95
Journal of Exercise Physiologyonline
October 2014
Volume 17 Number 5
Editor-in-Chief
Official Research
Tommy
Journal
Boone,
of thePhD,
American
MBA
Review
Board
Society
of Exercise
Todd Astorino,
Physiologists
PhD
Julien Baker, PhD
Steve Brock,
ISSN 1097-9751
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
Perceptual and Physiological Fatigue Thresholds
during Cycle Ergometry
Kristen C. Cochrane1, Terry J. Housh1, Haley C. Bergstrom 2,
Nathaniel D. M. Jenkins1, Glen O. Johnson1, Richard J. Schmidt1
Joel T. Cramer1
1Department
of Nutrition and Health Sciences, Human Performance
Laboratory, University of Nebraska-Lincoln, Lincoln, NE, 2Department
of Kinesiology and Health Promotion, University of Kentucky,
Lexington, KT
ABSTRACT
Cochrane KC, Housh TJ, Bergstrom HC, Jenkins NDM, Johnson
GO, Schmidt RJ, and Cramer JT. Perceptual and Physiological
Fatigue Thresholds during Cycle Ergometry. JEPonline 2014;17(5):
95-107. Thirteen subjects (mean ± SD age: 21.8 ± 2.6 yrs) performed
an incremental cycling test and 4, 8-min submaximal rides (65 to 80%
of VO2 peak) to: (a) compare power outputs and relative intensities
that corresponded to the gas exchange threshold (GET), ventilatory
threshold (VT), respiratory compensation point (RCP), physical
working capacity (PWC) at oxygen consumption PWCVO2, heart rate
(PWCHRT), and rating of perceived exertion (PWCOMNI) thresholds;
and (b) examine the relationships among the fatigue thresholds and
the exercise intensity domains. The RCP (184 ± 47 W) was
significantly (P≤0.0033) greater than the GET (142 ± 38 W), VT (143 ±
40 W), PWCVO2 (106 ± 34 W), PWCHRT (108 ± 34 W), and
PWCOMNI (112 ± 34 W). The GET and VT were significantly greater
than the PWCVO2, PWCHRT, and PWCOMNI, but there were no
differences among the PWCVO2, PWCHRT, and PWCOMNI. These
findings suggest that the PWCVO2, PWCHRT, and PWCOMN fell
within the moderate intensity domain, and share a common
physiological mechanism that was different from those associated with
the GET, VT, and RCP.
Key Words: Exercise Intensity, Power Output, Perception of Effort,
Aerobic Evaluation
96
INTRODUCTION
Fatigue thresholds such as the lactate threshold, gas exchange threshold (GET), ventilatory threshold
(VT), onset of blood lactate accumulation, physical working capacity (PWC) at the fatigue threshold
(PWC-FT), PWC at the heart rate threshold (PWC-HRT), PWC at the oxygen consumption threshold
PWC-VO2, PWC at the rating of perceived exertion threshold (PWC-RPE), electromyography (EMG)
fatigue threshold (EMG-FT), and the respiratory compensation point (RCP) have been used to
differentiate fatiguing from non-fatiguing work (13,14,20), demarcate the exercise intensity (moderate,
heavy, and severe) domains (3,4,14,15,22,23,26,35), identify the onset of metabolic acidosis (10,29),
prescribe exercise intensity (1,8), and examine the mechanisms associated with neuromuscular
fatigue (18,20,37). The problem is that these fatigue thresholds are derived from various measures
including gas exchange parameters, heart rate (HR), blood lactate, VO2, or the EMG signal. Hence,
more often than not these fatigue thresholds result in different exercise intensities that reflect different
physiological mechanisms of fatigue. For example, the GET, VT, and RCP are determined from gas
exchange parameters (VCO2, VE, and VO2) that reflect fatigue-related metabolic activity (15).
Typically, there is no difference between the intensities at the GET and VT, but both are less than the
RCP (2,5,15). The PWC-FT (13) is estimated using EMG fatigue curves, and the PWC-RPE (7) is
based on subjective ratings of perceived exertion (Borg or OMNI-Leg scale) that reflect the relative
“hardness” of the exercise bout (19). Recently, Bergstrom et al. (3) found that the PWC-FT was 17%
greater than the GET, and the PWC-RPE was not significantly different from the RCP. Mielke et al.
(22), however, reported a close agreement between the PWC-RPE and GET. Thus, the exercise
intensities that define specific fatigue thresholds are dependent upon the unique physiological and/or
perceptual responses associated with the onset of fatigue.
