Effect of Hamstring Flexibility Training, Rest, and Retraining on Extensibility and Sagittal Spine Disposition in Dancers: A Randomized Controlled Trial.

Background: Hamstring extensibility is essential for performing several technical movements present in dance.

Aim: The aim of this study was to analyze the changes produced by a specific hamstring stretching program, on the hamstring extensibility, sagittal spine curvatures, and pelvic posture during a period of training, rest, and retraining, of female dancers at a High Conservatory of Dance.

Hypothesis: The implementation of a stretching program will increase hamstring extensibility and improve sagittal spine disposition of female students of the High Conservatory of Dance.

Study design: A randomized controlled trial (RCT) was conducted for a single-blind intervention, including a pretest, retest 1, retest 2, and retest 3, and 2 sample groups.

Level of evidence: Level 3.

Methods: A total of 57 female dancers (24.63 ± 5.98 years old) completed the study. The experimental group (EG) performed a training period based on hamstring extensibility training for 7 weeks, followed by an 18-day rest period, and a 3-week retraining period. In the training period and retraining period, the EG performed hamstring extensibility training, including 3 sets of 20 seconds of 4 different exercises (240 seconds per session of effective stretching), with a frequency of 4 sessions/week. Hamstring extensibility was measured using the active and passive single leg raise (ASLR and PSLR) tests and the sit-and-reach (SR) test. Sagittal spinal curvatures and pelvic tilt in relaxed standing position, SR, and MacRae and Wright (MW) tests were assessed. The control group (CG) continued with their regular dance training sessions.

Results: The EG showed significantly higher scores in the SLR and SR tests (P < 0.01) after training and retraining; a significant increase in the anterior pelvic tilt in the SR and MW tests after the training (P < 0.01); and a significant increase in the thoracic curvature in the MW test after the training (P < 0.01). In general, during the rest period, significant changes were not observed in EG (P > 0.05). Regarding the CG, a significant decrease in the PSLR right leg value was found during the rest period, with a significant increase after the retraining, with just the practice of dance and without performing the stretching intervention (P < 0.01). Furthermore, a greater increase in hamstring extensibility was found in the EG compared with the CG after the training and retraining (P = 0.04 to P < 0.01), whereas a greater increase was also found in anterior pelvic tilt in the SR and MW test during the training (P < 0.01).

Conclusion: A 7-week training period consisting of 4 hamstring extensibility exercises and 3-week retraining period, with an 18-day rest period, effectively improved hamstring extensibility and pelvic tilt in the SR test of female students of the High Conservatory of Dance.

Clinical relevance: Incorporating flexibility training could improve the short-term hamstring extensibility of female dancers. This could be an effective tool for dancers whose hamstring extensibility is limiting performance.