Time to exhaustion at and above critical power in trained cyclists: The relationship between heavy and severe intensity domains

Abstract

Objectives. — The aim of this study was to determine the physiological responses and time to
exhaustion, at critical power and 5% above, in trained cyclists.
Equipments and methods. — Eleven male cyclists completed an incremental test, three constant
work rate tests to exhaustion to determine critical power (CP), and finally two tests until
exhaustion at CP and CP plus 5%.
Results. — The modeling of the power-inverse time relationship provided a mean critical power
of 295
±
39 W. Time to exhaustion at critical power was significantly higher than 5% above
(22.9
±
7.5 min versus 13.3
±
5.8 min). Oxygen uptake, pulmonary ventilation, and blood lactate
obtained at the end of the CP plus 5% exhaustion trial were not significantly different from the
maximal variables. However, the physiological end values during the CP test were significantly
lower compared to the incremental test.
Conclusions. — These data support the idea that CP in trained cyclists is the physiological index
that estimates the boundary between heavy to severe exercise domains. Thus, when cyclists
exercised at a power output 5% higher than CP, the VO2max was reached at the end of exercise.

Full text

Please
cite
this
article
in
press
as:
de
Lucas
RD,
et
al.
Time
to
exhaustion
at
and
above
critical
power
in
trained
cyclists:
The
relationship
between
heavy
and
severe
intensity
domains.
Sci
sports
(2012),
http://dx.doi.org/10.1016/j.scispo.2012.04.004
ARTICLE IN PRESS
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SCISPO-2704;
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6
Science
&
Sports
(2012)
xxx,
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ORIGINAL
ARTICLE
Time
to
exhaustion
at
and
above
critical
power
in
trained
cyclists:
The
relationship
between
heavy
and
severe
intensity
domains
Temps
d’épuisement
à
la
puissance
critique
et
au-dessus
chez
des
cyclistes
entraînés
R.D.
de
Lucas, K.M.
de
Souza∗,
V.P.
Costa,
T.
Grossl,
L.G.A.
Guglielmo
Sports
Center,
Federal
University
of
Santa
Catarina,
Physical
Effort
Laboratory,
Florianópolis,
CEP:
88040-900
Florianópolis
(SC),
Brazil
Received
3
December
2011;
accepted
5
April
2012
KEYWORDS
Physiological
responses;
Cycling;
Physiological
domains
Summary
Objectives.
—The
aim
of
this
study
was
to
determine
the
physiological
responses
and
time
to
exhaustion,
at
critical
power
and
5%
above,
in
trained
cyclists.
Equipments
and
methods.
—
Eleven
male
cyclists
completed
an
incremental
test,
three
constant
work
rate
tests
to
exhaustion
to
determine
critical
power
(CP),
and
finally
two
tests
until
exhaustion
at
CP
and
CP
plus
5%.
Results.
—
The
modeling
of
the
power-inverse
time
relationship
provided
a
mean
critical
power
of
295
±
39
W.
Time
to
exhaustion
at
critical
power
was
significantly
higher
than
5%
above
(22.9
±
7.5
min
versus
13.3
±
5.8
min).
Oxygen
uptake,
pulmonary
ventilation,
and
blood
lactate
obtained
at
the
end
of
the
CP
plus
5%
exhaustion
trial
were
not
significantly
different
from
the
maximal
variables.
However,
the
physiological
end
values
during
the
CP
test
were
significantly
lower
compared
to
the
incremental
test.
Conclusions.
—
These
data
support
the
idea
that
CP
in
trained
cyclists
is
the
physiological
index
that
estimates
the
boundary
between
heavy
to
severe
exercise
domains.
Thus,
when
cyclists
exercised
at
a
power
output
5%
higher
than
CP,
the
VO2max was
reached
at
the
end
of
exercise.
©
2012
Elsevier
Masson
SAS.
All
rights
reserved.
∗Corresponding
author.
