International  Journal  of
Environmental Research
and Public Health
Article
Sprint Interval Running and Continuous
Running Produce Training Speciﬁc Adaptations,
Despite a Similar Improvement of Aerobic Endurance
Capacity—A Randomized Trial of Healthy Adults
Sigbjørn Litleskare 1,2
, Eystein Enoksen 1, Marit Sandvei 1, Line Støen 1, Trine Stensrud 1
,
Egil Johansen 1 and Jørgen Jensen 1,*
1
Department of Physical Performance, Norwegian School of Sport Sciences, 0863 Oslo, Norway;
sigbjorn.litleskare@inn.no (S.L.); eystein.enoksen@nih.no (E.E.); maritsandvei@hotmail.com (M.S.);
linemor@gmail.com (L.S.); trine.stensrud@nih.no (T.S.); e.i.johansen@nih.no (E.J.)
2
Department of Sports and Physical Education, Inland Norway University of Applied Sciences,
2406 Elverum, Norway
*
Correspondence: jorgen.jensen@nih.no
Received: 9 April 2020; Accepted: 26 May 2020; Published: 29 May 2020


Abstract: The purpose of the present study was to investigate training-speciﬁc adaptations to eight
weeks of moderate intensity continuous training (CT) and sprint interval training (SIT). Young healthy
subjects (n = 25; 9 males and 16 females) performed either continuous training (30–60 min, 70–80%
peak heart rate) or sprint interval training (5–10 near maximal 30 s sprints, 3 min recovery) three
times per week for eight weeks. Maximal oxygen consumption, 20 m shuttle run test and 5·60 m
sprint test were performed before and after the intervention. Furthermore, heart rate, oxygen
pulse, respiratory exchange ratio, lactate and running economy were assessed at ﬁve submaximal
intensities, before and after the training interventions. Maximal oxygen uptake increased after CT
(before: 47.9 ± 1.5; after: 49.7 ± 1.5 mL·kg−1·min−1, p < 0.05) and SIT (before: 50.5 ± 1.6; after:
53.3 ± 1.5 mL·kg−1·min−1, p < 0.01), with no statistically signiﬁcant diﬀerences between groups.
Both groups increased 20 m shuttle run performance and 60 m sprint performance, but SIT performed
better than CT at the 4th and 5th 60 m sprint after the intervention (p < 0.05). At submaximal
intensities, CT, but not SIT, reduced heart rate (p < 0.05), whereas lactate decreased in both groups.
In conclusion, both groups demonstrated similar improvements of several performance measures
including VO2max, but sprint performance was better after SIT, and CT caused training-speciﬁc
adaptations at submaximal intensities.
Keywords: maximal oxygen consumption; heart rate; oxygen pulse; shuttle run; repeated sprint ability
1. Introduction
Manipulation of duration and intensity of exercise bouts change the demands of metabolic
pathways within muscle cells, as well as oxygen delivery to exercising muscles [1]. The training
adaptations that occur after repeated bouts of exercise are to some degree speciﬁc to that particular
exercise [1,2], but both high intensity interval training and continuous training bouts increase VO2max
and oxidative capacity in skeletal muscles [1–3]. Within this context, it is of interest to clarify the speciﬁc
adaptations of diﬀerent training protocols to optimize endurance training, health and performance.
There has recently been a lot of interest in a type of high intensity interval training known
as sprint interval training (SIT). SIT is (often) performed as 30 s of “all out” sprints with 2.5–4.5
min of rest between sprints [4–6]. Several cycling studies have reported that this type of training
Int. J. Environ. Res. Public Health 2020, 17, 3865; doi:10.3390/ijerph17113865
www.mdpi.com/journal/ijerph
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improves maximal oxygen consumption (VO2max), endurance performance and the oxidative capacity
of skeletal muscle [3–12]. Previous studies have also demonstrated that the magnitude of improvement
in endurance performance and VO2max after SIT is comparable to continuous cycling at moderate
intensity [3,4]. Furthermore, research also suggest that SIT is an eﬃcient approach to improve
several important health parameters in addition to VO2max, such as insulin sensitivity, blood pressure,
cardiovascular function, and body composition [13].
Because most previous studies on SIT adaptations have used a cycling protocol, there is limited
knowledge about sprint interval running [14]. This is unfortunate, as running is a basic and popular type
of exercise. More importantly, there are several fundamental diﬀerences between cycling and running
exercise. Power output during sprint exercise is substantially higher in cycling than in running [15].
