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Creatine supplementation alters the response to a graded cycle ergometer test

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Arnold G Nelson at Louisiana State University
Arnold G Nelson
Randy Day
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Ellen Glickman at Kent State University
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Abstract

To determine the effects of creatine supplementation on cardiorespiratory responses during a graded exercise test (GXT) 36 trained adults (20 male, 16 female; 21–27 years old) performed two maximal GXTs on a cycle ergometer. The first GXT was done in a non-supplemented condition, and the second GXT was done following 7 days of ingesting either 5 g creatine monohydrate, encased in gelatin capsules, four times daily (CS, 13 male, 6 female), or the same number of glucose capsules (PL, 7 male, 10 female). CS significantly (P < 0.05) improved total test time [pre-CS=1217 (240) s, mean (std. dev.) versus post-CS=1289 (215) s], while PL administration had no effect (P > 0.05) on total test time [pre-PL=1037 (181) s versus post-PL=1047 (172) s]. In addition, both oxygen consumption (V˙ O2) and heart rate at the end of each of the first five GXT stages were significantly lower after CS, but were unchanged after PL. Moreover, the ventilatory threshold occurred at a significantly greater V˙ O2 for CS [pre-CS=2.2 (0.4) l · min−1 or 66% of peak V˙ O2 versus post-CS=2.6 (0.5) l · min−1 or 78% of peak V˙ O2; pre-PL=2.6 (0.9) l · min−1 or 70% peak V˙ O2 versus post-PL=2.6 (1.1) l · min−1 or 68% of peak V˙ O2]. Neither CS nor PL had an effect on peak V˙ O2 [pre-CS=3.4 (0.7) l · min−1 versus post-CS=3.3 (0.7) l · min−1; pre-PL=3.7 (1.1) l · min−1 versus post-PL=3.7 (1.1) l · min−1]. Apparently, CS can alter the contributions of the different metabolic systems during the initial stages of a GXT. Thus, the body is able to perform the sub-maximal workloads at a lower oxygen cost with a concomitant reduction in the work performed by the cardiovascular system.
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ORIGINAL ARTICLE
Arnold G. Nelson áRandy Day
Ellen L. Glickman-Weiss áMaren Hegsted
Joke Kokkonen áB. Sampson
Creatine supplementation alters the response
to a graded cycle ergometer test
Accepted: 20 April 2000
Abstract To determine the eects of creatine supple-
mentation on cardiorespiratory responses during a
graded exercise test (GXT) 36 trained adults (20 male, 16
female; 21±27 years old) performed two maximal GXTs
on a cycle ergometer. The ®rst GXT was done in a non-
supplemented condition, and the second GXT was done
following 7 days of ingesting either 5 g creatine mono-
hydrate, encased in gelatin capsules, four times daily
(CS, 13 male, 6 female), or the same number of glucose
capsules (PL, 7 male, 10 female). CS signi®cantly
(P< 0.05) improved total test time [pre-CS 1217
(240) s, mean (std. dev.) versus post-CS 1289 (215) s],
while PL administration had no eect (P> 0.05) on
total test time [pre-PL 1037 (181) s versus post-
PL 1047 (172) s]. In addition, both oxygen con-
sumption (
_
VO2) and heart rate at the end of each of the
®rst ®ve GXT stages were signi®cantly lower after CS,
but were unchanged after PL. Moreover, the ventilatory
threshold occurred at a signi®cantly greater
_
VO2for CS
[pre-CS 2.2 (0.4) l ámin
)1
or 66% of peak
_
VO2versus
post-CS 2.6 (0.5) l ámin
)1
or 78% of peak
_
VO2; pre-
PL 2.6 (0.9) l ámin
)1
or 70% peak
_
VO2versus post-
PL 2.6 (1.1) l ámin
)1
or 68% of peak
_
VO2]. Neither CS
nor PL had an eect on peak
_
VO2[pre-CS 3.4
(0.7) l ámin
)1
versus post-CS 3.3 (0.7) l ámin
)1
; pre-
PL 3.7 (1.1) l ámin
)1
versus post-PL 3.7 (1.1) l á
min
)1
]. Apparently, CS can alter the contributions of the
dierent metabolic systems during the initial stages of a
GXT. Thus, the body is able to perform the sub-maxi-
mal workloads at a lower oxygen cost with a concomi-
tant reduction in the work performed by the
cardiovascular system.
Key words Heart rate áOxygen consumption á
Ventilatory threshold
Introduction
Recent research has shown that oral creatine supple-
mentation can increase skeletal muscle phosphocreatine
(PC) levels (Balsom et al. 1995; Febbraio et al. 1995;
Greenha et al. 1994; Harris et al. 1992), and that such
supplementation has ergogenic potential (Balsom et al.
1993, 1995; Greenha et al. 1993). For example,
Greenha et al. (1993) showed that following creatine
supplementation, peak torque production was higher in
bouts 2, 3, and 4 of a work protocol consisting of 5
bouts of 30 maximum voluntary isokinetic contractions
interspersed with 60 s rest. Balsom et al. (1993) showed
that following creatine supplementation the power out-
put of a single high-intensity 10-s exercise period pre-
ceded by ®ve 6-s work bouts (each separated by 30 s
rest) was greater than it had been prior to creatine
supplementation. Later, both Balsom et al. (1995) and
Prevost et al. (1997) reported that creatine supplemen-
tation signi®cantly extends one's capacity to maintain a
speci®c level of high-intensity intermittent exercise.
These post-creatine supplementation performance im-
provements have also been associated with a 2±5%
Eur J Appl Physiol (2000) 83: 89±94 ÓSpringer-Verlag 2000
A. G. Nelson (&)
Department of Kinesiology, Louisiana State University,
112 Long Field House, Louisiana State University,
Baton Rouge, LA 70803, USA
e-mail: anelso@lsu.edu
Tel.: +1-225-388-3114, Fax: +1-225-388-3680
R. Day áB. Sampson
Division of Math and Science,
Brigham Young University-Hawaii,
Laie, HI 96762, USA
E. L. Glickman-Weiss
School of Exercise, Leisure and Sport,
Kent State University,
Kent, OH 44242, USA
M. Hegsted
Department of Human Ecology,
Louisiana State University,
Baton Rouge, LA 70803, USA
J. Kokkonen
Division of Physical Education,
Brigham Young University-Hawaii,
Laie, HI 96762, USA
decrease in lactate accumulation (Balsom et al. 1993,
1995; Febbraio et al. 1995; Prevost et al. 1997), a 2±3%
lower oxygen consumption (
_
VO2) (Balsom et al. 1993;
Prevost et al., unpublished observations), a 2% lower
plasma hypoxanthine accumulation (Balsom et al.
1993), and a 2±12% lower accumulation of ammonia
(Birch et al. 1994; Greenha et al. 1993; Mujika et al.
1996).
Lower levels of blood lactate, ammonia, and
_
VO2
during high-intensity work following a creatine supple-
mentation program suggest that creatine supplementa-
tion might alter physiological and/or metabolic
responses to a graded exercise test (GXT). Presently,
there is little information concerning the eects of cre-
atine supplementation on responses measured during a
GXT. Stroud et al. (1994) found that steady-state
_
VO2,
heart rate, and blood lactate concentration during seven
stages (6 min per stage) of incremental treadmill exercise
did not change following creatine supplementation.