E-mail
address:
kristophersouza@yahoo.com.br
(K.M.
de
Souza).
0765-1597/$
–
see
front
matter
©
2012
Elsevier
Masson
SAS.
All
rights
reserved.
http://dx.doi.org/10.1016/j.scispo.2012.04.004

Please
cite
this
article
in
press
as:
de
Lucas
RD,
et
al.
Time
to
exhaustion
at
and
above
critical
power
in
trained
cyclists:
The
relationship
between
heavy
and
severe
intensity
domains.
Sci
sports
(2012),
http://dx.doi.org/10.1016/j.scispo.2012.04.004
ARTICLE IN PRESS
+Model
SCISPO-2704;
No.
of
Pages
6
2
R.D.
de
Lucas
et
al.
MOTS
CLÉS
Réponse
physiologique
;
Cyclisme
;
Domaines
physiologiques
Résumé
Objectifs.
—
Le
but
de
cette
étude
est
de
déterminer
les
réponses
physiologiques
et
le
temps
d’épuisement,
à
la
puissance
critique
et
à
5
%
au-dessus
de
la
puissance
critique
pour
des
cyclistes
entraînés.
Équipement
et
méthode.
—Onze
cyclistes
masculins
ont
complété
un
test
progressif,
trois
tests
à
charge
constante
jusqu’à
épuisement
pour
déterminer
les
puissances
critiques
et
enfin
deux
tests
jusqu’à
épuisement
à
la
puissance
critique
et
puissance
critique
plus
5
%.
Résultats.
—
La
modélisation
de
la
relation
entre
puissance
inverse
et
le
temps
a
fourni
une
puissance
critique
de
295
±
39
W.
Le
temps
jusqu’à
l’épuisement
à
la
puissance
critique
a
été
considérablement
plus
élevé
que
5
%
au-dessus
(22,9
±
7,5
min
versus
13,3
±
5,8
min).
La
consommation
d’oxygène,
la
ventilation
pulmonaire
et
le
lactate
sanguin
obtenu
à
la
fin
de
l’essai
de
l’épuisement
à
la
puissance
critique
+5
%
n’ont
pas
été
considérablement
différents
des
variables
maximales.
Néanmoins,
les
valeurs
physiologiques
finales
pendant
les
puissances
critiques
test
ont
été
considérablement
inférieures
comparativement
au
test
progressif.
Conclusions.
—
Les
informations
appuient
l’idée
que
la
puissance
critique
des
cyclistes
entraînés
est
l’index
physiologique
qu’estime
la
limite
entre
le
domaine
d’exercice
lourd
et
sévère.
Donc,
quand
les
cyclistes
sont
entraînés
à
une
puissance
5
%
plus
élevée
que
la
puissance
critique,
la
consommation
maximale
d’oxygène
a
été
atteinte
à
la
fin
de
l’exercice.
©
2012
Elsevier
Masson
SAS.
Tous
droits
réservés.
1.
Introduction
The
hyperbolic
relationship
between
work
rate
and
time
to
exhaustion
(TTE)
is
a
fundamental
property
of
exercise
performance
in
humans
[1—4]
and
rats
[5,6].
Monod
and
Scherrer
[1]
first
reported
this
hyperbolic
relationship
in
a
single
muscle
group,
and
this
relationship
was
subsequently
demonstrated
during
whole-body
exercise,
such
as
cycling
[2],
treadmill
running
[7],
swimming
[8],
and
rowing
[9].
The
work-rate
asymptote
of
this
hyperbolic
relationship
has
been
termed
critical
power
(CP),
whereas
curva-
ture
constant
(i.e.
the
total
amount
of
work
that
can
be
performed
above
the
CP)
has
been
termed
anaer-
obic
work
capacity
(AWC)
[1—4].