There are also several physiological diﬀerences, such as higher heart rate (HR), higher fat oxidation
and higher muscle mass activation in running than in cycling [16,17]. Thus, results from sprint interval
cycling may not be directly applicable to sprint interval running [18].
Only a few previous studies have investigated the eﬀects of sprint interval running. In most of
these studies, SIT is added to the training program of trained endurance athletes [19–21]. However,
one previous study has compared the eﬀect of sprint interval and traditional endurance running in
healthy untrained subjects [22]. Macpherson et al. [22] reported similar improvements of VO2max
and endurance performance after SIT and continuous running at moderate intensity. Interestingly,
VO2max improved in the SIT group without aﬀecting cardiac output, whereas continuous running
increased cardiac output, as expected. The study by Macpherson et al. [22] revealed that sprint
interval running and continuous running produced similar improvements of aerobic performance,
but still caused training-speciﬁc physiological adaptations. Because there is limited data available on
this topic, it is of great interest to investigate training-speciﬁc adaptations of sprint interval running
and continuous running.
The purpose of this study was therefore to compare performance and health related adaptations
of continuous training (CT) and SIT, performed as running, on VO2max, 20 m shuttle run performance,
repeated sprint ability (RSA) and the physiological response to submaximal exercise. We hypothesized
that both types of training would improve VO2max and 20 m shuttle run similarly, and that
training-speciﬁc adaptations would occur at submaximal exercise in favor of CT and during RSA in
favor of SIT.
2. Materials and Methods
2.1. Participants
Participants were recruited through the oﬃcial webpage of the Norwegian School of Sport
Sciences, and printed and electronic ﬂyers posted in various places in the local area of northern Oslo
and in social media, respectively. Forty-eight subjects volunteered and were screened for participation.
The inclusion criteria for participation were: (1) non-smokers; (2) body mass index (BMI) < 30 kg·m−2;
(3) no cardiovascular or metabolic disease; (4) no systematic endurance training during the last two
years (≤2 sessions per week). Twenty-nine subjects met these criteria and were invited to participate.
Subjects were matched based on gender and VO2max, and then randomly assigned by coin toss
to either CT or SIT. Four subjects dropped out during the training intervention; One dropped out
during week 1 due to receiving a job oﬀer (CT, male 21 years), one, during week 2, after realizing
that participation in the intervention was not compatible with his life situation (SIT, male, 21 years),
one during week 5, due to unspeciﬁed reasons (CT, male, 22 years), and one during week 8, due to
moving to a diﬀerent region (SIT, female, 22 years). Thus, 25 subjects (9 males and 16 females)
completed the training intervention.
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2.2. Training Protocol
Both groups completed eight weeks of training. Each week consisted of three training sessions,
separated by at least one resting day. Training sessions were organized and supervised by qualiﬁed
instructors.
Subjects were occasionally allowed to perform sessions at home if participation in
organized sessions was problematic. The training intensity was controlled during all sessions by heart
rate monitors (Polar Sport Tester RS800CX, Polar Electro, OY, Kempele, Finland). An adherence of
>85% (19 of 24 training sessions, including sessions performed at home) was required. Subjects were
instructed to maintain their normal diet and lifestyle throughout the intervention.
The CT group was instructed to maintain an intensity corresponding to 70–80% HRpeak at all
training sessions. Organized training sessions were performed on slightly undulating terrain. During
the ﬁrst week, the CT group performed 30 min of running. The time then increased by ﬁve minutes per
week, up to a total of 60 min. The SIT group consisted of 30 s sprints at near maximal eﬀort, with three
minutes of rest between each sprint. The training intensity of SIT sessions was evaluated subjectively
during sessions, while the HR data was used to verify that the individual participant did not have
a session or interval that deviated from their usual level of eﬀort. During the ﬁrst week, the SIT group
performed ﬁve sprints per session. The number of sprints then increased gradually, until a total of 10
sprints per session in weeks 7 and 8. When the number of sprints reached seven, subjects were given
six minutes of rest midway through the training session. All sprints were performed on slightly uphill
terrain. Prior to all training sessions, the CT group performed a ten-minute warm-up at an intensity
corresponding to 60–75% of HRpeak. The SIT group performed a ten-minute warm-up at an intensity
corresponding to 60–85% of HRpeak, followed by three incremental strides of about 80 m. After each
training session, all subjects performed ﬁve minutes of walking or running at intensities below 70% of
HRpeak. The training volume in CT and SIT was not matched.
