Altered Triceps Surae Muscle-Tendon Unit Properties after 6 Months of Static Stretching

Abstract

Introduction: This study examined the effects of 24 wk of daily static stretching of the plantarflexors (unilateral 4 × 60-s stretching, whereas the contralateral leg served as a control; n = 26) on joint range of motion (ROM), muscle–tendon unit morphological and mechanical properties, neural activation, and contractile function. Methods: Torque–angle/velocity was obtained in passive and active conditions using isokinetic dynamometry, whereas muscle–tendon morphology and mechanical properties were examined using ultrasonography. Results: After the intervention, ROM increased (stretching, +11° ± 7°; control, 4° ± 8°), and passive torque (stretching, −10 ± 11 N·m; control, −7 ± 10 N·m) and normalized EMG amplitude (stretching, −3% ± 6%; control, −3% ± 4%) at a standardized dorsiflexion angle decreased. Increases were seen in passive tendon elongation at a standardized force (stretching, +1.3 ± 1.6 mm; control, +1.4 ± 2.1 mm) and in maximal passive muscle and tendon elongation. Angle of peak torque shifted toward dorsiflexion. No changes were seen in tendon stiffness, resting tendon length, or gastrocnemius medialis fascicle length. Conformable changes in ROM, passive dorsiflexion variables, tendon elongation, and angle of peak torque were observed in the nonstretched leg. Conclusions: The present findings indicate that habitual stretching increases ROM and decreases passive torque, altering muscle–tendon behavior with the potential to modify contractile function.