The
parameters
CP
and
AWC
can
also
be
derived
through
linear
regression
analysis
after
transformation
of
the
hyperbolic
relation-
ship
into
a
linear
formulation
by
plotting
total
work
done
during
the
series
of
exercise
tests
versus
TTE
[1]
or
by
plotting
power
output
versus
the
inverse
of
TTE
(P
versus
1/TTE)
[3,4,10].
Tw o
decades
ago,
some
studies
aimed
to
better
under-
stand
the
definition
of
CP
by
investigating
the
intensity
domains
at
which
maximal
oxygen
uptake
(VO2max)
can
be
attained
[3,4].
It
was
demonstrated
that
CP
represented
the
highest
intensity
that
is
sustainable
for
a
prolonged
duration
without
eliciting
VO2max,
that
is,
the
lower
bound-
ary
for
severe
exercise
[3,4,11].
Accordingly,
some
authors
observed
a
non-attainment
of
VO2max,
despite
an
oxygen
uptake
slow
component
(VO2SC)
during
exercise
performed
at
CP
[3,4,11—13].
However,
the
variability
of
methods
proposed
to
deter-
mine
CP
has
not
provided
the
boundary
for
the
heavy
to
severe
exercise
domain,
since
previous
studies
reported
a
variation
of
24%,
depending
on
the
CP
mathematical
model
[14—16].
In
a
recent
review,
Dekerle
et
al.
[17]
highlighted
that
linear
model
P
versus
1/TTE
represents
the
best
esti-
mation
of
the
CP
concept,
showing
greater
absolute
value
when
compared
to
other
2-parameter
models.
Therefore,
this
model
has
been
used
to
investigate
the
physiological
responses
during
CP
exercise
[3,4,12,15].
However,
few
studies
have
analyzed
both
physiological
responses
and
TTE
at
CP
and
above.
Poole
et
al.
[3]
hypoth-
esized
that
CP
represented
an
intensity
that
was
slightly
above
physiological
steady
state
and,
hence,
would
lead
to
VO2max.
However,
the
authors
found
this
not
to
be
the
case,
and
power
needed
to
be
increased
by
approximately
16
W
(an
average
of
7%
of
CP)
to
elicit
VO2max in
a
group
of
active
subjects
[3].
A
subsequent
study
using
trained
cyclists
inves-
tigated
TTE
at
CP
and
found
an
average
end
value
of
91%
of
VO2max [12].
To
the
best
of
our
knowledge,
no
study
has
verified
these
physiological
responses
above
CP
in
trained
individuals
with
the
aim
of
analyzing
the
lower
limit
of
the
severe
domain.
Since
in
trained
subjects
CP
occurs
at
a
work
rate
closer
to
maximal
aerobic
power
output
(Pmax)
[18],
we
hypothesized
that
these
subjects
could
reach
VO2max at
a
lower
percentage
above
CP
(i.e.
5%)
than
active
people.
Thus,
the
aim
of
this
study
was
to
determine
the
physiological
responses
and
TTE
at
CP
(P
versus
1/TTE)
and
5%
above
(CP+5%)
in
competitive
cyclists.
2.
Subjects
Eleven
competitive
male
cyclists
(mean
±
SD;
20
±
5
years;
71
±
12
kg;
179
±
7
cm)
participated
in
the
study.
The
cyclists
had
been
training
for
and
competing
in
endurance
cycling
races
on
a
regular
basis
for
a
minimum
of
4
years.
At
the
time
of
testing,
they
were
in
the
beginning
of
the
yearly
training
program
and
were
cycling
approximately
400—450
km/wk.
After
being
fully
informed
of
the
risks
and
stresses
associ-
ated
with
the
study,
subjects
gave
their
written
informed
consent
to
participate.
The
study
was
performed
accord-
ing
to
the
Declaration
of
Helsinki,
and
the
protocol
was
approved
by
the
Ethics
Committee
of
the
Federal
University
of
Santa
Catarina,
Florianópolis,
Brazil.

Please
cite
this
article
in
press
as:
de
Lucas
RD,
et
al.