2.3. Measures
Incremental treadmill test to exhaustion. The test was performed on a motorized treadmill
(Woodway pps55 sport, Woodway Gmbh, Weil an Rhein, Germany). Oxygen consumption (VO2)
was measured through a 2-way mouthpiece (Hans Rudolph Instr., Shawnee, KS, USA) and a sling,
which was connected to an O2 and CO2 analyzer (Oxycon Champion, Jaeger Instruments, Hoechberg,
Germany). Samples of O2 and CO2 were collected continuously from a mixing chamber, with average
values obtained over 30-s intervals. The gas analyzer was calibrated before each test with ventilated
indoor air and standardized gas concentrations, to span the concentration range observed during
exercise. The expired volume was measured with a turbine (Triple V volume transducer, Leipzig,
Germany), and volume calibration was performed regularly with a 3-L syringe.
The incremental test to exhaustion followed current recommendations for test duration [23],
and was performed according to the standard protocol of the Norwegian Olympic Sports Centre
(see e.g., [24]). Prior to the pre-test, subjects performed two familiarization tests to reduce the learning
eﬀect, following the recommendations of Edgett et al. [25]. Identical procedures were conducted for
familiarization, pre- and post-test. All subjects performed a 15-min warm-up of gradually increasing
intensity. The last ﬁve minutes of the warm-up were performed with an inclination of 5.3%, as
was the incremental test. The starting speed was chosen in order to exhaust the subjects after ~5
min. Running speed was initially increased by 1 km·h−1 every minute. At the end of the test,
running speed was either maintained or increased by 0.5 km·h−1, to allow at least one minute running
at the ﬁnal speed. VO2max was determined as the average of the highest values achieved over
two subsequent 30-s measurements. Verbal encouragement was given throughout the test. Two
minutes after completion, a capillary blood sample was obtained and 20 µl of blood was injected
into a lactate analyzer (1500 SPORT, YSI Inc., Yellow Springs Instr., Yellow spring, OH, USA), with
the help of a standard injector. The lactate analyzer was calibrated before each test with a 5.0 mM
lactate standard. The main criterion for evaluating whether VO2max was achieved was a plateau in
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oxygen consumption. A levelling-oﬀ of the VO2 curve was used in conjunction with a lactate value
≥ 6 mmol·l−1 and respiratory exchange ratio (RER) > 1.10 as secondary criteria. HR was monitored
throughout the test (Polar Sport Tester RS800CX, Polar Electro, OY, Kempele, Finland) and the highest
value achieved was deﬁned as HRpeak.
Submaximal treadmill test. The submaximal treadmill test was conducted with the same equipment
as described above and consisted of four stages of ﬁve minutes on a motorized treadmill. The running
speed at each stage was individualized based on each subject’s VO2max and a general relationship
between running speed and VO2. This relationship was estimated based on data from a pilot study.
The purpose of the procedure was to establish four individualized stages of gradually increasing
running velocities at approximate intensities of 50%, 60%, 70% and 80% of VO2max. The same velocity
(absolute intensity) was used for both the pre- and post-test. Measurements of VO2 and RER were
made between the third and fourth minute. After the fourth minute, the mouthpiece was removed
and HR was monitored until the end of the stage. Between each stage, the subjects were given one
minute rest for measurement of lactate, as described above. The post-test was conducted at the same
running velocities as the pre-test. Running economy (RE; mL·kg−1·km−1) was deﬁned as VO2 divided
by body mass and running speed. O2 pulse (mL·beat−1) was calculated by dividing VO2 (mL·min−1)
by HR (beat·min−1).
Training adaptations at the same relative intensity were evaluated by examining the running
speed that elicited the VO2 value closest to 70% of the individual subject’s VO2max. This intensity was
chosen because it produced the least variation in VO2 values.
Repeated sprint test. After completing the submaximal treadmill test, all subjects performed
a 5·60 m repeated sprint test in an indoor sports hall. The test was considered appropriate to induce
the performance decrement associated with repeated sprint exercise [26]. All subjects performed
a test-speciﬁc warm-up prior to the sprint test consisting of 3·60 m incremental runs. The sprints were
performed with a 1 m ﬂying start and each sprint was separated by 30 s of rest. Time was measured by
photoelectric detectors (Brower Speed Trap II Timing system, Brower Timing system, Salt Lake USA).
Verbal encouragement was given throughout the test.
20 m shuttle run test. The 20 m shuttle run test procedure was the same as previously described [27].
In short, subjects ran repeatedly between two lines, 20 m apart. The test started at a running speed of
8.5 km·h−1, which then increased by 0.5 km·h−1 per minute. The test was terminated when subjects
failed to reach the 20 m line before the signal on two successive occasions. To stimulate competition,
the subjects ran in groups.
