Assessment of Muscle Architecture of the Biceps Femoris and Vastus Lateralis by Ultrasound After a Chronic Stretching Program

Objective: To evaluate the chronic effects of a static stretching program on the muscle architecture of biceps femoris (BF) and vastus lateralis (VL) muscles in ultrasound (US) images. Design: Randomized controlled longitudinal trial. Setting: Biomechanics Laboratory of Physical Education School of the Army, Rio de Janeiro, Brazil. Participants: The study included 24 healthy and physically active male volunteers (19.05 +/- 1.40 years, 1.73 +/- 0.07 m, and 73.15 +/- 8.33 kg), randomly allocated to 1 of 2 groups: stretching group (SG, n = 12) and control group (n = 12). Interventions: The SG was submitted to 3 sets of 30 seconds of static stretching 3 times a week during 8 weeks. Main Outcome Measures: Ultrasound equipment (7.5 MHz) was used for the evaluation of BF and VL muscle architecture variables (pennation angle, fiber length, muscle thickness, and fascicle displacement) before and after training. Knee range of motion (ROM) and isometric flexion and extension torque (TQ) were also measured. Results: There were no significant changes in muscle architecture, TQ, and maximum knee flexion angle (P > 0.05). However, maximum knee extension angle (MEA) increased significantly in the SG (pretraining: 159.37 +/- 7.27 degrees and posttraining: 168.9 +/- 3.7 degrees; P < 0.05). Conclusions: Volume or intensity (or both) of the stretching protocol was insufficient to cause structural changes in the VL and BF muscles. The increase in MEA could not be explained by muscle architecture changes. Clinical Relevance: To describe changes in the VL and BF muscle tendon unit using US after a long-term stretching program to identify which structures are responsible for ROM increase.