Improvement of VO2max by

Eur J Appl Physiol (2007) 101:377–383
DOI 10.1007/s00421-007-0499-3
ORIGINAL ARTICLE
_ 2 max; by cardiac output and oxygen
Improvement of VO
extraction adaptation during intermittent versus continuous
endurance training
Frédéric N. Daussin Æ Elodie Ponsot Æ Stéphane P. Dufour Æ
Evelyne Lonsdorfer-Wolf Æ Stéphane Doutreleau Æ
Bernard Geny Æ François Piquard Æ Ruddy Richard
Accepted: 21 May 2007 / Published online: 28 July 2007
Springer-Verlag 2007
Abstract Improvement of exercise capacity by continuous (CT) versus interval training (IT) remains debated. We
tested the hypothesis that CT and IT might improve
peripheral and/or central adaptations, respectively, by
randomly assigning 10 healthy subjects to two periods of
24 trainings sessions over 8 weeks in a cross-over design,
separated by 12 weeks of detraining. Maximal oxygen
_ 2 max Þ; cardiac output ðQ_ max Þ and maximal
uptake ðVO
arteriovenous oxygen difference ðDav O2 max Þ were obtained during an exhaustive incremental test before and
_ 2 max and Q_ max increased only
after each training period. VO
after IT (from 26.3 ± 1.6 to 35.2 ± 3.8 ml min–1 kg–1 and
from 17.5 ± 1.3 to 19.5 ± 1.8 l min–1, respectively;
P < 0.01). Dav O2 max increased after both protocols (from
11.0 ± 0.8 to 12.7 ± 1.0; P < 0.01 and from 11.0 ± 0.8 to
12.1 ± 1.0 ml 100 ml–1, P < 0.05 in CT and IT, respectively). At submaximal intensity a significant rightward
_ av O2 relationship appeared only after CT.
shift of the Q=D
These results suggest that in isoenergetic training, central
and peripheral adaptations in oxygen transport and utilization are training-modality dependant. IT improves both
_ 2 max whereas CT
central and peripheral components of VO
is mainly associated with greater oxygen extraction.
F. N. Daussin (&) E. Ponsot S. P. Dufour E. Lonsdorfer-Wolf S. Doutreleau B. Geny F. Piquard R. Richard
CHRU of Strasbourg, Physiology and Functional Explorations
Department, Civil Hospital, BP 426, 67091 Strasbourg, France
e-mail: fredericdaussin@wanadoo.fr
F. N. Daussin E. Ponsot S. P. Dufour E. Lonsdorfer-Wolf S. Doutreleau B. Geny F. Piquard R. Richard
Faculty of Medicine, Physiology Department,
University Louis Pasteur, UPRES E.A., 3072 Strasbourg, France
Keywords Training modality Cardiac output Arteriovenous difference Maximal oxygen consumption Sedentary subjects
Introduction
Sedentarity and all chronical diseases are associated with a
decline of functional capacity and endurance training is
included in rehabilitation programs in order to improve
quality of life (Geny et al. 1996; Hill 2006; Seals et al.
1984). The improvement depends on the frequency,
intensity and duration of the training sessions (Jones and
Carter 2000; Samitz and Bachl 1991), which can lead to
both central and peripheral adaptations in the oxygen
transport and utilization chain. For instance, increases in
_ are governed by changes in stroke
cardiac output ðQÞ
volume (SV) and/or heart rate (HR), reflecting a central
cardio-circulatory component of the training-induced
adaptation. Conversely, the arterio-venous oxygen difference ðDav O2 Þ depends mainly on the exchange area between the capillary blood and the muscle cells, as well as
on the skeletal muscle maximal oxidative capacity, providing information on the peripheral muscle adaptations to
training. However, the respective contributions of these
adaptations in the improvement of exercise capacity after
training are not clear.
Different training regimens have been studied to analyze
their effects on aerobic exercise capacity (Cunningham
et al. 1979; Geny et al. 1996; Seals et al. 1984; Shephard
1968), but no study has compared the effect of isoenergetic
training protocols featuring sessions of similar duration and
energy expenditure on the improvement of maximal oxy_ 2 max Þ: Interval training (IT) is assogen consumption ðVO
ciated with variation of oxygen (O2) demand and requires
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Eur J Appl Physiol (2007) 101:377–383
adaptation to maintain O2 supply and Q_ (i.e. central component). Conversely, continuous training (CT) is associated
with a constant O2 demand provided that exercise intensity
_ 2 slow component (about
is below the appearance of a VO
80% below peak power). Under such conditions, Q_ remains
far from its maximal value and the benefit of CT training
might mainly translate into peripheral adaptations allowing
an increase in O2 extraction (i.e. peripheral component).