2.4. Procedures
All tests were performed before and after the training interventions. The submaximal treadmill
test and the repeated sprint test were performed on the same day, and only separated by the time to
relocate from the laboratory to the sports hall. All other tests were separated by at least one resting day.
Subjects were familiarized with testing procedures to minimize any potential learning eﬀect.
The data for this study were collected in relation to a larger study [28]. The study was approved
by the Regional Ethics Committee of Oslo, Norway (ref. number 2010/1567-1) and was performed
according to the Declaration of Helsinki. All subjects were informed about the purpose of the study
and associated risks before they gave their written informed consent to participate.
A few subjects did not obtain valid results for all tests due to sickness, injury and unspeciﬁed
withdrawal from the study. These subjects were excluded from both pre and post analysis for these
particular tests. The number of participants for each test is stated in the captions of tables and ﬁgures.
2.5. Analysis
Data are presented as group means ± SEM. All statistical analyses were performed in SPSS version
18 (SPSS inc., Chicago, IL, USA). The assumption of normality was evaluated by a Shapiro–Wilk
test.
Student’s paired t-test was used to investigate within-group diﬀerences, and a Student’s
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unpaired t-test was used to investigate between-group diﬀerences. A repeated measures ANOVA with
a Greenhouse–Geisser correction was used to evaluate a potential increase in VO2max as a function of
the number of tests performed before the intervention. In cases where data was not normally distributed,
a Wilcoxon signed-rank test was used to verify within-group diﬀerences, and a Mann–Whitney test
was used to verify between-group diﬀerences. Statistical signiﬁcance was accepted at the p < 0.05 level.
3. Results
The number of females in each group was eight, while the number of males was four in CT and ﬁve
in SIT. The mean age, height, weight and BMI was 25 ± 1 years, 175 ± 2 cm, 72.6 ± 3.8 kg and 23.6 ± 0.9
kg·m−2 in CT at the start of the intervention. In SIT, the mean age, height, weight and BMI was 25 ± 1
years, 173 ± 3 cm, 71.2 ± 4.1 kg and 24.0 ± 0.8 kg·m−2. There was no statistical diﬀerence between
groups and these characteristics did not change during the intervention. Heart rate registrations
at all training sessions conﬁrmed that the subjects performed the training as recommended, including
the sessions performed at home (19% of sessions). Three participants experienced minor injuries
during the training intervention, including one injury unrelated to the intervention. All three were in
the SIT group, and all managed to complete > 85% of training sessions.
Maximal oxygen consumption and 20 m shuttle run performance. Maximal oxygen uptake was
measured three times prior to the intervention, and VO2max increased from test to test. The repeated
measures ANOVA revealed that VO2max increased from 48.2 ± 1.1 at the ﬁrst familiarization test to
49.3 ± 1.3 in the second, and eventually to 49.9 ± 1.3 mL·kg−1·min−1 at the third test when combining
both groups (F(1.434, 28.683) = 10.320, p < 0.01). VO2max was improved in both CT (p < 0.05) and SIT
(p < 0.01) after training (Table 1). The improvement of VO2max corresponded to a 3.8% increase in CT
and 5.5% in SIT. The increase in VO2max varied between subjects and ﬁve subjects did not increase
VO2max (Figure 1). In accordance with the improved VO2max, both groups also increased maximal O2
pulse (p < 0.05) and the number of laps performed on the 20 m shuttle run test (CT p < 0.05; SIT p < 0.01).
Figure 1. Individual change in maximal oxygen consumption (VO2max) after eight weeks of either
continuous training (CT) or sprint interval training (SIT) (one subject in CT did not experience
any change).
Repeated sprint test. Both the CT and SIT groups improved sprint performance for the ﬁrst
sprint (Table 2) and thereby improved maximal 60 m sprint performance. Both groups also improved
performance on all successive sprints. However, the SIT group performed better than the CT group on
sprints number four (p < 0.05) and ﬁve (p < 0.05) after the intervention (Table 2).
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Table 1. Parameters of maximal endurance performance before and after eight weeks of continuous
training (CT) and sprint interval training (SIT).
CT
SIT
Pre
Post
Pre
Post
VO2max (mL·kg−1·min−1)
47.9 ± 1.5
49.7 ± 1.5 *
50.5 ± 1.6
53.3 ± 1.5 *
Maximal O2 pulse
17.4 ± 1.0
18.1 ± 1.0 *
18.0 ± 1.0
19.2 ± 1.0 *
Laps
71.5 ± 6.1
79.4 ± 5.2 *
69.5 ± 3.8
81.7 ± 4.0 *
Values are mean ± SEM. CT, n = 12 (4 males, 8 females). SIT, n = 13 (5 males, 8 females). VO2max, maximal
oxygen consumption; O2 pulse, oxygen pulse; Laps, number of laps completed during the 20 m shuttle run test.
