33
Journal of Exercise Physiologyonline
June 2015
Volume 18 Number 3
Editor-in-Chief
Official Research Journal of
Tommy
the American
Boone, PhD,
Society
MBA
of
Review
Board
Exercise
Physiologists
Todd Astorino, PhD
Julien Baker,
ISSN 1097-9751
PhD
Steve Brock, PhD
Lance Dalleck, PhD
Eric Goulet, PhD
Robert Gotshall, PhD
Alexander Hutchison, PhD
M. Knight-Maloney, PhD
Len Kravitz, PhD
James Laskin, PhD
Yit Aun Lim, PhD
Lonnie Lowery, PhD
Derek Marks, PhD
Cristine Mermier, PhD
Robert Robergs, PhD
Chantal Vella, PhD
Dale Wagner, PhD
Frank Wyatt, PhD
Ben Zhou, PhD
Official Research Journal
of the American Society of
Exercise Physiologists
ISSN 1097-9751
JEPonline
Physiological Breakpoints and Maximal Steady-State of
Cycling
Cory Scott1, Frank Wyatt1, Jason Winchester1, Keith Williamson2,
Ashleigh Welter1, Sean Brown1
1Department
of Athletic Training and Exercise Physiology, Midwestern
State University, Wichita Falls, TX, 2Vinson Health Center,
Midwestern State University, Wichita Falls, TX
ABSTRACT
Scott C, Wyatt F, Winchester J, Williamson K, Welter A, Brown S.
Physiological Breakpoints and Maximal Steady-State of Cycling.
JEPonline 2015;18(3):33-45. The aim of this study was to examine
various physiological thresholds and their association with maximal
steady-state exercise. Elite level cyclists (n = 15) participated in the
study. All data were collected on a VelotronTM cycle ergometer, lactate
meter, metabolic cart, and a heart rate monitor. Blood lactate (mM),
VO2 (mL·kg-1·min-1), and heart rate (beats·min-1) data were collected
every minute for both the VO2 max test and the maximal steady-state
test. Statistical analysis included the descriptive mean (±SD) of the
subjects and the test results, the comparison of each physiological
measurement and the mean (±SD) values, and t-tests analyzing the
wattage corresponding to the said variable and physiological test.
Statistical significance was set at P≤0.05. There was no noticeable
trend of one threshold being indicative of another threshold. Heart rate
and ventilatory thresholds displayed strong correlations with their
respective values at steady-state intensity, while blood lactate values
at threshold exhibited weak, but significant correlations to values
obtained at steady-state efforts. The correlation shown in the study
between heart rate threshold and ventilatory threshold and their
respective values at steady-state can help provide evidence-based
training information, which can lead to an increase in athletic
performance by training the proper bioenergetic system.
Key Words: Steady State, VO2 max, Cycling, Threshold
34
INTRODUCTION
In any physical activity, it is safe to assume that as the workload increases there is a resulting
increase in the body’s metabolic responses. Specifically, in cycling, it has been found that as wattage
or work increases, there is an increase in heart rate, blood lactate, and ventilation (18). At a point in
these physiological responses, a threshold is established which is marked by a rapid change despite
the proportionate workload (18). These changes can be seen in the respiratory exchange ratio (RER)
when the ratio of the volume of oxygen (O2 inhaled) and carbon dioxide (CO2 exhaled) is 1.0 or higher
(4). During an incremental test of maximal oxygen uptake, thresholds are established for the
parameters mentioned above. These threshold changes, or physiological breakpoints, are exhibited
when a rapid change occurs despite the proportionate change in workload volume. Furthermore,
these thresholds are synonymous with the term maximal lactate steady-state (MLSS) when
referencing blood lactate, and maximal steady-state (MSS) when referring to heart rate (HR) and
ventilation (VE) (2). Maximal steady-state or its derivative (MLSS) can be defined as the highest point
at which a physiological response and workload can be sustained, and in the context of MLSS, blood
lactate values do not accrue (3). At rest and below threshold, there is a correlation between lactate
production and removal, HR response, and VE. Understanding bioenergetic responses can translate
into greater performances, and training at MLSS and MSS has been shown overtime to increase an
individual’s thresholds.