Time
to
exhaustion
at
and
above
critical
power
in
trained
cyclists:
The
relationship
between
heavy
and
severe
intensity
domains.
Sci
sports
(2012),
http://dx.doi.org/10.1016/j.scispo.2012.04.004
ARTICLE IN PRESS
+Model
SCISPO-2704;
No.
of
Pages
6
Time
to
exhaustion
at
and
above
critical
power
3
3.
Experimental
Protocol
Subjects
were
instructed
to
avoid
any
intake
of
caffeine
or
alcohol
and
strenuous
exercise
in
24
h
preceding
a
test
session
and
to
arrive
at
the
laboratory
in
a
rested
and
fully
hydrated
state,
at
least
3
h
postprandial.
All
tests
were
performed
at
the
same
time
of
day
in
a
controlled
envi-
ronmental
laboratory
condition
(19—22 ◦C;
50—60%
RH)
to
minimize
the
effects
of
diurnal
biological
variation
on
the
results
[19].
Athletes
reported
to
the
laboratory
to
perform:
•
an
incremental
continuous
cycling
test
for
the
measure-
ment
of
VO2max and
Pmax;
•
three
constant
work
rate
tests
in
random
order
to
deter-
mine
TTE
at
95,
100,
and
110%
Pmax to
calculate
CP
using
the
linear
model
P
versus
1/TTE
[3];
•
two
sessions
to
determine
TTE
at
CP
and
CP+5%.
Subjects
performed
only
one
test
on
any
given
day,
and
the
tests
were
each
separated
by
24—48
h
but
completed
within
a
period
of
two
weeks.
3.1.
Procedures
3.1.1.
Materials
All
exercise
testing
was
performed
on
the
cyclist’s
own
bicy-
cle,
which
was
mounted
on
the
ComputrainerTM ergometer
system
(ComputrainerTM Pro
3D,
RacerMate,
Seattle,
Wash-
ington,
USA).
The
rear
wheel
was
inflated
to
800
kPa
after
which
the
system’s
load
generator
was
calibrated
to
a
rolling
resistance
between
0.88
and
0.93
kg.
This
calibration
proce-
dure
was
done
before
and
directly
after
the
15-min
warm-up
to
ensure
accurate
calibration
as
recommended
by
Davidson
et
al.
[20].
Respiratory
and
pulmonary
gas
exchange
varia-
bles
were
measured
breath-by-breath
during
all
protocols
(Quark
PFTergo,
Cosmed,
Rome,
Italy).
Before
each
test,
the
O2and
CO2analysis
systems
were
calibrated
using
ambient
air
and
a
gas
of
known
O2and
CO2concentration
according
to
the
manufacturer’s
instructions,
while
the
Quark
PFTergo
turbine
flow-meter
was
calibrated
using
a
3-L
syringe
(Cali-
bration
Syringe
3-L,
Cosmed,
Rome,
Italy).
Heart
rate
(HR)
was
continuously
recorded
during
the
tests
by
a
HR
monitor
incorporated
into
the
gas
analyzer.
Breath-by-breath
oxygen
uptake
(VO2)
and
HR
data
were
reduced
to
15
s
stationary
averages
throughout
the
tests
(Data
Management
Software,
Cosmed,
Rome,
Italy).
Capillary
blood
samples
(25
␮l)
were
obtained
from
the
ear
lobe
of
each
subject
during
all
tests,
and
the
blood
lactate
concentration
([lac])
was
measured
using
an
electrochemical
analyzer
(YSL
2700
STAT,
Yellow
Springs,
Ohio,
USA).
The
analyzer
was
calibrated
in
accor-
dance
with
the
manufacturer’s
recommended
procedures.
3.1.2.
Incremental
exercise
testing
The
incremental
test
started
at
100
W
and
was
continuously
increased
by
30
W
every
3
min
until
volitional
exhaustion
[21].
Blood
samples
were
collected
during
the
final
15
s
of
every
3
min.
