An Investigation of the Effects of Frontal Plane Glenohumeral Joint Angle, Scapular Mobility and Lower-Back Orientation of the Horizontal Bench Press on Electromyographic Activity of Four Muscles for Male Subjects

Authors: Miguel Jagessar

Corresponding Author:
34 Zebrina Drive
Roystonia, Couva
Trinidad, West Indies
miguel.jagessar@gmail.com
868-784-5110

Dr. Miguel Jagessar is currently an Assistant Professor at The University of Trinidad and Tobago and Discipline Coordinator of the BASc/MEng Utilities Engineering Programme

An Investigation of the Effects of Frontal Plane Glenohumeral Joint Angle, Scapular Mobility and Lower-Back Orientation of the Horizontal Bench Press on Electromyographic Activity of Four Muscles for Male Subjects.

ABSTRACT
The purpose of this study was to determine the effects of frontal plane glenohumeral joint abduction (GHJA), scapular mobility and lower-back orientation of the horizontal bench press (HBP) on electromyographic activity of the upper clavicular and lower sternocostal heads of the pectoralis major (UCPM and LSPM), anterior deltoid (AD) and lateral head of triceps brachii (TB). Fourteen male subjects, with at least two years weight-training experience, volunteered for this study and signed informed consent forms prior to testing. Filtered EMG signals were full-wave rectified, integrated, and time normalized (EMG activity/time taken for concentric phase of lift) and expressed as a percentage of maximum mean integrated EMG (%MmIEMG) for each muscle. Repeated-measures ANOVA recorded overall differences in %MmIEMG between six exercise positions for each muscle with α level of 0.05. No significant differences in EMG activity were found in frontal plane GHJA, scapular mobility or lower-back position for anisometric measurements of the UCPM and LSPM and the lateral head of triceps brachii. Significant difference in EMG activity of the anterior deltoid was found for change in frontal plane GHJA from 70° to 90° (P = 0.046) and from 50° to 90° (P = 0.027) (fatigue screen applied) (with the 70º and 50° GHJAs producing greater activity than the 90°). This significant change in muscle fiber recruitment of the anterior deltoid from the 70º to 90º GHJA, together with the results of no significant changes in %MmIEMG activity of the UCPM, LSPM and lateral head of triceps brachii can aid in outlining specific techniques that can be employed by powerlifters, bodybuilders and fitness enthusiasts when performing the HBP.
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