Unfortunately, the experiment was terminated at 90%
of pre-supplementation maximal
_
VO2, so it is uncertain
whether maximal
_
VO2changed following supplementa-
tion. On the other hand, Gordon et al. (1995) discovered
that the performance of chronic heart failure patients on
a progressive incremental (10-W increase per minute)
cycle ergometer test increased by 10% following creatine
supplementation, but no
_
VO2values were reported.
This disagreement between Stroud et al. (1994) and
Gordon et al. (1995) might be due to the dierent
lengths of the exercise stages (6 min versus 1 min). While
6-min stages are recommended for obtaining steady-
state information for each stage of exercise (A
Êstrand and
Rodahl 1986), a GXT consisting of 2- or 3-min stages is
more frequently used. For some time it has been estab-
lished (Cotes et al. 1969) that the
_
VO2measured at each
stage of a GXT consisting of 3-min stages is lower than
that measured at each stage of a GXT comprised of
longer stages (>5 min). This lower
_
VO2is attributed, in
part, to a delay in adjustment by the cardiorespiratory
system to the changes in workload. During this delay,
the metabolic demands of the work are met by the ATP-
PC and glycolytic systems (A
Êstrand and Rodahl 1986;
Karlsson 1971; Sahlin et al. 1988; Scott and Bogdany
1998).
Interestingly, Paganelli et al. (1989) have shown that
a decrease in PC stores results in a higher
_
VO2at the
onset of exercise. Consequently, the capacity of the
ATP-PC system could in¯uence the
_
VO2response to a
short-stage GXT, since lower PC stores would necessi-
tate more reliance on aerobic metabolism. On the other
hand, during a short-stage GXT increasing the muscle
PC stores via a standard creatine supplementation pro-
gram could further delay the reliance upon aerobic
metabolism, and thus decrease the per-stage
_
VO2. Hence,
the purpose of this study was to characterize more
completely the eect of creatine supplementation upon
responses to a 3-min per-stage GXT. We hypothesized
that, following creatine supplementation,
_
VO2, and heart
rate would be lower at each stage of the GXT.
Methods
Participants
Thirty-six physically active healthy (male, n20, female, n16)
university students successfully completed all requirements of the
study, and their mean physical characteristics are presented in
Table 1. A physically active individual was de®ned as a person
whose peak
_
VO2from the initial GXT placed the individual into
either the good or excellent categories (males:
_
VO2max >43 ml á
kg
)1
ámin
)1
; females:
_
VO2max >38 ml ákg
)1
ámin
)1
) established by
the American Heart Association (1972). In addition, each partici-
pant had to have been engaged in lower-extremity rhythmic aerobic
activity for a minimum period of 20 min 3 days per week for at
least 3 months prior to the start of the study. The experimental
protocol was approved by the appropriate institutional review
board, and each volunteer gave written consent prior to performing
any part of the experiment.
Experimental protocol
All participants performed two GXTs to exhaustion on a Monark
cycle ergometer (model 818 E). The ®rst GXT was done while the
subject was in a non-supplemented condition. Following the ®rst
GXT, the subjects were randomly placed into either a creatine
supplementation group (CS, 13 male, 6 female) or a placebo group
(PL, 7 male, 10 female). Initially each group consisted of 15 males
and 10 females; however, non-compliance with study requirements
necessitated the removal of 14 individuals. Hence, at the end of the
study, CS had 13 males and 6 females, while PL had 7 males and 10
females.
Each GXT began at a work rate of 30 W (90 rev ámin
)1
against
a resistance of 3.24 N). The work rate was incremented by 30 W
every 3 min until the subject could no longer maintain the required
pedal cadence. Expired gases and minute ventilations (V
e
) were
monitored continuously with an automated system (SensorMedics
series 2500). Oxygen consumption was measured breath-by-breath,
and was averaged at 20-s time periods. Peak
_
VO2was
de®ned as the highest 20-s average
_
VO2obtained during the last 4 min
of the test. In addition, heart rate was recorded during the ®nal 15 s
of the 3rd min of each stage. To ensure unbiased results, each GXT
was administered by three to four technicians who were naive both
to the supplementation protocol, and to the results of the ®rst GXT.
The test administers were asked to give each participant maximal
Table 1 Subject characteristics.
Values are mean (SD). (CS
Creatine supplemented, PL
placebo)
Group Height (cm) Mass (kg) Age (years)
_
VO2peak (ml ákg
)1
ámin
)1
)
Mean SD Mean SD Mean SD Mean SD
CS male 187 9 90 17 24 1 47.7 7.6
CS female 162 4 61 10 23 2 45.0 5.7
PL male 178 7 79 10 25 2 51.5 9.0
PL female 167 5 63 8 24 2 45.2 8.1
90
encouragement to perform to exhaustion. At least one of the co-
authors was present at each test to assure that the test protocol was
strictly followed; but, to prevent investigator bias, the second GXT
was overseen by a co-author who was not present at the ®rst GXT,
and was unaware of the participant's prior performance.
After each GXT was completed, the 20-s outputs were used to
calculate T
vent
.T
vent
was de®ned as the
_
VO2(l ámin
)1
) at the in-
tersection point of the high and low slope portions of the
_
VE:
_
VO2
relationship and calculated according to the procedure outlined by
Orr et al. (1982). In brief, the intersection point of the high and low
slope portions of the
_
VE:
_
VO2relationship was calculated by deter-
mining the least-squares regression lines for each portion of the
_
VE:
_
VO2relationship.
Supplementation
Supplementation began on the day following the ®rst GXT, and
consisted of either placebo or creatine. Placebo administration
consisted of sugar encased in gelatin capsules. Creatine supple-
mentation consisted of 5 g creatine monohydrate encased in gelatin
capsules administered four times daily for 7 days. The placebo and
creatine capsules were distributed following a double-blind proto-
col, and were indistinguishable in appearance. The number of
placebo and creatine capsules ingested daily was the same.
Statistical analysis
Statistical comparisons between the creatine and placebo condi-
tions for peak
_
VO2, ventilatory breakpoint, and total work time
were made via a two-way (treatment ´pre-post) repeated-measures
ANOVA. A three-way (treatment ´pre-post ´GXT stage) re-
peated-measures ANOVA was used to analyze stage-by-stage
changes in
_
VO2and heart rate. The major term of interest in the
statistical models was either the two-way (treatment ´pre-post) or
the three-way (treatment ´pre-post ´GXT stage) interaction.
Post-ANOVA analyses of the signi®cant interactions involved the
use of Tukey's Protected t-test. The experimental error rate was set
at 0.05, and was maintained throughout all statistical tests.
Results
Maximal values
The initial peak
_
VO2was 3.41 (0.68) l ámin
)1
[mean
(SD)] for CS and 3.69 (1.06) l ámin
)1
for PL. Following
CS and PL, peak
_
VO2[CS 3.33 (0.72) l ámin
)1
;
PL 3.74(1.07) l ámin
)1
] remained unchanged (P
0.17 for the two-way interaction). Likewise, the maxi-
mum heart rate for both CS [pre 189 (8) bpm,
post 186 (4) bpm] and PL [pre 189 (10) bpm, 189
(12) bpm] was not signi®cantly changed (P0.25 for
the two-way interaction). However, a signi®cant
(P0.01) two-way interaction was found for total test
time. Post-hoc analysis revealed that CS signi®cantly
improved (P< 0.05) total test time by more than 70 s
[pre 1217 (240) s, post 1289 (215) s]. In contrast,
PL had no eect (P> 0.05) on total test time
[pre 1038 (181) s, post 1047 (172) s].
