THE EFFECTS OF CONSTANT-LOAD EXERCISE AT PERCENTAGES OF THE
VENTILATION THRESHOLDS ON THE MAGNITUDE OF HEART RATE DRIFT
Raymond Martinez Jr.
B.S., California State University, Sacramento, 2012
THESIS
Submitted in partial satisfaction of
the requirements for the degree of
MASTER OF SCIENCE
in
KINESIOLOGY
(Exercise Science)
at
CALIFORNIA STATE UNIVERSITY, SACRAMENTO
SPRING
2012
THE EFFECTS OF CONSTANT-LOAD EXERCISE AT PERCENTAGES OF THE
VENTILATION THRESHOLDS ON THE MAGNITUDE OF HEART RATE DRIFT
A Thesis
by
Raymond Martinez Jr.
Approved by:
__________________________________, Committee Chair
Daryl Parker
__________________________________, Second Reader
Roberto Quintana
____________________________
Date
ii
Student: Raymond Martinez Jr.
I certify that this student has met the requirements for format contained in the University format
manual, and that this thesis is suitable for shelving in the Library and credit is to be awarded for
the thesis.
__________________________, Graduate Coordinator
Michael Wright, Ph.D.
Department of Kinesiology and Health Sciences
iii
___________________
Date
Abstract
of
THE EFFECTS OF CONSTANT-LOAD EXERCISE AT PERCENTAGES OF THE
VENTILATION THRESHOLDS ON THE MAGNITUDE OF HEART RATE DRIFT
by
Raymond Martinez Jr.
Statement of Problem
The purpose of this study was to determine the effects of constant-load exercise
performed above and below TH1 on the magnitude of HR drift, a component of CV drift.
Sources of Data
Data was collected from 9 trained cyclists who have been cycling 3-5 hours per
week for greater than 1 year.
Methods
Subjects reported to the laboratory on three occasions. The first visit consisted of a
maximal exercise test and two power detection rides. These were conducted to determine
the workloads for the remaining two visits. Visits 2 and 3 consisted of rides to fatigue at
an exercise intensity that elicited a VO2 that was 5% below TH1 and at the midpoint of
TH1 and TH2 (midTH). Fatigue was determined when subjects could no longer maintain
a cadence within 5 rpms of their self-selected cadence. Heart rate was recorded every
minute; VO2 was collected continuously for the first 5 minutes then every 10 minutes for
2 minutes. Blood pressure and RPE were recorded every 10 minutes.
iv
Results
Subjects displayed a significant main effect for intensity. Average HR during the
-5%TH was 159±13 bpm and was significantly lower than the midTH trial with a HR of
167±15 bpm (p=.002). There was also a significant main effect of duration (p=.000).
Tukey’s post hoc analysis revealed a significant HR rise from 156±14 bpm at 20% TTF
to 161±14 bpm at 40% TTF (p=.000). Heart rate rose again from 40% TTF to 165±15
bpm at 60% TTF (p=.002). Heart rate did not rise again until 100% TTF (170±15bpm
p=.04) (see Figure 2) . The drift in HR represents a 9.1% change in HR in the -5%TH and
an 8.9% in the midTH trial. Despite the statistical significance for both intensity and
time, there was not a statistically significance interaction effect (p=0.645).
Conclusions Reached
HR was significantly different for intensity and time but there was not statistical
significance for the interaction of intensity vs. time. The magnitude of HR drift above and
below TH1 was nearly the same percent change. Prior CV drift studies utilizing
percentage of maximal oxygen consumption as the prescription of exercise yielded
similar magnitude of drift. Future CV drift studies can design methods like traditional
studies.
_______________________, Committee Chair
Daryl Parker
_______________________
Date
v
ACKNOWLEDGMENTS
I would like to start by acknowledging my wife Chelsea. Thank you for your
support and encouragement throughout this process. Aside from the physical help with
this thesis, your presence, your love, laughter, and prayers have made the completion of
this thesis a reality. You continue to believe in me and trust in my lead. For that I am
most thankful.
I would also like to thank my family for their support throughout my graduate
work here at CSUS. Mom and Dad thank you for instilling in me a passion to learn and a
will to work. These traits have been invaluable to me both at school and in life. Rick and
Barb; my other parents, you are a true blessing. Thank you. Your support has gone far
beyond emotional support throughout this process. Chelsea and I are so thankful for you
both and do not know what we would do without you guys.
I would also like to thank Dr. Daryl Parker Ph.D. and Dr. Roberto Quintanta
Ph.D. Daryl you have helped turn a spark of interest into a wildfire. You have helped
turn me into the student and scholar that I am now. You gave me the skills necessary to
break into the clinical field that I am so passionate about. And most importantly you
have been a mentor and have taught me lessons that extend beyond the classroom, lab, or
clinic. Dr. Quintana you have been an invaluable resource to me during my time at
CSUS. Your passion for exercise physiology has inspired me to become a more
vi
dedicated student and consumer of research. I have enjoyed our intellectual
conversations as well as our shooting the breeze.
I would also like to thank everyone else who helped to contribute to this study:
Rick Bradley, Roy Salgado, and Max Polin. This study would have never left the ground
without you guys. And if it did, it would not have flown very long. Thank you for
helping me work out the kinks during pilot work and early data collection. I would like to
thank my fearless subjects. You all knowingly walked into a big box of hurt. Thank you
for your loyalty and contributions. Lastly, thank you to the co-workers and management
at Mercy General and UC Davis Medical Center. You have been so understanding and
supportive while I was balancing being a student and an employee.
Lastly I would like to give praise and glory to God. Thank you for leading me to
this field of study and this line of work. Thank you for leading me through this process.
May your will be done with the experience and knowledge I have acquired.
vii
TABLE OF CONTENTS
Page
Acknowledgments.....................................................................................................................vi
List of Tables ............................................................................................................................ x
List of Figures .......................................................................................................................... xi
Chapter
1. INTRODUCTION…………………………………………………………………………1
Purpose of Study .................................................................................................................. 4
Significance of Research...................................................................................................... 4
Definition of Terms.............................................................................................................. 4
Limitations ......................................................................................................................... 5
Delimitations ....................................................................................................................... 6
Assumptions......................................................................................................................... 6
Hypotheses.... ...................................................................................................................... 6
2. REVIEW OF LITERATURE ............................................................................................. 7
The Role of Temperature on Heart Rate Drift .................................................................... 7
The Role of Fluid on Heart Rate Drift ................................................................................ 9
The Role of Skeletal Muscle on Heart Rate Drift .............................................................. 10
Thresholds and Heart Rate Drift ........................................................................................ 11
Determinants of Heart Rate Drift ....................................................................................... 13
Summary
...................................................................................................................... 14
3. METHODS ....................................................................................................................... 16
Subjects ............................................................................................................................. 16
Experimental Design ......................................................................................................... 17
Measurement Instruments .................................................................................................. 18
Procedures ......................................................................................................................... 18
Data Analysis .................................................................................................................... 20
4. RESULTS ......................................................................................................................... 21
Heart Rate ......................................................................................................................... 21
viii
VO2......................................................................................................................................24
Pulse Pressure.................................................................................................................... 26
Body Weight...................................................................................................................... 27
5. DISCUSSION .................................................................................................................... 28
Heart Rate During CLE ..................................................................................................... 29
VO2 During CLE ................................................................................................................ 31
Pulse Pressure During CLE ............................................................................................... 33
Body Weight During CLE ................................................................................................. 34
Conclusion ......................................................................................................................... 36
Appendix A Informed Consent Form ..................................................................................... 38
References ............................................................................................................................... 43
ix
LIST OF TABLES
Page
1.
