Background <p>Thoracic spine mobility is essential for trunk stability, rotational movement, and athletic performance in soccer players. This study aimed to investigate whether the addition of a six-week thoracic spine exercise program to routine soccer training affects sagittal thoracic alignment, segmental spinal mobility, and thoracic rotation in professional male football players, compared with routine training alone.</p> Methods <p>In this parallel-group randomized controlled trial, 42 professional male soccer players (mean age 20.85 ± 3.41 years) were randomly assigned in a 1:1 ratio to either the exercise or control group (<i>n</i> = 21/group). The exercise group performed thoracic spine exercises three times per week for six weeks in addition to their routine training, while the control group continued routine training without receiving any intervention. Pre- and post-intervention assessments included spinal alignment and mobility in the sagittal and frontal planes (using the Valedo^®Shape system), the Matthias test, and thoracic rotation angles (measured with a smartphone Compass application). Two-way repeated-measures ANOVA and post-hoc tests were used to analyze group (G) × time (T) interactions and within-group changes. Effect sizes (Cohen’s d) were calculated.</p> Results <p>The primary outcome, sagittal thoracic kyphosis angle measured using the Valedo^®Shape system, did not demonstrate a significant G × T interaction or T effect, indicating no differential change between groups over the intervention period. As a key secondary outcome, bilateral thoracic rotation angles showed significant G × T interactions, with the exercise group demonstrating substantially greater improvements than the control group. The thoracic spine exercise program demonstrated high feasibility, with 100% participation and no intervention-related adverse events reported. Effect sizes were large for thoracic rotation angles (d = 1.00-1.46) and Matthias test inclination angle (d = 1.42–1.97).</p> Conclusion <p>The six-week thoracic spine exercise program improved spinal alignment, segmental mobility, and thoracic rotation in professional male soccer players. These findings suggest that coaches, sports science specialists, and physiotherapists could consider incorporating thoracic spine exercises into training and rehabilitation programs to support spinal function and optimize athletic performance.</p> Trial registration <p>ClinicalTrials.gov (NCT07253415), retrospectively registered on 19 November 2025. <a href="https://clinicaltrials.gov/study/NCT07253415">https://clinicaltrials.gov/study/NCT07253415</a>.</p>