Sub-maximal values
All participants completed at least four stages during
both the ®rst and second GXT. Therefore, stage-by-stage
comparisons of
_
VO2and heart rate were made for stag-
es 1±4. For each stage, the last three 20-s readings for
_
VO2
were averaged, and the average used in the analyses. The
_
VO2responses are depicted in Figures 1 and 2. Fig. 1
shows the attenuating eect of the creatine supplemen-
tation on
_
VO2across stages 1±4 of the GXTs. The three-
way interaction for
_
VO2was signi®cant (P0.03). For
each stage, the post-CS
_
VO2was signi®cantly lower
(P< 0.05) than the pre-CS
_
VO2. In contrast, Fig. 2
shows that the pre-PL and post-PL
_
VO2did not dier
(P> 0.05) across stages. Likewise, the three-way inter-
action for heart rate was signi®cant (P0.03). Within
the CS group, post-supplementation heart rates were
signi®cantly (P< 0.05) lower at each stage. This dier-
ence was approximately 6 bpm (see Fig. 3). Heart rates
within PL were not signi®cantly dierent (P> 0.05)
between pre and post, at any stage (see Fig. 4).
The two-way interaction for T
vent
was signi®cant for
both absolute
_
VO2(P0.02) (see Fig. 5) and relative
_
VO2
(P0.02) (see Fig. 6). Again, post-hoc analysis revealed
that both measures of T
vent
were signi®cantly improved
(P< 0.05) following CS, but were unaected by PL.
Discussion
It is apparent that CS altered the contributions of the
dierent metabolic systems during these short-stage cy-
cle ergometer GXTs. This alteration resulted in the body
being able to perform a given sub-maximal workload at
a lower oxygen cost coupled with reduced work by the
cardiovascular system. Presumably, the reductions in the
sub-maximal
_
VO2and heart rate are due to increased PC
concentration within the muscle cells. Tissue oxygen
utilization is tied to mitochondrial respiration, and a
Fig. 1 The eect of creatine supplementation on oxygen consump-
tion
_
VO2during the graded exercise test (GXT). Values represented
are mean (SD). *The pre-supplemented mean
_
VO2at each GXT
stage is signi®cantly higher (P< 0.05) than the post-supplemented
mean
_
VO2at that stage
91
decrease in ATP coupled with an increase in ADP serves
as a stimulator of mitochondrial respiration (Balaban
1990; Scott 1995). Hence, an increase in muscle PC levels
due to creatine supplementation would have delayed the
decrease in the ATP/ADP ratio needed to stimulate
mitochondrial respiration and
_
VO2. Support for this idea
comes from the work of Connett and Honig (1989).
These authors showed that during in vivo stimulation of
muscle,
_
VO2was linearly related to PC concentration
signi®cantly. When PC concentrations were high,
_
VO2
was low, and vice versa.
While an increase in PC can yield a decrease in
_
VO2,
it should be noted that the lower
_
VO2of approxi-
mately 0.25 l ámin
)1
corresponds to approximately
60±70 mmol ATP. Since the usual increase in the total
creatine pool ranges from 15 to 35 mmol ákg
)1
dry
matter (Greenha et al. 1994; Harris et al. 1992), it is
unlikely that the increase in PC stores was the only
factor responsible for attenuating the
_
VO2response. In-
creased mechanical eciency could also have contrib-
uted to the decrease in
_
VO2. Pahud et al. (1980) reported
that the eciency during the oxygen-de®cit period of
exercise was 33%. This eciency was a combination of
both the aerobic eciency of 27% and the anaerobic
eciency of 41%. Since the eciency of anaerobic ex-
ercise is about 50% greater than that of aerobic exercise,
an increase in the relative contribution of the anaerobic
Fig. 2 The eect of placebo administration on
_
VO2during the
GXT. Values represented are mean (SD)
Fig. 3 The eect of creatine supplementation on heart rate during
the GXT. Values represented are mean (SD). *The pre-supple-
mented mean heart rate at each GXT stage is signi®cantly higher
(P< 0.05) than the post-supplemented mean heart rate at that
stage
Fig. 4 The eect of placebo administration on heart rate during
the GXT. Values represented are mean (SD)
Fig. 5 Eect of creatine and placebo supplementation on the
absolute
_
VO2at ventilatory breakpoint. Values represented are
mean (SD). *The post-creatine supplemented mean absolute
_
VO2is
signi®cantly greater (P< 0.05) than the pre-supplemented abso-
lute
_
VO2
92
energy systems results in an increase in the ratio between
work output and ATP utilization.
The ®ndings of this study suggest that CS can modify
the relationship between pulmonary gas exchange and
heart rate responses during a GXT. This modi®cation
could have important practical rami®cations. For ex-
ample, one of the methods recommended by the Amer-
ican College of Sports Medicine (ACSM) for
determining an appropriate exercise intensity is to plot
heart rate obtained during a GXT against either
_
VO2or
workload to determine a training-sensitive zone with
respect to exercise intensity (American College of Sports
Medicine 1995). Since CS apparently elicits a lower heart
rate at sub-maximal workloads of a short-stage GXT,
the work intensity range determined would be overesti-
mated. In addition, many sub-maximal tests for pre-
dicting maximal
_
VO2base extrapolations on the heart
rate: workload relationship at one or more workloads
(American College of Sports Medicine 1995). Again, the
lower than expected heart rate following CS could result
in the maximal
_
VO2being overestimated. The use of this
overestimated maximal
_
VO2could result in the prescrip-
tion of an exercise intensity that is too high. Finally,
ASCM also recommends that the exercise intensity for
pulmonary patients should exceed the anaerobic
threshold (American College of Sports Medicine 1995).
Since almost all of the automated gas analysis systems
currently available predict an individual's anaerobic
threshold from the T
vent
obtained during the GXT, it is
not unlikely that some clinicians might use this measure
to determine exercise intensity. Again, this study
demonstrates that the use of a GXT to obtain a T
vent
-
based prediction of anaerobic threshold would be
contraindicated in a CS individual.
In summary, creatine loading alters the initial meta-
bolic responses seen during a short-stage GXT. These
alterations are most signi®cant at the early stages of the
GXT and are manifested by a lower sub-maximal
_
VO2
and heart rate at the end of each GXT stage.
Acknowledgement This experiment complied with all current state
and federal laws in force at the time it was conducted.
References
American College of Sports Medicine (1995) ACSM's guidelines
for exercise testing and prescription. Williams and Wilkins,
Baltimore
American Heart Association (1972) Exercise testing and training of
apparently healthy individuals: a handbook for physicians.
