title: A slouched body posture decreases arm mobility and changes muscle recruitment in the neck and shoulder region.
abstract: OBJECTIVE
  Long-term use of unfavorable postures, congenital deformations and degenerative processes associated with aging or disease may generate an increased thoracic curvature resulting in pain and disability. We wanted to examine whether a slouched postural alignment with increased thoracic kyphosis changes the shoulder kinematics and muscle activity in upper trapezius (UT), lower trapezius (LT) and serratus anterior (SA) during arm elevation. The aim was to determine if a slouched posture influences range of motion, muscle activation patterns, maximal muscle activity and the total muscle work required when performing arm elevations.
  
  
  METHODS
  Twelve male subjects (23.3 ± 1.5 years) performed maximum arm elevations in upright and slouched postures. A combined 3D movement and EMG system recorded arm movements and spine curvature simultaneously with EMG activity in the UT, LT and SA.
  
  
  RESULTS
  Slouched posture affected the biomechanical conditions by significantly decreasing maximum arm elevation by ~15° (p < 0.001) and decreasing arm movement velocity by ~8 % during movements upwards (p < 0.001) and downwards (p = 0.034). The peak muscle activity increased in all muscles: UT (p = 0.034, +32.3 %), LT (p = 0.001, +48.6 %) and SA (p = 0.007, +20.9 %). The total muscle work increased significantly in the slouched posture during movements upwards: UT (p = 0.003, +36.6 %), LT (p < 0.001, +89.0 %), SA (p = 0.002, +19.4 %) and downwards: UT (p = 0.012, +29.8 %) and LT (p < 0.001, +122.5 %).
  
  
  CONCLUSIONS
  An increased thoracic kyphosis was found associated with marked increased physical costs when performing arm movements. Hence, patients suffering from neck-shoulder pain and disability should be investigated and treated for defective thoracic curvature issues.
authors.affiliation: Department of Pain Rehabilitation, Skåne University Hospital, Lasarettsgatan 13, 22185, Lund, Sweden. eva-maj.malmstrom@med.lu.se.|Department of Otorhinolaryngology, Clinical Sciences, Lund, Lund University, 22185, Lund, Sweden. eva-maj.malmstrom@med.lu.se.
authors.forename: Eva-Maj
authors.initials: EM
authors.lastname: Malmström
authors.affiliation: Department of Health Sciences, Faculty of Medicine, Lund University, Box 117, 22100, Lund, Sweden. joakim.olsson@resursteamet.se.|Resursteamet i Stockholm AB, Katrinebergsvägen 6, 117 43, Stockholm, Sweden. joakim.olsson@resursteamet.se.
authors.forename: Joakim
authors.initials: J
authors.lastname: Olsson
authors.affiliation: Department of Health Sciences, Faculty of Medicine, Lund University, Box 117, 22100, Lund, Sweden. johan.baldetorp@skane.se.|Vårdcentralen Kirseberg, Simrisbanvägen 10, 205 02, Malmö, Sweden. johan.baldetorp@skane.se.
authors.forename: Johan
authors.initials: J
authors.lastname: Baldetorp
authors.affiliation: Department of Otorhinolaryngology, Clinical Sciences, Lund, Lund University, 22185, Lund, Sweden. Per-Anders.Fransson@med.lu.se.
authors.forename: Per-Anders
authors.initials: PA
authors.lastname: Fransson
mesh_terms: D000293:Adolescent; D000328:Adult; D001132:Arm / Q000502:physiology*; D001696:Biomechanical Phenomena; D006801:Humans; D007738:Kyphosis / Q000503:physiopathology*; D008297:Male; D009068:Movement; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000502:physiology*; D009333:Neck / Q000502:physiology*; D011187:Posture; D016059:Range of Motion, Articular; D012782:Shoulder / Q000502:physiology*
keywords: Axioscapular; EMG; Muscle recruitment; Postural alignment