Table 1 Descriptive data for subjects.............................................................................17
x
LIST OF FIGURES
Page
1.
Figure 1 Average HR for the -5%TH trial to fatigue and midTH trial to fatigue..........22
2.
Figure 2 Heart Rate at percent time to fatigue.............................................................. 23
3.
Figure 3 Average VO2 for -5%TH trial to fatigue and midTH trial to fatigue...............25
4.
Figure 4 VO2 at percent time to fatigue........................................................................ 26
5.
Figure 5 Average body weight pre and post trials…….……………………………….27
xi
1
Chapter 1
INTRODUCTION
Heart rate (HR) is commonly used as a means of determining exercise intensity
amongst exercising populations. Monitoring HR is non-invasive, cost effective, and
easily measured by palpation or use of telemetry. Various populations utilize HR
monitoring to train at specific percentages of their maximal HR to elicit specific
intensities, in order to bring about physiological adaptations to the cardiovascular
systems. Training at percentages of maximal HR allows for exercise intensities to be
monitored during a workout. These methods of training are based on the physiological
principle that HR and exercise intensity are linearly related (Dennis et al. 1998). As
exercise intensity increases there is an increased demand for oxygen, resulting in linearly
increased cardiovascular responses such as HR (Dennis et al. 1998). Continual increases
in the cardiovascular responses will lead to improved function of the system as a result of
the principle of overload. Improvements in the cardiovascular system through training
lead to improved physical fitness, improved health, decreased risk of developing
hypokinetic diseases, and decreased mortality (ACSM’s Guidelines for Exercise Testing
and Prescription, 8th edition).
Although heart rate is commonly monitored during exercise, and used as a means
of prescribing exercise, the ability to maintain a specific heart rate is not easily achieved.
When exercising at a constant work rate, there is a tendency for HR to drift upward
overtime, despite no change in the exercise work rate. In order to maintain a steady and
2
constant HR, or to reduce a HR that has begun to drift, the exercise intensity must be
reduced (Kinerdmann et al. 1979). Kindermann and associates examined seven crosscountry skiers and exercised them at a constant speed and noticed an increase in HR over
time. When exercise was held at a constant HR, exercise intensity had to be progressively
reduced during a 30-minute exercise bout to maintain a constant HR. It can be argued that
decreasing the work rate over the duration of a training bout will result in a reduction in
training and a decrease in physiological adaptations to the cardiovascular system over
time.
The upward drift of heart rate without an increase in exercise intensity (HR drift),
is a component of a physiological phenomena known as, Cardiovascular Drift (CV drift).
Cardiovascular Drift (CV drift) has been characterized by an increase in heart rate (HR)
with a concomitant decrease in stroke volume (SV), and mean arterial pressure (MAP),
while maintaining a nearly constant cardiac output (Q) within the first 15 minutes of
exercise at a constant workload, speed or intensity (Rowell et al. 1986). It is well
understood what attenuates CV drift: heat, fluid loss, active muscle mass, and training
status, however there has yet to be a determination of the underlying cause of the
physiological phenomena (Coyle et al. 2001).
Several studies have been conducted to help explain the phenomena. However,
these studies have been conducted at exercise intensities that are set related to a
percentage of an individual’s VO2max; most commonly 50-75% VO2max (Fritzsche et al.
2009, Kounalakis et al. 2008,). Although the percent of maximal aerobic capacity elicited
is known during these studies, ventilation threshold (TH1) or respiratory compensation
3
point (TH2), have not been considered in these traditional CV drift studies. Omitting
these ventilation thresholds when setting constant workloads at a percentage of a
subject’s VO2max, causes uncertainty as to whether the subject is at, below, or above their
individualized ventilation thresholds. Gaesser and Poole (1996) describe exercise below
TH1 as moderate exercise, between TH1 and TH2 as heavy exercise, and beyond TH2 as
extreme exercise. Exercise beyond TH1 has been associated with non-steady state
exercise. Any workload above TH1 has a slow component for oxygen consumption and
VO2 drifts upward over time. Failure to incorporate TH1 or TH2 into to CV drift studies
can potentially allow for differences in exercise intensity for exercise performed at the
same percentage of VO2max. Furthermore, the discrepancy in exercise intensity between
subjects could lead to differences in the magnitude of CV drift between subjects.
There is an absence in the literature examining the effects on the magnitude of CV
drift while exercising at the intensities of moderate, hard, and severe exercise, as set by
TH1 and TH2. More specifically, there is an absence in the literature examining the
effects of exercising at intensities set at percentage of an individual’s ventilation
threshold (TH1) or respiratory compensation point (TH2) on CV drift. Exercise
conducted below TH1 has been defined as moderate exercise, between TH1 and TH2 as
heavy exercise, and beyond TH2 as extreme exercise (Gaesser and Poole 1998).
Therefore there is an absence in the literature examining the effects on the magnitude of
CV drift while exercising at the intensities of moderate, hard, and severe exercise, as set
by TH1 and TH2. Exercise performed at the varying intensities could potentially lead to
4
differences in the magnitude of CV drift as can be seen by the differences in the
magnitude of the slow component in the article published by Gaesser and Poole.
Purpose of Study
The purpose of this study was to determine the effects of exercising above and
below TH1 on the magnitude of HR drift, a component of CV drift.
Significance of Research
There has been a significant amount of research conducted as to what attenuates
cardiovascular drift, as well as what physiological markers define the phenomena, but
there has yet to be any research conducted examining the effects of exercising at
workloads below TH1and above TH1, more specifically the midpoint of TH1 and TH2
on CV drift. Examining exercise workloads at percentages of these thresholds will allow
for the observation of the change in magnitude of HR drift at certain exercise intensities.
These values can then be compared to those of previous CV drift studies that used
percentage of VO2max as a prescription of exercise intensity.
Definition of Terms
Cardiovascular Drift (CV drift)
An increase in heart rate (HR) with a concomitant decrease in stroke volume
(SV), and mean arterial pressure (MAP), while maintaining a nearly constant cardiac
output (Q) within the first 15 minutes of exercise at a constant intensity.
Heart Rate Drift (HR drift)
The progressive rise in HR over time despite no change in exercise intensity.
5
Stroke Volume (SV)
The amount of blood pumped from the ventricle per beat of the heart.
VO2max
The maximal amount of oxygen consumed during an incremental maximal
exercise test. VO2max is determined by: a plateau of oxygen consumption of 2
ml/kg/min from one stage to the next, a respiratory exchange ratio greater than 1.10, RPE
of 17, and achieving 90% of age predicted heart rate max.
Threshold 1
A systematic increase in the ventilatory equivilent for oxygen (VE/VO2) without
an increase in the ventilatory equivalent for carbon dioxide (VE/VCO2).