American Heart Association, New York
A
Êstrand PO, Rodahl K (1986) Textbook of work physiology:
physiological bases of exercise. McGraw-Hill, New York
Balaban RS (1990) Regulation of oxidative phosphorylation in the
mammalian cell. Am J Physiol 258: C377±C389
Balsom PD, Ekblom B, So
Èderlund K, Sjo
Èdin B, Hultman E (1993)
Creatine supplementation and dynamic high-intensity inter-
mittent exercise. Scand J Med Sci Sports 3: 143±149
Balsom PD, So
Èderlund K, Sjo
Èdin B, Ekblom B (1995) Skeletal
muscle metabolism during short duration high-intensity exer-
cise: in¯uence of creatine supplementation. Acta Physiol Scand
154: 303±310
Birch R, Noble D, Greenha PL (1994) The in¯uence of dietary
creatine supplementation on performance during repeated
bouts of maximal isokinetic cycling in man. Eur J Appl Physiol
69: 268±270
Connett RJ, Honig CR (1989) Regulation of
_
VO2max in red muscle:
do current biochemical hypotheses ®t in vivo data? Am J
Physiol 256: R898±R908
Cotes JE, Allsopp D, Sardi F (1969) Human cardiopulmonary
response to exercise: comparisons between progressive and
steady state exercise, between arm and leg exercise, and between
subjects diering in body weight. Q J Exp Physiol Cogn Med
Sci 54: 211±222
Febbraio MA, Flanagan TR, Snow RJ, Zhao S, Carey MF
(1995) Eect of creatine supplementation on intramuscular
TCr, metabolism and performance during intermittent, su-
pramaximal exercise in humans. Acta Physiol Scand 155: 387±
395
Gordon A, Hultman E, Kaijser L, Kristjansson S, Rolf CJ, Nyquist
O, Sylven C (1995) Creatine supplementation in chronic heart
failure increases skeletal muscle creatine phosphate and muscle
performance. Cardiovasc Res 30: 413±418
Greenha PL, Casey A, Short AH, Harris R, So
Èderlund K, Hult-
man E (1993) In¯uence of oral creatine supplementation on
muscle torque during repeated bouts of maximal voluntary
exercise in man. Clin Sci 84: 565±571
Greenha PL, Bodin K, So
Èderlund K, Hultman E (1994) Eect of
oral creatine supplementation on skeletal muscle phosphocre-
atine resynthesis. Am J Physiol 266: E725±E730
Harris RC, So
Èderlund K, Hultman E (1992) Elevation of creatine
in resting and exercised muscle of normal subjects by creatine
supplementation. Clin Sci 83: 367±374
Karlsson J (1971) Lactate and phosphagen concentrations in
working muscle of man with special reference to oxygen de®cit
at the onset of work. Acta Physiol Scand Suppl 358: 1±72
Mujika I, Chatard JC, Lacoste L, Barale F, Geyssant A (1996)
Creatine supplementation does not improve sprint perfor-
mance in competitive swimmers. Med Sci Sports Exerc
28: 1435±1441
Orr GW, Green HJ, Hughson RL, Bennett GW (1982) A computer
linear regression model to determine ventilatory anaerobic
threshold. J Appl Physiol 52: 1349±1352
Fig. 6 Eect of creatine and placebo supplementation on the
relative
_
VO2at ventilatory breakpoint. Values represented are mean
(SD). *The post-creatine supplemented mean relative
_
VO2is
signi®cantly greater (P< 0.05) than the pre-supplemented relative
_
VO2
93
Paganelli W, Pendergast DR, Koness J, Cerretelli P (1989) The
eect of decreased muscle energy stores on
_
VO2kinetics at the
onset of exercise. Eur J Appl Physiol 59: 321±326
Pahud P, Ravussin E, Jequier E (1980) Energy expended during
oxygen de®cit period of submaximal exercise in man. J Appl
Physiol 48: 770±775
Prevost MC, Nelson AG, Morris GS (1997) Creatine supplemen-
tation enhances intermittent work performance. Res Q Exerc
Sport 68: 233±240
Sahlin K, Ren JM, Broberg S (1988) Oxygen de®cit at the onset of
submaximal exercise is not due to a delayed oxygen transport.
Acta Physiol Scand 134: 175±180
Scott CB (1995) Anaerobic metabolic in¯uences on oxygen uptake
behavior. J Strength Condit Res 9: 59±62
Scott CB, Bogdany GM (1998) Aerobic and anaerobic energy
expenditure during exhaustive ramp exercise. Int J Sports Med
19: 277±280
Stroud MA, Holliman D, Bell D, Green AL, MacDonald IA,
Greenha PL (1994) Eect of oral creatine supplementation on
respiratory gas exchange and blood lactate accumulation dur-
ing steady-state incremental treadmill exercise and recovery in
man. Clin Sci 87: 707±710
94
... Consequently, 41 eligible studies were included for the fulltext screening. Finally, 13 articles were considered to be included in this SRMA, involving 277 participants [37][38][39][40][41][42][43][44][45][46][47][48][49]. Figure 1 displays the information concerning the PRISMA flow diagram. ...
... Concerning the body mass change, five studies showed a significant body mass increase after CrM supplementation [39,40,[43][44][45], while three studies observed no change in body mass after a period of CrM ingestion [37,42,48]. Five studies included in this SRMA did not provide data regarding body mass change [38,41,46,47,49]. ...
... Endurance performance was assessed through the following tests: 6-km terrain run [39], continuous treadmill test [39], Leger shuttle run test [40,47], incremental exercise test in a rowing ergometer [41,42], incremental exercise test in a cycle ergometer [43,45,46], maximal discontinuous incremental running test [44], maximal 2500-m rowing ergometer test [37], 1000-m time trial in a rowing ergometer [38], 2000-m rowing test [48], and 400-m swimming time trial [49]. Four studies reported significant improvements in endurance test outcomes after CrM supplementation. ...
Effects of Creatine Monohydrate on Endurance Performance in a Trained Population: A Systematic Review and Meta-analysis
Article
Full-text available
  • Mar 2023
  • SPORTS MED
Background There is robust evidence that creatine monohydrate supplementation can enhance short-term high-intensity exercise in athletes. However, the effect of creatine monohydrate supplementation on aerobic performance and its role during aerobic activities is still controversial. Objective The purpose of this systematic review and meta-analysis was to evaluate the supplementation effects of creatine monohydrate on endurance performance in a trained population. Methods The search strategy in this systematic review and meta-analysis was designed following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and PubMed/MEDLINE, Web of Science, and Scopus databases were explored from inception until 19 May, 2022. Only human experimental trials, controlled with a placebo group, evaluating the effects of creatine monohydrate supplementation on endurance performance in a trained population were analyzed in this systematic review and meta-analysis. The methodological quality of included studies was evaluated using the Physiotherapy Evidence Database (PEDro) scale. Results A total of 13 studies satisfied all the eligibility criteria and were included in this systematic review and meta-analysis. The results for the pooled meta-analysis showed a non-significant change in endurance performance after creatine monohydrate supplementation in a trained population (p = 0.47), with a trivial negative effect (pooled standardized mean difference = − 0.07 [95% confidence interval − 0.32 to 0.18]; I² = 34.75%). Further, after excluding the studies not evenly distributed around the base of the funnel plot, the results were similar (pooled standardized mean difference = − 0.07 [95% confidence interval − 0.27 to 0.13]; I² = 0%; p = 0.49). Conclusions Creatine monohydrate supplementation was shown to be ineffective on endurance performance in a trained population. Clinical Trial Registration The study protocol was registered in the Prospective Register of Systematic Review (PROSPERO) with the following registration number: CRD42022327368.
