Measurement of muscle thickness of the serratus anterior and lower trapezius using ultrasound imaging in competitive recreational adult swimmers, with and without current shoulder pain

Objectives: To compare serratus anterior and lower trapezius muscle thickness between swimmers with and without current shoulder pain, and between sides when measured by real-time ultrasound imaging. Design: A single blinded age and gender-matched case-control study with 26 symptomatic and 26 asymptomatic recreational swimmers. Methods: Muscle thickness of serratus anterior and lower trapezius were measured using previously validated real-time ultrasound imaging protocols. Serratus anterior thickness was measured in side lying with 90 of glenohumeral flexion at rest and during a scapular protraction contraction. Lower trapezius thickness was measured in prone with 145 of glenohumeral abduction whilst at rest and when holding the weight of the arm. Results: There was no statistically significant difference between the muscle thickness of serratus anterior and lower trapezius between the symptomatic shoulder and the dominance-matched shoulder in the asymptomatic group of swimmers. There was also no significant difference in muscle thickness between the symptomatic side and asymptomatic side within the symptomatic group. Conclusions: There appears to be no difference in serratus anterior and lower trapezius thickness between swimmers who have mild to moderate shoulder pain, who continue to swim and those who do not have shoulder pain. When imaging the serratus anterior and lower trapezius in swimmers with mild shoulder pain, clinicians should expect no differences between sides. If muscle thickness differences between sides are detected in recreational swimmers, this may indicate that the swimmer is participating in other asymmetrical activities or has a higher level of shoulder pain. (C) 2017 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.