Threshold 2
An increase in both VE/VO2 and VE/VCO2.
Constant Load Exercise
Exercise conducted against a fixed resistance or speed over a period of time.
Limitations
1. Subjects performed all exercise tests and trials on a laboratory cycle ergometer, and
not their own bicycle.
2. Subject motivation to ride to fatigue.
3. Subject motivation to drink fluid to minimized body weight loss through sweat.
4. Cooling was done with a fan and hydration, the temperature of the room could have
risen.
6
Delimitations
1. Each subject will be subjected to the identical warm up procedure before each
maximal exercise test.
2. The cycle ergometer will be fitted prior to each maximal exercise test
3. Subjects were asked to refrain from any intensive exercise for the 24 hour period
prior to each trial.
4. All subjects pedaled at a power that elicited the same percentage of their own
individual thresholds for the constant load exercise trials.
Assumptions
1. All participants used maximal effort when completing VO2max tests.
2. Subjects will be able to perform to the best of their abilities under the laboratory
conditions.
3. Subjects reported to the laboratory participating in little to no intense cycling activity
24 hours prior to the test days.
Hypotheses
1. There will be a statistically significant increase in the magnitude of HR drift for both
intensities from beginning of exercise to fatigue.
2. There will be a statistically significant difference in the magnitude of drift between
the two exercise intensities.
3. The magnitude of HR drift for exercise performed at the midpoint of TH1 and TH2
will be greater than the magnitude of HR drift at the workload set below TH1.
7
Chapter 2
REVIEW OF LITERATURE
The cardiovascular system is a highly regulated and controlled organ system.
O’Leary and Potts (2008) discuss the operation of the central command, skeletal muscle
afferents, and baroreflex, as the mechanisms mediating the cardiovascular responses at
rest and during exercise. Although the design and control of the heart is well understood,
such as the electrical pathways, mechanical action, and stimuli, the mechanism that
causes cardiovascular drift (CV drift) is not. There are however, known physiological
responses that are associated with CV drift, such as, an increase in heart rate despite no
change in workload over time. This chapter will examine literature that has been
conducted in efforts to better understand and help explain CV drift.
The Role of Temperature on Heart Rate Drift
Temperature seems to affect the severity of cardiovascular drift. Research has
been conducted to help understand the reasons for the increased magnitude of CVdrift as
well as what physiological effects are associated with the drift in a hot environment. A
study performed by Wingo et al. (2005), measured the effects of heat induced CV drift on
VO2max. Data collected by Wingo and associates suggested that CV drift in a heated
environment, is associated with decreases in maximal oxygen uptake and increased
metabolic intensity. CV drift was measured in 9 male cyclists between 15 and 45
minutes of cycling at 60% VO2max in 35C environment. There was a 12% increase in HR
and a 16% decrease in SV between 15 and 45 minutes of cycling that was accompanied
8
by a 19% decrease in VO2max, displaying the effects of exercise in a hot environment. Hot
temperature seems to increase the severity of CV drift. Lafrenz et al. (2008), examined
the magnitude of CV drift and the associated decrease in maximal oxygen uptake at 35C
(HEAT) and 22C (COOL); in a hot and cool environment. CVdrift was greater in the
HEAT versus COOL trials. HR drifted by 11%, SV was reduced by 11% and VO2max
was reduced by 15% during in the HEAT trial. Results from the study suggest that the
magnitude of CV drift during prolonged submaximal exercise, and the accompanying
decrease in VO2max was greater for the hot environment versus exercise in a cool
environment. Heats seems to increases the degree of CV drift and reduce VO2max,
however, body cooling attenuates the decrease in maximal oxygen uptake associated with
cardiovascular in a hot environment. A study performed by Wingo and Cureton (2006)
produced results that displayed a reduction in the decrement of maximal oxygen uptake
with body cooling during exercise in a hot environment. Subjects for this study cycled in
a 35 C environment at 60% VO2max for 15 min, 45 min with no cooling (NC), and for 45
min with fan air cooling (FAN). Each exercise trial was followed by a graded exercise
test to measure VO2max. During the FAN trial subjects produced a HR increase of 4%, a
SV decrease of 3%, and a decrease in VO2max of 5.7%. In comparison, the NC trial
experienced a 16% increase in HR, a 12% decrease in SV, and an 18% decrease in
VO2max. The addition of a fan for the purpose of body cooling reduces the magnitude of
CV drift by reducing the increase of HR drift, and reducing the amount of SV decline
during constant load exercise.
9
The Role of Fluid on Heart Rate Drift
The magnitude of CV drift seems to be more severe with an inadequate intake of
fluid during exercise. Such conditions further warrant a decline in maximal oxygen
consumption. In a study performed by Gaino et al. (2006), fluid ingestion reduced the
decrease in VO2peak that is associated with CV drift. In this study 11 subjects exercised at
60% VO2max in 30C with 40% relative humidity for durations of 15, 60, and 120 minutes
without fluid and for 120 minutes with fluid intake for a total of 4 trials. The data
collected from the study suggests that the decrease in SV associated with CV drift during
prolonged, submaximal exercise in a hot environment, as a result of inadequate fluid
ingestion, reduces VO2peak. However, ingesting fluid under such conditions improved
performance in prolonged exercise by preventing the decline in SV and preserving
VO2peak. During the 120-minute fluid ingestion trial subjects displayed a significantly
less increase in HR and decrease in VO2peak suggesting the influence of hydration status
of subjects and it’s negative effects on the magnitude of HR drift and the subsequent
decrease in maximal oxygen uptake.
The effect of fluid ingestion on CV drift was further displayed in a study
conducted by Rowland et al. (2008). Rowland and associates examined the influence of
hydration in prepubertal boys and assessed the relationship between CV drift and changes
in VO2. Temperature, heart rate, and cardiac output rose while stroke volume remained
the same for the subjects who hydrated during exercise. This data displayed the
importance of hydration on maintaining stroke volume to manage CV drift and preserve
10
VO2. Hydration status pre exercise and during exercise is an important factor during CV
drift study.
The Role of Skeletal Muscle on Heart Rate Drift
The amount of active muscle mass seems to play a role in CV drift. In a study
performed by Kounalakis et al. (2008), the role of active muscle mass on exerciseinduced CV drift was examined. During this study, subjects cycled using both legs
during one trial, and during a separate trial subjects cycled using one leg. Exercise
performed during the one leg trial resulted in subjects generating half the percentage of
VO2max elicited by the double leg trial. Cardiovascular measurements were taken and the
data recorded during both trials suggested that two-legged cycling generated a greater
decrease in stroke volume, greater increase in heart rate, greater decline in blood volume,
and higher sympathetic activation, and a greater decrease in cardiac output; all markers of
CV drift. Data collected by Kounalakis et al. (2008) suggests that active muscle mass
seems to play a role in the development of CV drift as well as the magnitude of CV drift
during exercise.