Based on the literature, it can be proposed that the concept of anaerobic threshold and maximal
steady-state efforts vary widely. It is understood that variations in the circadian rhythm from hour to
hour and day to day have an effect on physiological reactions and, consequently, the comparison of
studies. Thresholds and steady-states within the same person have been shown to fluctuate based
on the time of day, amount of rest, when the last bout of exercise occurred, and diet. In the current
study, these limitations were taken into account.
According to past studies, there is a breach in the literature between the relationship of physiological
breakpoints and the accompanied reactions as a whole. Theoretically, each one of the physiological
thresholds mentioned above should occur at approximately the same time and workload in a VO 2 max
test. However, exercise at a maximal steady-state has the potential to display dissimilar threshold
points through different bioenergetic responses. Thus, this study examined and compared the
following conditions: (a) lactate threshold and maximal lactate steady-state (MLSS); (b) ventilatory
threshold and maximal steady state (MSS); and (c) heart rate threshold and MSS. Moreover, it
examined the three observed parameters as a whole and their relationship to steady-state efforts. It
was hypothesized that each physiological threshold strongly correlates to the respective bioenegetic
response at steady-state, and the three combined physiological responses would display a significant
association with maximal steady-state.
METHODS
Subjects
A total of 15 subjects (13 males and 2 females) with an age range of 19 to 43 participated in a graded
exercise test to maximal exertion and/or volitional fatigue as well as a 20-min maximal steady-state
self-selected effort. Refer to Table 1 for the subjects’ demographics. Prior to the testing, all subjects
filled out a medical questionnaire to assure the absence of asymptomatic neuromuscular and
cardiovascular disorders. Each subject also signed an Internal Review Board informed consent form
approved at Midwestern State University. All subjects were familiarized with a bicycle, and each
35
subject qualified to participate in the study by ranking in the 90th percentile or higher per ACSM
guidelines for VO2 max.
Table 1. The Subjects’ Demographics.
Variable
Age (yrs)
Height (cm)
Weight (kg)
Body Fat (%)
Mean ± SD
24.9 ± 6.3
176.3 ± 5.0
72.7 ± 8.1
11.9 ± 6.1
Procedures
Each subject’s height, weight, blood pressure, and body fat were measured. Instrumentation for
determining the values included the mechanical beam scale with stadiometer, sphygmomanometer
and stethoscope, and Lange skin fold calipers measure on the right pectoral, right abdominal, and
right thigh for males and right tricep, right mid-axillary, and right thigh for females.
Equipment
The VelotronTM cycle is a computer controlled, chain driven, fixed ratio, electronic ergometer used for
obtaining and/or manipulating workload in watts. The cycle was configured with a cadence sensor
and magnet to monitor the subject’s revolutions per minute (rev·min-1). Furthermore, preceding the
exercise test the following measurements and equipment (saddle height, saddle setback, reach,
stack, crank arm length, and pedals) from the subject’s bike were extracted and transferred to the
VelotronTM.
The instrumentation used for testing ventilation was a ParVo Medics TrueMax 2400 Metabolic
Measurement SystemTM and a VelotronTM cycle ergometer. The ParVo MedicsTM flow meter was
calibrated before each trial with the ambient data entered for temperature, humidity, and atmospheric
pressure. Gas calibration was performed to analyze the percentage of oxygen and carbon dioxide.
Obtained measurements from the ParVo MedicsTM metabolic cart included, expired ventilation (VE),
oxygen consumption (VO2), carbon dioxide production (VCO2), respiratory exchange ratio (RER), and
maximal oxygen uptake (VO2 max). Before testing, the ParVo MedicsTM ventilation hose was affixed
from the machine to the subject’s mouth using a Hans Rudolf TM valve and, then, a nosepiece was
applied to prevent nasal breathing. Once testing was underway, VE measures were obtained via an
open spirometry system that recorded and averaged a breath-by-breath analysis every 20 sec.