The PWC-VO2, PWC-HRT, and PWC-RPE tests utilize the mathematical model that deVries et al.
(13) used to estimate the EMG fatigue threshold (EMG-FT). The EMG-FT is based on EMG amplitude
versus time relationships from three or four fatiguing work bouts at different power outputs. The
power outputs are plotted as a function of the slope coefficients for the EMG fatigue curves, with the
y-intercept defined as the EMG-FT. Thus, theoretically, the EMG-FT represents the maximal power
output that can be maintained with no evidence of neuromuscular fatigue (i.e., a slope coefficient of
zero for the EMG amplitude vs. time relationship) (13). For the PWC-VO2, PWC-HRT, and PWC-RPE
tests, VO2, HR, and RPE replace EMG amplitude in the mathematical model. Thus, in theory, during
continuous cycle ergometery, the PWC-VO2, PWC-HRT, and PWC-RPE represent the maximal
power outputs associated with “steady state” VO2, HR, and RPE responses, respectively.
Comparisons among fatigue thresholds can be used to examine the physiological and psychological
mechanisms that underlie the onset of fatigue. For example, Bergstrom et al. (4) compared the times
to exhaustion and power outputs associated with the PWC-Borg (PWC-RPE based on the Borg
scale), GET, and RCP during cycle ergometery. It was reported (4) that the PWC-Borg was greater
than the GET but similar to the RCP, which suggested that similar mechanisms may underlie both the
ventilatory response at RCP and the perception of effort at the PWC-Borg. In contrast, Mielke et al.
(22) reported that the PWC-Borg and PWC-OMNI (PWC-RPE based on the OMNI scale) did not differ
from the GET, PWC-VO2, or PWC-HRT, which indicated that there may be similarities among the
perceptual, metabolic, and physiological responses within the moderate intensity domain.
Furthermore, Miller et al. (23) found that there were no significant differences in power outputs among
the GET, PWC-VO2, and PWC-HRT. Thus, there is conflicting evidence regarding the specific
mechanisms associated with the onset of fatigue and the perception of effort during fatiguing cycling
exercise. Furthermore, no previous study has simultaneously compared the PWC-OMNI to fatigue
thresholds based on gas exchange (GET and RCP), ventilation (VT), and physiological (HR and VO2)
parameters during cycle ergometery.
97
Therefore, the purpose of this study was: (a) to compare the power outputs and relative exercise
intensities defined by the peak oxygen consumption rate (%VO2 peak) that corresponded to the GET,
VT, RCP, PWC-VO2, PWC-HRT, and PWC-OMNI; and (b) to examine the relationships among the
fatigue thresholds and exercise intensity domains (moderate, heavy, and severe). Based on the
findings of previous studies (22,23,35), it was hypothesized that there would be differences in power
outputs and/or %VO2 peak values among the GET, VT, RCP, PWC-VO2, PWC-HRT, and PWC-OMNI
(4,15,22,23). In addition, it was hypothesized that the GET, VT, PWC-VO2, PWC-HRT, and PWCOMNI would demarcate the moderate from the heavy exercise intensity domains and share a
common physiological mechanism, while the RCP would demarcate the heavy and severe domains,
and reflect a mechanism of fatigue that was different from the other fatigue thresholds (3,4,15,22).
METHODS
Subjects
Six male and 7 female subjects (Table 1) volunteered for this study. The subjects were moderately
trained (34), and none were competitive cyclists. According to the American College of Sports
Medicine (34), moderate training includes aerobic activity performed for a minimum of 30 min, 5
times·wk-1. The subjects’ physical activities included running (N = 8), walking and elliptical (N = 3),
and cycling (N = 5). This study was approved by the University’s Institutional Review Board for
Human Subjects. All subjects completed a health history questionnaire and signed a written informed
consent document prior to testing.
Table 1. Descriptive Characteristics of the Subjects (N = 13).
