title: Empty can exercise provokes more pain and has undesirable biomechanics compared with the full can exercise.
abstract: BACKGROUND
  The purpose of this investigation was to characterize the scapular position and scapular muscle activation during the empty can (EC) and full can (FC) exercises. The EC exercise has been shown to produce scapular kinematics associated with the mechanism leading to subacromial impingement syndrome (SAIS) but has not been investigated in patients with (SAIS). This investigation will help improve the treatment of patients with SAIS.
  
  
  METHODS
  Participants with SAIS (n = 28) performed 5 consecutive repetitions of FC and EC exercises. Scapular and clavicular 3-dimensional positions and scapular muscle activity were measured during each exercise. Pain was measured with the numeric pain rating 11-point scale.
  
  
  RESULTS
  Participants reported greater pain during the EC exercise vs the FC exercise (difference, 1; P = .003). During the EC exercise, participants were in greater scapular upward rotation (difference, 3°; P < .001), internal rotation (mean difference, 2°; P = .017), and clavicular elevation (difference, 3°, P < .001) and in less scapular posterior tilt (difference, 2°; P < .001). There was greater activity of upper trapezius (difference, 4%, P = .002), middle trapezius (difference, 3%; P < .001), and serratus anterior (difference, 0.5%; P = .035) during ascent, and during the descent of greater upper trapezius (difference, 2%, P = .005), and middle trapezius (difference, 1%; P = .003), but less activity of the lower trapezius (difference, 1%; P = .039).
  
  
  CONCLUSIONS
  The EC exercise was associated with more pain and scapular positions that have been reported to decrease the subacromial space. Scapular muscle activity was generally higher with the EC, which may be an attempt to control the impingement-related scapular motion. The FC exercise of elevation is preferred over the EC exercise.
authors.affiliation: School of Kinesiology, College of Health Professions, Marshall University, Huntington, WV, USA. Electronic address: timmonsm@marshall.edu.
authors.forename: Mark K
authors.initials: MK
authors.lastname: Timmons
authors.affiliation: Department of Veterans Affairs-Hunter Holmes McGuire VA Medical Center, Physical Medicine and Rehabilitation Section, Richmond, VA, USA.
authors.forename: Jeff J
authors.initials: JJ
authors.lastname: Ericksen
authors.affiliation: School of Physical Therapy and Rehabilitation, Dokuz Eylül University, İzmir, Turkey.
authors.forename: Sevgi S
authors.initials: SS
authors.lastname: Yesilyaprak
authors.affiliation: Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, USA.
authors.forename: Lori A
authors.initials: LA
authors.lastname: Michener
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D002968:Clavicle / Q000000981:diagnostic imaging / Q000503:physiopathology; D005260:Female; D006801:Humans; D006811:Humerus / Q000000981:diagnostic imaging / Q000503:physiopathology; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D055070:Resistance Training / Q000295:instrumentation*; D012189:Retrospective Studies; D012540:Scapula / Q000000981:diagnostic imaging / Q000503:physiopathology*; D019534:Shoulder Impingement Syndrome / Q000503:physiopathology / Q000628:therapy*; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000503:physiopathology
keywords: Subacromial impingement; rotator cuff; scapular kinematics