While the amount of active muscle mass seems to contribute to CV drift, the role
of the skeletal muscle pump on the development of cardiovascular drift does not seem to
have an effect. In a separate study performed by Kounalakis et al. (2008), the role of the
skeletal muscle pump on CV drift was examined. Cycling cadence was manipulated in
this study to influence the skeletal muscle pump of the lower extremities during this
study. Subjects cycled at a constant workload set at 60% of VO2max at either a low
cadence (40 rpm) or high cadence (80 rpm) for 90 minutes on two separate days.
11
Cardiovascular parameters such as HR, VO2, SV, and cardiac output (Q), were monitored
and recorded during the study. CV drift was achieved during both exercise protocols and
was determined by a decrease in SV and increase in HR. From minute 20 of exercise to
its termination, SV decreased 16.2 2.0 ml/beat and 17.1 1.0 ml/beat, HR increased 18.3
2.0 bpm and 17.5 3.0 bpm for 40 rpm and 80 rpm respectively, showing now statistical
significance between groups. Mean Q and mean arterial pressure showed now statistical
significance between trials. The data collected from the study suggests that the muscle
pump had no effect in the development of CV drift when cycling at two different
cadences producing and equal amount of power relative to VO2max. Although the amount
of active muscle mass plays a role in the magnitude of CV drift, the role of the skeletal
muscle pump in regards to venous return, plays no role in the development or magnitude
of CV drift.
Thresholds and Heart Rate Drift
Currently, little research has been conducted utilizing the physiological thresholds
in the design of CV drift studies. Studies have traditionally been conducted at a
percentage of a subjects VO2max; most commonly 60-75% VO2max. In a study performed
by Cheatman et al. (2000), 10 men (18-25) and 8 boys (10-13) exercised at an exercise
intensity that was set relative to their VO2 at their ventilatory threshold (TH1) for 40 min.
Subjects cardiovascular responses were monitored and compared during the exercise
trial. Heart rate increased significantly during the 40-minute bout of exercise 9.5% in the
boys and 13.6% in men, while SV significantly decreased 8.8% and 11.6% in the boys
and men respectively. Although the men displayed greater changes in HR and SV the
12
difference between the two groups was not statistically significant. Cardiac output was
greater in men and remained constant during the trial. Mean arterial blood pressure was
higher and decreased 4.2% during the trial in men whereas mean arterial blood pressure
remained constant for the boys during the trial. Total peripheral resistance was higher in
the boys compared to the men and remained constant during the trial. There was a greater
decrease in plasma volume in men 10.2% compared to boys 5.7% during the trial.
However, despite the reduction in plasma volume, the values were reported as
statistically unrelated to changes in SV. The cardiovascular changes during prolonged
exercise were similar in both groups; however, there was a greater magnitude in the CV
drift parameters in men compared to boys during exercise performed at TH1.
Gaesser and Poole (1995) discuss the effects of exercise intensity in relation to
TH1 and TH2 and its influence on the cardiovascular and metabolic systems. They
discuss the existence of three exercise domains with respect to VO2 and blood lactate
responses during exercise. Moderate exercise is the first domain and exists blow the
lactate threshold (TH1). Exercise performed at an exercise below this threshold will be
moderate in nature, resulting in a VO2 steady state where VO2 rises to meet exercise
demands and then remains stable at that level, can be attained and remain constant
throughout exercise should intensity remain constant. Exercise performed at an intensity
above TH1 becomes heavy in nature as described by Gaesser and Poole, and incurs an
additional slow component of VO2, prolonging the attainment of steady state exercise,
elevating VO2 above the expected value for the work rate. At this heavy intensity, blood
lactate remains elevated until it plateaus with VO2. The third domain of exercise
13
intensity is termed sever intensity. This intensity is reached when a workload is set
beyond the TH2. Characteristics of sever intensity include a VO2 and blood lactate
increase that will rapidly reach maximal exercise values at fatigue of a graded exercise
test. Knowing that these thresholds and thus exercise intensities are elicited at a
percentage of VO2max is of great importance when designing a CV drift study. If these
exercise thresholds are ignored, it is debatable as to whether the subjects are exercising at
equal intensities. Furthermore, the increase in VO2 will result in an increase in metabolic
intensity, which would cause HR to increase as well.
Determinants of Heart Rate Drift
Although the CV drift phenomenon is not completely understood, there are
determinants that are known. One of the solid determinants of CV drift is an increase in
HR overtime despite no change in exercise intensity. A study performed by Kindermann
et al. (1979), was one of the leading CV drift studies within the field. More specifically
Kindermann examined the HR drift and lactate parameters of subjects exercising at
constant workloads. In this study Kindermann had subjects exercise at a constant HR for
30 minutes on a treadmill. In order to maintain a constant HR during 30 minutes of
exercise, subjects had to progressively reduce treadmill speed. With the decrease in
treadmill speed oxygen uptake and lactate were progressively reduced while HR
remained stable. On a separate trial Kindermann had subjects exercise at a constant
treadmill speed for a duration of 30 minutes. During this trial subjects displayed HR drift
and an increase in lactate over time. This traditional and leading study of its time,
displayed the relationship between exercise intensity and HR in regards to CV drift.
14
More recently other physiological markers have been associated with CV drift. In
a review article Coyle and Gonzalez-Alonso (2001), review the common physiological
markers and identifiers of CV drift. The authors describe CV drift as a phenomenon
where CV responses begin a continuous time-dependent change after about 10 minutes of
prolonged and constant moderate exercise in a neutral or warm environment. Moderate
exercise in this article was described as 50-75% VO2max. Furthermore, the CV drift is
defined by a progressive decline in stroke volume and pulmonary and systemic mean
arterial pressure. This is followed by a progressive increase in HR with a nearly constant
maintenance of cardiac output. These markers have been the basis of research within the
realm of CV drift. Studies have not deviated from the use of exercise intensities set
relative to VO2max, and continue to disregard the incorporation of the physiological
thresholds that greatly help to define exercise intensity specific to each individual.
Summary
Although there are several suggested theories and mechanisms to explain CV
drift, none seem to completely explain the phenomena. In an article written by Coyle and
Gonzalez-Alonzso (2001), the most common theories are reviewed, and a traditional
hypothesis of cutaneous blood flows reduction causing CV drift is shown to no longer be
a speculated cause of CV drift, due to lack of data. What is certain about CV drift is that
stroke volume decline during prolonged exercise is influenced by the increase in heart
rate as shown by Fritzsche et al. (1999). Cardiovascular drift could possibly be a
combination of mechanisms ranging from ambient temperature, to the amount of active
15
skeletal muscle. However, further research is needed to determine the underlying cause of
the phenomena.
Future studies should continue to be conducted based on what has already been
done. However, the use of the ventilation thresholds in developing intensities and
workloads for CV drift studies should be taken into account. When thresholds are
neglected, as seen in the traditional CV drift studies, homogeneity is compromised
between subject workload due to VO2 measurements occurring at different spectrums of
individuals TH1 and TH2 values. This could potentially result in the selected exercise
intensity for the study being moderate, heavy, or severe exercise for the subject
depending on their own exercise tolerance as set by their individual exercising thresholds.
While one subject may be exercising at a moderate intensity because the study was set at
65% VO2max, another subject could potentially be exercising at a workload that is heavy
exercise above their TH1 due to the relative percent of VO2max for their individual
threshold. Such situations could lead to different magnitudes of CV drift between
subjects, resulting in inaccurate data analysis and interpretation.
