Static stretching duration-dependent changes in flexibility, muscle oxygen saturation, and blood flow in the forearm...

Static stretching (SS) is commonly performed to improve flexibility; however, whether mechanical responses and local haemodynamic responses are temporally coordinated remains unclear. This study examined the effects of SS duration on flexibility and haemodynamic responses in the forearm flexors. Seventeen healthy men completed a randomized, repeated-measures protocol including four SS durations (30, 60, 180, and 300 s) and a no-stretch control. Outcome measures included wrist range of motion (ROM), maximum dynamic passive torque (DPT_max, used as an index of stretch tolerance), passive stiffness, tissue oxygenation index (TOI), and muscle blood flow (mBF), assessed before and up to 9 min after stretching. Longer SS durations (≥ 180 s) resulted in greater increases in ROM and DPT_max and more persistent reductions in passive stiffness. In contrast, TOI exhibited a duration-dependent post-stretch overshoot, whereas mBF increased immediately after stretching but returned to baseline within 3 min irrespective of duration. Changes in ROM were more strongly associated with changes in DPT_max than with changes in passive stiffness, and no significant associations were observed between mechanical variables and haemodynamic responses. These findings indicate that mechanical and haemodynamic responses to SS follow distinct temporal profiles. Importantly, the present study was not designed to establish a causal relationship between these responses, but rather to determine whether they exhibit coordinated or independent temporal behaviour. Accordingly, improvements in flexibility appear to be primarily related to stretch tolerance, whereas haemodynamic responses occur in parallel but are not directly linked to mechanical changes.