January 1, 1998AJP Heart and Circulatory Physiology269 citationsOpen Access
Muscle blood f low at onset of dynamic exercise in humans
Structured PICO
How does muscle blood flow change at the onset of dynamic exercise in humans?
P
Population
Humans undergoing passive and voluntary one-legged dynamic knee-extensor exercise
I
Intervention
Voluntary, one-legged, dynamic knee-extensor exercise
C
Comparator
Passive exercise
O
Outcome
Femoral arterial inflow and blood velocity at onset of exercisesurrogate
The initial increase in muscle blood flow at the onset of exercise is driven by mechanical factors (the muscle pump), followed by a more potent vasodilator-mediated amplification within the second to fourth contraction.
Abstract
To evaluate the temporal relationship between blood flow, blood pressure, and muscle contractions, we continuously measured femoral arterial inflow with ultrasound Doppler at onset of passive exercise and voluntary, one-legged, dynamic knee-extensor exercise in humans. Blood velocity and inflow increased (P or = 75% of peak power output), where Q(t) = Qpassive + delta Q1.1 - e-(t - TD1/tau 1)+ delta Q2.1 - e-(t - TD2/tau 2)+ delta Q3.1 - e-(t - TD3/tau 3); Qpassive, the blood flow during passive leg movement, equals 1.17 +/- 0.11 l/min; TD is the onset latency; tau is the time constant; delta Q is the magnitude of blood flow rise; and subscripts 1-3 refer to the first, second, and third components of the exponential model, respectively. The time to reach 50% of the difference between passive and voluntary asymptotic blood flow was approximately 2.2-8.9 s. The blood flow leveled off after approximately 10-150 s, related to the power outputs. It is concluded that the elevation in blood flow with the first duty cycle(s) is due to muscle mechanical factors, but vasodilators initiate a more potent amplification within the second to fourth contraction.