146 |   
 
Scand J Med Sci Sports. 2023;33:146–159.
wileyonlinelibrary.com/journal/sms
Received: 22 May 2022 | Revised: 9 August 2022 | Accepted: 28 September 2022
DOI: 10.1111/sms.14251  
O R I G I N A L  A R T I C L E
Aerobic high- intensity intervals are superior to improve 
V̇O2max compared with sprint intervals in well- trained men
Håkon Hov1,2
 |   Eivind Wang2,3 |   Yi Rui Lim4 |   Glenn Trane5 |   
Magnus Hemmingsen4 |   Jan Hoff1,6 |   Jan Helgerud1,4
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided 
the original work is properly cited.
© 2022 The Authors. Scandinavian Journal of Medicine & Science In Sports published by John Wiley & Sons Ltd.
1Myworkout, Medical Rehabilitation 
Clinic, Trondheim, Norway
2Faculty of Health Sciences and Social 
Care, Molde University College, Molde, 
Norway
3Department of Psychosis and 
Rehabilitation, Psychiatry Clinic, St. 
Olavs University Hospital, Trondheim, 
Norway
4Department of Circulation and 
Medical Imaging, Faculty of Medicine 
and Health Sciences, Norwegian 
University of Science and Technology, 
Trondheim, Norway
5Physical Education, Sports Science and 
Outdoor Education, NORD University, 
Bodø, Norway
6Department of Physical Medicine and 
Rehabilitation, St. Olav's University 
Hospital, Trondheim, Norway
Correspondence
Håkon Hov, Myworkout, Medical 
Rehabilitation Clinic, Ingvald Ystgaards 
veg 23, 7047 Trondheim, Norway.
Email: hakon.hov@treningsklinikken.
no
Funding information
Norges Forskningsr aring;d
Maximal oxygen uptake (V̇O2max) may be the single most important factor for 
long- distance running performance. Interval training, enabling high intensity, is 
forwarded as the format that yields the largest increase in V̇O2max. However, it 
is uncertain if an optimal outcome on V̇O2max, anaerobic capacity, and running 
performance is provided by training with a high aerobic intensity or high over-
all intensity. Thus, we randomized 48 aerobically well- trained men (23 ± 3 years) 
to three commonly applied interval protocols, one with high aerobic intensity 
(HIIT) and two with high absolute intensity (sprint interval training; SIT), 3× 
week for 8 weeks: (1) HIIT: 4 × 4 min at ~95% maximal aerobic speed (MAS) with 
3 min active breaks. (2) SIT: 8 × 20 s at ~150% MAS with 10 s passive breaks. (3) 
SIT: 10 × 30 s at ~175% MAS with 3.5 min active breaks. V̇O2max increased more 
(p < 0.001) following HIIT, 4 × 4 min (6.5 ± 2.4%, p < 0.001) than SIT, 8 × 20 s 
(3.3 ± 2.4%, p < 0.001) and SIT, 10 × 30 s (n.s.). This was accompanied by a 
larger (p < 0.05) increase in stroke volume (O2- pulse) following HIIT, 4 × 4 min 
(8.1 ± 4.1%, p < 0.001) compared with SIT, 8 × 20 s (3.8 ± 4.2%, p < 0.01) and SIT, 
10 × 30 (n.s.). Anaerobic capacity (maximal accumulated oxygen deficit) increased 
following SIT, 8 × 20 s (p < 0.05), but not after HIIT, 4 × 4 min, nor SIT, 10 × 30 s. 
Long- distance (3000- m) endurance performance increased (p < 0.05– p < 0.001) 
in all groups (HIIT, 4 × 4 min: 5.9 ± 3.2%; SIT, 8 × 20 s: 4.1 ± 3.7%; SIT, 10 × 30 s: 
2.2 ± 2.2%), with HIIT increasing more than SIT, 10 × 30 s (p < 0.05). Sprint (300- 
m) performance exhibited within- group increases in SIT, 8 × 20 s (4.4 ± 2.0%) and 
SIT, 10 × 30 s (3.3 ± 2.8%). In conclusion, HIIT improves V̇O2max more than SIT. 
Given the importance of V̇O2max for most endurance performance scenarios, HIIT 
should typically be the chosen interval format.
K E Y W O R D S
aerobic power, anaerobic capacity, HIIT, MAOD, running economy, running performance, SIT, 
Tabata
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HOV et al.