Variable
Mean ± SD
Age (yr)
21.8  2.6
Body Mass (kg)
70.9  12.6
Height (cm)
VO2 Peak (L·min-1)
VO2 Peak (mL·min-1)
VO2 Peak (W)
PWC-OMNI (RPE)
171.7  11.9
2.80  1.03
40.54  6.82
220  63
41
Procedures
The subjects visited the laboratory on 5 occasions, with 24 to 48 hrs between visits. During the first
visit, the subjects performed an incremental cycle ergometer test to exhaustion for the determination
of VO2 peak, GET, VT, and RCP. During the next four visits, the subjects completed four (one during
each visit) randomly ordered, 8-min submaximal, continuous rides at power outputs that ranged from
65 to 80% of the power output at VO2 peak (range = 70 to 244 W) to determine PWC-VO2, PWCHRT, and PWC-OMNI. The power outputs were selected to be low enough so that the subject could
98
complete the full 8 min, but high enough to result in positive slope coefficients for the VO2, HR, and
RPE versus time relationships.
Determination of VO2 Peak, GET, VT, and RCP
Each subject performed an incremental test to exhaustion on a calibrated Lode (Corval V3,
Groningen, Netherlands) electronically braked cycle ergometer at a pedal cadence of 70 rev·min-1.
The ergometer seat height was adjusted so that the subject’s lower limbs were near full extension at
the bottom of the pedal revolution. Toe clips were used to maintain pedal contact throughout the test.
Each subject wore a nose clip and breathed through a 2-way valve (Hans Rudolph 2700 breathing
valve, Kansas City, MO). Expired gas samples were collected and analyzed using a calibrated
TrueMax 2400 metabolic cart (Parvo Medics, Sandy, UT). The gas analyzers were calibrated with
room air and gases of known concentration prior to all testing sessions. The O 2, CO2, and ventilatory
parameters were expressed as 30-sec averages (28) and the subjects were fitted with a Polar Heart
Watch system (Polar Electro Inc., Lake Success, NY). After 1-min of unloaded cycling, the test began
at 50 W and the power was increased by 30 W every 2 min until voluntary exhaustion or the subject’s
pedal rate decreased below 70 rev·min-1 for more than 10 sec, despite strong, verbal encouragement.
The VO2 peak was defined as the highest 30-sec VO2 value recorded during the test.
The GET, VT, and RCP were determined using the V-slope method described by Beaver et al. (2).
The GET, VT, and RCP were defined as the VO2 value corresponding to the intersection of 2 linear
regression lines derived separately from the data points below and above the breakpoint in the VCO2
versus VO2, minute ventilation (VE) versus VO2, and VE versus VCO2 relationships, respectively
(Figures 1-3). Power outputs from the incremental test were plotted versus VO2 values, and the
resulting regression equation was used to estimate the power outputs that corresponded to the GET,
VT, and RCP.
VCO2 (L·min-1)
7
6
5
4
3
G E T = 3.35 (L·min-1)
2
1
0
0
1
2
3
VO2
4
5
6
(L·min-1)
Figure 1. An Example of the Determination of the Gas Exchange Threshold (GET) from the Breakpoint
in VCO2 versus VO2 during the Incremental Cycle Ergometer Test for 1 Subject.
99
VE (L·min-1)
140
120
100
80
60
VT = 3.60 (L·min-1)
40
20
0
0
1
2
3
4
VO2
5
6
(L·min-1)
Figure 2. An Example of the Determination of the Ventilatory Threshold (VT) from the Breakpoint in VE
versus VO2 Relationship during the Incremental Cycle Ergometer Test for 1 Subject.
VE (L·min-1)
140.00
120.00
100.00
80.00
RCP = 4.18 (L·min-1)
60.00
40.00
20.00
0.00
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
VCO2 (L·min-1)
Figure 3. An Example of the Determination of the Respiratory Compensation Point (RCP) from the
Breakpoint in the VE versus VCO2 Relationship during the Incremental Cycle Ergometer Test for 1
Subject.
100
The PWC-VO2, PWC-HRT, and PWC-OMNI thresholds were determined from the four, submaximal
8-min work bouts (22,23,35). The seat height, toe clips, and warm up procedures were the same as
for the incremental test. The PWC-VO2, PWC-HRT, and PWC-OMNI thresholds were determined
using the protocols from previous studies (22,23,35). For the determination of PWC-OMNI, the OMNI
picture (0-10) scale with 0 representing “extremely easy” and 10 representing “extremely hard” was
presented following standardized instructions (22,30). The subjects were asked to give a rating of
perceived exertion during the last 10 sec of each min during the 8-min submaximal work bouts, while
VO2 and HR values were recorded as 30-sec averages during each min. The values for the first 3 min
of each work bout were discarded to account for the initial metabolic and cardiac adjustments to each
power output (22,23,35). The rates of rise in VO2, HR, and RPE as a function of time (linear slope
coefficients) were calculated for each of the four, 8-min submaximal work bouts for each subject. The
power outputs were then plotted as a function of the slope coefficients for the VO 2 versus time, and
HR versus time, and RPE versus time relationships (4,22,23,35). The PWC-VO2, PWC-HRT, and
PWC-OMNI were defined as the y-intercepts of the power output versus slope coefficient (VO2 vs.
time, HR vs. time, and RPE vs. time) plots (22,23,35).
