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Abstract Details

Kinetics And Fiber Distribution Of The Three Muscle Heads Of Triceps For a Better C7 Myotomal EMG Study
Neuromuscular and Clinical Neurophysiology (EMG)
P1 - Poster Session 1 (5:30 PM-6:30 PM)
12-034
Improving Triceps Muscle Needle EMG.
During training, residents and fellows, often learn a method of choosing one particular head out of the three heads of the triceps muscle. The triceps muscle provides a prime example where application of anatomy and neuro-kinetic principles can lead to a more meaningful needle EMG study.
Review of muscle anatomy and kinetic physiology from Gray’s Anatomy and available EMG books.

The activation sequence of the Triceps muscle that occurs with increasing efforts is medial followed by lateral followed by the long heads of triceps. With lower efforts, type 1 fibers are preferentially recruited, and with higher effort, larger type 2 fibers. Conventional needle EMG, basically, is a study of type 1 fibers. Selective activation of the medial head of the triceps or anconeus involve largely type 1 fibers. Lateral head activation involves a combination of type 1 and 2 fibers, while activation of the long head involves predominantly type 2 fibers. Most electromyographers check either the more proximal and deeper lateral or long head, both with a higher proportion of C6 contribution compared to the superficial medial head. The medial head has a lower chance of bleeding, is easily accessed with a 30 gauge needle, and is almost exclusively innervated by C7; evaluation of the C7 myotome is often the most important reason for including the triceps in the needle exam. The other heads of the triceps require stronger activation, often activating larger type 2 fibers which inadvertently shows ‘large units’ that can lead to an erroneous diagnosis of chronic C7 radiculopathy.

A better application of the knowledge of anatomy, fiber distribution, and muscle kinetics, as well as a willingness to change tradition, may be more rewarding scientifically in the EMG lab.
Authors/Disclosures
James Noto, DO
PRESENTER
No disclosure on file
Cheran Elangovan, MD (University of Tennessee Health Science Center) Dr. Elangovan has nothing to disclose.
Sankar Bandyopadhyay, MD, FAAN (Penn State Hershey Medical Center) Dr. Bandyopadhyay has nothing to disclose.