* Statistically signiﬁcant diﬀerence from pre (student’s t-test), p < 0.05. There were no statistically signiﬁcant
diﬀerences between groups.
Table 2. Performance on the repeated sprint test before and after eight weeks of continuous training
(CT) and sprint interval training (SIT).
CT
SIT
Pre
Post
Pre
Post
Time (s)
%dec.
Time (s)
%dec
Time (s)
%dec
Time (s)
%dec
1. 60 m
9.92 ± 0.25
9.69 ± 0.26 *
9.64 ± 0.26
9.20 ± 0.21 *
2. 60 m
10.44 ± 0.33
5.2
10.06 ± 0.27 *
3.8
9.98 ± 0.23
3.5
9.48 ± 0.18 *
3.0
3. 60 m
10.76 ± 0.29
8.5
10.31 ± 0.23 *
6.4
10.27 ± 0.22
6.5
9.89 ± 0.20 *
7.5
4. 60 m
10.87 ± 0.30
9.6
10.54 ± 0.23 *
8.8
10.37 ± 0.25
7.6
9.91 ± 0.19 *,†
7.7
5. 60 m
10.93 ± 0.21
10.2
10.70 ± 0.22 *
10.4
10.53 ± 0.25
9.2
9.96 ± 0.20 *,†
8.3
Values are mean ± SEM. CT, n = 10. SIT, n = 11. %dec = percent performance decrement compared to the fastest
sprint time * Statistically signiﬁcant diﬀerence from pre.† Statistically signiﬁcant diﬀerence from CT (student’s t-test),
p < 0.05.
Physiological response to submaximal exercise at the same absolute intensity. The submaximal
treadmill test was performed at the same velocity, before and after the intervention. Both groups ran
at a lower percentage of VO2max after eight weeks of training (Table 3). The CT group decreased VO2
at all stages (i.e., running economy), while the SIT group decreased VO2 at stage 4 and RE at stages
2 and 4 (Table 3). HR was lower after CT at all stages (p < 0.01), but remained unchanged after SIT
(Table 3). O2 pulse at submaximal intensities did not change in any group (Table 3).
Physiological response to submaximal exercise at the same relative intensity. Adaptations to
running, performed at the same relative intensity before and after the intervention, were evaluated
at the velocity closest to 70% VO2max. At this intensity, HR remained unchanged after CT, while O2
pulse increased by 0.6 mL·beat−1 (p < 0.05; Table 4). In contrast, HR increased (p < 0.05) and O2 pulse
remained unchanged after SIT (Table 4). RER was reduced at 70% VO2max after CT (p < 0.05), but not
statistically signiﬁcant after SIT (p = 0.07; Table 4). Lactate was reduced at 70% of VO2max in both
groups after the intervention.
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Table 3. Physiological responses at submaximal velocities, before (pre) and after (post) eight weeks of either continuous training (CT) or sprint interval training (SIT).
1
2
3
4
Pre
Post
Pre
Post
Pre
Post
Pre
Post
CT
VO2 (mL·min−1)
1553 ± 139
1381 ± 159 *,#
2307 ± 177
1876 ± 157 *
2414 ± 175
2275 ± 174 *
2754 ± 186
2620 ± 172 *
% VO2max
45.1 ± 3.4
37.8 ± 2.1 *
58.4 ± 3.1
52.4 ± 2.8 *
71.1 ± 2.3
64.6 ± 2.4 *
79.4 ± 2.0
73.3 ± 1.8 *
RE (mL·kg−1·km−1)
213 ± 16
186 ± 10 *,#
229 ± 12
213 ± 10 *
238 ± 8
224 ± 8 *
232 ± 6
223 ± 6 *
% HRpeak
66.9 ± 2.1
59.6 ± 2.3 *
76.8 ± 2.2
70.8 ± 2.5 *
85.3 ± 1.5
80.2 ± 2.1 *