1 | INTRODUCTION
Maximal oxygen uptake (V̇O2max) may be considered the 
single most important predictor for long- distance endur-
ance performance.1– 3 Furthermore, such events are also 
influenced by other physiological factors involved in aer-
obic energy processes, that is, running economy (CR) and 
lactate threshold (LT),1 as well as a contribution from an-
aerobic metabolism.4 However, the capacity to produce 
energy derived from anaerobic sources is limited,5 and 
when whole- body performance persists more than 75 s 
the majority of energy utilized originates from aerobic 
sources,6 a proportion which increases to ~90% when the 
event lasts ~10 min.4,7
Given the great importance for long- distance endur-
ance performance, a critical question is which training 
modality may yield the most potent V̇O2max improve-
ments. Of duration, frequency and intensity, the latter is 
forwarded as particularly important to increase V̇O2max.8,9 
To achieve high intensity, training can be organized as 
intervals separated by recovery periods, in which metab-
olites accumulated during the intervals can be removed, 
or accumulation at least alleviated. Aerobic high- intensity 
interval training (HIIT), applying intervals of 3– 5  min, 
is one well- documented format to effectively improve 
V̇O2max in healthy individuals8,10 and various patient 
populations.11,12 The rationale for this design is that a 
high overload on oxygen transporting organs may only 
be achieved after 1– 2  min because of sluggish oxygen 
kinetics,13 and that in the other end of the spectrum fa-
tiguing processes sets an upper limit to the length of the 
interval, likely around 8– 12 min.14 Consequently, intervals 
should be between these limits, and towards the lower 
end (e.g., 4 min) if repeated several times. The intensity in 
this format typically elicits 90– 95% of maximal heart rate 
(HRmax) within 2– 3 min, which corresponds to an inten-
sity of ~95% of maximal aerobic speed (MAS) and ~90% 
V̇O2max.10 However, of notice, HIIT may also be organized 
as series of shorter intervals (e.g., 30 s) if they are inter-
spersed by short breaks (e.g., 15 s) in which V̇O2 do not 
drop significantly, and thus, enabling a high aerobic inten-
sity over the course of several intervals (i.e., accumulated 
time spent ≥90% of V̇O2max).8,10
Supramaximal sprint interval training (SIT) is another 
intermittent format that is advocated for effective improve-
ments in V̇O2max and endurance performance. SIT is exe-
cuted at high absolute intensities, often ≥150% of MAS.15,16 
However, since fatigue occurs rapidly, the aerobic intensity 
is not necessarily accordingly high because of the sluggish 
V̇O2 kinetics. Again, this feature may be somewhat ma-
nipulated by the work/rest ratio of a protocol (i.e., short 
recovery periods may limit a drop in V̇O2 during breaks 
and enable a higher aerobic intensity).17 Indeed, SIT with 
short recovery periods (~10 s) commonly improve V̇O2max 
in moderately and well- trained individuals,16,18 while 
studies are conflicting regarding the capability of SIT 
with long recovery periods (~3 min) to increase V̇O2max in 
healthy and aerobically well- trained individuals.15,19,20 On 
the contrary, the very high overall intensity applied in SIT 
protocols may be important for improving the attributes 
limiting anaerobic capacity, which in well- trained subjects 
may be related to intramuscular ion handling.19,21
For HIIT and SIT, there is a trade- off between inten-
sity and volume, and they may both be organized with 
recovery periods ranging from a few seconds (~10  s) to 
several minutes. It is, by definition, the intensity (i.e., 
work output) that distinguishes HIIT and SIT from each 
other. The very high absolute intensity during SIT (≥150% 
of MAS) necessitates short intervals, and its potential to 
accumulate a high metabolic volume at ≥90% of V̇O2max 
compared with HIIT (~95% of MAS) is therefore impeded. 
Considering that SIT protocols often are conducted until 
absolute exhaustion at a severe work output, the volume 
of work conducted during a SIT- session must be limited. 
It is therefore, in a practical manner, not possible to match 
commonly applied protocols of HIIT and SIT for total 
work without drastically reducing the volume of HIIT 
protocols. Where, in the latter case, HIIT cannot be per-
formed as intended.
Given the great importance of V̇O2max for long- distance 
endurance performance, studies investigating which in-
terval training format may yield the largest increases in 
this crucial factor are warranted. High intensity appears 
to be imperative to achieve an optimal outcome, but direct 
comparisons between interval protocols with high aerobic 
or very high overall intensity, like HIIT and SIT, on V̇O2max 
are scarce. Thus, the aim of this study was to compare the 
effects of three commonly applied interval formats, one 
HIIT protocol, one SIT protocol with short recovery pe-
riods, and one SIT protocol with long recovery periods, 
on V̇O2max in aerobically well- trained men. Furthermore, 
to comprehensively outline how of these protocols affect 
running performance and its physiological determinants, 
we also compared the effects on anaerobic capacity, CR, 
LT, relevant hematological parameters and long- distance 
and sprint running performance. A high aerobic intensity 
during exercise, tailored to overload oxygen transporting 
organs, may be essential for enhancing V̇O2max,10 while a 
very high absolute intensity may more favor anaerobic ca-
pacity improvements.22 Accordingly, we hypothesized that 
(1) HIIT, carried out as 4 × 4 min at ~95% MAS with 3 min 
active recovery periods, would improve V̇O2max more than 
the two SIT protocols, carried out as 8 × 20 s until absolute 
exhaustion (~150% MAS) with 10 s passive recovery pe-
riods, and 10 × 30 s of maximal effort (~175% MAS) with 
3.5 min active recovery periods, respectively, (2) Both SIT 
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HOV et al.
protocols would improve anaerobic capacity more than 
HIIT, (3) HIIT would improve long- distance (3000 m) en-
durance performance more than both SIT protocols while 
sprint (300 m) endurance performance would exhibit the 
reverse result.
2 | METHODS
2.1 | Subjects
Forty- eight healthy non- smoking males volunteered to 
participate in the present study. Females were not invited 
to participate to ensure homogeneity of physiological fac-
tors and baseline training status. The subjects were aero-
bically well- trained and relatively accustomed to treadmill 
running, but not specialized runners nor engaged in 
long- distance or sprint running competitions or train-
ings. They were randomized into three training groups: 
HIIT 4 × 4  min, SIT 8 × 20 s, or SIT 10 × 30 s (Figure  1). 
A V̇O2max ≥ 50 ml kg−1 min−1 and whole- body endurance 
training at least once per week were set as inclusion cri-
teria. Subjects were excluded if they had a compliance to 
the training interventions of <80%. Subject characteristics 
are given in Table 1. The study was carried out in accord-
ance with the Declaration of Helsinki. Participants were 
informed with a written consent, and the Institutional 
Review Board of the Norwegian University of Science and 
Technology approved the protocol.
2.2 | Study timeline
After randomization, and within 2 weeks before the in-
tervention period, the subjects met three times in the 
laboratory where two of them were for metabolic testing 
and the last one for a blood draw. Additionally, the par-
ticipants met once at an indoor track and field arena. All 
subjects had at least 1 day of rest preceding each of the 
test days (see below). The tests were repeated in the same 
order for each individual post intervention. The training 
interventions all consisted of three sessions per week for 
8 weeks.
