Heart and musculoskeletal hemodynamic responses to repetitive bouts of quadriceps static stretching

The role of sympathetic and parasympathetic activity in relation to the repetitive exposure to static stretching (SS) on heart and musculoskeletal hemodynamics in stretched and resting muscles is still a matter of debate. The aim of the study was to determine cardiac and musculoskeletal hemodynamics to repetitive-bouts of unilateral SS. Sympathetic and parasympathetic activity contribution to the central hemodynamics and local difference in circulation of stretched and resting muscles were also investigated. In eight participants, heart rate (HR), cardiac output (CO), mean arterial pressure (MAP), HR variability (HRV), blood pressure variability (BPV), blood flow in passively stretched limb (SL) and control (CL, resting limb) were measured during 5 bouts of unilateral SS (45s of knee flexion and 15s of knee extension). SS increased sympathetic (≈20%) and decreased parasympathetic activity (≈30%) with a prevalence of parasympathetic withdrawal. During SS, HR, CO, and MAP increased by ≈18 BPM, ≈0.29 l∙min-1, ≈12 mmHg, respectively. Peak blood flow in response to the 1st stretching manoeuvre increased significantly (+377±95 ml⋅min-1) in the SL, and reduced significantly (-57±48 ml⋅min-1) in the CL. This between-limb difference in local circulation response to SS disappeared after the 2nd SS bout. These results indicate that heart hemodynamic responses to SS are primarily influenced by the parasympathetic withdrawal rather than by the increase in sympathetic activity. The balance between neural and local factors contributing to blood flow regulation was affected by the level of SS exposure, likely associated with differences in the bioavailability of local vasoactive factors throughout the stretching bouts.