Each
cyclist
was
verbally
encouraged
to
under-
take
maximum
effort.
VO2max was
considered
as
the
highest
value
obtained
in
a
15
s
interval.
The
attainment
of
VO2max
was
defined
using
the
criteria
proposed
by
Lacour
et
al.
[22].
Pmax was
determined
according
to
the
equation
Pmax
(W)
=
power
output
last
stage
completed
(W)
+
[t
(s)/step
duration
(s)
×
step
increment
(W)],
where
‘‘t’’
is
the
time
of
the
uncompleted
stage
[23].
3.1.3.
Determination
of
critical
power
The
CP
was
determined
using
three
TTE
values
measured
from
the
constant
work
rate
tests
(95,
100,
and
110%
Pmax).
Before
each
test,
subjects
completed
a
10-min
warm-up
at
50%
Pmax followed
by
a
5-min
rest,
after
which
the
sub-
jects
were
instructed
to
perform
the
required
power
output
until
they
were
unable
to
maintain
the
fixed
power
out-
put.
All
exercise
testing
was
performed
at
the
cyclist’s
preferred
cadence.
Subjects
were
verbally
encouraged
to
undertake
maximum
effort
for
as
long
as
possible
through-
out
the
tests.
Cardiorespiratory
variables
were
measured
continuously
during
all
protocols.
TTE
was
measured
to
the
nearest
second.
The
linear
model
P
versus
1/TTE
was
used
to
determine
CP
[24]:
P
=
(AWC/TTE)
+
CP;
where
TTE
=
time
to
exhaustion;
AWC
=
anaerobic
work
capacity;
P
=
power
out-
put;
CP
=
critical
power.
3.1.4.
Time
to
exhaustion
at
critical
power
and
5%
above
critical
power
After
a
10-min
warm-up
at
power
output
50%
Pmax followed
by
a
5-min
rest,
subjects
were
instructed
to
perform
the
required
power
output
(CP
and
CP+5%)
to
exhaustion.
Car-
diorespiratory
variables
were
measured
continuously
during
tests.
Both
exercise
tests
were
stopped
when
the
cadence
fell
below
the
preferred
cadence
and/or
until
volitional
exhaustion.
Athletes
were
blinded
to
the
time
elapsed
on
testing
protocols.
Blood
samples
were
collected
in
the
5th
min
and
at
exhaustion
to
determine
[lac].
TTE
was
measured
to
the
nearest
second.
The
VO2SC was
computed
as
the
dif-
ference
between
VO2at
exhaustion
and
the
3rd
min
of
the
exercise
[15].
3.1.5.
Statistical
analysis
All
data
throughout
are
expressed
as
mean
±
SD.
The
Shapiro-Wilk
test
was
applied
to
ensure
a
Gaussian
distri-
bution
of
the
data.
One-way
repeated-measures
ANOVA
was
used
to
compare
the
maximal
physiological
variables
from
incremental
exercise
test
with
end
physiological
variables
from
the
TTE
tests
at
CP
and
5%
above.
Two-way
repeated-
measures
ANOVA
was
used
across
intensities
(CP
and
CP+5%)
and
relative
time
(25%,
50%,
75%,
and
100%).
In
case
of
a
non-significant
interaction,
only
the
main
effect
of
the
test
was
considered.
When
intensity-by-time
interactions
were
significant,
post
hoc
one-way
ANOVA
was
performed
on
the
relevant
data,
and
the
Bonferroni-adjusted
paired
t-
test
was
used
as
appropriate
to
identify
differences
between
responses
at
specific
time
points.
The
level
of
significance
was
set
at
P
<
0.05.
4.
Results
VO2max,
Pmax,
HRmax,
VEmax,
and
[lac]max values
were
68.8
±
5.6
ml/kg/min,
344
±
43
W,
196
±
7
bpm,
164.1
±
26.4
l/min,
and
12.2
±
1.9
mmol/l,
respectively.