90.0 ± 1.0
86.3 ± 1.4 *
O2pulse (mL·beat−1)
11.5 ± 0.7
11.5 ± 1.0
13.1 ± 0.8
13.3 ± 0.9
14.2 ± 0.8
14.1 ± 0.9
15.3 ± 0.9
15.2 ± 0.9
RER (VCO2·VO2−1)
0.89 ± 0.01
0.84 ± 0.01 *
0.93 ± 0.01
0.88 ± 0.01 *
0.94 ± 0.01
0.90 ± 0.01 *
0.97 ± 0.01
0.93 ± 0.01 *
Lactate (mmol·l−1)
1.22 ± 0.13
0.77 ± 0.06 *
1.76 ± 0.26
1.16 ± 0.13 *
2.39 ± 0.25
1.75 ± 0.17 *
3.84 ± 0.30
2.66 ± 0.24 *
SIT
VO2 (mL·min−1)
1544 ± 152
1523 ± 150
2221 ± 168
2076 ± 158
2574 ± 181
2500 ± 165
2909 ± 204
2832 ± 196 *,#
% VO2max
42.6 ± 2.2
40.1 ± 2.5 *
61.9 ± 1.6
55.3 ± 2.0 *
71.8 ± 1.2
66.5 ± 1.5 *
81.2 ± 0.9
75.2 ± 1.2 *
RE (mL·kg−1·km−1)
201 ± 10
199 ± 10
243 ± 8
228 ± 8 *
240 ± 5
234 ± 4
237 ± 4
231 ± 4 *
% HRpeak
61.6 ± 2.4
61.6 ± 2.5
75.0 ± 1.6
72.0 ± 2.0
82.6 ± 1.2
81.1 ± 1.5
88.6 ± 0.9
87.2 ± 1.2
O2pulse (mL·beat−1)
12.8 ± 1.0
12.6 ± 1.0
14.9 ± 1.0
14.5 ± 1.1
15.8 ± 1.0
15.6 ± 0.9
16.6 ± 1.0
16.4 ± 1.0
RER (VCO2·VO2−1)
0.86 ± 0.02
0.83 ± 0.02
0.91 ± 0.01
0.87 ± 0.02 *,#
0.92 ± 0.01
0.89 ± 0.01 *
0.96 ± 0.01
0.92 ± 0.01 *
Lactate (mmol·l−1)
1.12 ± 0.08
0.89 ± 0.06 *
1.79 ± 0.15
1.20 ± 0.07 *,#
2.38 ± 0.17
1.68 ± 0.12 *
3.45 ± 0.24
2.66 ± 0.19 *,#
Values are mean ± SEM. VO2, oxygen consumption; % VO2max, percent of maximal oxygen consumption; RE, running economy; % HFpeak, percent of peak heart rate; O2 pulse, oxygen
pulse; RER, respiratory exchange ratio. Velocities at stage 1, 2, 3 and 4 equaled 6.2 ± 0.2, 7.5 ± 0.2, 8.8 ± 0.3 and 10.1 ± 0.3 km·h−1 in CT, and 6.4 ± 0.2, 7.7 ± 0.2, 9.1 ± 0.3 and 10.4 ± 0.3
km·h−1 in SIT. CT, n = 11. SIT, n = 13. Values for % HFpeak and O2 pulse represents only 12 subjects in SIT. * Statistically signiﬁcant diﬀerence from pre (student’s t-test), p < 0.05. #
Statistically signiﬁcant diﬀerence from pre (veriﬁed by Wilcoxon signed rank test), p < 0.05. There were no statistically signiﬁcant diﬀerences between groups.
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Table 4. Physiological responses to running at the velocity closest to 70 percent of maximal oxygen
consumption, before (pre) and after (post) eight weeks of either continuous training (CT) or sprint
interval training (SIT).
CT
SIT
Pre
Post
Pre
Post
Velocity (km·h−1)
8.7 ± 0.4
9.7 ± 0.3 *
8.8 ± 0.4
9.6 ± 0.3 *
% VO2max
70.5 ± 0.9
71.4 ± 0.7
70.3 ± 0.7
70.2 ± 0.6
% HRpeak
84.3 ± 1.0
85.1 ± 0.9
81.9 ± 1.6
84.9 ± 1.4 *
O2 pulse (mL·beat−1)
14.5 ± 0.9
15.1 ± 0.9 *
15.7 ± 1.0
16.0 ± 0.9
RER (VCO2·VO2−1)
0.94 ± 0.01
0.91 ± 0.01 *
0.93 ± 0.01
0.91 ± 0.01
Lactate (mmol·l−1)
2.62 ± 0.16
2.18 ± 0.19 *,#
2.33 ± 0.12
2.03 ± 0.15 *,#
Values are mean ± SEM. % VO2max, percent of maximal oxygen consumption; % HFpeak, percent of peak heart
rate; O2 pulse, oxygen pulse; RER, respiratory exchange ratio. CT, n = 11. SIT, n = 13. Values for % HFpeak and O2
pulse represents only 12 subjects in SIT. * Statistically signiﬁcant diﬀerence from pre (student’s t-test), p < 0.05.
