phase coherence

Voluntary contraction of skeletal muscles involves common in-phase neural oscillations in low frequencies (around 1-2 Hz) across muscles. The purpose of this study was to determine if anti-phase antagonistic cocontraction practice can attenuate the occurrence of in-phase low-frequency oscillations in antagonistic muscle activity. For this purpose, we determined the probability density function of phase coherence in surface electromyogram (EMG) between antagonistic muscles. Healthy young adults were assigned to one of three intervention groups. They performed an isometric transient and steady cocontraction test with elbow flexors and extensors before and after a session of distinct intervention. In the Cocontraction group, subjects practiced alternating anti-phase isometric cocontraction with the flexors and extensors concurrently. In the Contraction group, subjects practiced alternating isometric contraction levels with flexors or extensors independently. Subjects in the Control group did not perform motor practice. The occurrence of in-phase coherence < 3 Hz during the cocontraction test (including transient and steady portions) was determined from the probability density function of phase coherence in rectified EMG between pairs of elbow flexor and extensor muscles. The change in the probability of in-phase coherence after the intervention period was greatest in the Cocontraction group, followed by Contraction group, and then Control group, on average. The Cocontraction group showed significantly greater reductions than the Control group across the cocontraction test portions. The results suggest that a session of anti-phase cocontraction practice can consistently attenuate the occurrence of in-phase low-frequency oscillations between cocontracting antagonistic muscles across steady and non-steady cocontractions in healthy young adults.

Robotic finger perturbation training improves finger postural steadiness and hand dexterity

The purpose of the study was to understand the effect of robotic finger perturbation training on steadiness in finger posture and hand dexterity in healthy young adults. A mobile robotic finger training system was designed to have the functions of high-speed mechanical response, two degrees of freedom, and adjustable loading amplitude and direction. Healthy young adults were assigned to one of the three groups: random perturbation training (RPT), constant force training (CFT), and control. Subjects in RPT and CFT performed steady posture training with their index finger using the robot in different modes: random force in RPT and constant force in CFT. After the 2-week intervention period, fluctuations of the index finger posture decreased only in RPT during steady position-matching tasks with an inertial load. Purdue pegboard test score improved also in RPT only. The relative change in finger postural fluctuations was negatively correlated with the relative change in the number of completed pegs in the pegboard test in RPT. The results indicate that finger posture training with random mechanical perturbations of varying amplitudes and directions of force is effective in improving finger postural steadiness and hand dexterity in healthy young adults.

Slow Intermuscular Oscillations are Associated with Cocontraction Steadiness

PURPOSE

Voluntary muscle contraction often involves low-frequency correlated neural oscillations across muscles, which may degrade steady cocontraction between antagonistic muscles with distinct levels of activation per each muscle (unbalanced cocontraction). The purposes of the study were 1) to determine whether there is an association between the low-frequency correlated EMG oscillations and the performance of steady unbalanced cocontraction across individuals and 2) to determine whether a bout of out-of-phase cocontraction practice reduces the in-phase low-frequency correlated neural oscillations and improves the performance of steady unbalanced cocontraction.

METHODS

Healthy young adults were divided into three intervention groups: cocontraction, contraction, and control. All participants were tested for unbalanced steady cocontractions with antagonistic muscles about the elbow joint before and after a bout of intervention with the visual feedback of surface EMG. During the intervention period, the cocontraction group practiced an out-of-phase cocontraction, whereas the contraction group practiced agonist contractions.

RESULTS

Mean squared error and variance of EMG amplitude were positively correlated with low-frequency EMG coherence <3 Hz across subjects, which became more prevalent after the intervention period. There was no specific effect of the cocontraction intervention on these variables.

CONCLUSION

These findings suggest that individuals with less low-frequency correlated neural oscillations tend to perform steady cocontraction more skillfully, and the low-frequency correlated oscillations may not be acutely modulated by one bout of out-of-phase cocontraction practice.