Background: Activities requiring repetitive arm movements, including high velocity actions, have been identified as a risk factor for shoulder impingement. However, the effect of speed on upper limb motor strategies has yet to be evaluated for individuals with shoulder impingement. The aims of this study were to characterize upper limb motor strategies in individuals with and without shoulder impingement during reaching at natural speed and to evaluate their adaptation to higher speeds of movement.
Methods: Twenty healthy individuals and 33 individuals with shoulder impingement took part in one evaluation session. They performed reaching at natural and fast speeds, toward targets located at 90 degrees of arm elevation in two different planes. Reaching speed, upper limb kinematics and shoulder muscular activity were used to characterize motor strategies.
Findings: Individuals with shoulder impingement present altered motor strategies during reaching tasks. However, changes with speed were comparable in both groups, showing similar adaptation to speed. Larger intergroup differences were found when individuals with shoulder impingement were separated into groups presenting higher or lower than normal clavicular elevation. In the frontal plane, increased clavicular elevation for individuals with impingement was associated with more trunk rotation, less elbow flexion and upper trapezius electromyographic activity during reaching, and a more anterior plane of shoulder elevation at the end of reaching as compared to the healthy individuals.
Interpretation: The present results demonstrate that not all individuals with shoulder impingement present the same abnormal motor strategy. Therefore, characterizing motor strategies before implementing rehabilitation intervention is essential.