# Statistically signiﬁcant diﬀerence from pre (veriﬁed by Wilcoxon signed rank test), p < 0.05. There were no
statistically signiﬁcant diﬀerences between groups.
4. Discussion
The main ﬁndings of the present study were that both training protocols increased VO2max
and shuttle run performance, but also produced training-speciﬁc adaptations. The SIT group performed
better than the CT group on the last two 60 m sprints, while only CT improved HR and O2 pulse
adaptations at submaximal intensities.
The higher VO2max in both groups after eight weeks of training holds implications for both
performance and health, and is supported by previous research, showing a comparable improvement
of VO2max after sprint interval running and cycling [4,22]. Interestingly, previous research suggests
that the adaptations that lead to the comparable improvement of VO2max are diﬀerent in the two
types of training interventions. Macpherson et al. [22] showed that continuous endurance running
improved maximal cardiac output, while sprint interval running did not. These reports suggest that
the improvement of VO2max in the present study was due to peripheral adaptations [5,6]. Importantly,
the increase in VO2max varied substantially between participants whether they performed CT or SIT,
and ﬁve subjects did not increase their VO2max, even though the training was supervised by qualiﬁed
instructors, and heart rate recordings conﬁrmed that the training was performed with the recommended
HR. These data agree with previous studies showing large variation in the increase in VO2max after
endurance training [29,30]. Genetic variation has been suggested to explain diﬀerences in the increase
of VO2max, but research also suggests that a large number of genetic variations collectively determine
increases in VO2max [31]. No genetic variation predicting has so far been validated.
The increase of VO2max observed after endurance exercise is caused by an improvement of cardiac
output and/or arteriovenous oxygen diﬀerence [32], which results in higher VO2 per heartbeat (i.e., O2
pulse). At submaximal intensities, an increased O2 pulse results in lower HR [32]. In the present study,
HR was reduced after CT at all submaximal velocities, while it remained unchanged after SIT. However,
the participants improved running economy, which precludes the comparison of cardio-respiratory
adaptations at the same absolute intensities.
Therefore, to investigate the submaximal training
adaptations independent of running economy, we examined HR and O2 pulse at the same relative
intensity (~70% VO2max), pre and post training. At ~70% VO2max, O2 pulse increases after CT as
expected (please see Table 4). In contrast, SIT did not change O2 pulse at ~70% VO2max and HR was
higher after the training intervention, supporting Macpherson et al. [22], who reported unchanged
cardiac output after sprint interval running. Increased cardiac output leads to higher O2 pulse
and decreased HR at submaximal intensities [31].
The limited cardiac adaptations after SIT in
the present study suggest that CT is a superior option for cardiac adaptations, which holds implications
for the health beneﬁts of SIT, as improved cardiac function is an important part of the health beneﬁts of
exercise [33].
Int. J. Environ. Res. Public Health 2020, 17, 3865
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Several studies have shown that SIT increases the expression of oxidative enzymes in skeletal
muscle [3,5,6]. In the present study, blood lactate and RER were reduced after both CT and SIT
(although p = 0.07 for RER in SIT at 70% VO2max). It is well known that lactate production and RER
are inﬂuenced by the oxidative capacity of skeletal muscle [34] and, thus, our results suggest that
both CT and SIT improved the oxidative capacity of skeletal muscle. Results from the 20 m shuttle
run test also revealed that both groups improved endurance performance and that the improvement
was similar in both groups. These results are in accordance with previous investigations of both
sprint interval cycling and running [3,22]. Endurance performance is a complex characteristic that
is dependent on several factors, which makes it diﬃcult to identify any single factor responsible for
improved performance. Several adaptions could potentially contribute to the improved endurance
performance observed in this study, but the correlation between the change of VO2max and the change
of 20 m shuttle run performance (r = 0.56, p = 0.01) suggest that VO2max is central.
Results from the test of repeated sprints showed that both CT and SIT improved the performance
of the ﬁrst sprint and thereby improved maximal sprint performance. Improved maximal 60 m sprint
performance after CT may be surprising based on the “slow paced” nature of the training intervention.
However, previous research has reported similar results for untrained people, including two studies
of endurance cycling reporting improved sprint performance after continuous training [34,35].