In this study, Q_ was determined by impedancemetry
(Charloux et al. 2000; Richard et al. 2001) and together
_ 2 ; Dav O2 was calculated
with measurement of VO
according to Fick principle. The purpose of this study was
to determine the effect of two isoenergetic training
modalities on the adaptations to exercise in healthy sedentary subjects. We investigated the hypothesis that CT and
IT, respectively, improve mainly either the peripheral
_ components of VO
_ 2 max :
ðDav O2 Þ or the central ðQÞ
each subject was asked to engage in the alternative type of
training with the order of the two training programs randomized.
Two days before and after the training period, all subjects performed a cycling incremental test to exhaustion. In
the first evaluation we determined for each subject the
power associated to the two training programs and their
physical capacity. The effect of training was evaluated at
the end of each period.
The third incremental test was used to ensure that the
subject’s exercise capacities had returned to the initial level, as evaluated by peak power (Pmax), peak oxygen up_ 2 max ) and ventilatory thresholds and that the loads
take (VO
to be applied during the second training period did not
differ from those calculated initially. Moreover, the Baecke
questionnaire was used to confirm that the subjects did not
change their daily physical activity.
Incremental exercise tests
Methods
Sedentary subjects (five men and five women) who were
not taking medications that could alter cardiac, respiratory
or muscular responsiveness participated in this study (Table 1). Level of physical activity was evaluated by a
questionnaire (Baecke et al. 1982) to confirm sedentary
status of the subjects. All subjects were informed about the
potential risks associated with the experiments before
giving their written consent to participate.
Study design
The subjects were ascribed to either CT or IT. After
3 months of deconditioning and using a cross-over design,
Each subject performed incremental exercise to exhaustion
in the morning after a light breakfast on an upright electronically braked cycle ergometer (Medifit 1000S, Belgium). The pedalling frequency was 60–70 rpm and was
maintained throughout the test. We used an equation
(Hansen et al. 1984) to determine the maximal power for
sedentary subjects, allowing the power increments to be
adjusted so that exhaustion occurred within 12–15 min.
Each subject carried out a maximal effort according to
Howley et al. (1995). Ventilatory thresholds were determined graphically (Beaver et al. 1986); the first ventilatory
threshold (i.e. lactate threshold; LT) was obtained from a
regression analysis of the slope of the carbon dioxide
_ 2 Þ versus VO
_ 2 plot and the second venelimination ðVCO
Table 1 Physical characteristics of the subjects
Subject number
Gender male/female
Age (years)
Height (cm)
Weight (kg)
BMI (kg m– 2)
Body fat (%)
Baecke indexa
1
F
48
155
50
20.8
26.9
4.8
2
F
48
160
83
32.4
36.8
4.1
3
F
50
160
53
20.7
33.5
6.6
4
F
39
175
69
22.5
33.8
5.2
5
F
52
168
54
19.1
35.2
7.3
6
M
57
177
71
22.7
28.9
7.4
7
8
M
M
36
38
175
180
74
80
24.2
24.7
20.8
24.5
6.0
4.1
9
M
61
180
94
29.0
22.8
5.8
10
M
36
188
105
29.7
28.0
5.8
Mean (±SEM)
n = 10
47 ± 3
172 ± 3
73 ± 6
24.6 ± 1.4
29.1 ± 1.7
5.7 ± 0.4
Female (±SEM)
n=5
47 ± 2
164 ± 4
62 ± 6
23.1 ± 2.4
33.2 ± 1.7
5.6 ± 0.6
Male (±SEM)
n=5
46 ± 6
180 ± 2
85 ± 6
26.1 ± 1.4
25.0 ± 1.5
5.8 ± 0.5
a
Physical subject level was evaluated by a questionnaire, an index less or equal to 7.5 corresponded to a sedentary subject (Baecke et al. 1982)
and was the maximal value accepted to be included in this study. Body mass index (BMI) is weight (kg)/height2 (m2)
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Eur J Appl Physiol (2007) 101:377–383
379
tilatory threshold (i.e. respiratory compensation point;
RCP) was determined as the point where the increase of
_ 2
ventilation ðV_E Þ becomes larger than the increase in VCO
_ 2 ; VCO
_ 2 and Q_ were
(Wasserman et al. 1994). HR, V_E ; VO
monitored continuously. Blood lactate (LA) was collected
at rest, at the end of a 3 min warm-up, every second step
during exercise, at peak exercise, and in the recovery.
