The Effects of Posterior Shoulder Stretching and Pectoralis Minor Stretching on Alignment, Muscle Tone, and Muscle Activity in Subjects with Round Shoulders

Background Rounded shoulder posture, characterized by anterior translation of the humeral head and increased scapular anterior tilting, is common in individuals who spend prolonged time using smartphones and computers. Shortening of the pectoralis minor and increased posterior shoulder tightness are closely associated with rounded shoulder posture and may alter shoulder alignment, increase muscle tone, and contribute to impaired function of shoulder-stabilizing muscles. Purpose This study compared the effects of posterior shoulder stretching and pectoralis minor stretching, when combined with scapular posterior tilting exercises, on shoulder alignment, muscle tone, and muscle activity in adults with rounded shoulder posture. Study design Randomized comparative study with a two-way repeated-measures design Methods Twenty-six adults with rounded shoulder posture were randomly assigned to an experimental group (posterior shoulder stretching + scapular posterior tilting exercise) or a comparison group (pectoralis minor self-stretching + scapular posterior tilting exercise). Both groups received the intervention three times per week for 4 weeks. Outcome measures were rounded shoulder posture distance and pectoralis minor length, tone and stiffness of the pectoralis major and posterior deltoid, and electromyographic activity (%MVIC) of the upper trapezius and posterior deltoid during shoulder flexion. Data were analyzed using two-way repeated-measures ANOVA with Bonferroni-corrected t-tests. Results Both groups showed improvements in rounded shoulder posture distance and pectoralis minor length, with no significant between-group differences. Tone and stiffness of the pectoralis major and posterior deltoid decreased significantly in both groups. Upper trapezius activity showed limited changes. Posterior deltoid tone showed a significant group × time interaction, with a greater reduction in the experimental (posterior shoulder stretching) group. Posterior deltoid EMG activity at 60° shoulder flexion also showed a significant group × time interaction, with a greater increase in the comparison (pectoralis minor stretching) group. Conclusions Both stretching approaches, when combined with scapular posterior tilting exercises, were effective for improving rounded shoulder alignment and reducing muscle tone. These findings support considering both anterior and posterior soft tissue flexibility when selecting stretching targets for individuals with rounded shoulder posture.