A Polar RS800CXTM heart rate monitor was used to obtain HR (beats·min-1) for the duration of each
VO2 max test and steady-state test. The Polar WearLinkTM W.I.N.D. transmitter was the chest strap
device, which allowed for the subject’s HR signal to be transmitted to the training computer. Heart
rate data were recorded at an R-R interval, allowing for thousands of data points per test.
Lastly, a Nova Biomedical Lactate PlusTM was used to obtain whole blood lactate by removing 10 µl
from a finger during VO2 max and MLSS. Extractions were taken every minute in the VO2 max test
and the MSS test. Lactate was determined by a reflectance photometry at a wavelength of 657 nm in
a colorimetric lactate-oxidase mediator reaction.
36
Statistical Analyses
StatSoft® Statistica 7TM was used to statistically analyze the data. Means ± standard deviations
(mean ± SD) were determined for each subject’s demographics (height, weight, and VO2 max).
Physiological thresholds (lactate, VE, and HR) were compared for association with MSS through a
Pearson Product R Correlation Coefficient. A dependent sample t-test was used for comparison
between physiological parameters obtained during both VO2 max efforts and averaged steady-state
efforts. Moreover, a dependent sample t-test was used for comparison of workload at each
physiological parameter. An ANOVA test and a Tukey post hoc analysis were used to analyze the
individual slopes of each subject’s blood lactate, VE, and HR. Additionally, a means with error plot
examined the individual mean and standard deviation for each observed physiological threshold.
Statistical significance was set at P≤0.05.
RESULTS
Maximal Oxygen Uptake Data
The subjects’ mean VO2 max was 73.59 mL·kg-1·min-1. Blood lactate was obtained every minute
starting at the 5th-min of the test, and stopped once the subject reached volitional fatigue. Heart rate
was recorded beat by beat, and VE measures were averaged from a breath by breath analysis every
20 sec. Table 2 shows the recorded physiological measure of each subject during the VO2 max test,
and the corresponding work output during each threshold.
Table 2. VO2 Max Physiological Threshold Data and Work Output of Corresponding Threshold.
Subject
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
VO2 Max
Max HR
HRT
BLaT
Vent T
HRT
BLa
VentT
(mL·kg-1·min-1)
(beats·min-1)
(beats·min-1)
(mM·L -1)
(mL·kg-1·min-1)
(Watts)
(Watts)
(Watts)
79.5
81.3
73.9
85.8
68.2
67.8
68.7
86.5
58.9
83.4
55.8
63.6
70.8
72.3
87.3
192
225
193
205
175
189
200
202
177
211
184
194
193
185
200
167
207
179
185
152
167
184
163
155
190
160
178
178
160
179
2.9
3.1
2.1
2.4
2.9
2.7
4.7
1.6
1.7
2.3
4.1
4.7
2.7
2.1
3.0
62.01
65.04
64.29
74.65
53.88
56.27
62.52
69.20
56.54
65.05
42.97
56.60
61.60
60.01
70.71
275
250
250
275
275
300
225
300
250
325
175
200
225
275
325
300
275
250
250
275
300
200
275
250
325
200
200
250
300
350
275
250
250
275
275
275
250
275
275
300
200
200
250
300
325
In the maximal steady-state test, subjects self-selected a workload at which they completed a 20-min
steady-state effort to their highest achievable ability. Physiological responses were noted every
minute, including blood lactate, HR, and VE. Heart rate was recorded beat by beat, and VE measures
37
were averaged from a breath-by-breath analysis every 20 sec. For the following data analysis,
bioenergetic responses were averaged over the 20-min steady-state period and, then, compared with
each threshold value determined from the VO2 max test (Table 3).
Table 3. Mean Physiological Measurements during a 20-Min Maximal Steady-State Test.