_ 2 measured from expired gas reflects those occurring
VO
within the exercise legs. Moreover, this methodology was
validated during both constant-load and incremental exercise (Charloux et al. 2000; Richard et al. 2001) and used to
describe Dav O2 evolution during exercise (Richard et al.
_ 2 ; were calculated, using Q_ and
2004). Isopleths of VO
Dav O2 for various levels.
Training program
Statistics
The subjects performed 3 training sessions per week in the
laboratory over an 8 week period (24 sessions). For each
subject, the total mechanical work (kJ) and training duration were identical in both protocols. The duration of the
initial training session was 20 min and increased by 5 min
every 2 weeks, achieving 35 min during the last 2 weeks.
IT included in a series of 5 min blocks: 4 min at LT and
1 min at 90% of Pmax. The power used during CT allowed
a similar energy expenditure and duration as the IT sessions: PowerCT = [(4 · PowerLT + 90% of Pmax)/5].
Data are presented as means ± SEM. Statistical analyses
were performed using Sigma Stat for Windows (version
3.0, SPSS Inc., Chicago, IL). After testing for normality
and variance homogeneity, a two-way ANOVA with repeated measures was performed to test significance between and within training. To compare Dav O2 and Q_ on
_ 2 isopleths, a one-way ANOVA was used with a postVO
hoc Tuckey test. The significance level was set at P < 0.05.
Results
Measurements
Ventilatory parameters
_ 2 and VCO
_ 2 were measured breath-by-breath by an
V_E ; VO
open-circuit metabolic cart with rapid O2 and CO2 analy_ 2 max
sers (Sensor Medics, MSE, Yonba Linda, USA). VO
_
was defined as the highest 30 s average VO2 :
Cardiovascular parameters
HR was recorded by a cardiovit CS-200 (Schiller AG,
Baar, Switzerland) and Q_ was determined by bioimpedance
(Physioflow, Manatec, France, Charloux et al. 2000) and
validated both during submaximal constant-load and
maximal incremental exercise (Richard et al. 2001, 2004).
Metabolic parameters
During all tests, 2 ml venous blood samples were collected
into iced tubes for immediate determination of LA (ChironDiagnostics Serie 800, Bayer, Puteau, France).
Signal treatment
Gas exchange and Q_ data were reduced to 5 s averages. For
each parameter, the start of the test was stamped while
recording. This measured point permitted to obtain a single
_
_ 2 and Q:
synchronous database for both VO
We used the Fick equation to calculate the Dav O2 ;
_ 2 by Q_ values averaged over the corresponding
dividing VO
time interval. Poole et al. (1992) established that change of
Two women and three men started the first training period
with IT, while three women and two men began with CT.
Training intensity
The workload in CT corresponded to 106 ± 10 W or 61%
of Pmax. During IT, the subjects alternated 4 min at low
intensity (93 ± 8 W or 49% of Pmax) with 1 min at 90% of
Pmax (149 ± 16 W). The total mechanical work for the
8 weeks of training was similar between IT and CT:
4,126 ± 389 versus 4,177 ± 395 kJ.
Deconditioning period
_ 2 max returned to baseline after the deconditioning period
VO
following the first training modality and no significant
_ Dav O2 or LA appeared between
differences of power, Q;
the two pre-training periods at rest, LT, RCP and maximal
values.
Training and aerobic capacity
Pmax increased only after IT: 167 ± 19 versus 198 ± 24 W
(P < 0.01) as was the case for the power at RCP: 139 ± 15
versus 162 ± 18 W (P < 0.01). Power at LT increased after
the two training programs without difference between
modalities: 93 ± 9 versus 114 ± 12 W (P < 0.01) for CT
and 90 ± 9 versus 114 ± 12 W (P < 0.01) for IT. An in_ 2 max was observed after IT: 26.3 ± 1.6 versus
crease in VO
_ 2 in35.2 ± 3.8 ml min–1 kg–1 (P < 0.01, Fig. 1a) and VO
creased also at the two ventilatory thresholds: 15.4 ± 1.4
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380
versus 21.7 ± 2.2 ml min–1 kg–1 (P < 0.01) for LT and
21.8 ± 2.2 versus 29.8 ± 3.1 ml min–1 kg–1 (P < 0.01) for
_ 2 increased only at LT: 15.8 ±
RCP. In the CT group, VO
1.5 versus 20.4 ± 1.8 ml min–1 kg–1 (P < 0.01) and
_ 2 max trended to increase (27.9 ± 2.2 vs. 30.3 ± 2.4
VO
ml min–1 kg–1, P = 0.07). Expressed in percentage of
_ 2 max ; LT increase only with CT: 58 ± 2% versus 68 ±
VO
3% (P < 0.05), LT after training was higher with CT than
IT (P < 0.05). No significant evolution was observed for
RCP.