2.3 | Testing procedures
2.3.1 | Test day 1 (V̇O2max, running 
economy and lactate threshold)
The motorized treadmill (Woodway PPS 55 Sport, 
Germany) was set at 3° inclination throughout test 
day 1 and 2. Hence, all measurements of the relation-
ship between velocity and pulmonary oxygen uptake 
(V̇O2) (e.g., CR, LT, MAS) was collected at this incline. 
Following 10  min of warm- up, the participants pro-
ceeded into 5- min stages of running at 1 km h−1 increas-
ing velocities to determine LT. At least three stages had 
to be completed. Heart rate (HR) and V̇O2 was continu-
ously measured throughout the test using a HR moni-
tor (Polar Electro Oy, Finland) and a Cortex Metamax 
II (Cortex Biophysik GmbH, Leipzig, Germany), respec-
tively. Blood was drawn from the fingertip following 
warm- up and each stage and analyzed using a Biosen C- 
line lactate analyzer (EKF- diagnostic GmbH, Germany). 
LT was defined as the V̇O2, HR, or velocity associated 
with a blood lactate concentration ([la−]b) 1.5 mM above 
the lowest measured [la−]b.8 CR was assessed as an aver-
age of the V̇O2 measurements the last 30 s at 7 km h−1, 
and visual inspection to control that a steady state had 
FIGURE 1 
Flow chart of the study.
   | 149
HOV et al.
been achieved was conducted. The CR stage was imple-
mented in the LT protocol, and a [la−]b measurement as-
sured that 7 km h−1 was below LT. Subsequent to the CR 
and LT procedure, subjects walked for about 5 min be-
fore performing an incremental V̇O2max- test. Starting at 
an intensity ≥ LT, the velocity was increased by 1 km h−1 
every minute until exhaustion, resulting in the test last-
ing 4– 7 min. Verbal encouragement was given during 
the last minutes of the V̇O2max- test. A capillary blood 
sample was drawn within 1 min after termination of the 
test to measure [la−]b. The highest recorded HR was re-
garded as HRmax. V̇O2max was calculated as the highest 
30- s average V̇O2 and maximal O2 pulse was calculated 
as V̇O2max/HRmax. The presence of a plateau in V̇O2 de-
spite increased workload or ventilation (V̇E), combined 
with either a [la−]b above 8 mM and/or a respiratory ex-
change ratio above 1.10 were used as V̇O2max criteria.23 
Additionally, V̇O2max- values from the incremental pro-
tocol were confirmed during the second test day.24 If ei-
ther 30- s average V̇O2 and/or HR reached higher values 
during the second test day, these values were used as 
V̇O2max and/or HRmax.
Empirically, V̇O2 does not increase proportional to 
body mass (Mb) but with an exponent of approximately 
0.75.25 Consequently, V̇O2max, CR expressed as V̇O2, and 
V̇O2 at LT should be scaled with Mb raised to the power of 
0.75 (ml kg−0.75 min−1). Both stroke volume and anaerobic 
capacity (absolute volumes), as well as O2 pulse (volume 
per time unit divided by frequency), should be scaled with 
body mass raised to the power of 1.26
2.3.2 | Test day 2 (maximal accumulated 
oxygen deficit and V̇O2max verification)
A linear regression was established between V̇O2 and 
velocity, using at least three submaximal measurements 
from test day 1 and a Y- intercept of 5.0 ml kg−1 min−1 
(representing standing resting metabolism). MAS was 
defined as the velocity corresponding to a subjects' 
V̇O2max, according to his linear regression. Anaerobic 
capacity was measured as maximal accumulated oxygen 
deficit (MAOD) based on the simplified procedure nr. 3 
in Medbø et al.5
Test day 2 started with a 15- min warm- up at ~70% of 
HRmax, including 2 × 10 s at 120 ± 10% of MAS, which was 
the intensity for the upcoming supramaximal bout. The 
warm- up procedure was followed by 10 min of rest and 
a [la−]b measurement to ensure low [la−]b prior to the su-
pramaximal bout. Subjects received verbal instructions to 
run until absolute exhaustion, without revealing the target 
duration of 2– 3 min. If the target duration was missed by 
±15 s, the test was repeated on a separate day. Data from 
the supramaximal bout were used to calculate MAOD and 
verify V̇O2max from test day 1. Additionally, peak rate of in-
crease in V̇O2 was measured as the mean rate (ml kg−1 s−1) 
during the steepest 60- s period.
Total accumulated oxygen cost (in VO2) of the supra-
maximal bout was estimated as a theoretical value by ex-
trapolating the linear relationship between submaximal 
V̇O2 and velocity to the supramaximal intensity of the test, 
giving an estimated oxygen cost per unit of time equiva-
lent to 120 ± 10% of V̇O2max. The actual accumulated VO2 
during this bout was measured, and MAOD was then cal-
culated as:
However, since the relationship between V̇O2 and ve-
locity might be slightly curvilinear, total accumulated ox-
ygen cost was also calculated applying the velocity during 
the supramaximal bout (−7 km h−1) raised to the power of 
1.05, based on Equation 1 in Hill and Vingren:27
(1)
Estimatedtotaloxygencost − measuredaccumulatedVO2
(2)
O2 cost = O2 costat7kmh−1 + [a(velocity−7kmh−1)1.05]
HIIT 4 × 4 min 
(n = 10)
SIT 8 × 20 s 
(n = 12)
SIT 10 × 30 s 
(n = 9)
Pre
Pre
Pre
Age (year)
23 ± 2
23 ± 2
24 ± 4
Height (cm)
178 ± 5
180 ± 5
184 ± 6*
Body mass (kg)
75.2 ± 6.5
75.2 ± 11.0
81.0 ± 8.1
V̇O2max (ml kg−1 min−1)
62.1 ± 4.8
64.0 ± 6.1
63.1 ± 5.3
Note: Data are presented as mean ± SD. 4 × 4 min, 4 × 4 min running at ~95% of maximal aerobic speed 
(MAS) interspersed by 3 min active recovery; 8 × 20 s, 8 × 20 s exhaustive running at ~150% of MAS 
interspersed by 10 s passive recovery; 10 × 30 s, 10 × 30 maximal running (average of ~175% MAS) 
interspersed by 3.5 min active recovery; V̇O2, oxygen uptake. *Significantly different from 4 × 4 min at 
baseline (p ≤ 0.05).