In order to ensure that subjects are exercising at equal workloads and that CV drift
magnitudes are not a result of unequal workloads between subjects, the exercise induced
thresholds (TH1 and TH2), need to be incorporated into future CV drift studies.
Threshold identification is easily achieved during a graded exercise test and will
significantly help in exercise prescription for the participants of CV drift studies.
16
Chapter 3
METHODS
Cardiovascular drift is a physiological phenomenon that is characterized by an
increase in heart rate and a decrease in stroke volume despite a constant workload held
over a period of time. The exact mechanism that causes the phenomenon is unknown.
Only factors that either increase or decrease the magnitude of CVdrift are known.
Although several studies have been conducted to determine what attenuates HR drift, the
magnitude of heart rate drift (HR drift) at percentages of the ventilatory thresholds has
not been thoroughly researched. Studies concerning CV drift set intensities at 50-75%
VO2max. This study will examine the magnitude of HR drift while exercising at a constant
workload at percentages of the ventilation thresholds (TH1 and TH2) as well as where the
HR drifts up to at exercise exhaustion.
Subjects
All subjects involved in this study were trained cyclists (see Table1). All volunteers
had been actively riding competitively or recreationally for at least one year for at least 35 hours a week upon agreeing to participate in the study. Each volunteer was informed
both in written and verbal statements of the necessary procedures involved in the study.
All subjects singed an informed consent document of the associated risks of the stud
(Appendix A).
17
Table 1
Descriptive data for subjects
Descriptive Data
Variable
Age
Height
Weight
VO2max
Watt Max
9 Subjects
Mean
26.1 yrs
175.1 cm
76.9 kg
55.9 ml/kg/min
373.4 watts
Standard Deviation
4.9
6.1
18.6
10.2
54.6
Experimental Design
Subjects were aware of the purpose of the study and will all be included in the
same experimental group. There were 3 visits to the exercise laboratory. Lab visit 1
included a VO2max test and two power identification rides. Lab visits 2 and 3 consisted of
endurance rides to fatigue. Visit 2 was set at a workload that was equal to a power output
that elicited a VO2 that is 5% less than TH1 (-5%TH1). Visit 3 included an endurance
ride to fatigue at a power output that elicited a VO2 value that was intermediate of TH1
and TH2 (midTH). The power identification rides yielded VO2 values that will be used
during the endurance rides to fatigue. The tests start date a wattage that was15% and
20% less than that of the calculated -5%TH1 and midTH power respectively, and were
increase by 5 watts every 4 minutes with continuous expired air collection until subject
reached a VO2 value equal to -5%TH1 and midTH VO2 values. Subjects exercised to
volitional fatigue so that HR drift can be tracked through its entire course. Fatigue will be
determined when subjects can no longer maintain their cadence within 5 rpm of their
18
chosen cadence. Heart rate was recorded every minute. Subjects performed the exercise
test in a neutral temperature environment with a fan providing cooling, so heat was not a
factor for explaining cardiovascular drift. Subjects were given water during the test ad
libitium and body weight was measured pre and post trial to track body weight loss so
that hydration was not an explanation for the HR drift that was observed during the study.
Measurement Instruments
Exercise tests were conducted on a Lode Excaliber cycling ergometer to measure
the workload intensity using wattage at percentage of ventilation thresholds. A Parvo
Medics True One 2400 Metabolic Cart was used to determine VO2max and ventilation
thresholds as well as to collect ventilation equivalents during constant load exercise to
fatigue. Heart rate monitors were used to record heart rates during the exercise tests and
prolonged exercise trials to exhaustion. Rating of perceived exertion (RPE) was recorded
every five minutes using the Borg 6-20 scale.
Procedures
Data collection began with obtaining subjects initial values prior to exercise test. These
values included height, weight, age, VO2max, and identification of ventilation thresholds
(TH1 and TH2). Height was recorded in centimeters, weight was recorded in kilograms,
VO2max was recorded using a ramp cycling protocol starting at 70 watts with a 35-watt
increase every minute. From the VO2max data, threshold values were determined from
VE/VO2 and VE/VCO2 values. Two reviews had to agree on the ventilation thresholds. If
thresholds were not agreed upon, a Dmax method was used to determine the TH1.
Following the VO2max test, subjects received a 20-minute rest period and then underwent
19
two threshold power identification rides. The threshold identification rides were then
used to determine the power that would elicit the desired VO2 for the endurance rides to
fatigue. All trials were performed at a constant load exercise to the point of exhaustion.
Exhaustion was determined when subjects could not keep their self selected pedaling rate
within 5 rmp’s of where they began the trail. Trial 1 was set at an exercise intensity that
elicited a VO2 that is 5% below TH1 VO2 (-5%TH). Trial 2 was set at an intermediate
workload of TH1 and TH2 and elicited a VO2 that is intermediate of these thresholds
(midTH). During the exercise protocol, subjects had their heart rate recorded every
minute by a Polar heart rate monitor, ventilation equivalents were recorded continuously
by way of expired air for the first 5 minutes of the endurance rides and then every 10
minutes thereafter for two minutes until exhaustion. Subjects were asked to report their
RPE after each 2 minute expired air collection. Blood pressure was recorded at the end
of each expired air collection using traditional blood pressure instruments and techniques.
Nude body weight was measured pre and post exercise in a private and secured room by
the subjects themselves, and was reported to researchers. In addition to the first lab visit,
subjects had to complete the two trials on two separate days with at least a day separating
each trial.
20
Data Analysis
Data was analyzed using Statistica software. The two independent variables for the study
that were analyzed were exercise intensity as defined by the ventilation thresholds and
percent time to fatigue. A 2-way ANOVA with repeated measures with a Tukey’s post
hoc analysis was used to assess the collected parameters, and a level of significance of
p<0.05 was used.
21
Chapter 4
RESULTS
For this study subjects completed a VO2max test and power detection trials on their
first visit to the lab. Subjects then returned on two separate occasions to engage in a
prolonged exercise trial to fatigue at an intensity that elicited a VO2 equal to -5% of TH1
and a VO2 equal to a midTH value between TH1 and TH2. During the study, subjects
varied widely in time to fatigue (TTF) for both the -5%TH trial and the midTH trail. As a
result, data was analyzed using a percent TTF scale ranging from 20-100% of TTF.
Analyzing data in this manner allowed for comparisons at relative time points from
subject to subject.
Heart Rate
Subjects displayed a significant main effect for intensity. The average heart rate
during the -5%TH was 159±13 bpm and was significantly lower than the midTH trial
with a heart rate of 167±15 bpm (p=.002) (see Figure 1). There was also a significant
main effect of duration (p=.000). Tukey’s post hoc analysis revealed a significant HR rise
from 156±14 bpm at 20% TTF to 161±14 bpm at 40% TTF (p=.000). Heart rate rose
again from 40% TTF to 165±15 bpm at 60% TTF (p=.002). Heart rate did not rise again
until 100% TTF (170±15bpm p=.04) (see Figure 2) . The drift in HR represents a 9.1%
change in HR in the -5%TH and an 8.9% in the midTH trial. Despite the statistical
significance for both intensity and time, there was not a statistically significance
interaction effect (p=0.645).