Training and central versus peripheral adaptations
As seen on Fig. 1b, Q_ max rose after IT (17.5 ± 1.3 to 19.5 ±
1.8 l min–1; P < 0.01), through concomitant increases of
maximal HR (165 ± 5 vs. 172 ± 4 beats min–1, P < 0.05,
Fig. 1e) and maximal SV (107 ± 7 vs. 113 ± 8 ml,
P < 0.05, Fig. 1c). CT affected neither Q_ max ; maximal HR
nor maximal SV.
Dav O2 max increased with the two protocols without
training specificity (CT: 11.0 ± 0.8 vs. 12.7 ± 1.0 ml 100
ml–1 P < 0.01 and IT: 11.0 ± 0.9 vs. 12.1 ± 1.0 ml 100
ml–1; P < 0.05, Fig. 1d). Thus there was a rightward
_ av O2 relationship after training (Fig. 2),
shift of the Q=D
observed only in CT. The maximal LA rose from 8.2 ±
0.5 to 9.8 ± 0.8 mmol l–1 after IT (P < 0.05) but no
Fig. 1 Training effect on
maximal values of oxygen
uptake (a), cardiac output (b),
stroke volume (c), arteriovenous
oxygen difference (d) and heart
rate (e)
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Eur J Appl Physiol (2007) 101:377–383
increase was observed after CT (8.2 ± 1.0 vs. 8.4 ± 1.1
mmol l–1).
Discussion
The main findings of the study are that the mechanisms
allowing improvement of exercise capacity are different
between CT and IT when the same total amount of work is
carried out. Thus, IT had both central and peripheral effects
with increases in Q_ and Dav O2 at maximal exercise and at
the ventilatory threshold. On the other hand, the isoenergetic CT improved the sedentary subject’s sub-maximal
aerobic exercise capacity, through increased Dav O2 values.
Baseline fitness and detraining period
To compare the effects of the two training modalities, we
studied a group of sedentary subjects because they are
more sensitive to training than sportsmen. The sedentary
status was confirmed by a Baecke index below 7.5 and by a
_ 2 max within 80–100% of sedentary values (Wasserman
VO
et al. 1986). Similarly, the Dav O2 max values were in line
with data reported for sedentary (Beere et al. 1999;
McGuire et al. 2001; Ogawa et al. 1992).
Eur J Appl Physiol (2007) 101:377–383
381
Training effects on aerobic exercise capacity
Fig. 2 Training effect on the cardiac output and arteriovenous
oxygen difference contributions to submaximal to maximal oxygen
uptake. Group mean ± SEM. Isopleths are those calculated from Fick
_ 2 values. At an exercise
_ 2 ¼ Q_ Dav O2 ; for various VO
equation: VO
_ 2 of 1.5 l min–1, some subject reach their
intensity exceeding a VO
maximal values and the dotted line was build with the subjects who
attained the isopleths. a Isopleths for continuous training and b
isopleths for interval training. *P < 0.05, **P < 0.01 before versus
after training
Between the two training periods, the subjects stopped
training in order to return to their initial fitness level. This
was confirmed by comparing the two pre-training evaluations of their aerobic exercise capacity. A previous study
had demonstrated that a 2 month detraining period is sufficient to negate the beneficial effect of an endurance
_ HR, Dav O2 ; and SV at rest
_ 2 ; Q;
training program on VO
and during maximal exercise (Mujika and Padilla 2000).
Accordingly, Ready and Quinney (1982) found similar
_ 2 max in sedentary subjects after 4 constant-load
gain on VO
_ 2 max
endurance training sessions per week at 80% of VO
during 9 weeks. In that study, the effect of training on LT
_ 2 max disappeared after 6 and 9 weeks of detraining,
and VO
respectively. In line with these results, 12 weeks of detraining is long enough for the subjects to return to their
initial fitness level.
