Abstract
Muscle activity is typically normalized to maximal activation from isometric maximum voluntary exertions (MVE) in posture and direction specific exertions for each muscle. This is challenging for the shoulder complex due to the large number of muscles. The objective of this investigation was to compare maximum shoulder muscle activity elicited from a multi-muscle MVE test protocol versus individual muscle MVE tests and determine their reliability. Ten healthy males had muscle activity recorded from 12 trunk and upper extremity muscles while performing 3 repetitions of 12 individual and 4 multi-muscle MVEs. Peak surface EMG (sEMG) amplitudes were compared using paired sample t-tests between the two protocols for each muscle. Individual muscle test maximum sEMG amplitudes differed significantly from the multi-muscle test protocol in 3 of 12 muscles (p < 0.05). In muscles that did not attain statistical significance, maximum amplitude differences of 6–15% were found. There was high reliability (Interclass Correlation Coefficient, ICC = 0.831–0.986) and no significant differences between the second and third repetitions of the protocol. Since differences of 6–15% could have functional significance, 8 MVE tests (3 multi-muscle, 5 individual muscle) were selected for future use. Using two repetitions of the reduced MVE protocol will reduce time, risk of pain and injury during experiments.
Highlights
Surface electromyography is an important tool in many therapeutic and rehabilitation applications of the shoulder
We aimed to evaluate the reliability of these protocols, and to determine the maximum voluntary exertions (MVE) test protocol, consisting of both multi-muscle and individual muscle (IM) tests, that should be used in future shoulder investigations
Muscle activity was recorded from 12 right trunk, and upper extremity muscles using a wireless surface EMG system (Trigno, Delsys Inc., Natick, MA, USA)
Summary
Surface electromyography (sEMG) is an important tool in many therapeutic and rehabilitation applications of the shoulder. Boettcher et al (2008), developed a protocol of four tests to elicit maximal activity from a large subset of the shoulder muscles They examined many postures and exertion directions, they did not include traditional IM tests in their design. Previous work examined the utility of combining multiple and single muscle tests, and they have found this method to be successful, only a subset of shoulder muscles were examined (Chopp et al 2010; Rota et al 2013) Attempts to expand this four test protocol to include rhomboid major and teres major demonstrated IM tests elicited greater activation levels for these muscles (Ekstrom et al 2005).
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