Statistical Analyses
Separate one-way repeated measures ANOVAs were used to determine if there were differences
among the mean values for the power outputs, percent peak power outputs (%PP-output), and
percent of VO2 peak (%VO2 peak) associated with GET, VT, RCP, PWC-VO2, PWC-HRT, and PWCOMNI (Table 2). Post-hoc paired t tests with Bonferonni correction were used for post-hoc analyses.
An alpha level of P≤0.0033 was used for all analyses (0.05/15 = 0.0033). A zero-order correlation
matrix (Table 3) was used to determine the significant (P≤0.05) relationships among the fatigue
thresholds. The analysis was conducted using Statistical Package for the Social Sciences software
(Version 21.0, SPSS, Chicago, IL).
Table 2. Descriptive Characteristics of the Fatigue Thresholds (Mean ± SD).
Power Output
(W)
% Peak Power Output
%VO2 Peak
GET
142 ± 38*
65 ± 9*
69.1 ± 6.3*
VT
143 ± 40*
65 ± 7*
70.8 ± 5.5*
184 ± 47
84 ± 10
87.4 ± 4.8
PWC-VO2
106 ± 34*Ŧ
48 ± 8*Ŧ
53.7 ± 6.7*Ŧ
PWC-HRT
108 ± 34*Ŧ
50 ± 13*Ŧ
55.0 ± 11.7*Ŧ
PWC-OMNI
112 ± 34*Ŧ
51 ± 7*Ŧ
56.2 ± 4.9*Ŧ
RCP
*
Significantly less than RCP at Bonferonni alpha of P≤0.0033
Significantly less than GET, VT, and RCP at Bonferonni alpha of P≤0.0033
Ŧ
101
Table 3. Zero-order Correlation Matrix for the Power Outputs Associated with the Gas
Exchange Threshold (GET), Ventilatory Threshold (VT), Respiratory Compensation
Point (RCP), Physical Working Capacity at the OMNI Threshold (PWC-OMNI), PWC at the
Oxygen Consumption Threshold PWC-VO2, and PWC at the Heart Rate Threshold (PWCHRT).
GET
VT
RCP
PWC-OMNI
PWC-VO2
GET
1.00
VT
0.97
1.00
RCP
0.97
0.93
1.00
PWC-OMNI
0.89
0.87
0.90
1.00
PWC-VO2
0.83
0.84
0.80
0.94
1.00
PWC-HRT
0.81
0.79
0.76
0.81
0.79
PWC-HRT
1.00
r(df=11) = 0.55, P≤0.05
RESULTS
The mean ± SD values for the GET, VT, RCP, PWC-VO2, PWC-HRT, and PWC-OMNI are presented
in Table 2. The r2 values for the VO2, HR, and RPE versus time relationships during the 4, 8-min work
bouts to determine the PWC-VO2, PWC-HRT, and PWC-OMNI ranged from 0.02 – 0.99, 0.14 – 0.99,
and 0.50 – 0.97, respectively. The r2 values for the power output vs. slope coefficient relationships
(for VO2 vs. time, HR vs. time, and RPE vs. time) ranged from 0.50 – 0.99, 0.14 – 0.99, and 0.25 –
0.99, respectively. The results of the one-way repeated measures ANOVA indicated that there were
significant differences among the mean power outputs, (%PP-output), and %VO2 peak that
corresponded to the six thresholds (Table 2).
Post-hoc paired t tests with Bonferroni correction showed that the mean power outputs, %PP-output,
and %VO2 peak at RCP were significantly (P<0.0033) greater than the GET, VT, PWC-VO2, PWCHRT, and PWC-OMNI (Table 2). The GET and VT were not significantly different. The GET and VT
were significantly greater than the PWC-VO2, PWC-HRT, and PWC-OMNI, but there were no
differences among the PWC-VO2, PWC-HRT, and PWC-OMNI. In addition, the RCP was the highest
for each subject. Furthermore, the fatigue thresholds were inter-correlated at r = 0.76 – 0.97 (Table
3). The individual threshold (GET, VT, RCP, PWC-VO2, PWC-HRT, and PWC-OMNI) values for each
subject are plotted in Figure 4.