Subject
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
HRSS
VO2SS
BLaSS
WattsSS
(Mean)
(Mean)
(Mean)
(Mean)
178.8
208.5
183.2
183.9
162.9
159.7
186.1
160.7
168.5
192.7
154.3
170.2
178.4
168.4
178.1
68.96
65.33
58.62
71.04
56.06
55.81
58.78
68.75
55.73
73.63
40.20
49.10
61.59
57.87
74.67
8.76
8.20
8.69
6.86
7.39
5.01
11.94
3.63
4.46
5.47
5.67
5.11
6.99
6.53
6.70
289
255
228
267
275
270
200
269
250
342
167
186
235
290
348
Figure 1 presents the percentage of the physiological
parameter during steady-state exercise compared to
the maximal value of the respective physiological
variable. Thus, the percentages are indicative of how
close to maximal exercise an individual is working
during a 20-min steady-state effort. From the Table it
can be noted that HR per subject at steady-state is
typically in the 90% range of maximal heart rate, with
the average being 90.1%. Ventilation at a steadystate effort was consistently at the lower percentage
compared to HR, with the average being 82.9%, while
blood lactate was significantly lower at 58.5%.
100
90.08
90
82.90
80
70
60
58.46
50
40
30
20
A dependent samples t-test (P≤0.05, see Table 4)
10
examined the measured variables in the study. Two
sets of variables were not found to be significantly
0
Mean
BL Work
HR work
Mean±0.95 Conf. Interval
different (e.g., ventilatory threshold and the average
VO2 work
VO2 at steady-state (P=0.765) and the heart rate Figure 1. Percentages of Mean Steady-State
threshold and the average HR at steady-state Values Related to Maximal Physiological Values.
(P=0.263).
38
The variable found to be significantly different was blood lactate, when comparing the lactate
threshold and the average lactate at steady-state. Moreover, additional dependent samples t-test
were implemented (P≤0.05) for the analysis of threshold power output at each measured variable
(Table 5), and for the comparison of the threshold wattage derived from each variable, with the
average wattage during the steady-state effort (Table 6).
Table 4. Dependent Samples t-test Comparing Threshold and Steady-State Values.
Variable
BLa Threshold
BLaSS avg
Vent Threshold
VO2SS avg
HRT
HRSS avg
Mean ± SD
2.83 ± 0.89
6.76 ± 2.09
61.42 ± 7.70
61.08 ± 9.50
173.60 ± 14.88
175.63 ± 14.23
N
t
p
15
-8.36
0.00
15
0.31
0.76
15
-1.17
0.26
N
t
p
15
0.29
0.77
15
1.00
0.33
15
0.69
0.50
Table 5. Dependent Samples t-test Comparing Threshold Wattage.
Variable
BLa T Watts
Vent Threshold Watts
BLa T Watts
HRT Watts
Vent Threshold Watts
HRT Watts
Mean ± SD
266.67 ± 44.99
265.00 ± 33.81
266.67 ± 44.99
261.67 ± 43.16
265.00 ± 33.81
261.67 ± 43.16
Table 6. Dependent Samples t-test Comparing Threshold Variable Watts with Steady-State Watts.
Variable
Bla T Watts
WattsSS
Vent Threshold Watts
WattsSS
HRT Watts
WattsSS
Mean ± SD
266.66 ± 44.99
258.07 ± 50.78
265.00 ± 33.81
258.07 ± 50.78
261.67 ± 43.16
258.07 ± 50.78
N
t
p
15
2.27
0.04
15
1.19
0.25
15
0.78
0.45
DISCUSSION
The main purpose of this study was to examine the differences in physiological thresholds and their
association with maximal steady-state. Analysis of the results compared: (a) lactate threshold and
maximal lactate steady-state (MLSS); (b) ventilatory threshold and maximal steady state (MSS); (c)
heart rate threshold and MSS; and (d) the relationship between each of the measured bioenergetic
responses to steady-state exercise. Thresholds were established from a VO2 max test, in which a
later comparison correlated the significance between thresholds and a steady-state effort. Heart rate
39
threshold values and ventilatory threshold values were found to be strongly correlated to their
respective values at a steady-state effort. Meanwhile, blood lactate was found to be significantly
different and showed no correlation to its steady-state value. Furthermore, there was a strong
correlation between each measured physiological threshold wattage and average wattage exerted at
steady-state intensities. Thus, the values obtained at heart rate threshold and ventilatory threshold
are a good indicator of the achievable physiological magnitude of work an individual is capable of
during a 20-min steady-state effort. Conversely, blood lactate values at threshold are not indicative of
the values obtained during a 20-min steady-state effort.
