Single 1-s isometric forearm contractions produced immediate increases in forearm blood flow proportional to intensity, which were greater in below-heart vs above-heart positions (P<0.05).
Does contraction intensity determine immediate exercise hyperemia in healthy subjects?
Immediate exercise hyperemia is proportional to contraction intensity, supporting the existence of rapid-acting vasodilatory mechanisms at the onset of human forearm exercise.
Effect estimate: slope = 4.4 +/- 0.5%DeltaFBF/%MVC in AH
p-value: p=<0.05
We tested the hypothesis that rapid vasodilation proportional to contraction intensity contributes to the immediate (first cardiac cycle after initial contraction) exercise hyperemia. Ten healthy subjects performed single 1-s isometric forearm contractions at 5, 10, 15, 20, 30, 50, and 70% maximal voluntary contraction intensity (MVC) in arm above heart (AH) and below heart (BH) positions. Forearm blood flow (FBF; brachial artery mean blood velocity, Doppler ultrasound), mean arterial pressure (arterial tonometry), and heart rate (electrocardiogram) were measured beat by beat. Venous emptying (measured with a forearm strain gauge) was already maximized at 5% MVC, indicating that increases in contraction intensity did not further empty the forearm veins. Immediate increases in FBF were linearly proportional to contraction intensity from 5 to 70% MVC in AH (slope = 4.4 +/- 0.5%DeltaFBF/%MVC). In BH, the immediate increase in FBF demonstrated a curvilinear relationship with increasing contraction intensity and was greater than AH at 15, 20, 30, and 50% MVC (P < 0.05). Peak changes in FBF were greater in BH vs. AH from 10 to 50% MVC, even when venous refilling was complete (P < 0.05). These data support the existence of a rapid-acting vasodilatory mechanism(s) at the onset of human forearm exercise.
Tschakovsky et al. (Sat,) conducted a other in Healthy (n=10). Single 1-s isometric forearm contractions at varying intensities (5-70% MVC) and arm positions vs. Arm above heart (AH) vs arm below heart (BH) positions was evaluated on Immediate increases in forearm blood flow (FBF) (slope = 4.4 +/- 0.5%DeltaFBF/%MVC in AH, p=<0.05). Single 1-s isometric forearm contractions produced immediate increases in forearm blood flow proportional to intensity, which were greater in below-heart vs above-heart positions (P<0.05).