DOES STRETCHING OF HAMSTRINGS STRETCH THE MUSCLE OR THE NEURAL TISSUE? EFFECT OF THREE STRETCHING MODALITIES FOR HAMSTRING MUSCLES ON GLOBAL FLEXIBILITY. RANDOMIZED CONTROLLED TRIAL

ABSTRACT Background: Stretching techniques for hamstrings muscles are described both to increase muscle length and to evaluate nerve mechanosensitivity. Therefore, the target tissue of these techniques is unknown. Ankle dorsiflexion, used as structural differentiation movement, has shown to produce differential biomechanical behaviour between sciatic nerve and hamstring muscles. The aim of the present study is to document the type of response (neural or muscular) produced by ankle dorsiflexion in three stretching modalities for hamstring muscles in asymptomatic subjects. Material and Methods: A single-blind randomized controlled trial was carried out. Thirty-five subjects were recruited. Straight-leg-raise, passive knee extension and maximum hip flexion were performed in the dominant leg, with an interval of one week. The type of response to structural differentiation, the global flexibility, the intensity and the localization of the sensory responses were assessed for each stretching modality after the technique application (T1) and 2 minutes later (T2). Results: All stretching techniques produced an increased global flexibility (p<0.05). The Straight-leg-raise produced the greatest increase at T1, showing a difference of 4.24cm in the modified back-saver sit-and-reach test (p<0.001). According to the structural differentiation, the Straight-leg-raise showed the greatest percentage of neural responses (77.1%). Conclusions: All stretching techniques increased global flexibility. The greatest percentage of neural responses was observed in the Straight-leg-raise modality, followed by the passive knee extension. This could suggest a potential effect of these techniques on nerve instead on muscle tissue. The Straight-leg-raise mode was the one that produced the greatest increase in global flexibility.