Empty can exercise provokes more pain and has undesirable biomechanics compared with the full can exercise.
Level 3 - non-randomized controlled study
Single-group within-subject repeated-measures biomechanical comparison
PubMed 26577128 · doi:10.1016/j.jse.2015.08.046
What was done
Twenty-eight participants with subacromial impingement syndrome performed 5 consecutive repetitions of full can (FC) and empty can (EC) exercises. Researchers evaluated pain on an 11-point numeric rating scale, measured 3-dimensional scapular and clavicular positions, and recorded scapular muscle electromyographic activation during both exercises.
What was found
Pain was significantly higher during the EC exercise compared to the FC exercise (difference: 1 point, P = .003). For kinematics, the EC exercise resulted in greater scapular upward rotation (difference: 3°, P < .001), greater internal rotation (mean difference: 2°, P = .017), greater clavicular elevation (difference: 3°, P < .001), and less scapular posterior tilt (difference: 2°, P < .001). Muscle activation during ascent was greater with EC for upper trapezius (difference: 4%, P = .002), middle trapezius (difference: 3%, P < .001), and serratus anterior (difference: 0.5%, P = .035). During descent, EC produced higher upper trapezius (difference: 2%, P = .005) and middle trapezius activity (difference: 1%, P = .003), but lower activity of the lower trapezius (difference: 1%, P = .039).
Why it matters
These findings show that empty can elevation induces scapular orientations associated with subacromial space narrowing and provokes more pain than full can elevation in symptomatic patients, supporting the preference for full can exercises in rehabilitation.
Limits
The study had a small sample size (n = 28) and evaluated only immediate biomechanical and pain responses rather than longitudinal clinical outcomes. Additionally, absolute kinematic differences (2°–3°) and muscle activation differences (0.5%–4%) were small.