During the 20-min timed steady-state effort, numerous physiological responses occurred that led to
the resulting relationships between HR, VE, and blood lactate. Examining HR during the steady-state
effort, an increase can be seen throughout the measured time (Figure 2).
Steady State HR
200
Heart Rate (b*min.-1)
180
160
y = 1.2133x + 163.14
140
120
100
80
60
40
20
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Time (minutes)
Figure 2. Heart Rate (beats·min-1) throughout the 20-Min Steady-State Test.
This is not an unfamiliar concept, and is a profuse finding throughout the literature. Most studies
examining the physiological effects of steady-state report an increase in HR as time is increased
(15,17). This physiologic augmentation is a phenomenon known as the cardiovascular drift (CVD).
Cardiovascular drift is known to occur around 10 min of moderate intensity exercise or between 60 to
75% of VO2 max. Commonalities seen with CVD are a decrease in stroke volume (SV) as well as a
decrease in mean arterial pressure (MAP). If cardiac output (Q) continues to increase across time, it
is due to the gradual increase HR while the SV stays the same (13). In a study using a β-blockade to
prevent HR from increasing, CVD was found to be attributed to other physiological variables (5). The
researchers concluded that CVD can also be a resultant of blood volume, cutaneous blood flow,
esophageal core temperature, and skin temperature (5). Another study examining CVD and the role
of muscle activation found that a greater amount of muscle recruitment can lead to a greater increase
in HR (8). Like the current study displaying CVD, this could be due in part from the spatial summation
of muscle fibers in the working muscle groups. As a muscle fiber fatigues, more fibers are needed in
40
order to maintain the same workload, leading to larger activation and, therefore, an increase in HR
(1).
Additionally, different central and peripheral chemoreceptors including carotid bodies and aortic
bodies detect metabolites being discharged, and transduce a signal causing an action potential. The
action potential transmitted from the different chemoreceptors may act as stimuli to increase HR
during steady-state exercise by increasing the rate of ventilation. Therefore, when exercising at a high
intensity, oxygen consumption is increased, which may eventually lead to a decreased oxygen
concentration and an increased carbon dioxide concentration. These fluctuations are sensed by the
chemoreceptors causing vasodilation and, additionally, resulting in an increase the rate of blood flow
to the heart. The larger volume of blood causes the heart to stretch and pressure to increase. This
stretch activates mechanoreceptors in the heart initiating a cascade of events leading to an increase
in HR.
During continuous steady effort exercise, low muscle efficiency has been shown to increase the need
for VE (11). Furthermore, studies that examined VO2 during maximal lactate steady-state found a
continual increase in VE, which is supported by the subsequent ventilatory drift notion (9,11). The
concomitant rise in VE, which is observed with an increase in HR is referred to as the “ventilatory drift”
that is associated with a gradual rise in VE despite a constant workload (6) (Figure 3).
Steady State Ventilation Average
70
VO2 (mL*kg-1*min.-1)
60
50
y = 0.1411x + 56.775
40
30
20
10
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Time (minutes)
Figure 3. Average VO2 (mL·kg-1·min-1) during the 20-Min Steady-State Test.
Potential causes for this drift are speculated to be from an increase in body temperature, and are
thought to be both unproductive and advantageous. To an extent, the drift is considered to be
uneconomical because of the amount of VE for the given workload and, conversely, it is beneficial for
gas exchange and the maintenance of the acid-base balance (6).
