The Pressor Response:

Large vs. Small Muscle Exercise

Dustin Grinnell

Physiology Department

Pennsylvania State University

The challenge of exercise

• During exercise, cardiovascular system must:

– Deliver adequate oxygen to working muscles

– Remove waste products (lactate, CO2)

– Regulate body temperature

– Maintain arterial pressure

• In other words, maintain homeostasis

Background

Arterial Blood Pressure

• Pressure: force exerted by blood against arterial walls

• Systolic

– Pressure generated as blood is ejected from the heart during systole

• Diastolic

– Pressure during ventricular relaxation

Background

Blood Pressure with Exercise

• 120/80 mmHg at rest

• 200/60 mmHg at max aerobic exercise

Background

• The Pressor Response

- This blood pressure response to exercise is called the “pressor response”

Topic: Today I am going to talk about the blood pressure response to two modes of dynamic exercise

and why we see a heightened response with small muscle dynamic exercise.

Introduction

Aim of the Study

• It was the aim of this study to:

1) Explore the blood pressure response to two modes of dynamic exercise.

- The first exercise model used was the treadmill running exercise, which employs the use of many large muscles.

- The second exercise was a one-leg knee extension exercise, which contracts only a few small muscles.

2) Understand if the pressor response was determined by the active muscle mass.

MethodsLarge vs. Small Muscle Exercise

VO2max Test Knee Extension Exercise

Methods• The Proctor lab’s “fitness study”

-recruited 56 normotensive healthy men and women. -Subjects fell into 6 groups based on age and fitness level. -Young men, young women, low fit old men, high fit old men, low fit old women, and high fit old women.

• All subjects performed:- a large muscle exercise, a VO2max treadmill running test- a small muscle exercise, a one-legged knee extensor exercise.

• Variables recorded: -Heart rate -systolic blood pressure-diastolic -blood pressure -mean arterial blood pressure was calculated post-exercise.

Results

A ge G roup

Y M Y W O M (LF ) O W (LF ) O M (H F ) O W (H F )

dS

BP

(m

m H

G)

0

10

20

30

40

50

60

70

dS B P

A g e G ro u p

Y M Y W O M (LF ) O W (LF ) O M (H F ) O W (H F )

dM

AP

(m

m H

g)

0

5

10

15

20

25

30

35

dM A P

Pressor Response to Large Muscle Treadmill Running

Systolic Blood Pressure Mean Arterial Blood Pressure

Results

A g e G ro u p

Y M Y W O M (LF ) O W (LF ) O M (H F ) O W (H F )

dS

BP

(m

m H

G)

0

10

20

30

40

50

60

dS B P

A ge G roup

Y M Y W O M (LF ) O W (LF ) O M (H F ) O W (H F )

dM

AP

(m

m H

g)

0

5

10

15

20

25

30

35

dM A P

Pressor Response to Small Muscle Knee Extension

Mean Arterial Blood PressureSystolic Blood Pressure

More pronounced systolic blood pressure response during small muscle exercise

M E T

0 2 4 10 12 14 16

SB

P (

mm

Hg

)

130

140

150

160

170

180

T readm ill - S lope = 8 .0

K nee K ick - S lope = 26

Large Muscle Exercise vs. Small Muscle Exercise Results

Systolic Blood Pressure vs. MET

Results

M E T

0 2 4 10 12 14 16

MA

P (

mm

Hg

)

85

90

95

100

105

110

115

120

125

T readm ill - S lope = 4

K nee K ick - S lope = 16

Large Muscle Exercise vs. Small Muscle Exercise

More pronounced mean arterial blood pressure response during small muscle exercise

Mean Arterial Blood Pressure vs. MET

Results

• Pressor Response• In response to both large muscle and small muscle exercise all

groups showed significant increases in:

-Systolic blood pressure

-Mean arterial blood pressure

• Mode-specific Response• The blood pressure response was more pronounced during the

small muscle knee extension exercise compared to the large muscle treadmill running exercise.

Summary Why is the pressor response exaggerated in small muscle exercise

when compared to large?

• Treadmill Running– An aerobic activity like running, involves the rhythmic and alternative

contraction and relaxation of many muscles which causes systemic vasodilatation and a reduction in total peripheral resistance and a large drop in blood pressure.

• Knee Extension– During a knee kicking exercise, which involves the contraction and

relaxation of only a few small muscles only local, not systemic, vasodilatation is seen, which results in little or no change to total peripheral resistance and much higher pressor response.

Clinical Significance

• Why is an exaggerated blood pressure response a problem?

• Cardiovascular Risk- The effects of an increased, or exaggerated pressor response to

exercise, in healthy people has important consequences in cardiovascular disease such as coronary heart disease.

• Literature - Many studies have looked at this exaggerated blood pressure response

to graded dynamic exercise in healthy people and have found it to be a predictor of future hypertension and risk of cardiovascular mortality.

Clinical Significance• Bond, et at.

– showed a higher pressor response to physical stress is found in normotensives with a family history of hypertension.

• Stewart, et al. – showed that the exaggerated blood pressure response is related to

impaired endothelial vasodilator function.

• Chang et al.– showed that patients with exercise-induced hypertension have impaired

endothelium-dependent vasodilatation.

• Jae et al. – showed that inflammation may be associated with an exaggerated blood

pressure to exercise.

Conclusions

• The pressor response during small muscle exercise, during knee extension, exceeds the response seen in exercise using many large muscles seen during treadmill running.

• This exaggerated blood pressure response seen in small muscle exercise has important cardiovascular implications.

Future Directions

• Individual pressor responses may differ between the fitness study’s 6 groups.

• Factors that can alter the blood pressure response to exercise are:• Age

• Sex

• Fitness levels.

• It is the aim of an upcoming paper, and the seminar talk to present the data concerning these results.

Acknowledgements

Collaborators

Funding

Research Team

David Proctor, PhD (PI)

Joaquin Gonzales, PhD (Postdoc)

Sandy Smithmyer (Study Coordinator)

Julie Miedlar (Doctoral Candidate)

Seed Grant in Gerontology

Training Grants in Physiology, Gerontology

GCRC (University Park, Hershey)