TABLE 1 Subjects' descriptive data.
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HOV et al.
Stored oxygen bound to myoglobin and hemoglobin 
constitutes about 9% of the MAOD and was not corrected 
for in the calculation.5
2.3.3 | Test day 3 (long- distance and sprint 
running performance)
Performance tests were conducted on a banked 200- m 
indoor track and field. 10 min of individual warm- up, in-
cluding 2– 4 short sprints, preceded a sprint running test 
of 300 m. After the sprint test, subjects rested for 30 min 
before the long- distance running test of 3000 m, of which 
the last 10 min were dedicated to another warm- up. The 
sprint test was performed as an interval start with sub-
jects in random order while the long- distance test was 
performed as mass start with up to 10 participants. Time 
was measured manually using a stopwatch and rounded 
to the nearest tenth of a second for the sprint test and to 
the nearest second for the long- distance test. The subjects 
received verbal encouragement during both tests.
2.3.4 | Test day 4 (hematological parameters)
Fasting venous blood samples were drawn from the ante-
cubital area. Bicarbonate were analyzed using a Siemens 
Advia Chemistry XPT (Siemens Healthliners, Germany). 
Erythrocytes, hemoglobin, mean corpuscular volume, 
mean corpuscular hemoglobin, and hematocrit were an-
alyzed using a Sysmex XN (Sysmex Corporation, Kobe, 
Japan).
2.4 | Training interventions
Subjects were instructed to refrain from other high- 
intensity endurance training during the study. However, 
subjects were encouraged to continue as usual with other 
physical activities (e.g., soccer, handball, hiking). For all 
interventions, treadmills (Gymleco LTX200, Sweden) 
were set at ~3° inclination and the warm- up consisted of 
running at ~70% of HRmax for 10 min. Additionally, for the 
SIT groups, 2– 3 supramaximal bouts of 10– 15 s near the 
interval training intensity were included in the warm- up.
2.4.1 | HIIT 4 × 4 min
The HIIT group performed 4 intervals of 4 min duration 
at ~95% of MAS, aiming to elicit 90– 95% of HRmax within 
3 min of each interval.8 The intervals were separated by 
3 min of active recovery at an intensity corresponding to 
70% of HRmax, and finally 3 min of cool- down at the same 
intensity ended the sessions. Throughout the intervention 
period, treadmill velocity was regularly adjusted to reach 
the target HR within 3 min of every interval. Including 
warm- up and cool- down, the HIIT 4 × 4 min protocol 
lasted 38 min.
2.4.2 | SIT 8 × 20 s
Consisted of ~8 × 20- s intervals at ~150% of MAS sepa-
rated by 10  s of passive rest, aiming to exhaust the 
subject during the eighth or ninth interval. If a ninth in-
terval was completed, the velocity was increased in the 
following training session. Every subject had one- to- one 
follow- up and received verbal encouragement during 
all intervals, ensuring that absolute exhaustion was at-
tained. Including the warm- up and a 10- min cool- down 
at an intensity corresponding to 70% of HRmax, the SIT 
8 × 20 s protocol lasted ~25 min. Originally, this proto-
col was reported to be carried out at ~170% of MAS.16 
However, a pilot study in our laboratory revealed that 
subjects were exhausted before the seventh interval at 
this intensity and had to jump off the treadmill during 
the fourth to sixth interval before the allotted time of 20 s 
had passed. Therefore, an intensity of ~150% of MAS was 
chosen for the first training session. Thereafter, perfor-
mance during the previous training session determined 
the intensity.
2.4.3 | SIT 10 × 30 s
The protocol was carried out in accordance with 
Skovgaard et al.,15 consisting of 10 × 30 s running inter-
vals of maximal effort separated by active rest periods of 
3.5 min at <70% of HRmax. The starting workload during 
the first session was calculated to represent each sub-
jects' average workload from their 300- m performance. 
The intensity within a training session was, when nec-
essary to endure 30 s, gradually reduced from interval 
to interval since the fatiguing intensity of a 30- s maxi-
mal sprint cannot be maintained for 10 consecutive 
bouts. The average interval intensity during a training 
session was ~175% of MAS. During all intervals, every 
subject had one- to- one follow- up and received verbal 
encouragement, ensuring that the intensity was maxi-
mal during every single interval. 3 min of cool down, 
at an intensity corresponding to ≤70% of HRmax, were 
added at the end of each session, giving a total duration 
of 49 min.
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HOV et al.
2.5 | Statistical analysis
All statistical analyses were conducted using IBM SPSS 
Statistics 27 software (IBM Corp., USA). Figures were 
created using GraphPad Prism 9.0 (GraphPad Software, 
USA). In all cases, p ≤ 0.05 were used as the level of sig-
nificance. V̇O2max and MAOD data were tested for nor-
mality using QQ- plots and the Shapiro– Wilk test, and the 
assumptions of normal distribution were met. Two- way 
ANOVAs were used to investigate differences between 
groups, and Tukey's WSD post hoc analysis was used 
when appropriate. Differences within groups were ana-
lyzed using paired samples t- tests. Results are presented 
as mean ± SD in tables and mean ± SE in figures.