The ventilatory drift displayed in this study could be a result partially from muscular fatigue in addition
to low economy of muscle working at steady-state. High intensity exercise is known to increase the
intramuscular temperature as well as adjust the muscle metabolism leading to fatigue, which has
previously been thought to be a casual effect of the upward drift in ventilation (9). Muscular fatigue is
41
brought upon by insufficient energy supply and oxygen deficiency to working skeletal muscles. A type
of fatigue called peripheral fatigue is comprised of the peripheral nervous system and relates to force
reduction in working muscles as a result from the lessening of muscle action potentials (7,12). As
mentioned previously, a larger recruitment of fibers would be needed in order to maintain the same
work output, leading to a drift in both VE and HR.
Blood lactate, unlike HR and VE, was found to have significant differences when comparing the
average threshold value with the average steady-state value. However, the workload determined to
be the threshold wattage strongly correlated to the average wattage exerted during the 20-min
steady-state test. Moreover, like the trend seen in HR, VE, and RPE, blood lactate was found to have
an upward slope for the entire period of the steady-state effort, with small oscillations fluctuating up
and down between individual subjects. These fluctuations are not evident in the average slope
displayed in Figure 4. Given this slope and the changes in blood lactate throughout the steady-state
effort, the workload at a 20-min maximal steady was reasoned to not be the maximal lactate steadystate. Inclusion for MLSS involves the parameters of blood lactate not increasing more than 1 mM·L-1
during a steady-state effort, or exercising at the highest steady-state level that balances the rate of
lactate appearance and lactate disappearance. Consequently, as seen with HR and VE, a proposed
term for the purpose of this study is “lactate drift”. This drift in lactate is from exercising at an intensity
slightly above the MLSS, causing a disequilibrium between the rate at which lactate appears in the
blood and the rate at which it is removed from the blood.
Steady State Blood Lactate Average
Blood Lactate (mM*L.-1)
12
10
8
6
y = 0.3057x + 3.5512
4
2
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Time (minutes)
Figure 4. Average Blood Lactate during the 20-Min Steady-State test.
It is important to recall that the human body burns a mixture of energy systems during exercise and
for several reasons, exercising at a higher intensity utilizes a greater amount of carbohydrates. One
of the end products of this is lactate, which does not cause fatigue. Instead, it is metabolized and
used as an energy source. During steady-state exercise, cells are using glycolysis to make energy in
addition to consuming muscle glycogen. One of the culminating steps in breaking down glucose is the
production of 2 molecules of pyruvate. During low intensity exercise, pyruvate goes directly into the
mitochondria, but in strenuous activity the energy demands exceed the electron transport chain
causing a cascade of events to reduce pyruvate to lactate. The main indication is that because
42
metabolic acidosis coincides with an increased lactate production, the measurement of blood lactate
is principally an indirect marker for the metabolic state of a cell.
As noted earlier, the main producer of lactate in the body is skeletal muscle. The main proponent in
the transportation of lactate across the plasma membrane of a cell is a variety of protein linked
monocarboxylate transporters (MCT), notably aiding metabolism and the regulation of homeostatic
pH within muscles. The MCTs within skeletal muscles that assist in this transport of lactate are known
to be MCT1 and MCT4. Fundamentally, MCT1 is found in higher concentrations in muscle identified
to be more oxidative, while MCT4 is predominately in muscles that are primarily glycolytic, although it
is found in all muscles. A high glycolytic rate in skeletal muscle is correlated to an increased rate of
lactate production, which is taken up by the heart, kidney, liver, brain, and skeletal muscle for
metabolism into a fuel source. MCT1 is recognized for its acceptance of lactate into a cell, while
MCT4 is acknowledged for its export properties of lactate out of a cell. As glycolysis exceeds
oxidative capacity, excess lactate is produced and begins to drift.