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... Moreover, the assessment of VO 2 max through an incremental exercise test seems to be one of the most reproducible measurements, irrespective of the protocols used (Chidnok et al. 2013). Some studies have investigated the effect of CS on VO 2 max (Balsom et al. 1993;Nelson et al. 2000). The ATP energy supply by the energy-rich phosphate bond of phosphocreatine (CrP) occurs during the first seconds of a high-intensity exercise in anaerobic conditions due to the limited CrP stores requiring a recovery period of several minutes before its regeneration (Gastin 2001). ...
... Two studies used a single-blind design (Reardon et al. 2006;Canete et al. 2006), but all participants were blinded to supplementation. Three studies declared a dropout of more than twenty percent (Nelson et al. 2000;Reardon et al. 2006;Kuethe et al. 2006). All studies mentioned ethical approval. ...
... The duration between baseline and after supplementation ranged from 4 (Barnett, Hinds, and Jenkins 1996) to 180 days (Carvalho et al. 2012). The nineteen included studies aimed to evaluate the effect of CS on performance or quality of life in elderly and patients with heart failure (Canete et al. 2006;Carvalho et al. 2012;Kuethe et al. 2006;Villanueva, He, and Schroeder 2014), among which nine studies aimed specifically at assessing aerobic performance (Balsom et al. 1993;Nelson et al. 2000;Murphy et al. 2005;Hickner et al. 2010;Smith et al. 2011;Reardon et al. 2006;Forbes et al. 2017;Graef et al. 2009;Lawrence et al. 1997). Seventeen studies recruited healthy individuals, while two studies recruited patients with heart failure (Carvalho et al. 2012;Kuethe et al. 2006) ( Table 1). ...
Creatine supplementation and VO2max: a systematic review and meta-analysis
Article
Full-text available
  • Dec 2021
Although creatine supplementation is well-known to increase exercise performance in acute high-intensity exercises, its role in aerobic performance based on VO2max is more controversial. Thus, we performed a systematic review and meta-analysis on the effects of creatine supplementation on VO2max. PubMed, Cochrane, Embase, and ScienceDirect were searched for randomized controlled trials (RCTs) reporting VO2max in creatine supplementation and placebo groups before and after supplementation. We computed a random-effects meta-analysis on VO2max at baseline, within groups following supplementation, on changes on VO2max between groups, and after supplementation between groups. Sensitivity analyses and meta-regression were conducted. We included 19 RCTs for a total of 424 individuals (mean age 30 years old, 82% men). VO2max did not differ at baseline between groups (creatine and placebo). Participants in both groups were engaged in exercise interventions in most studies (80%). Using changes in VO2max, VO2max increased in both groups but increased less after creatine supplementation than placebo (effect size [ES] = −0.32, 95%CI = −0.51 to −0.12, p = 0.002). Comparisons after creatine supplementation confirmed a lower VO2max in the creatine group compared to the placebo group (ES= −0.20, 95%CI = −0.39 to −0.001, p = 0.049). Meta-analysis after exclusion from meta-funnel resulted in similar outcomes in a subgroup of young and healthy participants. Meta-regressions on characteristics of supplementation, physical training, or sociodemographic were not statistically significant. Creatine supplementation has a negative effect on VO2max, regardless of the characteristics of training, supplementation, or population.
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... Los principales alimentos que contienen Cr son la carne roja y los mariscos [70][71][72][73]. Habitualmente, una dieta aporta entre estudios en los que se pueden observar mejoras significativas [78][79][80] y otros en las que no [81][82][83][84][85][86]. Aunque cabe añadir que en ninguno de estos estudios se han superado las 4 semanas de periodo de suplementación para analizar cómo afecta a largo plazo. ...
... En general, estos suplementos han sido investigados sin mezclarse con otros [78][79][80][81][82][83][84][85][86][118][119][120][121][122][123], a pesar de que habitualmente se utilizan de forma conjunta [60]. Dado que estos suplementos tienen diferentes vías fisiológicas para mejorar el rendimiento y la recuperación [92][93][94]110,129,[143][144][145], se podría asumir que la combinación de CrM y HMB pudiese tener mayor efecto que tomándolos por separado. ...
EFECTO DE LA SUPLEMENTACIÓN CON Β-HIDROXI Β-METILBUTIRATO (HMB) Y/O CREATINA EN EL RENDIMIENTO DEL REMO TRADICIONAL DE TRAINERA
Thesis
Full-text available
  • Jun 2021
El monohidrato de creatina (CrM) y el β-hidroxi β-metilbutirato (HMB) son suplementos deportivos ampliamente estudiados. Sin embargo, no está claro cómo actúan cuando se utilizan conjuntamente en el ámbito deportivo. Hay que añadir que la incógnita es todavía mayor, cuando hablamos de un deporte de carácter predominantemente aeróbico como el remo. Los objetivos de esta tesis han sido: 1) determinar mediante una revisión sistemática la eficacia de mezclar CrM más HMB en comparación con sus efectos aislados sobre el rendimiento deportivo, la composición corporal, los marcadores de daño muscular inducidos por el ejercicio (EIMD) y las hormonas anabólico-catabólicas. 2) determinar la eficacia y el grado de potenciación de 10 semanas de suplementación con CrM más HMB en el rendimiento deportivo, que se midió mediante una prueba incremental en remeros tradicionales de élite masculinos. 3) determinar el efecto y el grado de potenciación de 10 semanas de suplementación con CrM más HMB en los EIMD y hormonas anabólicas/catabólicas. En base a los objetivos planteados, los principales resultados de la tesis indican que: 1) La combinación de CrM más 3 g/día de HMB durante 1–6 semanas podría producir efectos positivos en el rendimiento deportivo (fuerza y rendimiento anaeróbico) y durante 4 semanas en la composición corporal (aumento de grasa masa libre y disminución de la masa grasa). 2) La ingesta de CrM más HMB durante 10 semanas mostró un efecto sinérgico sobre la potencia aeróbica durante una prueba incremental. 3) La combinación de CrM más HMB presentó un efecto sinérgico sobre la testosterona y la ratio testosterona/cortisol y un efecto antagonista sobre el cortisol en comparación con la suma de la suplementación individual o aislada. Las conclusiones obtenidas en la presente tesis doctoral indican que la combinación de estos dos suplementos puede ser de gran ayuda para los profesionales que rodean al deportista para mejorar el rendimiento aeróbico y la recuperación.
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... Smith, Stephens, Hall, & Jackson (1998) utvrdili su da suplementacija kreatinom (20 g / dan x 5 dana) povećava radni vrijeme tokom izvođenja vježbi koji traju između 90-600 sec, prvenstveno u kraćim, intenzivnijim aktivnostima. Nelson et al., (2000) utvrdili su da suplementacija kreatinom (20 g / dan x 7 dana) smanjuje submaksimalni broj otkucaja srca i unos kisika (VO2), dok se povećava ventilacijski anaerobni prag (VANT) i ukupno vrijeme do iscrpljenosti tokom maksimalnog programa vježbanja kod 36 odraslih odraslih osoba. Rico-Sanz & Mendez (2000) utvrdili su su da suplementacija kreatinom (20 g / dan x 5 dana) povećava vrijeme do iscrpljenosti (29,9 ± 3,8 do 36,5 ± 5,7 min), istovremeno smanjujući nivo amonijaka (marker razgradnje nukleotida adenina) pri biciklizmu na 30 i 90% od maksimalnog praga opterećenja. ...
