Neural and Mechanical Adaptations During Static Stretching With Different Amplitudes

This study examined neural and mechanical responses at the onset of prolonged static stretching performed at different amplitudes, their progression during the stretching period, and alterations immediately after its completion. Thirteen healthy adults completed three randomized sessions: control (15-min rest in neutral ankle angle), 15 min of submaximal stretching (ROM_max - 5°), and 15 min of supramaximal stretching (ROM_max + 5°). Spinal excitability (H_max/M_max), evoked contractile properties (PTT), voluntary strength (MVC), passive torque, and maximal range of motion (ROM_max) were assessed at baseline (PRE), during stretching (T₀₀, T₀₅, T₁₀, and T₁₅), and immediately after stretching (POST). Spinal excitability decreased at stretch onset but progressively increased during stretching (T₀₀-T₁₅, p < 0.05), with greater facilitation in supramaximal (soleus and gastrocnemius, p < 0.001) than submaximal conditions (soleus only, p < 0.001). These changes were transient, returning to baseline at POST (p < 0.001). Passive torque increased during both stretching (p < 0.05); however, in supramaximal, it declined after 5 min and stabilized until 15 min (p = 0.001), while in submaximal, it declined only at 15 min (p = 0.043). Both conditions reduced PTT (p < 0.05), with slightly greater decreases in the supramaximal condition. MVC decreased similarly after both protocols (p < 0.05). ROM_max improved in both (p < 0.05), with slightly greater gains in the supramaximal condition. Static stretching amplitude modulates neuromechanical adaptations. Both supramaximal and submaximal protocols reduced voluntary strength but improved flexibility, with greater spinal excitability after the initial decrease and slightly larger ROM_max gains at supramaximal amplitude.