Intermittent Stretching Prevents Prolonged Sitting-Induced Popliteal Artery Endothelial Dysfunction

OBJECTIVE: Sedentary behavior is associated with increased cardiovascular disease (CVD) risk, with office workers sitting 8-10 hours daily. Prolonged sitting impairs endothelial function assessed by flow-mediated dilation (FMD), a well-established marker of cardiovascular risk. The objective of this study was to determine whether breaking up prolonged sitting with intermittent stretching breaks mitigate sitting-induced endothelial dysfunction. HYPOTHESIS: We hypothesized that intermittent stretching would preserve endothelial function during prolonged sitting compared to uninterrupted sitting. METHODS: In a randomized crossover design, twelve young adults (6M/6F; age: 21±2 yrs; BMI: 23.5±1.8 kg/m 2 ) completed two 3.5-hour conditions: uninterrupted sitting (SIT) or sitting with 5-minute lower extremity static stretches every 45 minutes (STRETCH). Popliteal artery FMD assessed endothelium-dependent dilation before and after each condition using Doppler ultrasound. Hemodynamics (blood flow/shear rate), leg congestion (calf circumference via Gulick tape, total concentration of blood volume [Hbtot] via near-infrared spectroscopy), blood pressure, and heart rate were measured at baseline and 45-minute intervals. Data were analyzed using repeated measures ANOVA with condition and time as factors. Statistical significance was set a priori at P≤0.05. RESULTS: SIT significantly impaired popliteal FMD by 41% (pre: 6.8±2.4% vs. post: 4.0±1.3%; P< 0.05). STRETCH preserved FMD with no change (pre: 6.5±2.5% vs. post: 5.8±2.5%; P=0.34). Resting blood flow and shear rate were lower after SIT (pre: 71.4±11.5 vs. post: 43.7±10 mL∙min-1, and pre: 21.5±6.1 vs. post: 19.7±6.3 s-1 both P< 0.01), whereas no changes were found in the STRETCH condition (pre: 69.5±14 vs. 66.2±13.2 mL∙min-1; P=0.83, and pre: 21.0±7.3 vs. post: 20.9±7.4 s-1; P=0.86). Leg circumference and [Hbtot] increased after SIT (both P< 0.05) but remained unchanged with STRETCH (P=0.84 and P=0.61), respectively. Blood pressure and heart rate showed no changes within or between conditions. CONCLUSIONS: Brief intermittent stretching prevents prolonged sitting-induced lower limb endothelial dysfunction in young, healthy adults. This simple, accessible intervention provides a practical strategy to reduce cardiovascular risk in sedentary populations. Protective mechanisms may involve reduced venous congestion and preserved arterial shear stress. 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.