Hindawi Publishing Corporation
The Scientific World Journal
Volume 2013, Article ID 680326, 4 pages
http://dx.doi.org/10.1155/2013/680326
Research Article
Oxygen Uptake in Maximal Effort Constant Rate and
Interval Running
Daniel Pratt, Brendan J. O’Brien, and Bradley Clark
School of Health Sciences, University of Ballarat, Mt Helen, Ballarat, VIC 3353, Australia
Correspondence should be addressed to Brendan J. O’Brien; b.obrien@ballarat.edu.au
Received 30 June 2013; Accepted 30 July 2013
Academic Editors: N. Berretta and R. Inoue
Copyright © 2013 Daniel Pratt et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This study investigated differences in average
̇VO2 of maximal effort interval running to maximal effort constant rate running
at lactate threshold matched for time. The average
̇VO2 and distance covered of 10 recreational male runners ( ̇VO2 max: 4158 ±
390 mL⋅min−1) were compared between a maximal effort constant-rate run at lactate threshold (CRLT), a maximal effort interval
run (INT) consisting of 2 min at
̇VO2 max speed with 2 minutes at 50% of
̇VO2 repeated 5 times, and a run at the average speed
sustained during the interval run (CR submax). Data are presented as mean and 95% confidence intervals. The average ̇VO2 for INT,
3451 (3269–3633) mL⋅min−1, 83%
̇VO2 max, was not significantly different to CRLT, 3464 (3285–3643) mL⋅min−1, 84%
̇VO2 max, but
both were significantly higher than CR sub-max, 3464 (3285–3643) mL⋅min−1, 76% ̇VO2 max. The distance covered was significantly
greater in CLRT, 4431 (4202–3731) metres, compared to INT and CR sub-max, 4070 (3831–4309) metres. The novel finding was that
a 20-minute maximal effort constant rate run uses similar amounts of oxygen as a 20-minute maximal effort interval run despite
the greater distance covered in the maximal effort constant-rate run.
1. Introduction
The principal objective of endurance training is to evoke
supracompensation in the physiological systems restraining
the maximal sustainable competition speed. The physio-
logical systems most noted for regulating the speed of an
endurance runner are the convective supply of oxygen to the
muscles and the rate at which oxygen can be metabolized
in the muscles to resynthesize adenosine triphosphate (ATP)
[1]. It is proposed that the training strategy that sustains
the highest oxygen use ( ̇VO2) for the longest is the most
effective strategy to improve running performance [2].
̇VO2
is typically assessed by the minute rate of pulmonary oxygen
uptake during running [3]. The training strategies used by
athletes can be broadly classed into constant rate running
or interval running, where interval involves higher speeds of
running interspersed with slower “recovery” speeds.
Interval running evokes a greater total ̇VO2 than constant
rate running [4] when the average speed of the treatments
is controlled. Additionally, Daussin et al. [5] revealed that
interval training over several weeks’ results in greater gains
in cycling performance, metabolic, and cardiorespiratory
adaptation. However, any assumption interval training is
superior to constant rate training may be erroneous and
an artefact of the research design. Generally, the work (run
speed or cycle wattage) completed in a specific time frame
has been controlled in the experimental treatments to ensure
that comparisons in training adaptation are not biased by
differences in work of the training strategies. However, by
controlling work in the constant rate to interval training,
the sustainable constant rate speed/wattage is less than the
maximal sustainable speed (i.e., the constant rate training
is still “submaximal”). For example, in O’Brien et al.’s [4]
investigation, it was reported that interval running used more
oxygen than constant rate running; however, the participants
performed the constant rate run at a speed equivalent to
the interval running mean speed, estimated to be only
75%
̇VO2 max, which was most likely below the lactate thresh-
old or the fastest speed able to be sustained continuously
by the runner. Consequently, equalising speed or work of
the interval or constant rate runs may mask the optimal
training strategy for athletes, and for all practical purposes,
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The Scientific World Journal
matching maximal effort over a duration recommended to
improve cardiorespiratory fitness is more appropriate. The
ACSM currently recommends that 20 minutes of exercise is
required to improve cardiorespiratory fitness [6]. Therefore,
we aim to compare the total ̇VO2 of a maximal effort interval
run to a maximal effort constant rate run, matched for time,
20 minutes.