3 | RESULTS
3.1 | Withdrawal and compliance to 
training
Of the 48 subjects randomized to the three training 
groups, nine withdrew before the interventions started 
(Figure  1). During the training period, two subjects 
dropped out due to injuries not related to the study, 
four subjects withdrew without giving any reason, and 
two subjects dropped out because they were not able to 
commit to the SIT 10 × 30 s protocol (Figure 1). Of the 
24 training sessions planned, the compliance was 23 ± 1 
(98 ± 3%) for HIIT 4 × 4 min, 23 ± 1 (95 ± 6%) for SIT 
8 × 20 s, and 21 ± 2 (89 ± 7%) for SIT 10 × 30 s, respectively. 
All participants included in the analysis completed the 
intervention in accordance with their respective protocol 
and accomplished at least 20 of the 24 sessions (>83%). 
In the SIT 8 × 20 s group, subjects on average conducted 
7.7 ± 0.4 intervals per training session. Examples of typi-
cal HR and V̇O2 responses during the three exercise in-
terventions are shown in Figure 2.
3.2 | Maximal oxygen uptake and 
oxygen pulse
HIIT 4 × 4 min and SIT 8 × 20 s exhibited within- group 
increases (p < 0.01) in V̇O2max and maximal O2 pulse, 
while SIT 10 × 30 s did not (Figure  3; Table  2). The in-
creases in V̇O2max (ml kg−0.75 min−1 and ml kg−1 min−1) 
and maximal O2 pulse (ml kg−1  beat−1) were larger in 
HIIT 4 × 4 min compared with both SIT groups (p < 0.05, 
Figure  3; Table  2). There was no difference between 
V̇O2max from test day 1 and V̇O2peak from test day 2 in any 
of the groups.
3.3 | Maximal accumulated 
oxygen deficit
The calculation of MAOD is illustrated in Figure 4. SIT 
8 × 20 s exhibited a 11.6 ± 15.6% within- group increase 
(p < 0.05) from pre-  to posttest in MAOD (ml kg−1) while 
no such increase was observed for HIIT 4 × 4 min or SIT 
10 × 30 s (Table  3). This was also apparent as a larger 
(p < 0.05) increase in MAOD in SIT 8 × 20 s compared with 
HIIT 4 × 4 min (Table 3).
3.4 | Long- distance and sprint running 
performance
HIIT 4 × 4 min, SIT 8 × 20 s, and SIT 10 × 30 s improved 
3000- m time trial by 5.9 ± 3.2%, 4.1 ± 3.7% and 2.2 ± 2.2%, 
respectively (p < 0.05, Figure 3; Table 2), and the increase 
following HIIT 4 × 4 min was larger (p < 0.05) than SIT 
10 × 30 s. SIT 8 × 20 s and SIT 10 × 30 s exhibited within- 
group improvements (p < 0.01) in the 300- m time trial by 
4.4 ± 2.0% and 3.3 ± 2.8%, respectively, while no such im-
provement was seen following HIIT 4 × 4 min (Figure 3; 
Table  2). No between- groups differences were observed 
for the performance on 300- m (Figure 3; Table 2).
3.5 | Hematological variables
HIIT 4 × 4 min increased (p < 0.01) bicarbonate concen-
tration by 6.9 ± 4.0%. The bicarbonate concentration 
increased more (p < 0.01) following HIIT 4 × 4 min com-
pared with SIT 8 × 20 s and SIT 10 × 30 s (Table 4).
3.6 | Noteworthy correlations
Post training, V̇O2max, MAS, and velocity at LT were as-
sociated with (p < 0.001) long- distance (3000- m) running 
performance (V̇O2max (ml kg−1 min−1): r = −0.80; V̇O2max 
(ml kg−0.75  min−1): r  =  −0.74; MAS: r  =  −0.82; velocity 
at LT: r  =  −0.87). Sprint running performance (300- m) 
post training was associated with V̇O2max measured as 
ml kg−1 min−1 (r = −0.43, p < 0.05) and ml kg−0.75 min−1 
(r = −0.49, p < 0.01), MAS (r = −0.41, p < 0.05), velocity 
at LT (r = −0.42, p < 0.05), MAOD measured as ml kg−1 
(r  =  −0.53, p < 0.01), and long- distance running perfor-
mance (r = 0.56, p < 0.001). The change in 3000- m perfor-
mance from pre- to posttest were associated with change in 
MAS (r = −0.45, p = 0.012) and velocity at LT (r = −0.46, 
p = 0.009). No other parameters were associated with the 
changes in long- distance or sprint running performance.
152 |   
HOV et al.
4 | DISCUSSION
V̇O2max is a crucial indicator for endurance performance, 
and it may be effectively improved through high- intensity 
interval training. It is, however, elusive which interval 
training format that yields an optimal outcome. Therefore, 
we sought to compare the effects of three popular and well- 
documented protocols, one with high (HIIT) and two with 
very high (SIT) intensity, on V̇O2max. We also sought to in-
vestigate the protocols' effect on anaerobic capacity as well 
as long- distance and sprint endurance performance. Our 
main findings were that HIIT 4 × 4 min increased V̇O2max 
more than the two SIT protocols, while SIT 8 × 20 s also 
improved V̇O2max more than SIT 10 × 30 s. Furthermore, 
HIIT 4 × 4 min enhanced long- distance endurance per-
formance more than SIT 10 × 30 s, while SIT 8 × 20 s in-
creased anaerobic capacity more than HIIT 4 × 4 min. Our 
findings imply that HIIT should be the interval format of 
choice if the objective is to improve V̇O2max and aerobic 
endurance performance.