... Smith, Stephens, Hall, & Jackson (1998) established that creatine supplementation (20 g / day x 5 days) increases the time of performance of exercises which last 90-600 secons, mostly in short, more intensive activities. Nelson et al., (2000) established that cretaine supplementation (20 g / day x 7 days) reduces sub-maximal number of heart pulses and oxygen intake volume (VO2), while the ventilation anaerobic threshold increases (VANT) as well as total time to exhaustion during maximum exercising program in 36 adults. Rico-Sanz & Mendez (2000) established that creatinine supplementation (20 g / day x 5 days) increases time to exhaustion (29,9 ± 3,8 do 36,5 ± 5,7 min), simultaneously reducing the ammonia levels (marker of adenine nucleotides decomposition) in cycling to30% and 90% from maximum load threshold. ...
KNEE DEFORMITES IN FOOTBALL PLAYERS – META ANALYSIS
Article
Full-text available
  • Dec 2020
In football, the knee joint is one of the most stressed joints during the game itself, especially for professional football players where there are higher physical requirements. Factors such as race, weight, vitamin contribution, metabolic / hormone disorders, environment and football practice can affect the knee angle. The aim of the study was to determine the impact of playing football on changes in the knee joint. The following electronic databases were used to search the literature: PubMed, MEDLINE, Google Scholar, EBSCO in the period from 2006 to 2019. The sample of respondents included the male participants who played football, who were of different training status and age categories. The studies were included only if there were differences in the angle of the knee – genu varum or genu valgum in football players. Most researchers concluded that there are significant differences in the knee joint in respondents who played football and respondents who play no sports. The authors believe that the most critical period in which deformities can occur is the period of adolescence, while later this process slows down. People who have played other sports, as well as football players, have an increased risk of developing knee deformities. From the reviewed works, we can conclude that intense physical exercise and frequent competition can encourage the development of deformities.
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... W without any added load for 1min. The work rate was then increased by 30 watts/3min up until the patient could no longer maintain the required pedal cadence. Their symptom-limited maximum heart rate was recorded during the final 15sec. of the 3rd min of each stage. Participants were given encouragement to perform the maximum effort to exhaustion (Nelson.,et al., 2000).Exercise test was finished with a cool down stage at which the patient pedalsthe bicycle for a brief period against zero resistance ( Chatterjee et al., 2013) ...
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... Along the same lines, there was a group effect on average exercising HR, as the CM group experienced an overall increase, but no effect of time (P = 0.47). In comparison to our study, others have reported reductions in submaximal and maximal HR after a brief loading period through decreases in the muscle metaboreflex [31,32]. It is important to note that this was not a mechanistic study, thus rationale for these discrepancies are speculative. ...
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... Smith, Stephens, Hall, & Jackson (1998) established that creatine supplementation (20 g / day x 5 days) increases the time of performance of exercises which last 90-600 secons, mostly in short, more intensive activities. Nelson et al., (2000) established that cretaine supplementation (20 g / day x 7 days) reduces submaximal number of heart pulses and oxygen intake volume (VO2), while the ventilation anaerobic threshold increases (VANT) as well as total time to exhaustion during maximum exercising program in 36 adults. Rico-Sanz & Mendez (2000) established that creatinine supplementation (20 g / day x 5 days) increases time to exhaustion (29,9 ± 3,8 do 36,5 ± 5,7 min), simultaneously reducing the ammonia levels (marker of adenine nucleotides decomposition) in cycling to30% and 90% from maximum load threshold. ...
EFEKTI KREATIN MONOHIDRATA NA SNAGU I TJELESNU KOMPOZICIJU
Article
Full-text available
  • Jun 2020
Kreatin je postao popularan dodatak prehrani među sportistima. Najnovija istraživanja takođe s sugerišu da postoji veliki broj potencijalnih terapijskih primjena kreatina. Cilj ovog sistematskog pregleda je da se ispitaju efekti CR na mišićnu snagu i tjelesnu kompoziciju, na temelju prikupljenih podataka i analiziranih radova objavljenih u periodu 2018.-2020 godine. Pretraživanje literature izvršeno je pomoću sledećih baza: PubMed, Scholar Google, DOAJ. Radovi su odabrani na osnovu više kriterijuma. Rezultati ukazuju da CR u kombinaciji sa nekim programom vježbanja rezultira povećanjem mišićne mase, povećava snagu, smanjuje vrijeme izvođenja određene aktivnosti. Promjene u tjelesnoj kompoziciji ogledaju se u povećanju ukupne mase i mišićne mase kao i količine vode u sastavu tijela. Korišćenje CR u omjeru 10-20gr na dnevnom nivou i učestalosti korišćenja od 4-5 dana nedeljno, predstavlja efikasno sredstvo za poboljšanje sportskih performansi i pozitivnih promjena u sastavu tijela.
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Fueling the Firefighter and Tactical Athlete with Creatine: A Narrative Review of a Key Nutrient for Public Safety
Article
Full-text available
  • Sep 2024
Background/Objectives: Firefighters, tactical police officers, and warriors often engage in periodic, intermittent, high-intensity physical work in austere environmental conditions and have a heightened risk of premature mortality. In addition, tough decision-making challenges, routine sleep deprivation, and trauma exacerbate this risk. Therefore, identifying strategies to bolster these personnel’s health and occupational performance is critical. Creatine monohydrate (CrM) supplementation may offer several benefits to firefighters and tactical athletes (e.g., police, security, and soldiers) due to its efficacy regarding physical performance, muscle, cardiovascular health, mental health, and cognitive performance. Methods: We conducted a narrative review of the literature with a focus on the benefits and application of creatine monohydrate among firefighters. Results: Recent evidence demonstrates that CrM can improve anaerobic exercise capacity and muscular fitness performance outcomes and aid in thermoregulation, decision-making, sleep, recovery from traumatic brain injuries (TBIs), and mental health. Emerging evidence also suggests that CrM may confer an antioxidant/anti-inflammatory effect, which may be particularly important for firefighters and those performing tactical occupations exposed to oxidative and physiological stress, which can elicit systemic inflammation and increase the risk of chronic diseases. Conclusions: This narrative review highlights the potential applications of CrM for related tactical occupations, with a particular focus on firefighters, and calls for further research into these populations.
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Characteristics of physical activity during recess: an analysis with Galician Elementary and Secondary Education students
Article
Full-text available
  • Nov 2018
El análisis de las características de la actividad física durante el recreo es de gran importancia en la lucha contra las tasas de obesidad infantil y el estilo de vida sedentario en edades tempranas. Se necesita ampliar el conocimiento sobre este tema, profundizando en la tipología de actividades, su intensidad, la zona geográfica, etc. Por ello, el objetivo de este estudio fue examinar las características de la actividad física durante el recreo en los dos últimos cursos de Educación Primaria y en Educación Secundaria Obligatoria en centros del eje atlántico.
