Background Kyphotic postures in both thoracic and lumbar curves have been associated to increased shear and compressive forces in the intervertebral joints. Hamstring extensibility influences pelvic, thoracic and lumbar curvatures when trunk bending movements are performed. Some studies have found higher hamstring muscle extensibility in dancers than other athletes.

Objective To classify sagittal thoracic and lumbar curves when performed a maximum trunk flexion with knees extended (sit-and-reach test) in female dancers with high hamstring extensibility.

Design Descriptive study.

Setting Dance Conservatory professional. The sample included dance students of Professional education teaching.

Participants 86 female dancers (mean±SD, age: 15.18±2.62 years-old) with a straight leg raise test greater than 90° were recruited for this study.

Interventions Not applicable.

Main outcome measurements Thoracic and lumbar curvatures were measured when maximal trunk flexion with knees extended (sit-and-reach test) was reached using a Spinal Mouse^®. Thoracic values were classificated in three categories: slight (<45°), mild (45–60°) or high (>60°) kyphotic curve. Lumbar values were also classificated in three categories: slight (<23°), mild (23–31°) or high (>31°) kyphotic curve.

Results Most dancers showed slight (43.02%) and mild (33.72%) thoracic curvature whereas the frequency of high thoracic kyphosis was 23.26%. Thirty-seven dancers showed thoracic angles between -5 and 44° (slight group) (mean value: 30.35±11.42°). The mean thoracic kyphosis of mild group was 51.55±4.80°. The high group showed values between 61 and 79° (mean value: 66.95±5.43°). With regards to the lumbar curvature, a large amount of the sample showed high (46.51%) and mild (37.20%) kyphotic curves.

Conclusions Dance training is associated to increased lumbar kyphosis when maximum trunk flexion with knees extended is performed. Greater intervertebral bending of the lumbar spine in dancers could be associated to their high hamstring extensibility.