22
Figure1.
Average HR for the -5%TH trial to fatigue and midTH trial to fatigue
Average HR for -5%TH and midTH
190
180
*
170
Heart Rate
160
150
140
130
120
110
100
* Statistically Significant p=.002
5%TH
midTH
23
Figure 2.
Heart Rate at percent time to fatigue.
Heart Rate
190
Heart Rate
180
***
170
**
*
-5%TH
midTH
160
150
140
20
40
60
80
% Time To Fatigue
* Significant difference 20-40% p=.000
** Significant difference 40-60% p=.002
*** Significant difference 60-100% p=.04
100
24
VO2
Subjects displayed a significant main effect for intensity. The average VO2
during the -5%TH was 3.03±.46 L/min and was significantly lower than the midTH trial
with a VO of 3.33±.46 L/min (p=.002) (see Figure 3). There was also a significant main
effect of duration (p=.000). Tukey’s post hoc analysis revealed a significant rise in VO2
from 3.03±.45 L/min at 20% TTF to 3.12±.45 L/min at 40% TTF (p=.000). There was a
significant rise in VO2 from 40% TTF to 3.26±.50 L/min at 80% TTF (p=.000), there was
also a significant rise in VO2 from 3.19±.47 L/min 60% TTF to 3.3±.53 L/min at 100%
TTF (p=.000) (see Figure 4). The drift in VO2 represents a 10.5% change in VO2 during
the -5%TH and a 7.2% change in VO2 during the midTH trial. Despite the statistical
significance for both intensity and time, there was not a statistically significant
interaction effect (p=0.645).
25
Figure 3.
Average VO2 for -5%TH trial to fatigue and midTH trial to fatigue
VO2 for -5%TH and midTH
4.5
4
*
3.5
L/min
3
2.5
2
1.5
1
0.5
0
*Statistically Significant p=.000
-5%TH
midTH
26
Figure 4.
VO2 at percent time to fatigue
VO2 %TTF
4
3.8
L/min
3.6
3.4
-5%TH
midTH
3.2
3
2.8
2.6
2.4
20
40
60
80
100
Time to fatigue
* Significant difference 20-40% (p=.000)
** Significant difference 40-80% (p=.000)
*** Significant difference 60-100% (p=.000)
Pulse Pressure
Pulse was determined by taking the difference of systolic blood pressure and
diastolic blood pressure obtained during the trials. Although there was no statistical
significance for pulse pressure and intensity (p=.062) there was a trend for the pressure to
be higher at the midTH trial for the subjects. No statistical significance (p=0.165) was
achieved for pulse pressure and time. This suggests that there was no meaningful change
27
in stroke volume during the rides to fatigue for the 9 subjects. Furthermore, there was not
a statistically significant interaction effect (p=.235) for intensity and time.
Body Weight
Nude body weight was obtained for each subject before the beginning of each trial and
then immediately following dismount of the ergometer at the end of the trial. Subjects
had a significant main effect for pre and post body weight measurements 76.319.5 kg
and 75.619.5 kg respectively (p=.0005) (see Figure 5). There was no statistically
significant main effect for intensity (p=.248). No statistically significant main effect for
interaction was produced (p=.203).
Figure 5.
Average body weight pre and post trials.
PRE-POST BW
100
95
*
Kilograms (kg)
90
85
80
75
70
65
60
*Statistically Significant p=.001
Pre Wt
Post Wt
28
Chapter 5
DISCUSSION
Cardiovascular drift is a physiological phenomenon where CV responses begin a
continuous time-dependent change after about 10 minutes of prolonged and constant
moderate exercise in a neutral or warm environment (Coyle et al 2001). Furthermore, the
CV drift is defined by a progressive decline in stroke volume and pulmonary and
systemic mean arterial pressure. There is a concomitant progressive increase in HR to a
maintain cardiac output. These markers have been the basis of research within the realm
of CV drift. Studies have not deviated from the use of exercise intensities set relative to
VO2max, and continue to disregard the incorporation of the physiological thresholds that
greatly help to define exercise intensity specific to each individual. In order to ensure
that subjects are exercising at equal workloads and that CV drift magnitudes are not a
result of unequal workloads between subjects, the exercise induced thresholds (TH1 and
TH2), were incorporated into the design of this CV drift study.
In addition to not incorporating the ventilation thresholds into the design of
previous CV drift studies, trials were conducted at predetermined trial times. Exercise
duration for previous studies have ranged from 45-120 minutes, and were referred to as
prolonged trials (Gaino et al. 2006, Lafrenz et al. 2008, Wingo and Cureton 2006, and
Wingo et al. 2005). Our study trials were conducted to volitional fatigue. To our
knowledge only one CV drift study has been conducted at submaximal workloads
29
maintained to the point of fatigue. (Lafrenz et al. 2008) Furthermore, this study was
conducted at constant load exercise intensity set relative to percentages of the ventilation
thresholds rather than being set relative to percent VO2max.
Heart Rate During CLE
During both the -5%TH and midTH trials, the phenomenon of HR drift was
observed. Similar to traditional studies, HR began to increase from its steady state
condition early on in both trials and continued to rise up to the point of fatigue. Although
subjects were exercised at the same intensities relative to their thresholds, their time to
fatigue (TTF) varied greatly. Due to the variability of trial TTF between participants for
each trial, data was analyzed by creating a TTF percentage scale. Time to fatigue could
then be compared between subjects at 20, 40, 60, 80, and 100% of TTF.
Heart rate displayed a statistically significant difference for the -5%TH and
midTH intensity (p=.002). The main effect for intensity represented a 159±13 bpm
average HR for the -5%TH and a 167±15 bpm average HR for the midTH. Heart Rate
increased from 152±12bpm to 166±15bpm for the -5%TH trial this represents about a
9.1% change from 20% to 100% TTF. Exercise performed at the midTH produced an
increase in HR from 159±15bpm to 173±15bpm representing a 8.9% change from 20%100% TTF. The magnitude of HR drift that was observed in the current study is
comparable but not similar to that of prior CV drift studies conducted at percentages of
VO2max. For an example, a change in HR equal to 11% was observed in two separate
studies examining different variables (Fritzsche et al. 1999, Lafrenz et al. 2008).
Ambient temperater and its effect on CV drift was examined by Lafrenz, while utilization
30
of beta blockers on the preservation of SV was examined by Fritzsche. Although the
magnitude of drift was not exactly the same, the magnitude was similar. The difference
could be due to the fact that subjects did not receive water ad libitum in either study,
while the subjects in the current study did. Fluid replacement during 120 minutes of
exercise conducted at 70% of VO2max resulted in a 5% increase in HR (Hamilton et al.
1991). Similarly the subjects in the current study displayed an 8.9% increase in HR from
20% TTF to 100%TTF at the midTH. The difference in magnitude between the two
studies could have resulted from fluid being consumed as in the current study, rather than
intravenous infusion as done in the previous CV drift study. The infusion of fluid most
likely resulted in better diffusion and utilization of the fluid. Further more the infusion of
fluid may have resulted in maintenance of a cooler core temperature.