_ 2 max depended on training modality for
Improvement of VO
sedentary subjects submitted to isoenergetic training programs, featuring similar training duration, and total energy
_ 2 max
expenditure. IT induced a greater improvement in VO
than CT (+34% for IT vs. +11% for CT, P < 0.05). In our
_ 2 max increase observed with CT was
study, the small VO
similar to the data presented by Wenger et al. (1986) who
predicted a rise of 3–5 ml min–1 kg–1 for similar intensity,
frequency, training duration and subject’s fitness level.
_ 2 max
Some studies demonstrated that CT increases VO
significantly (Beere et al. 1999; McGuire et al. 2001;
Stratton et al. 1994). However, most of these effects of CT
appeared when higher exercise intensity (75–85% of
maximal HR) and/or longer training duration (3–6 months)
were used. However, the scope of this study being to
compare the effects of CT and IT on the central and
peripheral adjustments to exercise, it was of importance to
perform isoenergetic training protocols and thus we adapted the CT characteristics to that of the IT protocol.
Concerning ventilatory threshold, we observed an
improvement in LT (+27%) and RCP (+22%) after IT and
only LT (+22%) after CT. In a review, Londeree (1997)
compared the impact of training-intensity on ventilatory
threshold changes. Studies using similar intensities as the
present experiment found equivalent responses of ventilatory thresholds, ranging from +26 to +36% (Edge et al.
2006; Londeree 1997). These results emphasize that
training-intensities near the target ventilatory threshold are
adequate stimulus to improve that threshold (Londeree
1997) as both CT and IT intensity were near LT but only IT
during heavy block was near the RCP.
Central versus peripheral adaptations
An improvement of Q_ max was observed selectively after IT
by enhancement of both maximal HR and SV. These results are in line with studies demonstrating an effect of IT
on Q_ max (Beere et al. 1999; McGuire et al. 2001). Conversely, Q_ max remained unchanged after CT with unaffected maximal HR and SV. However, Stratton et al.
(1994), using higher training intensities and a greater total
work load observed that CT improved Q_ max in untrained
subjects. In our design, CT involved a constant intensity
around 60% of maximal power. Therefore, we assumed
that both Q_ and muscle blood flow would have been relatively constant during the training session and it appears
plausible that CT needs a minimum training intensity to
induce significant enhancement of Q_ max and systemic O2
delivery.
Conversely, both training modalities ameliorated
Dav O2 max suggesting that the skeletal muscle capacity to
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382
extract O2 from the arterial blood was not training modality
dependent. Endurance training also improves muscle capillarity, increasing the surface available for blood-tissue
exchange (Hepple et al. 2000). Functional consequences
are an increase of the surface area for diffusion, a decrease
of the average diffusion path length within the muscle and
an increase of the length of time for diffusive exchange
between blood and tissue (Kalliokoski et al. 2001; Prior
et al. 2004). Qualitative improvement in muscle perfusion
has also been reported after endurance training allowing for
a better homogeneity of perfusion (Kalliokoski et al.
2001).
After CT, we observed an improvement of Dav O2 max
and a rightward shift of the Q=Dav O2 relationship. These
results suggest that O2 extraction improved at each workload. Accordingly, Gorostiaga et al. (1991) demonstrate
that CT is more effective at increasing muscle oxidative
capacity than IT. Conversely, the Q=Dav O2 relationship
remained unaltered with IT, even if Dav O2 max increased.
Similar values of Q_ after training at any given level of O2
uptake suggest that IT did not modify the mechanisms
regulating the Q=Dav O2 relationship, except at maximal
exercise where Dav O2 is enhanced. Lactic acidosis is an
important contributor to oxyhemoglobin dissociation during exercise (Grassi et al. 1999; Richard et al. 2004;
Stringer et al. 1994). Grassi et al. (1999) demonstrate that
_ 2 max ; haemoglobin desaturation is
above 60–65% of VO
greatly influenced by the rightward shift of the O2Hb dissociation curve. IT increased also maximal LA (8.2 ± 0.5
mmol l–1 before training vs. 9.8 ± 0.8 mmol l–1 after
training) while CT did not (8.2 ± 1.0 vs. 8.4 ± 1.1 mmol l–1).
Therefore, Dav O2 max in the IT group may have been enhanced through a greater Bohr effect which was not present
in the CT group, again arguing for different underlying
mechanisms. In conclusion, these data support that the
choice of the training modality (CT vs. IT) might be guided
upon the objective to achieve, either better central or
peripheral adjustments to exercise.
Acknowledgments This research was supported by the Clinical
Research Department of Strasbourg’s civil hospital and financed by
Ministry for Health and Solidarity with a Regional Hospital Protocol
of Clinical Research (2002).
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