2. Methods
2.1. General Design of Study. This study is a quantitative
study with a crossover design where participants in ran-
dom sequence completed constant rate and interval training
treadmill running at their individual-perceived maximal
effort speed to investigate which strategy results in greater
pulmonary oxygen uptake per minute ( ̇VO2).
2.2.
Participants. Ten
“fit”
males
( ̇VO2 max 4158
±
390 mL⋅min−1) were tested through recruitment via the
university and personal contacts. The participants were aged
from 18 to 40 years old.
2.3. Experimental Protocol. Each participant included com-
peted two preliminary running tests and three experimental
runs which were compared.
Preliminary test 1: an initial maximal treadmill test
to establish
̇VO2 max and the speed at which it is
achieved.
Preliminary test 2: a 5 km run time trial to estimate the
maximal constant-rate speed approximating lactate
threshold.
Experimental test 1: a maximal effort interval tread-
mill run consisting of 5 × 2 minute intervals at the
speed corresponding to
̇VO2 max (s ̇VO2 max) during
the high periods and 5 × 2 minute intervals at 0.5
s ̇VO2 max.
Experimental test 2: a maximal effort constant rate
treadmill run at the highest velocity that could be
sustainable speed over 20 minutes (constant rate
approximating lactate threshold run). This was deter-
mined from the speed calculated from a 5 km time
trial performed on a public park.
Experimental test 3: a constant rate treadmill run at
a speed determined from the average speed of the
interval protocol used in Experimental test 1.
2.4. Experimental Procedure. The initial preliminary test of
̇VO2 max and its corresponding speed was conducted in an
exercise physiology laboratory. Prior to the
̇VO2 max test,
participants were fitted with a two-way breathing valve
(Hans Rudolph, USA), and expired air was collected into
an online metabolic system (Moxus, USA) to analyse
̇VO2.
The metabolic system was calibrated before each test using
ambient air and gas of known composition. The ̇VO2 max test
commenced at 9 km⋅h−1at a gradient of 1%, and treadmill
speed was increased by 1 km⋅h−1 every 2 minutes until
volitional exhaustion. ̇VO2 max was determined as the highest
60-second
̇VO2 value recorded during the test. Within a
week of
̇VO2 max determination, the 5 km time trial test was
performed on flat terrain at a public park.
After the two preliminary tests, the participants com-
pleted the interval and the constant rate runs on the exercise
physiology laboratory treadmill on separate days in random
sequence. The experimental runs were preceded by a stan-
dardized 5-minute warm-up run on the treadmill at 60% of
̇VO2 max followed by 2-minute rest. To control the confound-
ing variables of diet, hydration, and fatigue, the participants
were asked to consume 8–10 g of carbohydrate per kg of body
weight, drink adequate fluid to maintain hydration, and sleep
a minimum of 7 hours the night prior to testing.
During all experimental treadmill runs, expired air was
collected for metabolic analysis as per the initial maximal test.
The
̇VO2 was recorded continuously in 30-second segments
during each 20-minute run to determine the average
̇VO2.
To confirm if the runs were the highest sustainable perceived
effort for 20 minutes, each participant initially ran at the
speed determined from the preliminary tests. The constant-
rate run at lactate threshold was initially attempted by all
participants at the speed determined from the 5 km time
trial performed at the public park. The interval run on the
treadmill was initially attempted at the final treadmill speed
from the
̇VO2 max test, with the recovery periods set at 50%
of the final treadmill speed. If the participant completed the
20 minutes in either the interval or constant rate run at
lactate threshold, they undertook the run on another day at
a higher speed. If the participant could not complete the 20-
minute run, they ran on another day at a lower speed. The
increase or decrease in speed was subjectively determined
by the participant to their projected perception of what
they felt could be a maximal effort. Originally, we planned
to alter increments or decrements in speed by 0.2 km⋅h−1,
although it quickly became apparent that some individuals
felt 0.2 km⋅h−1 changes would be too “easy” or “not enough,”
so we decided it was more appropriate for the individual
to determine their own speed adjustments to establish a
maximal perceived effort. The number of runs to determine
a maximal effort was capped at three attempts for ethical and
time constraints. The fastest speed able to be sustained for 20
minutes by the participant was used in the statistical analysis.