TTE
at
95,
100,
and
110%
Pmax values
were
9.9
±
3.8,
6.8
±
2.7,
and
3.8
±
2.0
min,
respectively.
The
model-
ing
of
the
power-inverse
time
relationship
(adjusted

Please
cite
this
article
in
press
as:
de
Lucas
RD,
et
al.
Time
to
exhaustion
at
and
above
critical
power
in
trained
cyclists:
The
relationship
between
heavy
and
severe
intensity
domains.
Sci
sports
(2012),
http://dx.doi.org/10.1016/j.scispo.2012.04.004
ARTICLE IN PRESS
+Model
SCISPO-2704;
No.
of
Pages
6
4
R.D.
de
Lucas
et
al.
r2=
0.95
±
0.05)
provided
mean
CP
values
of
295
±
39
W
(SEE
=
7.5
±
4.2
W).
TTE
at
CP
(22.9
±
7.5
min)
was
signifi-
cantly
higher
(P
<
0.01)
than
TTE
at
CP+5% (13.3
±
5.8
min).
The
ranges
of
the
TTE
values
for
the
two
intensities
were
15.6—42.5
min
at
CP
and
10.3—30.1
min
at
CP+5%.
In
addition,
TTE
values
from
the
two
intensities
were
highly
correlated
(r
=
0.90,
P
<
0.05).
However,
no
other
variable
was
associated
with
TTE
at
CP
and
CP+5%.There
was
no
significant
difference
between
VO2(68.0
±
6.3
ml/kg/min),
VE
(155.8
±
26.6
l/min),
and
[lac]
(11.0
±
2.4
mmol/l)
obtained
at
the
end
of
CP+5% exhaustion
trial
compared
to
the
incremental
test.
However,
the
end
value
of
VO2
(64.8
±
5.7
ml/kg/min),
VE
(145.7
±
22.5
l/min),
and
[lac]
(9.5
±
2.1
mmol/l)
during
the
CP
test
was
significantly
lower
than
VO2max,
VEmax,
and
[lac]max,
respectively.
The
VO2at
exhaustion
averaged
94%
of
VO2max.
The
end
HR
values
at
CP
(190
±
8
bpm)
and
CP+5% (189
±
7
bpm)
were
significantly
lower
than
the
HRmax (P
<
0.01).
The
mean
physiological
responses
during
exercise
at
CP
and
CP+5% are
shown
in
Fig.
1.
Two-way
ANOVA
with
repeated
measures
across
intensity
and
relative
time
revealed
no
significant
intensity-by-time
interaction
for
any
dependent
variables
(VO2,
P
=
0.99;
VE,
P
=
0.97;
HR,
P
=
0.96).
How-
ever,
the
main
effect
showed
that
VO2increased
over
time
until
75%
of
TTE.
In
contrast,
VE
and
HR
increased
over
the
entire
duration
of
the
tests.
We
did
not
find
sig-
nificant
differences
in
the
VO2SC between
the
intensities
(247
±
82
ml/min
versus
222
±
106
ml/min
for
CP
and
CP+5%,
respectively).
5.
Discussion
The
aim
of
this
study
was
to
determine
the
physiological
responses
during
TTE
at
CP
and
CP+5% in
competitive
cyclists.
The
main
finding
was
that
when
subjects
were
exercising
at
intensities
slightly
above
CP
(i.e.
5%),
VO2max was
attained.
Few
studies
have
analyzed
physiological
responses
at
CP
and/or
above
in
trained
cyclists
[12,25,26].
The
mean
value
of
CP
observed
in
our
study
was
∼300
W,
unlike
classic
stud-
ies
by
Poole
et
al.
[3,4]
conducted
with
physically
active
subjects
(CP
=
∼200
W).
The
subjects
different
fitness
levels
could
change
the
percentage
above
CP
in
which
VO2max was
reached
and
hence
the
lower
boundary
of
severe
domain
[18].
In
a
recent
review,
Jones
et
al.