These values suggest that the difference in the magnitude of drift were minor
despite their significance. Previous CV drift studies that used %VO2max as a means of
prescribing CLE do not need to be reexamined as hypothesized by this current study.
The ventilation thresholds in regards to HR drift do not seem to elicit large enough
differences in the magnitude of HR drift as hypothesized.
In addition to intensity, HR in relation to TTF was another interesting observation
from the current study. Although HR had a significant increase from 20-100% of TTF,
there were times where HR did not change significantly. Statistical significance in HR
was achieved from 20-40%, from 40-60%, and 60-100% TTF. However, from 60-80%
TTF HR did not have a statistically significant increase in HR. Overall HR increased
31
from 20% TTF to 100% TTF, however there were times when HR was not significantly
increasing.
From applied standpoint the data suggests that at any given workload that is either
below TH2 or at any percentage of VO2max within the range of 50-75% as seen in prior
CV drift studies, HR drift will be similar in magnitude. In the current study subjects
exercised at an intensity of moderate and hard as characterized by Gaesser and Poole.
And according to the work of Gasser and Poole work performed above TH1 resulted in a
slow component of oxygen that was not present at workloads below TH1. However, HR
did not follow this same model. Despite the difference in intensities the magnitude of HR
drift was very similar to one another as well as prior CV drift studies. This information
can be applied with exercise prescription or in the explanation of prolonged exercise
when HR or rate of perceived exertion (moderate or hard) is used as a means of exercise
prescription. For workloads prescribed according to HR or perceived exertion at
moderate or hard intensities the change in HR will be similar and will only represent
about a 9% change.
VO2 During CLE
In addition to HR drift occurring over the course of both intensities, interestingly
enough VO2 drifted as well. There was a statistically significant increase for VO2 for both
intensity and time (p=.000 and p=.000 respectively). The term that has been used to
describe this drift in consumption of oxygen during CLE has been termed aerobic drift
(Rowell 1986). This physiological response should not be confused with the VO2 slow
component. Gaesser and Poole 1985, suggest that CLE exercise performed above the
32
lactate threshold results in a rise in VO2. When the CLE is maintained for durations
greater than 10 to 15 minutes, VO2 can achieve a steady state in oxygen consumption.
During the current study, subjects VO2 progressively increased from 20-40% time to
fatigue, from 40-80% TTF, and from 60-100% TTF (p=.000). Therefore, the term
aerobic drift will be used as used by Rowell 1986 to describe the increase in VO2
throughout the CLE trial.
The increase in VO2 during CLE in conjunction with HR drift has been noted in
prior CV drift studies when dehydration was prevented. Hamilton et al. 1991
demonstrated that when subjects are well hydrated during exercise, HR will continue to
drift, however stroke volume could be maintained and cardiac output could increase. The
findings in the current study are similar in that VO2 and HR increased while pulse
pressure remained unchanged. When fluid is given in adequate amounts to prevent
dehydration in subjects during prolonged CLE, VO2 can increase as shown by Rowland et
al. 2008, that observed an aerobic and CV drift in 8 euhydrated boys who had an increase
in HR of 13.2% and an 8% increase in VO2. The rise in VO2 is comparable to the 7.2%
magnitude of drift that was observed in the current study for VO2 at the midTH trial.
Methodology for hydration was similar between the current study and Rowland in efforts
to prevent dehydration and decreases in SV.
Concerning the importance of aerobic drift in the current study, it has been
suggested that aerobic and CV drift are mechanistically related (Hamilton et al. 1991,
Rowell 1986, Rowland et al. 2008). Rowland et al. 2008 included a schematic model for
dynamics of cardiovascular and aerobic drift: during CLE there is an increase in muscle
33
temperature, which leads to an increased metabolic rate, which leads to increased aerobic
drift as well as local arteriolar vasodilation, causing an increase in cardiac output.
Aerobic drift from the increased metabolic rate then leads to an increase in cardiac
output. This model displays the relationship between both aerobic and cardiovascular
drift.
From an applied standpoint, future studies should consider the relationship
between CV drift and aerobic drift. Aside from studies considering the relationship of
the two physiological responses, clinicians, coaches, and trainers should consider the
relationship of the two responses. In a non-study setting people drink water ad labitium
during exercise. If it is consumed to the point at which dehydration is prevented, there
will be an increased cardiovascular and metabolic rate despite no change in exercise
intensity. This increases the metabolic cost of exercise.
Pulse Pressure During CLE
In the current study, blood pressures were measured on subjects every 10 minutes
during each exercise trial up to the point of fatigue. From this blood pressure data, pulse
pressure was calculated by taking the difference of the systolic blood pressure and
diastolic blood pressure. Pulse pressure has been used as a representation of stroke
volume (SV). Although it is an indirect measure of SV, pulse pressure is less invasive
cost effective means of inferring SV in a non-clinical setting.
Traditionally in CV drift studies; the decline in SV has been used as a
characteristic of defining CV drift. There are competing theories as to the way in which
SV is decreased during traditional CV drift. The longer standing theory regarding the
34
decline of SV with CV drift stems from the thought that the increase in cutaneous blow
flow during CLE, in response to an increase in skin and core temperature, causes a
reduction in SV as blood is being moved to the skin surface (Rowell et al. 1986). More
recently, the theory that SV decreases in response to reduced filling time of the ventricles
caused by the increase in HR during CLE has been used to explain CV drift (Coyle et al.
2001).
One of the findings of this study was the pulse pressure not reaching a statistical
significant difference for intensity (p=.062) or time (p=.235). Although the data is only a
trend, most likely resulting from the sample size of the study, it does suggest that pulse
pressure did not change significantly at either intensity. The finding also suggests that
there was no change in pulse pressure from the beginning of exercise to its end point at
fatigue. In this study pulse pressure was used to represent SV. Knowing that pulse
pressure did not significantly change for intensity or time, suggests that SV did not
change significantly over time or during either exercise intensity, -5%TH or midTH.
This finding challenges the contemporary theories concerning the decrease in SV as the
cause of CV drift. The findings open new possibilities as to the cause of CV drift.
Body Weight During CLE
Body weight (BW) was a measure that was taken at the beginning of each trial
and again at the end of each trial. From the pre-post measurements of body weight for
each trial, a statistically significant difference level was achieved (p=.001). Body weight
for both trials decreased from 76.3±19.5kg to 75.6±19.5kg, representing a 0.7 kg
difference. This equates to about a 0.9% decrease in body weight from the beginning of
35
the trial to the end. Although the results for BW suggest a significant decrease in body
weight, prior literature may suggest otherwise.
The effects of fluid loss on the magnitude of CV drift have been well reviewed.
A 2.5% reduction in BW is necessary to add to the magnitude of CV drift physiological
markers (Wingo et al. 2012). A further reduction in body weight, resulting in a net loss
of 3.5% body weight, further influences the HR and SV components of CV drift (Ekland,
L. G. 1967, Gonzalez-Alonso et al 1995, Montain, et al. 1992). When the percentage
change of body weight is below these values, HR drift is still present. However, SV is
preserved while, VO2 and cardiac output are increased (Rowland et al. 2008). The
results of the current study, a change in BW representing a decrease of 76.3±19.5kg to
75.6±19.5kg suggests that the decrease although significant (p=.001), may not be enough
to contribute or influence, CV drift.
