Impact of breaking up prolonged sitting with intermittent stretching on vasoconstrictor responsiveness during plantar flexion exercise

OBJECTIVE: Prolonged sitting is well established to induce vascular dysfunction measured at rest. The primary objective of this study was to examine whether prolonged sitting impairs skeletal muscle blood flow and vasoconstrictor responsiveness (functional sympatholysis) during exercise. A secondary objective (if evident) was to determine whether breaking up prolonged sitting with intermittent stretching could ameliorate this detrimental response. It was hypothesized that prolonged sitting would impair functional sympatholysis, but when broken up with intermittent stretching this would be improved. METHODS: 12 young, recreationally fit subjects (age, 21±3 yr; body mass index, 23.5±2 kg/m 2 ) participated in two testing sessions in randomized order: 1) 3.5-h of uninterrupted sitting, or 2) 3.5-h of sitting interrupted with an 8-min bout of static stretching exercises every 45 minutes. Plantar flexion exercise occurred pre- vs. post-conditions. Exercise consisted of five minutes of steady-state exercise at 15% maximum, with the final two minutes involving a cold-pressor test (CPT) to induce sympathetic vasoconstriction. Popliteal artery diameter and blood velocities (Doppler ultrasound) determined leg blood flow (LBF). Leg (gastrocnemius) microvascular muscle tissue oxygenation ([O2Hb]) was determined via near infrared spectroscopy (NIRS). Leg vascular conductance (LVC) was calculated from LBF and mean arterial pressure (MAP). The degree of vasoconstriction [% change in LVC; (%∆LVC)] that occurred during CPT relative to rest or exercise was calculated as [%∆LVC=LVC*(CPT)−LVC/LVC]×100. Variables were analyzed using analysis of variance to assess group (SIT vs. STRETCH) and condition (rest vs. 15%). Statistical significance was set at P≤0.05. RESULTS: Prolonged sitting decreased LBF during exercise (pre: 274±44 vs. post: 212±48 mL/min; P< 0.05). This was accompanied by a decrease in NIRS-derived [O2Hb] during exercise (pre vs. post; P< 0.05). The SIT condition had a greater decrease in %∆FVC than STRETCH (−19.6±3.3 vs. −11.7±2.5%; P< 0.05). Steady state exercise LBF was greater with STRETCH vs. SIT (267±43 vs. 212±48 mL/min; P< 0.05). NIRS-derived [O2Hb] during exercise was 37% greater in STRETCH vs. SIT (P< 0.05). The pressor response during exercise with CPT tended to be lower in STRETCH vs. SIT (93±5 vs. 95±6 mmHg; P=0.09). No other changes in central hemodynamics (heart rate, stroke volume, cardiac output) were observed during exercise between groups. Conclusions: This is the first study to identify that prolonged sitting impairs functional sympatholysis in young healthy men and women. The study also shows for the first time that breaking up prolonged sitting with intermittent stretching improves functional sympatholysis leading to improves distribution of blood flow and oxygenation during exercise. Funding Sources: This study was supported by research start-up funds at Central Michigan University and a research equipment loan by the University of Iowa (R01HL134738, PI Jalal). This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.