[27]
highlighted
that
CP
was
found
to
occur
at
80%
of
VO2max,
approximately
midway
between
the
gas
exchange
threshold
and
VO2max
(50%
).
In
contrast,
Caputo
and
Denadai
[18]
showed,
in
trained
cyclists
(CP
=
∼303
W),
that
the
upper
bound-
ary
of
the
heavy
intensity
domain
lies
at
approximately
75%
,
suggesting
that
aerobic
training
modifies
the
rela-
tionship
between
CP
and
the
difference
between
first
lactate
threshold
and
VO2max.
In
the
present
investigation,
we
found
an
average
of
65%
,
and
this
value
could
be
explained
by
the
fact
that
experimental
procedures
were
held
in
the
beginning
of
the
competitive
season.
Never-
theless,
the
athletes
had
at
least
4
years
of
training
on
a
regular
basis,
ensuring
a
good
development
of
aerobic
fitness.
To
our
knowledge,
this
is
the
first
study
in
trained
cyclists
(VO2max =
68.8
ml/kg/min)
that
has
analyzed
TTE
Figure
1
Cardiorespiratory
measures
(mean,
SD)
during
time
to
exhaustion
at
critical
power
(CP)
and
5%
above
(CP+5%).
VO2
(A);
HR
(B);
VE
(C);
different
letters
mean
significant
difference
over
time
(P
<
0.05).
and
VO2response
at
and
above
CP.
We
have
used
a
fixed
percentage
above
CP
(i.e.
5%)
instead
of
the
fixed
work
rate
used
by
others
[11,28],
i.e.
10
or
15
W
above
CP
to
measure
physiological
responses
in
untrained
sub-
jects.
The
studies
published
by
Poole
et
al.
[3,4]
have
been
misunderstood
by
others
[11,12,29]
since
the
percentage

Please
cite
this
article
in
press
as:
de
Lucas
RD,
et
al.
Time
to
exhaustion
at
and
above
critical
power
in
trained
cyclists:
The
relationship
between
heavy
and
severe
intensity
domains.
Sci
sports
(2012),
http://dx.doi.org/10.1016/j.scispo.2012.04.004
ARTICLE IN PRESS
+Model
SCISPO-2704;
No.
of
Pages
6
Time
to
exhaustion
at
and
above
critical
power
5
above
CP
cited
does
not
represent
the
actual
value.
In
fact,
Poole
et
al.
[3,4]
used
5%
of
peak
power
output
from
the
incremental
test
to
calibrate
the
intensity
above
CP.
Con-
sequently,
the
subjects
exercised
at
different
percentages
above
CP
(i.e.
6—8%),
values
slightly
different
than
those
aforementioned
authors
have
described
(i.e.
8—11%
above
CP)
about
studies
from
Poole
et
al.
[3,4].
It
is
important
to
note
that
the
imprecision
of
the
CP
estimate
would
influ-
ence
VO2and
[lac]
responses,
as
well
as
TTE.
These
facts
lead
us
to
choose
a
fixed
percentage
over
a
fixed
work-
load,
since
our
results
showed
an
average
SEE
of
2.5
±
1.4%
(7.5
±
4.2
W)
and
hence
ensured
that
subjects
cycled
just
above
CP.
When
exercise
was
performed
at
CP+5%,
the
TTE
decreased
approximately
40%
compared
with
TTE
at
CP.
However,
the
VO2at
the
end
of
exercise
was
significantly
different
from
the
CP
test
but
not
different
from
VO2max
(Fig.
1A).
The
HR
values
were
very
close
to
HRmax (∼97%),
and
VE
had
no
significant
differences
from
VEmax (Figs.
1B
and
C,
respectively).
Also,
the
end
[lac]
was
not
sub-
stantially
different
from
the
incremental
exercise
testing.
Brickley
et
al.
[12]
reported
that
the
VO2at
CP
averaged
91%
of
VO2max.