4.1 | HIIT, SIT, and V̇O2max 
improvements
The present study shows that HIIT 4 × 4 min is more effec-
tive than SIT with short (8 × 20 s) and long (10 × 30 s) recov-
ery periods for improving V̇O2max, of which the first finding 
is novel and the second is in line with Laursen et al.28 The 
improvement in V̇O2max following HIIT 4 × 4 min in the 
current study was ~0.3% per training session, and this is 
in accordance with what has previously been documented 
for aerobically trained men.8 As expected, the improve-
ment was somewhat smaller in comparison with what 
may be expected for less trained individuals.29 Although 
the increase was lower than HIIT 4 × 4 min, the SIT 8 × 20 s 
group exhibited an increase in V̇O2max, in accordance with 
previous studies of comparable subjects.16,18
In accordance with our hypothesis, aerobic intensity 
(i.e., accumulated time spent ≥90% V̇O2max), and not over-
all intensity (% of MAS), seems paramount for enhanc-
ing V̇O2max. Indeed, in line with previous research,30– 32 
FIGURE 2 
Representative examples 
of the three exercise interventions. Dotted 
line (-  - - ) represents heart rate whereas 
solid line (– ) represents oxygen uptake. 
Notice how the heart rate typically 
relates to oxygen uptake during the three 
interval formats. Gray area represents 
≥90% of maximum. (A) HIIT 4 × 4 min 
running at ~95% of maximal aerobic 
speed (MAS) interspersed by 3 min active 
recovery. (B) SIT 8 × 20 s exhaustive 
running at ~150% of MAS interspersed 
by 10 s passive recovery. (C) SIT 10 × 30 s 
maximal running (average of ~175% 
MAS) interspersed by 3.5 min active 
recovery. During these training sessions, 
accumulated time ≥90% of V̇O2max was 
7 min (A), 1.5 min (B), and 0 min (C).
   | 153
HOV et al.
Figure 2 illustrates this point as HIIT 4 × 4 min results in 
several minutes at a high aerobic intensity. In comparison, 
despite a high HR, only about 1– 2 min appears to be per-
formed at this aerobic intensity during a SIT 8 × 20 s ses-
sion and no time at all during SIT 10 × 30 s. Therefore, even 
though V̇O2max may be elicited by a SIT 8 × 20 s training ses-
sion,17 the oxygen transporting system is not highly taxed 
for a long period during this intervention. Interestingly, it 
can also be seen in Figure 2 that the short recovery periods 
following SIT 8 × 20 s prevented a drop in V̇O2 and HR, and 
thus appearing, physiologically, as a single interval.
It is also noteworthy that during SIT with longer recov-
ery periods, such as 10 × 30 s, the decrease in V̇O2 during 
recovery is so large that the interval length is not sufficient 
to reach a high aerobic intensity in the following interval, 
likely because of the relatively slow V̇O2 kinetics (Table 3). 
In accordance with this notion, no change in V̇O2max was 
observed following the SIT 10 × 30 s intervention, and it 
was different from both the other training groups. This 
finding is in line with most previous studies investigating 
similar SIT interventions conducted on endurance trained 
runners (55– 63 ml kg−1  min−1),19,20 but in contrast to 
Skovgaard et al.15 Despite that 30- s SIT with long recovery 
periods may effectively increase V̇O2max in unfit popula-
tions,33 this protocol appears to be an inadequate stimulus 
to improve V̇O2max for males with a baseline V̇O2max ex-
ceeding 55 ml kg−1 min−1.
Exercise at ~95% of MAS can be maintained for sev-
eral minutes, while an intensity ≥150% of MAS necessi-
tates very short intervals because fatigue occurs rapidly. 
This limits the capability of SIT protocols to accumulate as 
large volumes as HIIT protocols are designed to achieve, 
and any attempt to match for total work between such 
protocols would be futile. Essentially, one cannot com-
bine a very high work output (≥150% of MAS) with a vol-
ume associated with less intense exercise (e.g., ≥ 10 min). 
However, it should be noted that the total work during 
the SIT protocols (excluding warm- up, breaks, and cool- 
down) were 29% (8 × 20 s) and 63% (10 × 30 s) of the total 
work during HIIT 4 × 4 min.
The superior improvement in V̇O2max following HIIT 
4 × 4 min in the current study was likely due to a greater 
overload on oxygen transporting organs from air to mi-
tochondria. Although no single factor limits V̇O2max, 
improvements following HIIT 4 × 4 min have previously 
been largely attributed to increases in heart stroke vol-
ume.8,34 Indeed, in support of this, indicating an im-
proved heart stroke volume, HIIT 4 × 4 min increased 
maximal O2 pulse (ml kg−1 beat−1) (8%) and decreased 
submaximal HR (9%) at 7 km h−1 more than both SIT 
protocols in the present study. Albeit, an increased 
arterio- venous oxygen difference cannot be excluded 
as a contributing component. However, following pre-
vious HIIT 4 × 4 min interventions with healthy young 
FIGURE 3 
Percentage change in 
V̇O2max (A), O2 pulse (B), 3000- meter 
running performance, (C) and 300- m 
running performance (D) from pre- to 
posttest. 4 × 4 min, 4 × 4 min running at 
~95% of maximal aerobic speed (MAS) 
interspersed by 3 min active recovery; 
8 × 20 s, 8 × 20 s exhaustive running 
at ~150% of MAS interspersed by 10 s 
passive recovery; 10 × 30 s, 10 × 30 s 
maximal running (average of ~175% MAS) 
interspersed by 3.5 min active recovery. 
