Biomechanical Response to Acute Stretching in Dancers and Non-Dancers

Abstract

This study aimed to investigate the bio- mechanical response of the hamstring muscles to acute stretching in dancers (D) compared to non-dancers (ND). Maximal range of motion (ROMMax) and stiffness of the hamstrings were assessed in 46 young males, 23 undergraduate students (ND) and 23 professional dancers (D). Ages of the two groups were D 21.5 ± 0.60 years; ND 27.5 ± 0.98 years). Testing was performed in two sessions, familiarization with procedures in the first session and the tests themselves (pre- and post-test and intervention) in the second, with a 24- to 48-hour interval between. The pre-test consisted of three trials of passive knee extension to the point of increased tension in the hamstrings, defined as ROMMax. The resistance torque recorded at ROMMax was defined as torqueMax. Six 30-second constant torque stretches were performed at 100% of the torqueMaxreached in the pre-test in one lower limb only (intervention), with the contralateral limb used as control. The torque measured at an identical ROM before (pre-test) and after (post-test) the intervention was defined as torqueROM, and represented stiffness in this study. Reliability of the ROMMax, torqueMax, and torqueROMwas assessed via intraclass correlation coefficients (ICC3, k) and standard error of the measurements (SEM). Comparison between dancers and non-dancers, control, and intervention conditions for all dependent variables was performed using ANOVA repeated measures followed by Tukey post hoc comparisons to highlight any interaction. The submaximal stretch intensity applied caused torqueROM to decrease in both D and ND groups (p < 0.01), indicating a decrease in stiffness, but no difference between the groups was found. A significantly greater increase in ROMMax was found for the D group compared to the ND group (p < 0.01), suggesting that other aspects in addition to MTU biomechanical adaptations may have played a role in the ROMMax increase, especially for the D group. Further research is needed to explore what those other adaptations are. Meanwhile, coaches and physical therapists should be aware that dancers may require different stretch training protocols than non-dancers.