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Anaerobic Metabolic Influences on Oxygen Uptake Behavior
Article
  • Feb 1995
Both oxygen uptake kinetics at the start of exercise and the plateau of maximal oxygen uptake upon heavy physical exertion are greatly influenced by circulatory lag time, oxygen diffusion limitations, or perfusion of muscle by maximal cardiac output. Local muscle factors may also influence oxygen uptake. It is known that the energetic status of the cell, the ATP/ ADP ratio, is a stimulus for both aerobic and anaerobic energy production. Upon activation of the motor unit, anaerobic energy production could explain an immediate energy fulfilling role in working muscle that precedes the exponential increase in oxygen uptake. When a fully activated anaerobic energy system supplies ATP, it could rob muscle mitochondria of an important start-up signal and thereby slow oxygen uptake. Evidence suggests that some anaerobic metabolites then act to stimulate mitochondrial activity. In either case, oxygen uptake would be influenced by the anaerobic metabolic system.
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The effect of decreased muscle energy stores on the V˙O2\dot V_{O_2 } kinetics at the onset of exercisekinetics at the onset of exercise
Article
  • Dec 1989
  • Eur J Appl Physiol Occup Physiol
The kinetics of adjustment of oxygen uptake ([(V)\dot]O2 )(\dot V_{O_2 } ) at the onset of a square wave of exercise in man has been shown to be variable and related mainly to factors located distal to the capillary. The present study examined the effects of decreasing oxygen and high energy phosphates (∼P) stores, by blood flow occlusion (BFO) and/or preceding exercise, on the half time of the [(V)\dot]O2 \dot V_{O_2 } on-response ( t\tfrac12 [(V)\dot]O2 t_{\tfrac{1}{2}} \dot V_{O_2 } on-) during arm exercise. Twelve male subjects performed an arm exercise test at a standard intensity of 75 W (75 WA) following six procedures designed progressively to decrease O2 and/or ∼P stores. Breath-by-breath [(V)\dot]O2 \dot V_{O_2 } and lactic acid accumulation in blood (Δ[lab]) during the [(V)\dot]O2 \dot V_{O_2 } transient were measured. Preceding the 75 WA by 5 min of 125 W leg exercise decreased significantly the t\tfrac12 [(V)\dot]O2 t_{\tfrac{1}{2}} \dot V_{O_2 } on- (63–47 s). Preceding the 75 WA with either arm BFO and isometric exercise (1 min), no-load or 25 W (25 WA) arm cranking (5 min) did not significantly affect t\tfrac12 [(V)\dot]O2 t_{\tfrac{1}{2}} \dot V_{O_2 } on- or Δ[lab]. Preceding 75 WA with 5–10 min BFO or BFO plus 25 WA resulted in a significant decrease in t\tfrac12 [(V)\dot]O2 t_{\tfrac{1}{2}} \dot V_{O_2 } on- (20% and 50%, respectively). The Δ[lab] increased linearly with t\tfrac12 [(V)\dot]O2 t_{\tfrac{1}{2}} \dot V_{O_2 } on-responses greater than 24 s. These data suggest that the local depletion of O2 and/or ∼P stores play an important role in determining the kinetics of adjustment of [(V)\dot]O2 \dot V_{O_2 } to exercise.
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The effect of decreased muscle energy stores on the VO2 kinetics at the onset of exercise
Article
  • Feb 1989
  • Eur J Appl Physiol Occup Physiol
The kinetics of adjustment of oxygen uptake (VO2) at the onset of a square wave of exercise in man has been shown to be variable and related mainly to factors located distal to the capillary. The present study examined the effects of decreasing oxygen and high energy phosphates (approximately P) stores, by blood flow occlusion (BFO) and/or preceding exercise, on the half time of the VO2 on-response (t1/2 VO2 on-) during arm exercise. Twelve male subjects performed an arm exercise test at a standard intensity of 75 W (75 WA) following six procedures designed progressively to decrease O2 and/or approximately P stores. Breath-by-breath VO2 and lactic acid accumulation in blood (delta [1ab]) during the VO2 transient were measured. Preceding the 75 WA by 5 min of 125 W leg exercise decreased significantly the t1/2 VO2 on- (63-47 s). Preceding the 75 WA with either arm BFO and isometric exercise (1 min), no-load or 25 W (25WA) arm cranking (5 min) did not significantly affect t1/2 VO2 on- or delta [1ab]. Preceding 75 WA with 5-10 min BFO or BFO plus 25 WA resulted in a significant decrease in t1/2 VO2 on- (20% and 50%, respectively). The delta [1ab] increased linearly with t1/2 VO2 on-responses greater than 24 s. These data suggest that the local depletion of O2 and/or approximately P stores play an important role in determining the kinetics of adjustment of VO2 to exercise.
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Regulation of VO2 in red muscle: Do current biochemical hypotheses fit in vivo data?
Article
  • May 1989
  • Am J Physiol
Observations used to test biochemical models of the regulation of O2 consumption (VO2) by cytosolic phosphate energy state must include a change in intracellular pH and/or a change in the adenine nucleotide or phosphate pools [Connett, R. J. Analysis of metabolic control: new insights using a scaled creatine kinase model. Am. J. Physiol. 254 (Regulatory Integrative Comp. Physiol. 23): R949-R959, 1988]. Data were collected over a wide range of energy turnover from canine muscles in situ. Intracellular PO2, glycolytic intermediates, adenine nucleotides, creatine, phosphocreatine (PCr), phosphate, and intracellular pH were determined for each muscle. PO2 was used to eliminate muscles in which VO2 could have been O2 limited (PO2 less than 0.5 Torr). This removed an important source of heterogeneity. Because adenine nucleotide and phosphate pools were constant relative to the creatine pool, discrimination among models depended solely on pH. The observed pH range from 7.2 to 5.9 did not permit separation of [PCr] from log[( ATP4-]/[ADP3-][H2PO4-]) (phosphorylation potential) as a regulatory parameter for VO2. However, [ADP] could be eliminated as an independent regulator. Because 90% of variability in VO2 was accounted for by phosphate energetics, an independent redox component must be small when intracellular PO2 greater than 0.5 Torr.
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Oxygen deficit at the onset of submaximal exercise is not due to a delayed oxygen transport
Article
  • Nov 1988
Six subjects cycled on two occasions for 10 min at power output of 188 +/- 11 W (means +/- SEM), which corresponded to 70 +/- 2% of their maximal oxygen uptake (VO2 max). The exercise intensity was either increased gradually in a stepwise manner over about 15 min (slow transition-S), or increased directly (direct transition-D) to the predetermined power output. Muscle samples from the quadriceps femoris muscle were taken at rest and immediately after exercise in both trials. During exercise with both D and S muscle lactate increased approximately 10 times (P less than 0.01), phosphocreatine decreased about 50% (P less than 0.01) and ADP increased about 20% (P less than 0.05). There were no significant differences between S and D (P greater than 0.05). Furthermore, blood lactate, O2 deficit, O2 debt, and the calculated increase in muscle content of inorganic phosphate (Pi) were all similar between D and S (P greater than 0.05). It is concluded that the O2 deficit and the anaerobic energy utilization is not affected by the rate of transition from rest to exercise. Consequently, the O2 deficit at the onset of exercise is not due to a delay in O2 transport, but may be due to a limited peripheral O2 utilization as a result of metabolic adjustments at the cellular level. Increases in ADP and Pi are suggested to be primary metabolic regulators which activate both aerobic and anaerobic energy production resulting in the O2 deficit.
