Muscles within Muscles: : The classical triphasic EMG burst and its applicability to segments of large radiate agonist/antagonistic muscles

James Wickham, Mark Brown, Rodney Green, Darryl McAndrew

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3 Citations (Scopus)
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The purpose of the current study was to determine if the classically described triphasic EMG burst was applicable in describing the EMG patterns across the breadth of three large radiate muscles during the production of a rapid shoulder joint movement. Miniature (6.5 mm inter-electrode distance) bipolar surface electrodes were placed across the breadth of the pectoralis major (6 off), latissimus dorsi (6 off) and the deltoid (7 off). Subjects performed a series of rapid shoulder joint adduction movements (<400 ms) against the resistance of a free weight and pulley apparatus whilst seated in an experimental chair. EMG data sampled from the multiple recording sites of the three muscles identified four different types of EMG waveforms. This was based on the presence, or absence, of multiple bursts, the length of each burst and the level of the silent period between bursts from the same segment of a muscle. The four bursts included a one-burst pattern, a one-continuous burst pattern, a two-continuous burst pattern and a two non-continuous burst pattern. Upon further analysis it was established that a relationship existed between the type of burst displayed by a segment and the functional role of that segment (prime mover, synergist, primary or secondary antagonist), hence a uniform type of burst pattern was not apparent across the breadth of the agonist (pectoralis major and latissimus dorsi) and antagonist (deltoid) muscles. It was evident that the triphasic EMG burst was most applicable for the EMG patterns arising from the prime mover segments of the pectoralis major and the latissimus dorsi and the primary antagonist segment of the deltoid. In conclusion, these results suggest that caution is warranted if stating that popular motor control theories10, 11 based on EMG patterns produced by small agonist and antagonist muscles during rapid limb movement, apply to all segments of large radiate muscles.
Original languageEnglish
Pages (from-to)107-117
Number of pages11
JournalJournal of Musculoskeletal Research
Issue number2/3
Publication statusPublished - 2004


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