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Disentangling Task Influence and Synergist Muscle Contributions to Evaluate Neurophysiological Mechanisms of the Bilateral Deficit Phenomenon

Beethe, Anne (2020) Disentangling Task Influence and Synergist Muscle Contributions to Evaluate Neurophysiological Mechanisms of the Bilateral Deficit Phenomenon. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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The bilateral deficit (BLD) phenomenon is an inability to maximally contract bilaterally compared to the summed unilateral contractions. The mechanism is unknown but presence of bilateral homologous (BH) BLD opposed to bilateral non-homologous (BNH) contractions suggests BLD reflects differences in corticospinal control. Yet the influence of methodological factors such as BLD calculation technique, task familiarity, and differences in synergist muscle contributions have received less attention. Purpose: Examine corticospinal and methodological contributions to BLD to determine its mechanistic basis. Methods: Eleven healthy adults (6 women/5 men, 25.6±3.7years; 171.81±11.44cm; 74.4±21.2kg) participated in a counterbalanced repeated measures study. Sessions one and seven, transcallosal inhibition (TCI) and voluntary activation were assessed with transcranial magnetic stimulation during maximal BH, BNH, and dominant flexion (DF) of the proximal elbow. Sessions two through six, bilateral and unilateral isometric contractions were performed repetitively with electromyographic measures of agonists, antagonists, and scapular stabilizing muscle activity. Results: BH BLD was present sessions 2-7 while BNH displayed no BI. Corticospinal measures did not differ between contractions or sessions. Task practice increased all measures of maximal force, but without translation to BH and BNH BLD performance, with poor reliability across test sessions. BLD varied as a function of task-specific stabilization practices. Specifically, BNH and DF were stabilized by upper extremity horizontal rotation, resulting in greater forces compared to BH, which was stabilized through the sagittal plane. Conclusion: The results of this study indicate BLD reflects subtle differences in muscle stabilization during BH, BNH, and DF contractions, over differences in corticospinal control or task familiarity. Synergistic muscle co-activation during maximal isometric BNH and unilateral contractions likely improves stability, increasing force. The most significant finding of the study, however, is the poor reliability of BH and BNH BLD measures, which raises the need to consider the thresholds used to determine the presence of BLD.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Beethe, Anneabeethe@pitt.eduabeethe0000-0001-7619-3759
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairFlanagan, Shawnsdf29@pitt.edusdf290000-0002-6531-4567
Committee CoChairConnaboy, Chrisconnaboy@pitt.educonnaboy0000-0002-9031-2192
Committee MemberLovalekar, MitaMital@pitt.edumital0000-0002-4536-8656
Committee MemberFisher, Leelef44@pitt.edulef440000-0002-9072-3119
Committee MemberNindl, Bradleybnindl@pitt.edubnindl0000-0001-7088-5930
Date: 19 June 2020
Date Type: Publication
Defense Date: 4 February 2020
Approval Date: 19 June 2020
Submission Date: 27 March 2020
Access Restriction: 2 year -- Restrict access to University of Pittsburgh for a period of 2 years.
Number of Pages: 160
Institution: University of Pittsburgh
Schools and Programs: School of Health and Rehabilitation Sciences > Sports Medicine and Nutrition
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Transcranial Magnetic Stimulation Bilateral Deficit Phenomenon Voluntary Activation Transcallosal Inhibition
Date Deposited: 26 Aug 2020 12:46
Last Modified: 19 Jun 2022 05:15


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