The BW data in conjunction with pulse pressure data further supports the
argument that the change in BW, although significant (p=.001), may have not influenced
CV drift to a large degree. If the decrease in body weight were truly a significant
amount, the pulse pressure would have had a significant change as well. Hamilton et al.
(1991) demonstrated that when fluid was not adequately replaced, subjects lost 2.1%
BW, resulting in a reduction of SV by 15%. However, as stated earlier pulse pressure did
not reach statistical significance for time (p=.165), suggesting SV was unchanged from
start of trials to fatigue. When SV is preserved there is a rise VO2. This was displayed by
Rowland et al. 2008 with the preservation of SV through the maintenance of body
weight, resulting in a 8% increase in VO2 drift over time. In the current study, pulse
36
pressure, which indirectly represents SV, was not significantly different from the -5%TH
to the midTH intensity or at any time point of TTF. Furthermore, VO2 significantly
increased from the beginning of exercise to fatigue (p=.000). These finding support that
although statistically significant, the decrease in BW did not decrease SV thereby
influencing the HR drift as the traditional rational for CV drift would suggest.
Conclusion
Cardiovascular drift is physiological phenomena which will occur after about 15
minutes of CLE exercise. An increase in HR is an expected response that will continue
to increase until exercise is discontinued. If the subject is well hydrated and substantial
decreases in body weight are prevented, SV can be maintained, and VO2 will increase
along with HR until exercise is discontinued.
This study displayed that during CLE, HR will increase significantly overtime and
at different intensities. However, the amount that HR will increase is similar whether
exercise is prescribed below TH1 or above TH1. Findings from this study display that
exercise intensity performed above and below TH1 resulted in similar magnitude of HR
drift. Furthermore, HR will increase in a similar fashion using the ventilation thresholds
or percentages of VO2max as a means of prescribing exercise. Like HR, VO2 also drift
from the beginning of exercise to exhaustion. However, the magnitude of drift was not
the same as HR drift. In addition to the difference in drift between HR and VO2, there
was a disconnect between the time points at which they were increasing in regard to
%TTF. Further the results show that HR drift is independent of SV and euhydration as
displayed by the minimal change in BW of the subjects.
37
Although this study questioned the design of previous CV drift studies, the
results, although significant, reveal that the traditional method of designing CV drift
studies is sufficient, due to the similar increases in HR when the two methods of
prescription are compared. Future research should continue to examine the relationship
between the two physiological variables of HR and VO2. Interaction of the two variables
may be linked by the muscle mechanoreceptors and metaboreceptors. Stimulation of
both receptors cause increases in HR and VO2. Stimulation of the receptors further
stimulates the sympathetic nervous system; which plays a major role in HR during
exercise. Although there appears to be a relationship between HR and aerobic drift, there
is also disconnect at varying time points during CLE to fatigue. Although this study
displayed statistical significance for time and intensity for HR during CLE, further
research is needed to better understand the importance of the ventilation thresholds and
their role in CV drift and its physiological markers.
38
APPENDIX A
Informed Consent Form
39
Informed Consent
The Effects of Constant-Load Exercise at the Percentages of the Ventilation Thresholds
on the Magnitude of Heart Rate Drift
Testing Procedures
Maximal stress testing will be completed on an electronically braked bicycle.
The testing procedure will begin at 70 Watts (50Watts for females). Every minute
thereafter the load will increase 35 Watts and will be terminated when 70 rpm can no
longer be maintained. During the testing procedure you will have to breathe through a
two-way valve while wearing a headgear and nose clip. During the test heart rate will be
monitored continuously. Heart rate will be monitored with a heart rate monitor strapped
around your torso.
Power Detection Rides will be carried out 20 minutes after the maximal stress
test on an electronically braked bicycle. A workload will be set at -15% of power at
TH1. Workload will increase by 5 watts every 3-5 minutes until a wattage is reached that
elicits a VO2 equal to -5% of TH1. After a 20-minute rest period power will be set at 20% of TH2 power. A 5 watts power increase every 3-5 minutes will take place until the
correct wattage that elicits the VO2 intermediate of TH1 and TH2 is found.
Endurance Rides To Fatigue will be performed on separate days and under two
different exercise workloads determined by the power detection rides. A 5 minute active
warm-up will be given for both trials. Following the warm-up period a endurance ride to
fatigue will be completed in which subjects will as long as they physiologically can. The
40
point of fatigue will be determined when the riders can no longer maintain an rpm within
5 rpm’s of their chosen rpm
*Total time commitment for the study is approximately six hours.
Risks and Discomforts
Vigorous exercise, such as graded exercise testing and time trialing, involves a
certain amount of risk. The associated death rate with vigorous exercise is very low in
low risk individuals. During the testing procedures you will experience increased blood
pressure, rapid breathing, increased heart rate, increased exertion, sweating, muscular
discomfort, and fatigue. Also during this procedure it is possible that you will experience
an alteration in heart rhythm and in rare cases a heart attack or stroke. However, risks of
these events taking place will be minimized by pre-health screening and monitoring
during the tests.
In the event of an emergency, we will activate the emergency medical response
process for the university. Any medical treatment or response that incurs a charge will be
the responsibility of the research participant and not the university. The investigators of
this study are trained in CPR and basic first aid.
Responsibilities of the Participant
Knowledge of your current health status and any abnormalities associated with it
could profoundly affect the outcomes of your test, as well as your safety during the
testing procedure. It is your responsibility to disseminate accurate and complete
information regarding your health and condition prior to undergoing the test procedures.
During the procedure it is your responsibility to provide the technicians with accurate
41
information regarding how you feel during the test. It is also your responsibility to report
any chest pain, tightness, or other abnormal discomfort during the testing procedures.
Benefits of the Testing Procedure
The exercise test may provide you with information regarding your current state
of health and physical fitness. These tests can be used as a baseline beginning assessment
to determine changes in physical state over time as well as various states of conditioning.
Further, depending on the testing procedure this information may be beneficial in
developing an exercise program for the enhancement of your current physical fitness.
Use of Medical Records
The data collected during this study will be treated as confidential. No one may
view your results without your expressed written consent. This data will be coded with a
random ID number and used for statistical analysis with your right to privacy maintained.
Consent to Participate
This testing procedure is voluntary and you are free to withdraw from the
procedure at any time. Please feel free to ask questions regarding the procedure at any
time. This may include clarification on the consent form, instructions on the procedure,
or any part of the testing process that you are not comfortable with. You may also feel
free to contact Daryl Parker PhD, the primary investigator, at any time regarding
questions that you have 916-278-6902 or parkerd@csus.edu.
42
I have read this consent form, and understand the procedure, risks involved and my
responsibilities during the testing process. Knowing the risks involved and having had
my questions answered to my satisfaction I hereby consent to participate in this study.
__________
Date
______________________________________
Print Name
______________________________________
Signature
__________
Date
______________________________________
Print Name of Witness
______________________________________
Signature of Witness
43
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