Abstract
BackgroundScapular stabilization is a common focus of shoulder rehabilitation.ObjectiveExamine contraction of serratus anterior during a bilateral arm extension exercise with axial compression using an exercise device (GravityFit) by magnetic resonance imaging (MRI).MethodsMRI was performed under two conditions: rest and static arm extension with axial compression. Load was set at 20% of age, sex and weight estimated bench press one-repetition maximum. A T2-weighted sequence was used to collect 14 axial images of the upper thoracic spine and shoulder bilaterally. Mean muscle length and thickness were calculated for the whole muscle and in equidistant subregions of the muscle in its anterior (superficial), central and posterior (deep) portions. Adjustment of p-values to guard against false positives was performed via the false discovery rate method.ResultsNine participants without a history of shoulder or spine pathology were included. When compared to rest, arm extension with the exercise device led to 11% increased overall muscle thickness (P = 0.038) and 6.1% decreased overall muscle length (P = 0.010). Regionally, thickness increased in anterior (superficial, +19%; P = 0.040) and central (+17%; P = 0.028) portions of the muscle more than posterior (deep, +3.9%, P = 0.542).ConclusionContraction of serratus anterior occurred during static arm extension with axial compression produced by a novel exercise approach, as measured via MRI. The activation of serratus anterior differed across its length with greater contraction of the anterior and central portions. This may indicate compartmentalization of function within this muscle. Overall, the proof-of-principle findings justify the use of this exercise approach for the activation of serratus anterior.
Highlights
The improvement of scapular stabilization is a common focus of shoulder rehabilitation following injury, overuse syndromes and surgery (Duncan and Flowers, 2015)
Surface electromyography has been primarily used to study serratus anterior to determine which exercises result in optimal activation of this muscle, (Ekstrom et al, 2003, 2005; Ludewig et al, 2004) as well as how the function of the muscle is affected in shoulder pain or injury (Kinsella and Pizzari, 2017)
Surface electromyography is limited in its ability to quantify the posterior portions of serratus anterior located deep to the scapula, which may be more effectively quantified with magnetic resonance imaging (MRI)
Summary
The improvement of scapular stabilization is a common focus of shoulder rehabilitation following injury, overuse syndromes and surgery (Duncan and Flowers, 2015). Surface electromyography has been primarily used to study serratus anterior to determine which exercises result in optimal activation of this muscle, (Ekstrom et al, 2003, 2005; Ludewig et al, 2004) as well as how the function of the muscle is affected in shoulder pain or injury (Kinsella and Pizzari, 2017). Surface electromyography is limited in its ability to quantify the posterior portions of serratus anterior located deep to the scapula, which may be more effectively quantified with magnetic resonance imaging (MRI). Scapular stabilization is a common focus of shoulder rehabilitation
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