It can be expected that during a high intensity steady-state effort, the rate of blood lactate production
and removal is high. Lactate metabolism can be trained via endurance and high intensity exercise,
and through these exercise activities the removal of lactate has been shown to increase (10). In
regards to this study, the general trend for the superiorly fit subjects (VO 2 max = 80+ mL·kg-1·min-1)
exhibited the estimated blood lactate threshold determined from the VO 2 max test to be higher than
either the ventilatory threshold or heart rate threshold, or both. A potential reasoning behind this is
that highly trained athletes may have greater mitochondrial density and muscle economy, leading to a
higher, more sustainable equilibrium of lactate production and removal. One study that examined
humans with a vast assortment of fitness abilities reported a wide array of lactate transport capacity,
with the higher fit subjects displaying the greatest potential (14). Thus, the rate of lactate metabolism
providing oxidative substrates and gluconeogenic precursors is related to the expression level of
MCTs. This is supported by Thomas and colleagues who found (16) an inverse relationship to MCT1
expression with the fatigue index during intermittent supramaximal exercises (16). A probable
explanation for blood lactate being related to fatigue is when a high accumulation of lactate occurs,
pH levels decrease leading to a greater inhibition of glycolysis, consequently decreasing the
bioenergetics and decelerating work to a greater oxidative capacity allowing for MCT1 to recycle the
excess lactate (i.e., turning it into pyruvate and oxidizing it in the mitochondria for ATP production).
In addition to the physiological measurements of HR, VE, and blood lactate, a measurement of RPE
was obtained every minute for the duration of the maximal steady-state test. As indicated in the
results in Figure 5, an increasing slope was existent in the average rating of all subjects. Going back
to the central command model, the RPE slope is associated to the trend of the increasing slopes
found in HR, VE, and blood lactate. This hypothetically demonstrates that not only were the constant
changes on a physiological level during steady-state efforts, but also on the psychological level. This
can relate back to understanding the pre-anticipatory effect, which would cause a possible release of
supplementary catecholamines to match with the RPE.
43
Borg RPE Steady State Average
20.00
18.00
Borg RPE
16.00
14.00
12.00
10.00
8.00
6.00
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Time (minutes)
Figure 5. Average Perceived Exertion for steady-State Exercise using the
Borg RPE Scale.
CONCLUSIONS
The findings from this study indicate that the physiological thresholds of HR and VE are significantly
correlated to the average measurements obtained during a 20-min maximal steady-state test. In
regards to training and exercise prescription, these data can assist in understanding the duration and
intensity for cyclists. Blood lactate levels at threshold showed to be an inaccurate predictor of the
levels acquired from a maximal steady-state effort. In the field, blood lactate measurements are
difficult to acquire and an invasive process, therefore leading to laboratory testing being the only
efficient and practical way of obtaining measurements. Furthermore, like blood lactate, ventilatory
measurements are very difficult to attain in a field setting leaving this measurement for laboratory
purposes. Heart rate is an excellent and noninvasive measurement, and it can be easily acquired
from both the laboratory and field.
Additionally, aside from power measurements obtained from a variety of power devices made for
bicycles, HR is the most popularly used physiological variable for exercise prescription. What needs
to be considered when prescribing short, intense exercises is the well-known physiological
occurrence of heart rate drift. When exercising at the same workload for ~10 min, HR will begin to
increase slightly over time despite of the steady-state workload. Taking into account for this drift, an
individual should not adjust their workload, but rather should maintain their wattage as much as
possible. In addition, findings from the RPE using the Borg scale suggest that psychologically the
workload and effort increased with time despite no change in exercise intensity. Thus, the decrease
in workload during interval training should be eradicated and the increase in HR and perceived
exertion should be overlooked but not unnoticed.
44
ACKNOWLEDGMENTS
Thanks to Hotter’ N Hell Hundred and Midwestern State University for their financial support of the
research.
Address for correspondence: Cory M Scott, Department of Athletic Training and Exercise
Physiology, Midwestern State University, Wichita Falls, Texas, Email: corymscott87@gmail.com
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