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Aaron Derouin and Jim R. Potvin

/(EMG AG  + EMG ANT ) × 100, where EMG AG and EMG ANT refer to agonist and antagonist muscle activations, respectively. Co-contraction was also calculated for the gastrocnemius medialis and vastus lateralis. The statistical analysis for each of the 18 conditions included a calculation of the means and

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James W. Youdas, Hannah E. Baartman, Brian J. Gahlon, Tyler J. Kohnen, Robert J. Sparling and John H. Hollman

from low to high. Of the 16 estimates of torso muscle activation (4 muscles × 4 exercise conditions) in the present study, 11 were classified as moderate recruitment according to DiGiovine classification of muscle recruitment. 15 This finding is consistent with McGill et al’s work, 8 who found

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Deepika Singla and M. Ejaz Hussain

neuromuscular adaptations in the upper body to MBPT in cricket players of different age groups. Overall, the results of the present study showed that 8 weeks of plyometric training can elicit significant neuromuscular adaptations in cricketers from different age groups by improving their muscle activation

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Sean A. Jones, Derek N. Pamukoff, Timothy C. Mauntel, J. Troy Blackburn and Joseph B. Myers

dyskinesis is an alteration of static scapular position and dynamic scapular motion that contribute to a lengthening of the posterior musculature and shortening of the anterior musculature, which may contribute to abnormal muscle activation. 3 Fortunately, scapular dyskinesis and SIS can be effectively

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William P. Berg and Michael R. Hughes

Muscle activation was measured using EMG in 28 males (n = 28) while participants caught visually identical balls of known and unknown weights (50, 1.32, 2.18, and 2.99 kg) under variable (1–10s) and constant (3s) foreperiods. EMG integrals were computed for three time intervals before the catch (anticipatory), and one after (compensatory). Load uncertainty caused the CNS to use an anticipatory strategy characterized by preparation to catch balls of an unknown weight by utilizing about 92% of the muscle activation used to catch the heaviest possible ball under the known weight condition. The CNS appeared to scale anticipatory muscle activation to afford an opportunity to catch a ball of an unknown weight between .50 and 2.99 kg. The constant 3s foreperiod, which permitted temporal anticipation, did not influence the anticipatory neuromotor strategy adopted by the CNS to cope with load uncertainty. Load uncertainty also altered compensatory neuromotor control in catching.

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Thomas S. Buchanan, David G. Lloyd, Kurt Manal and Thor F. Besier

This paper provides an overview of forward dynamic neuromusculoskeletal modeling. The aim of such models is to estimate or predict muscle forces, joint moments, and/or joint kinematics from neural signals. This is a four-step process. In the first step, muscle activation dynamics govern the transformation from the neural signal to a measure of muscle activation—a time varying parameter between 0 and 1. In the second step, muscle contraction dynamics characterize how muscle activations are transformed into muscle forces. The third step requires a model of the musculoskeletal geometry to transform muscle forces to joint moments. Finally, the equations of motion allow joint moments to be transformed into joint movements. Each step involves complex nonlinear relationships. The focus of this paper is on the details involved in the first two steps, since these are the most challenging to the biomechanician. The global process is then explained through applications to the study of predicting isometric elbow moments and dynamic knee kinetics.

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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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David Parsons and Wendy Gilleard

Patellofemoral taping is a technique used in the management of patellofemoral pain that has been shown to alter the pattern of muscle activation onset in symptomatic subjects. It is unknown, however, if this taping technique directly influences the patterns of muscle activity that controls patella position or if its benefits are more related to the effect of pain reduction. The purpose of this study was to investigate the effect of a taping technique on the muscle activation onset of selected quadriceps muscles where pain was not a confounding factor. Thirteen asymptomatic subjects completed a stair ascent and descent task with the right patella untaped and taped for a medial patella glide. Muscle activation onset was determined by computer algorithm from surface EMG of vastus lateralis (VL) and vastus medialis obliquus (VMO). Taping significantly delayed the muscle activation onset of VMO and VL during stair ascent. There was no significant change for stair descent. This effect may be an attempt by the motor control system to counter the mechanical effect of patella perturbation or may be due to cutaneous stimulation affecting threshold or recruitment of motor units.

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Jun G. San Juan, Peter Kosek and Andrew R. Karduna

Subacromial impingement syndrome is the most common shoulder disorder. Abnormal superior translation of the humeral head is believed to be a major cause of this pathology. The first purpose of the study was to examine the effects of suprascapular nerve block on superior translation of the humeral head and scapular upward rotation during dynamic shoulder elevation. The secondary purpose was to assess muscle activation patterns during these motions. Twenty healthy subjects participated in the study. Using fluoroscopy and electromyography, humeral head translation and muscle activation were measured before and after a suprascapular nerve block. The humeral head was superiorly located at 60 degrees of humeral elevation, and the scapula was more upwardly rotated from 30 to 90 degrees of humeral elevation after the block. The differences were observed during midrange of motion. In addition, the deltoid muscle group demonstrated increased muscle activation after the nerve block. The study’s results showed a compensatory increase in humeral head translation, scapular upward rotation, and deltoid muscle activation due to the nerve block. These outcomes suggest that increasing muscular strength and endurance of the supraspinatus and infraspinatus muscles could prevent any increased superior humeral head translation. This may be beneficial in reducing shoulder impingement or rotator cuff tears over time.

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Alan R. Needle, Thomas W. Kaminski, Jochen Baumeister, Jill S. Higginson, William B. Farquhar and C. Buz Swanik

Context:

Rolling sensations at the ankle are common after injury and represent failure in neural regulation of joint stiffness. However, deficits after ankle injury are variable and strategies for optimizing stiffness may differ across patients.

Objective:

To determine if ankle stiffness and muscle activation differ between patients with varying history of ankle injury.

Patients:

Fifty-nine individuals were stratified into healthy (CON, n = 20), functionally unstable (UNS, n = 19), and coper (COP, n = 20) groups.

Main Outcome Measures:

A 20° supination perturbation was applied to the ankle as position and torque were synchronized with activity of tibialis anterior, peroneus longus, and soleus. Subjects were tested with muscles relaxed, while maintaining 30% muscle activation, and while directed to react and resist the perturbation.

Results:

No group differences existed for joint stiffness (F = 0.07, P = .993); however, the UNS group had higher soleus and less tibialis anterior activation than the CON group during passive trials (P < .05). In addition, greater early tibialis anterior activation generally predicted higher stiffness in the CON group (P ≤ .03), but greater soleus activity improved stiffness in the UNS group (P = .03).

Conclusion:

Although previous injury does not affect the ability to stiffen the joint under laboratory conditions, strategies appear to differ. Generally, the COP has decreased muscle activation, whereas the UNS uses greater plantar-flexor activity. The results of this study suggest that clinicians should emphasize correct preparatory muscle activation to improve joint stiffness in injury-rehabilitation efforts.