102
300
250
Power Output (W)
200
150
100
50
0
GET
VT
RCP
PWCVO2
PWC
! 2
VO
PWCHRT
PWC
HRT
PWCOMNI
PWC
OMNI
Fatigue Thresholds
Figure 4. The Power Outputs Associated with the GET, VT, RCP, PWC-VO2 , PWC-HRT, and PWC-OMNI,
for Each of the 13 Subjects.
DISCUSSION
The subjects in the present study were moderately fit (34) with a range of VO2 peak values of 1.2 to
4.9 L·min-1 (30.56 to 55.06 mL∙ kg-1∙ min-1) (Table 1). The mean VO2 peak, GET, VT, and RCP values
were 2.80 ± 1.03 L·min-1, 1.97 ± 0.62 L·min-1, 2.03 ± 0.63 L·min-1, and 2.52 ± 0.75 L·min-1,
respectively. These GET and VT values (69.1 ± 6.3 % and 70.8 ± 5.5% of VO2 peak) were typical of
those previously reported for untrained to moderately trained (54-75% VO2 peak) subjects (7,10,33).
The RCP occurred at 87.4 ± 4.8% of VO2 peak, which was similar to that reported by Bergstrom et al.
(4) and typical of healthy subjects (10).
The PWC-VO2 (23), PWC-HRT (35), and PWC-RPE (22) are based on the mathematical model of
deVries et al. (13) for determining the EMG-FT. The PWC-VO2 and PWC-HRT are estimated using
oxygen consumption (VO2) and HR responses, respectively, while the PWC-RPE can be estimated
using either the OMNI (30) or Borg RPE scale (6). These thresholds rest on the assumption that there
are positive, linear relationships for VO2, HR, or RPE versus time as well as power output versus
slope coefficient during continuous, fatiguing, 8-min cycle ergometer work bouts (13,22,23, 35). In the
present study, the r2 values for the VO2, HR, and OMNI RPE versus time relationships ranged from
0.10 - 0.97 and the power output versus slope coefficient relationships ranged from 0.25-0.99. These
findings were consistent with those of Miller et al. (23), Wagner et al. (35), Mielke et al. (22), and
Bergstrom et al. (4) who reported coefficients of determination for the VO2, HR, and RPE (OMNI and
Borg scales) versus time, and power output versus slope coefficient relationships that ranged from r2
103
= 0.21 - 1.00 and r2 = 0.44 - 1.00, respectively. Thus, the current findings supported the application of
the mathematical model of deVries (13) for estimating the PWC-VO2, PWC-HRT, and PWC-OMNI.
In the present study, there was no significant difference between the GET and VT, but both were less
than the RCP (Table 1). These findings are consistent with previous studies (15,27,32) that reported
the GET and VT demarcate the moderate from heavy exercise intensity domains (2,17). Although
there is conflicting evidence (19), it has traditionally been suggested that the GET results from the
production of excess CO2 due to lactic acid buffering and the VT is the breakpoint in ventilation in
response to excess CO2 (Figure 2) (2,29,36). The RCP, however, demarcates the heavy from severe
exercise intensity domains (5,12). It is defined by a non-linear increase in the VE versus VCO2
relationships during an incremental exercise test (2). It has been suggested that the mechanism
underlying the dissociation of VE from VCO2 at the RCP is related to the stimulation of peripheral
chemoreceptors by elevated levels of interstitial and/or arterial potassium [K +] (11,25). Thus, the
mean differences among fatigue thresholds in the current study supported previous findings that have
suggested that different physiological mechanisms underlie the GET and VT (metabolic acidosis)
versus the RCP (hyperkalemia).
In the present study, the power outputs that corresponded to the PWC-VO2, PWC-HRT, and PWCOMNI were significantly less than the GET and VT and, therefore, within the moderate exercise
intensity domain (4,5,15) These findings were not consistent with previous studies (4,22) that have
reported PWC-VO2, PWC-HRT, and PWC-OMNII values that were greater than or equal to the GET.