In
agreement
with
this
study,
the
VO2response
at
CP
indicated
a
progressive
increase
reaching
94%
of
VO2max
at
exhaustion.
Therefore,
the
data
from
our
study
support
the
suggestions
that
VO2max is
not
elicited
at
CP
and
that
the
intensity
of
exercise
needs
to
be
increased
by
about
5%
for
VO2max to
be
reached.
This
is
in
accordance
with
the
description
of
the
severe
domain
(>
CP),
in
which
both
VO2and
[lac]
do
not
stabi-
lize
but
rise
continuously
over
time
until
VO2max is
reached
and/or
fatigue
resulting
from
the
metabolic
acidosis
termi-
nates
exercise
[30].
The
short
tolerance
observed
during
exercise
above
CP
has
been
associated
with
the
gradual
depletion
of
AWC,
which
is
determined
by
the
limited
sup-
plies
of
energy
[2].
A
previous
study
performed
with
an
exercise
intensity
of
10%
above
CP
found
a
gradual
deple-
tion
of
phosphocreatine
and
pH
and
an
increase
in
inorganic
phosphate
[31].The
TTE
observed
at
CP
agreed
with
stud-
ies
on
trained
cyclists
that
indicate
the
overestimation
of
maximal
lactate
steady
state
[12,32—34].
Housh
et
al.
[35]
reported
that
TTE
at
CP
was
33.3
min
±
14.4
s.
Brickley
et
al.
[12]
found
that
TTE
ranges
from
20.1
min
to
40.4
min
during
CP
tests.
In
the
study
by
Brickley
et
al.
[12],
the
subjects
who
had
the
highest
VO2max and
the
highest
CP
reached
their
exhaustion
time
earlier
(r
=
−0.78;
r
=
−0.92
P
<
0.05,
respectively).
In
the
present
study,
we
failed
to
demonstrate
any
significant
correlation
between
TTE
and
VO2max,
Pmax or
CP.
The
identification
of
meaningful
markers
of
the
inten-
sity
at
which
exercise
is
performed
is
useful
for
training
programs
and
studies
designed
for
athletes.
However,
the
methods
used
to
determine
the
CP
may
demarcate
the
exer-
cise
intensity
domains
at
a
different
power
output.
Some
studies
have
reported
that
CP
estimates
differ
significantly
depending
upon
the
mathematical
model
used
to
determine
the
power-time
relationship
(data
can
vary
by
up
to
24%)
[14,36].
More
recently,
Bull
et
al.
[15]
found
in
runners
that
critical
velocity
estimates
from
the
five
models
varied
by
18%.
Therefore,
these
studies
support
the
idea
that
the
lin-
ear
model
used
in
our
study
is
acceptable
to
estimate
the
boundary
of
heavy
to
severe
exercise
domain.
Thus,
CP
could
be
an
important
and
practical
index
to
prescribe
interval
training
between
these
domains.
6.
Conclusion
The
data
from
our
study
support
the
idea
that
CP
deter-
mined
in
trained
cyclists
(CP
=
∼300
W)
is
the
physiological
index
that
estimates
the
boundary
between
heavy
to
severe
exercise
intensity
domains.
In
addition,
the
physiological
variables
did
not
reach
steady
state
during
the
CP
test
to
exhaustion,
but
the
VO2max was
not
elicited.
However,
when
cyclists
had
exercised
at
a
power
output
5%
higher
than
CP,
the
VO2max was
reached
at
the
end
of
exercise.
Disclosure
of
interest
The
authors
declare
that
they
have
no
conflicts
of
interest
concerning
this
article.
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Please
cite
this
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as:
de
Lucas
RD,
et
al.
Time
to
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at
and
above
critical
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in
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The
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heavy
and
severe
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Sci
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(2012),
http://dx.doi.org/10.1016/j.scispo.2012.04.004
ARTICLE IN PRESS
+Model
SCISPO-2704;
No.
of
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6
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