title: Isometric muscle activation of the serratus anterior and trapezius muscles varies by arm position: a pilot study with healthy volunteers with implications for rehabilitation.
abstract: BACKGROUND
  This study aimed to determine the most appropriate angle and moving direction of the arm for improving coordination of the periscapular muscles, including the serratus anterior (SA), upper trapezius (UT), middle trapezius (MT), and lower trapezius (LT).
  
  
  METHODS
  Muscle activation amplitudes were evaluated in the SA, UT, MT, and LT in 11 healthy subjects by use of surface electromyography. The subjects were asked to maintain the arm position at 5 elevated positions with maximal effort against applied manual forces, which were directed from upper to lower (test 1), lower to upper (test 2), posterior to anterior in the frontal plane and lateral to medial in the sagittal plane (test 3), and anterior to posterior in the frontal plane and medial to lateral in the sagittal plane (test 4). The relative activity of the UT with respect to the SA, MT, and LT was calculated, resulting in the UT/SA, UT/MT, and UT/LT ratios.
  
  
  RESULTS
  Test 4 in all positions but 150° of elevation in the frontal plane showed high activity of the SA with a low UT/SA ratio. High MT activity with a low UT/MT ratio was observed during test 3 at the 90° elevated position, whereas high LT activity without UT hyperactivation was not found.
  
  
  CONCLUSIONS
  To strengthen the periscapular muscles in the balanced condition, horizontal adduction is recommended for the SA. Horizontal abduction at the 90° elevated position should be effective for the MT. Because no technique in this study was effective for the LT, further studies are needed.
authors.affiliation: Rehabilitation Unit, Kyoto University Hospital, Kyoto, Japan. Electronic address: miyasaka@kuhp.kyoto-u.ac.jp.
authors.forename: Junsuke
authors.initials: J
authors.lastname: Miyasaka
authors.affiliation: Department of Orthopedic Surgery, Kyoto University, Kyoto, Japan.
authors.forename: Ryuzo
authors.initials: R
authors.lastname: Arai
authors.affiliation: Medic Media, Tokyo, Japan.
authors.forename: Taisuke
authors.initials: T
authors.lastname: Ito
authors.affiliation: Rehabilitation Unit, National Hospital Organization Kyoto Medical Center, Kyoto, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Shingu
authors.affiliation: Human Health Sciences, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Hasegawa
authors.affiliation: Human Health Sciences, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Satoko
authors.initials: S
authors.lastname: Ibuki
authors.affiliation: Human Health Sciences, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Noriaki
authors.initials: N
authors.lastname: Ichihashi
authors.affiliation: Department of Orthopedic Surgery, Kyoto University, Kyoto, Japan.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Matsuda
authors.affiliation: Laboratory of Applied Physiology, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan.
authors.forename: Toshio
authors.initials: T
authors.lastname: Moritani
mesh_terms: D001132:Arm / Q000502:physiology*; D004576:Electromyography / Q000379:methods; D005081:Exercise Therapy / Q000379:methods; D064368:Healthy Volunteers; D006801:Humans; D064169:Intermediate Back Muscles / Q000502:physiology*; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D010865:Pilot Projects; D016059:Range of Motion, Articular; D019534:Shoulder Impingement Syndrome / Q000534:rehabilitation; D064171:Superficial Back Muscles / Q000502:physiology*; D055815:Young Adult
keywords: Electromyography; exercise; muscle activation; muscle balance; periscapular muscles; shoulder