The mechanisms behind these improvements are uncertain, but mechanical eﬃciency has been
suggested as the most important factor [35]. In the present study, CT improved RE, which is a common
measure of mechanical eﬃciency [36]. Improved RE could therefore oﬀer an explanation for improved
maximal sprint performance after CT. Improvements of mechanical eﬃciency is often associated with
increased stiﬀness of muscles and tendons, but improved running technique by wasting less energy
on braking forces and excessive vertical oscillation may be a likely cause for the improvement in
CT [36], since the participants were inexperienced runners with a high potential for improving running
technique. Improved maximal running velocity after SIT has previously been reported [22], and is
supported by ﬁndings of improved peak power after sprint interval cycling [4,8,9,19].
Both groups also improved repeated sprint ability.
These results are in accordance with
previous studies that have investigated RSA after continuous training and high intensity interval
training [34,35,37]. Interestingly, the SIT group performed better than the CT group on sprints number
four and ﬁve after the intervention, thus demonstrating a superior ability to resist fatigue. The reason
for the improved performance on the last two sprints could be related to the ability of SIT to increase
muscle buﬀer capacity and levels of anaerobic enzymes [3,6], and to prevent metabolic and ionic
perturbation during high-intensity exercise [8]. All of these adaptations can potentially improve
performance during repeated sprint exercise [26]. The beneﬁt of improved buﬀer capacity and ability
to prevent ionic and metabolic perturbations would be progressively more beneﬁcial during repeated
sprint exercise, which may explain why SIT performed better at sprint number 4 and 5, and not 1, 2
and 3.
Some limitations in the present study need to be recognized. The number of participants included
in this study was based on an a priori power analysis for the between group comparison of VO2max.
However, the statistical power may still be limited for the other comparisons in this study, in particular
for tests with missing data. The results at the 70% intensity should be considered carefully. As explained
in the methods, running speed was not adjusted to exactly 70% VO2max and there was some individual
variation in running intensity from pre- to post-test. However, these variations were small, and mean
relative intensity varied by less than one percentage-point between pre- and post-test (Table 4).
The majority of participants were female, and although training groups were gender matched, we did
not control for oral contraceptive use and menstrual cycle phase. Furthermore, high intensity exercise
is commonly associated with increased risk of injury [38], and in the present study, we were unable to
prevent the occurrence of injuries in the SIT group, despite a standardized warm-up and supervision
of highly qualiﬁed personnel. Strengths of this study include the fact that heart rate was recorded
at all training sessions, and that both females and males were included. Furthermore, a substantial
Int. J. Environ. Res. Public Health 2020, 17, 3865
10 of 12
eﬀort was made during familiarization, to reduce the potential impact of a learning eﬀect on VO2max
from pre- to post-test. VO2max did increase during the familiarization process, but levelled oﬀ from
the last familiarization test to the pre-test, which indicates that the eﬀorts was successful at minimizing
the learning eﬀect in this study. However, the inclusion of the familiarization tests in addition to
an already high number of pre-tests may have resulted in some minor training adaptations before
the onset of the training interventions.
5. Conclusions
In conclusion, both types of training produced similar improvements of VO2max, endurance
capacity and sprint performance. Despite these similarities, O2 pulse and HR during submaximal
exercise was improved after CT only, which suggests superior adaptations of cardiac health after CT
compared to SIT. In addition, SIT improved RSA signiﬁcantly more compared to CT. The present study
therefore suggest that training-speciﬁc adaptations occur after sprint interval running and continuous
running with moderate intensity. The presumption of training-speciﬁc adaptations should be taken
into consideration when composing an optimal endurance training program.
Author Contributions: Conceptualization, S.L., E.E., M.S., L.S., E.J., T.S. and J.J.; methodology, S.L., E.E., M.S.,
L.S., E.J., and J.J.; formal analysis, S.L.; investigation, S.L., E.E., M.S., L.S., E.J. and J.J.; writing—original draft
preparation, S.L.; writing—review and editing, E.E., M.S., L.S., E.J., T.S. and J.J.; supervision, E.E. and J.J.; project
administration, S.L., M.S. and L.S. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Acknowledgments: The authors thank Puma, Norway, for supplying subjects with training equipment. We also
thank Line Hårklau for technical assistance and Kristoﬀer Jensen Kolnes for help as training instructor.
Conﬂicts of Interest: The authors declare no conﬂict of interest.
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Sprint Interval Running and Continuous Running Produce Training Specific Adaptations, Despite a Similar Improvement of Aerobic Endurance Capacity-A Randomized Trial of Healthy Adults.
Litleskare, Sigbjørn,Enoksen, Eystein,Sandvei, Marit,Støen, Line,Stensrud, Trine,Johansen, Egil,Jensen, Jørgen