Empty can exercise provokes more pain and has undesirable biomechanics compared with the full can exercise

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.

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.

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).

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.