For example, Mielke et al. (22) reported no mean differences among the GET, PWC-VO2, PWC-HRT,
PWC-OMNI, and PWC-Borg, and found that the PWC-OMNI was more highly correlated with the
GET, PWC-VO2, and PWC-HRT than was the PWC-Borg. The authors (22) hypothesized that the
PWC-OMNI, which is based on the OMNI-Leg scale, is more specific to fatigue of the legs than is the
PWC-Borg, which provides an assessment of overall body fatigue (22). Furthermore, the differences
among the fatigue thresholds and their associations with GET, VT, and RCP between the current
study and previous studies (4,22,23,35) may be attributable to differences in testing protocols.
Mielke et al. (22) and Bergstrom et al. (4) determined the PWC-VO2, PWC-HRT, and PWC-OMNI
from rides to exhaustion at power outputs (85 to 105% VO2 peak) that were greater than those used
in the current study. However, in the present study, as well as the previous studies (23,35), 8-min
non-exhaustive rides were used to estimate the PWC-VO2, PWC-HRT, and PWC-OMNI. Thus, the
magnitudes of the slope coefficients for the VO2, HR, and RPE versus time relationships used to
determine the PWC-VO2, PWC-HRT, and PWC-OMNI may have been affected by the intensities and
durations of the work bouts as well as their exhaustive versus non-exhaustive natures. For example,
the exhaustive rides of Mielke et al. (22) ranged from 8 to 20 min, while those of Bergstrom et al. (4)
were all less than 10 min in duration and resulted in slope coefficients for the RPE, VO2, and HR
versus time relationships that were greater than those in the present study. Thus, it is possible that
the relationships among the fatigue thresholds and estimations of PWC-VO2, PWC-HRT, and PWCOMNI were affected by differences in rates of increases in RPE, VO2, and HR across time during the
8-min non-exhaustive rides used in the present study versus the exhaustive rides used in previous
studies (4,22).
Theoretically, PWC-VO2, PWC-HRT, and PWC-OMNI represent the maximal exercise intensities that
can be maintained continuously without increases in VO2 (8), HR (10), and RPE (22), respectively.
However, during moderate intensity exercise (i.e., 50 to 75% VO2 peak), there are slight increases in
VO2 (called the O2 drift) and HR (called the cardiovascular drift) that Coyle and Gonzalez-Alonso (9)
suggested result from increases in core temperature and/or fatigue-induced increases in sympathetic
activation. Therefore, it is likely that continuous work bouts at the PWC-VO2 and PWC-HRT in the
104
present study would not result in true zero slope coefficients for the VO2 and HR versus time
relationships, but rather small increases in VO2 of less than approximately 200 mL (15) and HR of
less than or equal to 0.1 beats·min-1 (31). Wagner et al. (35) found that 1-hr rides at the PWC-HRT
resulted in a mean increase in HR (0.066 beats·min-1) that Rohmert (31) suggested could be
maintained across an 8-hr workday. Thus, although the precise pattern and magnitude of responses
for RPE at the PWC-OMNI is unknown, it may include a “drift” upward similar to that expected for the
PWC-VO2 and PWC-HRT (9,23,35).
CONCLUSIONS
The results of the present study supported the application of the mathematical model of deVries et al.
(13) for estimating the PWC-VO2, PWC-HRT, and PWC-OMNI (22,23,35). However, the relative
intensities of these fatigue thresholds differed from those previously reported (4,22). These results
indicate that the estimations of PWC-VO2, PWC-HRT, and PWC-OMNI may be influenced by
differences in the testing protocol. Hence, the use of exhaustive versus non-exhaustive work bouts,
heavy versus severe exercise intensities, and shorter (1 to 10 min) versus longer (8 to 20 min)
duration constant power output rides must be taken into consideration.
In the present study, the PWC-VO2, PWC-HRT, and PWC-OMNI were less than the GET and VT,
and, therefore, were within the moderate intensity domain. These findings suggest that different
physiological mechanisms underlie the various fatigue thresholds. At exercise intensities similar to the
present study, it was hypothesized that afferent feedback associated with increases in the subjects’
core temperature, sympathetic activation, and motor unit recruitment may underlie VO2, HR, and RPE
responses seen at PWC-VO2, PWC-HRT, and PWC-OMNI (9,22,23). Other studies have suggested
that sensory information fed from the central command links the sensations from locomotor and
respiratory muscles, thus contributing to the integration of the perception of effort during aerobic
exercise (17,21,24).