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Human cardiopulmonary responses to exercise: comparisons between progressive and steady state exercise, between arm and leg exercise, and between subjects differing in body weight
Article
  • May 1969
The regressions of the oxygen uptake on rate of work, of the ventilation and cardiac frequency on oxygen uptake, and of the ventilation on tidal volume have been obtained over the ranges where they were linear during pedalling and during cranking a cycle ergometer. The regression coefficients for ventilation and cardiac frequency on oxygen uptake are higher for light than for heavy subjects, and for work which is performed with the arms instead of the legs; possible reasons are discussed. The respiratory frequency in relation to tidal volume is also higher for arm than for leg work. In the comparison of progressive and steady state exercise no systematic differences were observed, except for the relationship of the consumption of oxygen to the rate of work; this finding is relevant to the planning of exercise studies on normal subjects.
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Energy expended during oxygen deficit period of submaximal exercise in man
Article
  • Jun 1980
Aerobic (MR) and anaerobic (Man) metabolism was determined during the transition from mild (50 W external work) to heavier exercise (50% VO2max) in six subjects. The overall exercise efficiency was calculated during the oxygen deficit period and during steady-state exercise. MR was obtained by indirect calorimetry and Man by solving the heat balance equation: MR + Man - S = (R + C + E) + W, where radiative, convective, and evaporative heat losses (R + C + E) were measured by direct calorimetry, work output (W) by ergometry, and heat storage (S) by thermometry. (MR + Man) during the oxygen deficit period was found to be lower than MR during steady state. In the 1st min of exercise, mean mixed work efficiency (aerobic + anaerobic) was 33%, which was greater than aerobic efficiency (26.6%) during steady state. The mean anaerobic efficiency efficiency was 41%. This difference reflects the fact that the energy released by splitting of preformed high-energy bonds (i.e., creatine phosphate) is less than the energy released when high-energy bonds expended during mechanical work are continuously regenerated through oxidative phosphorylation. The reported measurements of overall energy metabolism in man provide means for estimating in vivo the coupling efficiency of physical work (i.e., 41%) as well as the efficiency with which energy released by substrate oxidations is recovered in the form of high-energy bonds (i.e., phosphorylation efficiency = 64%).
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Skeletal muscle metabolism during short duration high-intensity exercise: Influence of creatine supplementation
Article
  • Jul 1995
Seven male subjects performed repeated bouts of high‐intensity exercise, on a cycle ergometer, before and after 6 d of creatine supplementation (20 g Cr H 2 O day ‐1 ). The exercise protocol consisted of five 6‐s exercise periods performed at a fixed exercise intensity, interspersed with 30‐s recovery periods (Part I), followed (40 s later) by one 10 s exercise period (Part II) where the ability to maintain power output was evaluated. Muscle biopsies were taken from m. vastus lateralis at rest, and immediately after (i) the fifth 6 s exercise period in Part I and (ii) the 10 s exercise period in Part II. In addition, a series of counter movement (CMJ) and squat (SJ) jumps were performed before and after the administration period. As a result of the creatine supplementation, total muscle creatine [creatine (Cr) + phosphocreatine (PCr)] concentration at rest increased from (mean + SEM) 128.7 (4.3) to 151.5 (5.5)mmolkg _1 dry wt ( P < 0.05). This was accompanied by a 1.1 (0.5) kg increase in body mass ( P < 0.05). After the fifth exercise bout in Part I of the exercise protocol, PCr concentration was higher [69.7 (2.3) vs. 45.6 (7.5) mmol kg“‘ dry wt, P < 0.05], and muscle lactate was lower [26.2 (5.5) vs. 44.3 (9.9) mmol kg” ¹ dry wt, P < 0.05] after vs. before supplementation. In Part II, after creatine supplementation, subjects were better able to maintain power output during the 10‐s exercise period ( P < 0.05). There was no change in jump performance as a result of the creatine supplementation ( P > 0.05). These findings show that enhanced fatigue resistance during short duration high‐intensity exercise following creatine supplementation is associated with a greater availability of PCr and a lower accumulation of lactate in the muscle. The finding that jump performance was not enhanced suggests that short‐term creatine feeding does not influence peak power output.
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Creatine supplementation in chronic heart failure increases skeletal muscle creatine phosphate and muscle performance
Article
  • Oct 1995
Cardiac creatine levels are depressed in chronic heart failure. Oral supplementation of creatine to healthy volunteers has been shown to increase physical performance. To evaluate the effects of creatine supplementation on ejection fraction, symptom-limited physical endurance and skeletal muscle strength in patients with chronic heart failure. With a double-blind, placebo-controlled design 17 patients (age 43-70 years, ejection fraction < 40) were supplemented with creatine 20 g daily for 10 days. Before and on the last day of supplementation ejection fraction was determined by radionuclide angiography as was symptom-limited 1-legged knee extensor and 2-legged exercise performance on the cycle ergometer. Muscle strength as unilateral concentric knee extensor performance (peak torque, Nm at 180 degrees/s) was also evaluated. Skeletal muscle biopsies were taken for the determination of energy-rich phosphagens. Ejection fraction at rest and at work did not change. Performance before creatine supplementation did not differ between placebo and creatine groups. While no change was seen in the placebo group compared to baseline, creatine supplementation increased skeletal muscle total creatine and creatine phosphate by 17 +/- 4% (P < 0.05) and 12 +/- 4% (P < 0.05), respectively. Increments were seen only in patients with < 140 mmol total creatine/kg d.w. (P < 0.05). One-legged performance (21%, P < 0.05), 2-legged performance (10%, P < 0.05), and peak torque, Nm (5%, P < 0.05) increased. Both peak torque and 1-legged performance increased linearly with increased skeletal muscle phosphocreatine (P < 0.05). The increments in 1-legged, 2-legged and peak torque were significant compared to the placebo group, (P < 0.05). One week of creatine supplementation to patients with chronic heart failure did not increase ejection fraction but increased skeletal muscle energy-rich phosphagens and performance as regards both strength and endurance. This new therapeutic approach merits further attention.
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The influence of dietary creatine supplementation on performance during repeated bouts of maximal isokinetic cycling in man
Article
  • May 1994
  • Eur J Appl Physiol Occup Physiol
The effect of dietary creatine (Cr) supplementation on performance during 3, 30 s bouts maximal isokinetic cycling and on plasma ammonia and blood lactate accumulation during exercise was investigated. Placebo (P) ingestion had no effect on peak power output (PPO), mean power output (MPO) and total work output during each bout of exercise. Cr ingestion (4 x 5 g.day-1 for 5 days) significantly increased PPO in exercise bout 1 (p < 0.05) and MPO and total work output in exercise bouts 1 (p < 0.05, p < 0.05, respectively) and 2 (p < 0.05, p < 0.05, respectively). Cr ingestion had no effect on any of the measures of performance during exercise bout 3. No difference was observed in peak plasma ammonia accumulation before (146 + 30 mumol.l-1) and after (122 +/- 17 mumol.l-1) P ingestion, however the corresponding concentration was lower following Cr ingestion (129 +/- 22 mumol.l-1) compared with before Cr ingestion (160 +/- 18 mumol.l-1, p < 0.05), despite subjects performing more work. No difference in peak blood lactate accumulation was observed before and after P or Cr ingestion. The results demonstrate that Cr ingestion can increase whole body exercise performance during the initial two, but not a third, successive bout of maximal exercise lasting 30 s. The lower accumulation of plasma ammonia under these conditions suggests this response is achieved by an effect on muscle ATP turnover.
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