The mean final treadmill speed from the initial ̇VO2 max test
was 16.1 km⋅h−1, and the mean final effort sustainable interval
speed was 16.3/8.15 km⋅h−1. The mean time of the 5 km time
was 14 km⋅h−1 although this was not tolerated well on the
laboratory treadmill by the majority of participants, with the
mean maximal effort speed being 13.4 km⋅h−1.
2.5. Statistical Analyses. Differences in average
̇VO2 and
mean distance covered between the three run protocols
were analysed using linear mixed models (LMMs), with
“type” as a fixed effect. Two error covariance structures were
tested—independence (zero covariance) and repeated mea-
sures structures (compound symmetry—constant covari-
ance between each pair of types). Models were compared
The Scientific World Journal
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Table 1: Mean average
̇VO2 (mL⋅min−1),
̇VO2/ ̇VO2 max (%), and distance covered (metres) for the three treatments with 95% confidence
intervals.
Interval
Submaximal constant rate
Constant rate at lactate threshold
Mean average ̇VO2
3451 (3269, 3633)†
3141 (2969, 3314)∗∧
3464 (3285, 3643)†
̇VO2/ ̇VO2max (%)
83 (79, 88)†
76 (72, 80)∗∧
84 (80, 89)†
Distance covered (metres)
4070 (3831, 4309)
4070 (3831, 4309)
4470 (4202, 4737)∗†
∗P < 0.05 versus respective value in the interval run.
†𝑃 < 0.05 versus respective value in submaximal constant rate run.
∧P < 0.05 versus respective value in constant rate at lactate threshold run.
using likelihood ratio tests, which confirmed the compound
symmetry structure. Paired 𝑡-tests with Bonferroni correc-
tion were conducted to determine the significance of pairwise
differences. Assumptions of normality and homogeneous
variance of errors were tested by graphical display and
analysis of residuals and found to be normally distributed.
Significance was assumed at the 5% level. All statistical
analyses were carried out using SPSS Version 19.
3. Results
The mean
̇VO2 of the three running protocols is presented in
Table 1.
The mean
̇VO2 and
̇VO2/ ̇VO2 max (%) were similar
between the interval and constant rate at lactate threshold
runs but were significantly greater in both maximal effort
runs compared to submaximal constant rate run. The dis-
tance covered during the constant rate at lactate threshold run
was significantly greater (𝑃 < 0.05) than the distance covered
during the maximal Interval and submaximal constant rate
runs.
4. Discussion
The purpose of this study is to elucidate whether constant-
rate running has the potential to equal or exceed the oxygen
uptake of maximal effort interval training by comparing the
̇VO2 between maximal interval and constant rate run efforts,
matched for duration of running, 20 minutes. The major
finding of this study is that interval running and constant-
rate running use similar amounts of oxygen when performed
at the maximal sustainable speed for an individual.
