Aim To evaluate the effects of a 9-month Pilates exercise programme on the sagittal spinal posture and hamstring extensibility of adolescents with thoracic hyperkyphosis.

Design Randomised controlled trial with blinded examiner.

Patients One-hundred and three adolescents with thoracic hyperkyphosis.

Interventions Participants were randomly placed into an experimental group which participated in a Pilates exercise programme implemented for a total of 38 weeks (two sessions/week, 15 min/session) (Pilates group (PG), sample=49, or control group (CG), sample=48).

Main outcome measures The outcome measures were the thoracic curve in sagittal spinal curvature in relaxed standing, sagittal spinal curvatures and pelvic tilt in relaxed standing and sit-and-reach positions, and hamstring extensibility.

Results There was a significant adjusted mean difference between groups in favour of the PG in the thoracic curve in relaxed standing position (−5.6°, p=0.003), pelvic tilt (−2.9°, p=0.03) and all straight leg tests (p<0.001). The PG showed a significant change in thoracic curve (−5.9, p<0.001) and in lumbar angle (4.0, p=0.001) in relaxed standing position and in all straight leg raise tests (+6.4 to +15°, p<0.0001).

Conclusions The adolescents with thoracic hyperkyphosis from the PG had a decreased thoracic kyphosis in relaxed standing position, and improved hamstring extensibility as compared with the CG. More than 50% of the participants obtained kyphosis values inside normality, showing an adjusted mean difference between groups in the thoracic curve of about 73% of the baseline mean, resulting in a large improvement and high clinical importance.

Trial registration number NCT03831867.