Data presented as mean and standard 
error of the mean. Significant different 
change from pre- to posttest within 
group (*p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001), 
compared to 10 × 30 s (ap ≤ 0.05, 
aaap ≤ 0.001), compared to 8 × 20 s 
(bp ≤ 0.05, bbbp ≤ 0.001).
154 |   
HOV et al.
TABLE 2 Data from pre- and posttests of V̇O2max, running economy, lactate threshold and running performance.
HIIT 4 × 4 min (n = 10)
SIT 8 × 20 s (n = 12)
SIT 10 × 30 s (n = 9)
Pre
Post
Pre
Post
Pre
Post
V̇O2max
L min−1
4.66 ± 0.35
4.92 ± 0.30*** aa
4.76 ± 0.36
4.95 ± 0.49*** a
5.10 ± 0.47
5.13 ± 0.49
ml kg−1 min−1
62.1 ± 4.8
66.1 ± 5.0*** aaa,bbb
64.0 ± 6.1
66.0 ± 4.9***
63.1 ± 5.3
64.1 ± 5.5
ml kg−0.75 min−1
182.6 ± 12.8
194.0 ± 12.7*** aaa,b
187.4 ± 11.1
193.8 ± 8.9***
189.0 ± 13.9
191.4 ± 14.5
V̇E (L min−1)
151.7 ± 13.2
156.2 ± 10.8
150.7 ± 14.2
154.4 ± 17.4
153.2 ± 16.7
159.7 ± 15.7
RER
1.14 ± 0.06
1.14 ± 0.04
1.12 ± 0.05
1.14 ± 0.04
1.13 ± 0.04
1.11 ± 0.04
[La−]b (mM)
13.2 ± 1.6
13.1 ± 1.5
13.5 ± 1.8
13.7 ± 3.0
13.7 ± 1.9
13.3 ± 3.1
HRmax (beats min−1)
203 ± 5†
199 ± 6**
195 ± 7
194 ± 7
197 ± 11
195 ± 8
Maximal O2 Pulse
ml beat−1
23.0 ± 1.9
24.7 ± 1.6*** a
24.4 ± 2.2
25.6 ± 3.0**
25.9 ± 2.9§
26.3 ± 2.7
ml kg−1 beat−1
0.307 ± 0.025
0.332 ± 0.026*** a,b
0.328 ± 0.031
0.340 ± 0.023**
0.321 ± 0.030
0.328 ± 0.027
MAS (km h−1)
13.2 ± 1.6
14.7 ± 1.6*** aa,b
13.3 ± 1.4
13.9 ± 1.1**
13.5 ± 1.6
13.8 ± 1.9
Running Economy
L min−1
2.63 ± 0.34
2.52 ± 0.28*
2.69 ± 0.41
2.67 ± 0.42
2.87 ± 0.37
2.74 ± 0.43
ml kg−1 min−1
34.9 ± 2.7
33.8 ± 2.0
35.8 ± 1.8
35.4 ± 2.5
35.4 ± 1.5
34.0 ± 2.9
ml kg−0.75 min−1
102.7 ± 8.6
99.3 ± 6.4
105.3 ± 6.4
104.2 ± 7.8
106.1 ± 6.4
101.8 ± 10.0
HR (beats min−1)
149 ± 17
135 ± 15*** aa,bb
140 ± 10
140 ± 12
143 ± 12
144 ± 10
[La−]b (mM)
1.7 ± 0.6
1.4 ± 0.4
2.0 ± 0.7
1.8 ± 0.6
1.8 ± 0.7
1.5 ± 0.6
Lactate Threshold
L min−1
3.40 ± 0.31
3.56 ± 0.34
3.60 ± 0.32
3.69 ± 0.39
3.87 ± 0.54§
3.86 ± 0.42
ml kg−1 min−1
45.4 ± 3.9
47.8 ± 4.7*
48.5 ± 4.5
49.2 ± 4.0
47.7 ± 4.5
48.1 ± 3.0
ml kg−0.75 min−1
133.6 ± 10.7
140.5 ± 13.0*
142.2 ± 8.8
144.4 ± 8.0
143.1 ± 14.1
143.8 ± 8.7
% V̇O2max
73 ± 5
73 ± 5
76 ± 3
75 ± 3
76 ± 5
75 ± 3
HR (beats min−1)
177 ± 8
170 ± 10* aa,b
172 ± 7
171 ± 7
173 ± 11
175 ± 9
% HRmax
87 ± 3
86 ± 4
88 ± 3
88 ± 3
88 ± 2
90 ± 2
vLT (km h−1)
9.4 ± 1.4
10.2 ± 1.3**
9.7 ± 1.1
10.0 ± 0.9
9.6 ± 1.1
10.0 ± 1.0**
[La−]b (mM)
3.0 ± 0.5
2.8 ± 0.3a
3.3 ± 0.5
3.5 ± 0.7
2.9 ± 0.4
3.2 ± 0.4
Time Trial
300- m (s)
46 ± 3
45 ± 3
45 ± 2
43 ± 2**
45 ± 5
43 ± 5**
3000- m (s)
709 ± 58
668 ± 62*** a
714 ± 75
684 ± 60**
711 ± 66
695 ± 63*
Body mass (kg)
75.2 ± 6.5
74.8 ± 6.1
75.2 ± 11.0
75.7 ± 11.2
81.0 ± 8.1
80.4 ± 8.6
Note: Data are presented as mean ± SD. 4 × 4 min, 4 × 4 min running at ~95% of maximal aerobic speed (MAS) interspersed by 3 min active recovery; 8 × 20 s, 8 × 20 s exhaustive running at ~150% of MAS interspersed by 
10 s passive recovery; 10 × 30 s, 10 × 30 s maximal running (average of ~175% MAS) interspersed by 3.5 min active recovery; V̇O2max, maximal oxygen uptake; V̇E, pulmonary ventilation; RER, respiratory exchange ratio; 
[La−]b, blood lactate concentration; HR, heart rate; O2 pulse, oxygen pulse; MAS, maximal aerobic speed; vLT, velocity at lactate threshold. Significant different change from pre-  to posttest; within group (*p ≤ 0.05, 
**p ≤ 0.01, ***p ≤ 0.001), compared to 10 × 30 s (ap ≤ .05, aap ≤ 0.01, aaap ≤ 0.001), compared to 8 × 20 s (bp ≤ 0.05, bbp ≤ 0.01, bbbp ≤ 0.001). Significantly different at baseline compared to; 4 × 4 min (§p ≤ 0.05), 8 × 20 s (†p ≤ 0.05).
