Concentration of NE and EPI (ng/mL)
Figure 2.1: Changes in Epinephrine and Norepinephrine during incremental
increase to maximum exercise
3
2.5
2
1.5
EPI (ng/mL)
1
NE (ng/mL)
0.5
0
0
50
100
150
200
250
300
350
400
Speed (m/s)
Figure 2.1 depicts the changes in catecholamine (epinephrine and norepinephrine) concentrations
during a graded treadmill test to exhaustion performed by a trained male at 21°C at sea level. The
speed of the subject at rest was 0 m/s. The first increment was to 100 m/s and then the speed was
increased by increments of 25 m/s up until the subject reached exhaustion (375 m/s)
Figure 2.2: A decrease in Splanchnic Blood Flow and an increase in Muscle Blood
Flow causing a decrease in total peripheral restistance
20
18
16
14
12
10
8
6
4
2
0
Blood Flow (L/min)
25
20
15
10
5
0
0
50
100
150
200
250
300
350
Muscle Blood
Flow (L/min)
TPR (TPR units)
30
Splanchnic
Blood Flow
(L/min)
TPR (TPR
units)
400
Speed (m/s)
Figure 2.2 depicts the changes in muscle blood flow and splanchnic blood flow during a graded treadmill
test to exhaustion performed by a trained male at 21°C at sea level. We can also observe a decrease in
TPR along with these changes in blood flows. The speed of the subject at rest was 0 m/s. The first
increment was to 100 m/s and then the speed was increased by increments of 25 m/s up until the
subject reached exhaustion (375 m/s).
During exercise the sympathetic nervous system (SNS) plays a role in regulating blood
flow to different parts of the body. Activation of the SNS causes an increase in release of the
neurotransmitter norepinephrine (NE) by its neurons. The neurotransmitter NE will then
stimulate the adrenal medulla causing it to release the hormones epinephrine (EPI) and NE
(Plowman & Smith, 2011). As figure 2.1 demonstrates, our subjects EPI and NE levels
increased during an increase to maximum exercise. The reason being is that these
catecholamines induce smooth muscle contraction of the visceral vasculature causing these
vessels to constrict (McAllister, 1998). This occurs in order to increase blood flow to the heart
and active skeletal muscles and decrease the blood flow to inactive muscles, skin, kidneys, and
organs served by the splanchnic circulation (McAllister, 1998). However, this increase in
catecholamines only really begins once the subject reaches a speed of close to 200 m/s. In fact,
during incremental increase to maximum exercise, the neurotransmitter NE starts to be released
at intensities close to 70% of VO2 max (Plowman & Smith, 2011). This release of
neurotransmitter can increase the basal concentrations of catecholamines by 5 to 10 times more
(Zouhal, Jacob, Delamarche, & Gratas-Delamarche, 2008). Furthermore, as exercise intensity
increases the metabolic needs of the active muscles and heart increase which is why the SNS
causes more blood to be redirected towards the contracting muscles (Plowman & Smith, 2011).
This idea is shown in figure 2.2 where we can see a large increase in muscle blood flow and a
slight decrease in splanchnic blood flow as the intensity of the exercise increases; the intensity in
this case being the speed that the subject is running at. We can also observe in figure 2.2 that the
total peripheral resistance (TPR) also decreases as the intensity increases. TPR is the resistance
that results from factors opposing the flow of blood like vasoconstriction which can be caused by
the SNS (Plowman & Smith, 2011). Therefore, a decrease in TPR must be due to the fact that
there is a greater increase in vasodilation in the active muscle vasculature then there is
vasoconstriction in the splanchnic vasculature (Sprangers, Wesseling, Imholz, Imholz, &
Wieling, 1991).
What mechanisms exist in muscle to counteract these effects (ie blood vessel function).
References
Marx, H. J., Rowell, L. B., Conn, R. D., Bruce, R. A., & Kusumi, F. (1967). Maintenance of
aortic pressure and total peripheral resistance during exercise in heat. J Appl Physiol,
22(3), 519-525.
McAllister, R. M. (1998). Adaptations in control of blood flow with training: splanchnic and
renal blood flows. Med Sci Sports Exerc, 30(3), 375-381.
Zouhal, H., Jacob, C., Delamarche, P., & Gratas-Delamarche, A. (2008). Catecholamines and the
effects of exercise, training and gender. Sports Med, 38(5), 401-423.