Both maximal interval and the constant rate at lactate
threshold run resulted in a significantly greater (𝑃 < 0.05)
mean
̇VO2 consumption compared to the submaximal con-
stant rate run (3451 and 3434 versus 3141 mL⋅min−1). This
difference can be explained by the higher average relative
intensity of the exercise of the maximal interval and the
constant rate at lactate threshold runs compared to the
submaximal constant rate run (83% and 84% versus 76%
̇VO2/ ̇VO2 max (%)). The similar oxygen requirement of both
maximal running strategies challenges the assumption that
interval training is a superior form of training to maximal
effort constant rate training. Previous studies report interval
training results in greater total
̇VO2 of a workout compared
to constant-rate training [2, 4, 7, 8] and Daussin et al. [5]
clearly showed physiological adaptations were superior after
interval training. However, Billat et al. [2] and Demarie
et al. [7] used a very high intensity for the constant rate
run (approximately 92% of v ̇VO2 max) that did not allow
exercise to be sustained for a duration from (eight to ten
minutes) normally sustained in typical endurance athlete
training (at least 20 minutes). On the other hand, the studies
by O’Brien et al. [4] and Daussin et al. [5] performed the
constant rate run at a submaximal intensity (72% ̇VO2 max and
approximately at 60% ̇VO2 max, resp.) that does not drive ̇VO2
near
̇VO2 max. The significance of our finding is that when
matched for duration, constant rate approximating lactate
threshold training places similar aerobic “load” as maximal
interval training and therefore may be equally effective in
enhancing running performance. Future research is required
to compare a constant rate at lactate threshold training versus
maximal effort interval training performed over several
weeks to determine if any has a superior outcome on time
trial performance. Interestingly, the constant rate at lactate
threshold running resulted in a significantly greater distance
being covered than interval running (4470 versus 4070 m),
despite using similar amounts of oxygen. Consequently,
maximal effort constant-rate running is a more effective and
more economic strategy to cover a set distance in 20 minutes.
The most likely explanation of the greater oxygen use in
interval running is the excess postoxygen consumption that
accumulates after each of the 2 min high intensity efforts. The
excess post oxygen consumption is attributable to a number
of factors but most likely is consequential to greater need
for phosphate creatine restoration [9] and sodium/potassium
regulation associated with repeated high intensity efforts that
have a high anaerobic reliance [10].
4.1. Limitations. A limitation of this study was the determi-
nation of maximal effort that was capped at three attempts
for each of the interval and constant-rate at lactate threshold
runs. In the ideal experimental model, we would have
requested participants to report more frequently to the
laboratory to pinpoint maximal effort more precisely (i.e.,
any further increase in treadmill speed would lead to failure
to complete the 20-minute run). Our treadmills minimum
increment capability is 0.1 km⋅h−1. However for logistical
and ethical reasons, volunteers subjectively nominated the
treadmill running speed they perceived approximated their
personal maximal tolerable effort, with the knowledge the
third and final effort was the last opportunity to determine a
“maximal” effort. The initial speeds were based on the initial
speeds they ran at, which were based on the 5 km time trial
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The Scientific World Journal
and final speed of the
̇VO2 max test. Unfortunately due to
technical malfunction, blood lactate concentration changes
during the incremental test to determine lactate threshold
could not be analysed, although we believe the best gauge of
maximal constant-rate effort is ultimately determined from
actual time trial performance. Hence, 5 km was chosen as
the time trial distance as it was estimated to be completed in
approximately 20 minutes. The mean time of the 5 km time
trial completed was 21 min and 24 seconds.
5. Conclusion
The primary aim of this paper is to contribute to the
knowledge of the most effective training regimens athletes
should embrace to optimise improvements in 5 km run per-
formance. It is acknowledged to address this question further
research needs to compare the effects of training strategies
over time. Our data indicates that constant-rate running at
lactate threshold should be considered worthy of inclusion
in investigations as it imposes an identical aerobic metabolic
load as interval running over the duration of a time-matched
training bout. Another interesting finding is that constant-
rate running at lactate threshold allows more distance to be
covered and is therefore a more economic training strategy if
covering distance is the goal.
5.1. Practical Applications
(i) The similar mean ̇VO2 between constant rate at lactate
threshold and interval runs indicates that both train-
ing strategies may be equally effective in stimulating
physiological adaptation and enhancing run perfor-
mance.
(ii) Constant rate at lactate threshold running will allow
athletes to cover 10% further distance in 20 minutes
compared to interval running.
Conflict of Interests
The authors declare that they have no conflict of interests.
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Oxygen uptake in maximal effort constant rate and interval running.
Pratt, Daniel,O'Brien, Brendan J,Clark, Bradley