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Updated: Aug 9, 2026

Non-invasive Assessment of Microvascular and Endothelial Function
Published on: January 29, 2013
Upright posture reduces forearm blood flow early in exercise
J K Shoemaker1, P M McQuillan, L I Sinoway
1Section of Cardiology, The Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, Hershey, Pennsylvania 17033, USA. kshoemak@gcrc.hmc.psghs.edu
Upright posture reduces forearm blood flow (FBF) during early exercise. This reduction is mainly due to lower venous pressure, not sympathetic vasoconstriction, impacting exercise hyperemia.
Area of Science:
- Physiology
- Exercise Physiology
- Cardiovascular Regulation
Background:
- Upright posture influences cardiovascular responses, including blood flow dynamics.
- Understanding how posture affects exercise-induced hyperemia is crucial for exercise physiology.
Purpose of the Study:
- To test the hypothesis that upright posture modulates forearm blood flow (FBF) early in exercise.
- To investigate the roles of venous pressure and sympathetic activity in posture-induced changes in FBF.
Main Methods:
- Six subjects performed single and repeated handgrip contractions in supine and 70° head-up tilt (HUT) positions.
- Forearm blood flow (FBF), brachial artery mean blood velocity (MBV), and mean arterial pressure (MAP) were measured.
- Venous pressure (Pv) was manipulated by arm position, and sympathetic activity was altered via blockade.
Main Results:
- Head-up tilt (HUT) reduced antecubital venous pressure (Pv) compared to the supine position.
- Both single and repeated contractions showed reduced FBF and vascular conductance in HUT.
- Sympathetic blockade augmented FBF but did not alter the effect of HUT on postcontraction hyperemia.
Conclusions:
- Upright posture diminishes the early exercise hyperemic response.
- Reduced venous pressure, not sympathetic vasoconstriction, is the primary factor for attenuated FBF in HUT.
- Venous pressure significantly influences exercise-induced hyperemia, particularly in upright postures.
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