A-15R Free Communication/Poster Peripheral Circulation
Debate continues regarding the contribution of muscle pump vs. vasodilation to the “immediate” increase (first second following initial contraction release) in blood flow at the onset of exercise. Furthermore, studies have exclusively focused on this issue in the context of rest-to-exercise transitions.
To test the hypothesis that there is an “immediate” vasodilatory contribution to the increase in blood flow in an exercise-to-exercise transition.
7 healthy young volunteers (2 female, 5 male) lay supine with the forearm elevated above heart level. In this position, veins are virtually empty and no additional contraction-induced venous emptying occurs in either rest-to-exercise or exercise-to-exercise transitions (i.e. muscle pump is ineffective). A step increase from rest to 3 min of mild (10% maximal voluntary contraction, MVC;R-10step) rhythmic, dynamic forearm handgrip exercise (1-s contraction/2-s relaxation duty cycle) was followed by a further step to moderate (20% MVC; 10-20step) exercise. Beat-by-beat measures of brachial artery diameter and mean blood velocity (MBV; Doppler ultrasound), heart rate (HR; ECG) and arterial blood pressure (ABP; arterial tonometry) were performed.
All data are mean ± SE. HR and ABP did not change during the first few seconds of each transition. Forearm blood flow (FBF) increased following release of the initial contraction in the 10-20step by the same absolute amount as the R-10step, despite no gain in muscle pump effectiveness (Δ FBF: R-10step: 52.2 ± 12.3 ml/min vs. 10-20step: 63.5 ± 13.7 ml/min, P = 0.65). These values represent a different % Δ (R-10step: 126.3 ± 25.6% vs. 10-20step: 20.3 ± 5.2%, P = 0.001).
These data support the hypothesis that there is an “immediate” further vasodilation in exercising muscle in an exercise-to-exercise transition. The mechanisms responsible remain to be determined.
Supported by NSERC; CFI New Opportunities Fund.