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Akito Miura, Kazutoshi Kudo, Tatsuyuki Ohtsuki, Hiroaki Kanehisa, and Kimitaka Nakazawa

In this study, we investigated muscle cocontraction during a street dance movement task to provide evidence that the level of muscle cocontraction is associated with degree of proficiency in whole-body sensorimotor synchronization movement. Skilled street dancers and nondancers were required to synchronize a knee-bending movement in a standing position to a metronome beat. The dancer group showed significantly smaller variability of temporal deviation (defined as the peak kneeflexion time minus beat onset time), and lower level of muscle cocontraction analyzed by electromyographic data of the agonist and antagonist muscles of the upper and lower leg than did the nondancer group. In addition, multiple regression analyses revealed that the group effect significantly predicted the level of muscle cocontraction. These results show that the level of muscle cocontraction in the lower limbs during whole-body sensorimotor synchronization movement is associated with the degree of proficiency of the movement.

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Andrea Biscarini, Roberto Panichi, Cristina V. Dieni, and Samuele Contemori

Antagonist cocontraction is inherent in natural knee flexion and extension, and serves important physiological functions, such as stabilizing the tibiofemoral joint. 1 , 2 The effects induced by antagonist cocontraction during knee flexion and extension exercises are mainly determined by the line

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Richard E. Hughes, James C. Bean, and Don B. Chaffin

Concurrent activation of muscles on opposite sides of joints is a common phenomenon. In simple planar mechanical systems, it is easy to identify such an electromyographic pattern as co-contraction of agonist and antagonist muscles. In complex 3-D systems such as the lumbar spine, it is more difficult to precisely identify whether EMG recordings represent co-contraction. Qualitative definitions of antagonist muscles emphasize that their actions wholly oppose the action of the prime movers. The qualitative definition of antagonist muscles was used to formulate a mathematical requirement for there to be co-contraction of agonists and antagonists. It was shown that the definition of co-contraction implies muscle activity beyond what is required to maintain equilibrium. The method was illustrated by classifying EMG recordings made of the lumbar region musculature during tasks involving combined torso extension and axial twisting loads. The method, which identified muscle activity in excess of that required to maintain static equilibrium, could be used to identify conditions in which muscle activation is required for something other than merely maintaining moment equilibrium.

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Lindsey K. Lepley, Abbey C. Thomas, Scott G. McLean, and Riann M. Palmieri-Smith


As individuals returning to activity after anterior cruciate ligament reconstruction (ACLr) likely experience fatigue, understanding how fatigue affects knee-muscle activation patterns during sport-like maneuvers is of clinical importance. Fatigue has been suggested to impair neuromuscular control strategies. As a result, fatigue may place ACLr patients at increased risk of developing posttraumatic osteoarthritis (OA).


To determine the effects of fatigue on knee-muscle activity post-ACLr.


Case control.


University laboratory.


12 individuals 7–10 mo post-ACLr (7 male, 5 female; age 22.1 ± 4.7 y; 1.8 ± 0.1 m; mass 77.7 ± 11.9 kg) and 13 controls (4 male, 9 female; age 22.9 ± 4.3 y; 1.7 ± 0.1 m; mass 66.9 ± 9.8 kg).


Fatigue was induced via repetitive sets of double-leg squats (n = 8), which were interspersed with sets of single-leg landings (n = 3), until squats were no longer possible.

Main Outcome Measures:

2 × 2 repeated-measures ANOVA was used to detect the main effects of group (ACLr, control) and fatigue state (prefatigue, postfatigue) on quadriceps:hamstring cocontraction index (Q:H CCI).


All subjects demonstrated higher Q:H CCI at prefatigue compared with postfatigue (F 1,23 = 66.949, P ≤ .001). Q:H CCI did not differ between groups (F 1,23 = 0.599, P = .447).


The results indicate that regardless of fatigue state, ACLr individuals are capable of restoring muscle-activation patterns similar to those in healthy subjects. As a result, excessive muscle cocontraction, which has been hypothesized as a potential mechanism of posttraumatic OA, may not contribute to joint degeneration after ACLr.

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Shinya Fujii, Kazutoshi Kudo, Masahiro Shinya, Tatsuyuki Ohtsuki, and Shingo Oda

This study investigated performance and wrist muscle activity during rapid-repetitive unimanual tapping with a drumstick in right-handed drummers and nondrummers. Analyses of performances revealed no difference in tapping frequency and peak tap force between drummers and nondrummers, although the drummers showed less variability in intertap interval than the nondrummers. Analyses of the electromyographic (EMG) data obtained by recording the activity of the flexor carpi ulnalis and the extensor carpi radialis muscles of the right wrist revealed several distinct differences between the two groups: the drummers showed a lower level of muscle cocontraction together with an earlier decline of wrist flexor muscle activity and a smaller variability of muscle activation time in the wrist flexors compared with the nondrummers. We suggest that these characteristics in wrist muscle activity in the drummers have been acquired following extensive practice for the efficient use of wrist muscles and stable drumming performance.

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Gerald L. Gottlieb

Muscle stress is plainly one of the physical variables that the central nervous system probably wishes to minimize. This criterion does not uniquely define the patterns of muscle activation. It fails to explain the degree of coactivation of muscle antagonists that is widely found, and it cannot explain why two movements or movement segments that follow an identical trajectory driven by identical joint torques can be driven by different patterns of muscle activation. Muscle contraction provides for both net joint torque and limb stability. The minimization of the sum of muscle stresses, raised to any power, is an insufficient rule.

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Jacey Baldridge and Adam C. King

standing depends, in part, on the capacity of the ankle joint muscles to produce adequate torques against expected or unexpected perturbation. One postural response is the simultaneous contraction of agonist and antagonist muscles crossing the joint, commonly referred to as muscle co-contraction, and

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Serkan Uslu and Emel Çetin Özdoğan

with plantar flexion. EMG Signal Processing and Cocontraction Ratio Each epoch was defined as 800 ms before and after kicking the ball. First raw EMG signals band-pass filtered with 20–500 Hz. After that, all signals are rectified and converted to a linear envelope with 40 ms root mean square for

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Alison R. Oates, Aaron Awdhan, Catherine Arnold, Joyce Fung, and Joel L. Lanovaz

added task ( Batistela, Oates, & Moraes, 2018 ), while a reduction may suggest improved control of walking ( Forero & Misiaszek, 2015 ). Integrated EMG (iEMG) values were normalized to walking velocity ( Hof, Elzinga, Grimmius, & Halbertsma, 2002 ). A cocontraction index (CCI) was calculated at the

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Xin He, Hio Teng Leong, On Yue Lau, Michael Tim-Yun Ong, and Patrick Shu-Hang Yung

the muscle activity pattern (onset/time to peak/amplitude/cocontraction) and corresponding phase, normalization method, and main findings were also extracted. The data were analyzed by limb using 2 comparisons: (1) the ACLR limb compared with the contralateral uninjured limb and (2) the ACLR limb