However, the GET and VT are mediated by metabolic acidosis (15). The RCP, which was greater
than all of the other fatigue thresholds, may be related to hyperkalemia. Future studies should
investigate the effects of exhaustive versus non-exhaustive work bouts as well as the intensities and
durations of the constant power output rides on the VO2, HR, and RPE responses versus time
relationships. Furthermore, additional research is needed to determine the effect of changes in core
temperature and sympathetic activation on the VO2, HR, and RPE responses during continuous work
bouts at the PWC-VO2, PWC-HRT, and PWC-OMNI.
Address for correspondence: Kristen C. Cochrane, Department of Nutrition and Health Science,
University of Nebraska-Lincoln, Lincoln, NE, USA, 68583, Email: kcochrane@unl.edu
REFERENCES
1. Amann M, Sobudhi AW, Foster C. Predictive validity of ventilatory and lactate thresholds for
cycling time trial performance. Scand J Med Sci Sports. 2006;16:27-34.
2. Beaver WL, Wasserman K, Whipp BJ. A new method for detecting anaerobic threshold by gas
exchange. J Appl Physiol. 1986;60(6):2020-2027.
105
3. Bergstrom HC, Housh TJ, Cochrane KC, Jenkins DM, Lewis RW Jr, Traylor DA, et al. An
examination of neuromuscular and metabolic fatigue thresholds. Physiol Meas. 2013;34:
1253-1267.
4. Bergstrom HC, Housh TJ, Zuniga JM, Camic CL, Taylor DA, Schmidt RJ, et al. Estimated
times to exhaustion and power outputs at the gas exchange threshold, physical working
capacity at the rating of perceived exertion threshold, and respiratory compensation point. J
Appl Physiol Nutrit Metab. 2012;37:872-879.
5. Bergstrom HC, Housh TJ, Zuniga JM, Traylor DA, Camic CL, Lewis RW Jr, et al. The
relationships among critical power determined from a 3-min all-out test, respiratory
compensation point, gas exchange threshold, and ventilatory threshold. Res Q Exerc Sport.
2013;84:232-238.
6. Borg G. Perceived exertion as an indicator of somatic stress. Scand J Rehab Med. 1970;2(2):
92-98.
7. Camic CL, Housh TJ, Johnson GO, Hendrix CR, Zuniga JM, Mielke M, et al. An EMG
frequency-based test for estimating the neuromuscular fatigue threshold during cycle
ergometery. Eur J Appl Physiol. 2010;108(2):337-345.
8. Cassburi R, Storer TW, Sullivan CS, Wasserman, K. Evaluation of blood lactate elevation as
an intensity criterion for exercise training. Med Sci Sports Exerc. 1995;27:852-862.
9. Coyle EF, Gonzalez-Alonso J. Cardiovascular drift during prolonged exercise: New
perspectives. Exerc Sport Sci Rev. 2001;29(2):88-92.
10. Davis JA. Anaerobic threshold: Review of the concept and directions for future research. Med
Sci Sports Exer. 1985;17(1):6-21.
11. Darabi S, Dehghan MH, Refahi S, Kiani E. Ventilation, potassium and lactate during
incremental exercise in men athletes. Res J of Bio Sci. 2009;4(4):427-429.
12. Dekerle JB, Baron L, Dupont J, Vanvelcenaher J, Pelayo P. Maximal lactate steady state,
respiratory compensation threshold, and critical power. Eur J Appl Physiol. 2003;89:281-288.
13. deVries HA, Moritani T, Nagata A, Magnussen K. The relation between critical power and
neuromuscular fatigue as estimated from electromyographic data. Ergonomics. 1982;25(9):
783-791.
14. deVries HA, Tichy MW, Housh TJ, Smyth D, Tichy AM, Housh, DJ. A method for estimating
physical working capacity at the fatigue threshold (PWCFT). Ergonomics. 1987;35(9):783-791.
15. Gaesser GA, Poole D C. The slow component of oxygen uptake kinetics in humans. Exerc
Sport Sci Rev. 1996;241:35-71.
16. Garcin M, Vautter JF, Vandewalle H, Wolff M, Monod H. Ratings of perceived exertion (RPE)
during cycling exercises at a constant power output. Ergonomics. 1998;41:1500-1509.
106
17. Grazzini M, Stendardi L, Gigliotti F, Scano G. Pathophysiology of exercise dyspnea in health
subjects and in patients with chronic obstructive pulmonary disease (COPD). Respr Med.
2005;99:1403-1412.
18. Hendrix CR, Housh TJ, Johnson GO, Mielke M, Camic CL, Zuniga, JM, et al. A new EMG
frequency-based fatigue threshold test. J Neurosci Met. 2009;181:45-51.
19. Hopker JG, Jobson SA, Pandit JJ. Controversies in the physiological basis of the ‘anaerobic
threshold’ and their implications for clinical cardiopulmonary exercise testing. Anesthesia.
2011;68:111-23.
20. Housh TJ, deVries HA, Johnson GO, Evans SA, McDowell S. The effect of ammonium chloride
and sodium bicarbonate ingestion on the physical working capacity at the fatigue threshold.
Eur J Appl Physiol. 1991;62:189-192.
21. Marcora S. Perception of effort during exercise is independent of afferent feedback from
skeletal muscles, heart, and lungs. J Appl Physiol. 2009;106:2060-2062.
22. Mielke M, Housh TJ, Malek MH, Beck TW, Schmidt RJ, Johnson GO. The development of
rating of perceived exertion-based tests of physical working capacity. J Strength Cond Res.
2008;22(1):293-302.
23. Miller JM, Housh TJ, Coburn JW, Cramer JT, Johnson GO. A proposed test for determining
physical working capacity at the oxygen consumption threshold (PWC-VO2). J Strength Cond
Res. 2004;18(3):618-624.
24. O’Donnell DE, Banzett RB, Carrieri-Kohlman V, Cassburi R, Davenport PW, Gandevia SC, et
al. Pathophysiology of dyspnea in chronic obstructive pulmonary disease: A roundtable. Proc
Am Thorac Soc. 2007;4:145-168.
25. Paterson DJ, Friedland JS, Bascom DA, Clement ID, Cunningham DA, Painter R, et al.
Changes in arterial K+ and ventilation during exercise in normal subjects with McArdle’s
syndrome. J Physiol. 1990;429:339-348.
26. Perry S, Housh TJ, Johnson GO, Ebersole KT, Bull AJ. Heart rate and ratings of perceived
exertion at the physical working capacity at the heart rate threshold J Strength Cond Res.
2001;15(2):225-229.
27. Riley M, Nicholls DP, Nugent AM, Steele LC, Bell N, Davies PM, et al. Respiratory gas
exchange and metabolic responses during exercise in McArdle’s disease. J Appl Physiol.
1993;75(2):745-754.
28. Robergs RA, Dwyer D, Astorino T. Recommendations for improved data processing from
expired gas analysis indirect calorimetry. J Sports Med. 2010;40:95-111.
29. Robergs RA, Ghiasvand F, Parker D. Biochemistry of exercise-induced metabolic acidosis.
Am J Physiol Reg Integ Comp Physiol. 2004;287:502-516.
107
30. Robertson RJ, Goss FL, Dube J, Rutkowski J, Dupain M, Brennan C, et al. Validation of the
adult OMNI scale of perceived exertion for cycle ergometer exercise. Med Sci Sport Exer.
2004;36:102-108.
31. Rohmert W. Determination of the recovery pause for static work of man. Internationale
Zeitschrift für Angewandte Physiologie. 1960;18:23-164.
32. Smith CGM, Jones AM. The relationship between critical velocity, maximal lactate steady-state
velocity and lactate turnpoint velocity in runners. Eur J Appl Physiol. 2001;85:19-26.
33. Soldberg G, Robstad B, Skjonsberg OH, Borchsenius F. Respiratory gas exchange indices for
estimating the anaerobic threshold. J Sport Sci Med. 2005;4:29-36.
34. Thompson WR, Gordon NF, Pescatello LS. ACSM's Guidelines for Exercise Testing and
Prescription. Hubsta Ltd, 2014.
35. Wagner LL and Housh, TJ. A proposed test for determining physical working capacity at the
heart rate threshold. Res Q Exerc Sport. 1993;64(3):361-364.
36. Wasserman K, Beaver WL, Whipp BJ. Gas exchange theory and the lactic acidosis
(anaerobic) threshold. Circulation. 1990;811:Suppl II 14.
37. Zuniga JM, Housh TJ, Camic CL, Hendrix CR, Schmidt RJ, Mielke M, et al. A
mechanomyographic fatigue threshold test for cycling. Int J Sports Med. 2010;31:636-643.
Disclaimer
The opinions expressed in JEPonline are those of the authors and are not attributable to JEPonline,
the editorial staff or the ASEP organization.