   | 155
HOV et al.
men (V̇O2max ≥ 50 ml kg−1  min−1), the arterio- venous 
oxygen difference has been documented to remain 
unchanged.8,34
4.2 | Running economy and 
lactate threshold
Aside V̇O2max, CR and LT are two other important fac-
tors determining aerobic endurance performance. In the 
present study, CR was improved by 4% (L min−1) follow-
ing HIIT 4 × 4 min while no change was observed follow-
ing the SIT protocols. Lack of adaptations in CR may be 
explained by the subjects being relatively accustomed to 
treadmill running at baseline combined with the low vol-
ume of training, especially following the shorter SIT pro-
tocols. However, contrary to the present study, enhanced 
CR following SIT with long recovery periods have previ-
ously been demonstrated in aerobically trained males.19,20 
This discrepancy with previous studies may be attributed 
to methodological differences, that is, the velocity during 
the CR- test.
LT as a percentage of V̇O2max was not altered in any of 
the groups, a finding in line with other studies including 
above averagely trained subjects.8,35 Therefore, the pres-
ent investigation is in agreement with existing literature 
and the suggestion by Sjodin and Svedenhag,36 that im-
provements in LT as a percentage of V̇O2max do not occur 
in already aerobically trained subjects. This implies, be-
cause LT as a percentage of V̇O2max remains unaltered, 
that increased V̇O2 and velocity at LT is expected when 
V̇O2max increase.
4.3 | HIIT, SIT, and anaerobic capacity
In the current study, anaerobic capacity, measured as 
MAOD, increased more after SIT 8 × 20 s compared with 
HIIT 4 × 4 min, and no changes were observed following 
HIIT 4 × 4 min or SIT 10 × 30 s. As HIIT 4 × 4 min is de-
signed to enable a high aerobic intensity with minimal 
anaerobic contribution, it is unsurprising that MAOD re-
mained unchanged following training with this interval 
format.
SIT protocols are, in contrast to the HIIT 4 × 4 min 
format, typically designed to also overload the anaerobic 
energy system. Thus, the improved MAOD following SIT 
8 × 20 s in the present study was expected and in line with 
previous studies.16,18 However, the finding that SIT 10 × 30 s 
did not increase MAOD was against our hypothesis. This 
finding is novel as, to the best of our knowledge, no other 
studies have investigated how a SIT intervention with 
maximal effort and long recovery breaks (≥3 min break) 
affects MAOD. Albeit, it has been reported improved an-
aerobic performance following similar protocols.19,37 The 
explanation for the two SIT protocols’ different effect on 
MAOD in the current study is likely the different length 
of the recovery periods separating the supramaximal in-
tervals. Although more energy is released from anaerobic 
sources during SIT 10 × 30 s compared with SIT 8 × 20 s, 
both in absolute terms and relative to the accumulated 
time of intervals, the anaerobic capacity was likely more 
challenged during the latter. Indeed, previous literature 
has demonstrated that MAOD is regularly reached during 
SIT 8 × 20 s, but not during SIT 4 × 30 s separated by 2 min 
recovery.17 Our study suggests that the percentage of 
MAOD attained during exercise is a better estimate for 
a protocols' potential to improve MAOD rather than the 
total quantity of anaerobic energy released. Interestingly, 
this has striking similarity to the established principle for 
aerobic training; that aerobic intensity (% of V̇O2max) is 
more important than volume (accumulated VO2) for im-
proving V̇O2max.8,9
4.4 | HIIT, SIT, and long- distance 
endurance performance
All three training groups in the current study improved 
long- distance endurance performance. Recognizing the 
greater aerobic energy contribution (90– 95%) to an event 
lasting 11– 12 min,7 it was not surprising that HIIT 4 × 4 min 
FIGURE 4 Illustration of the calculation of maximal 
accumulated oxygen deficit (MAOD) for a subject, with a V̇O2max 
of 65.5 ml kg−1 min−1. The subject ran at 118% of maximal aerobic 
speed (16.0 km h−1 at 3° inclination) and with a theoretical O2 cost 
of 76.1 ml kg−1 min−1. During the time to exhaustion of 157 s, the 
total accumulated O2 cost (white and gray area combined) was 
calculated to equal 199.2 ml kg−1. The accumulated VO2 (gray area) 
during the 157 s was 116.2 ml kg−1, giving a MAOD (white area) of 
83.0 ml kg−1.
156 |   
HOV et al.
was superior to SIT 10 × 30 s, and exhibited a clear tendency 
to be better than SIT 8 × 20 s, for improving the long- 
distance endurance performance (Figure 3C). Supported 
by the strong correlation between V̇O2max and 3000- meter 
running performance in the present study (r  =  −0.74), 
despite our sample's relatively homogenous V̇O2max, it is 
likely that the enhanced time trial improvement following 
HIIT 4 × 4 min was mainly a consequence of the increased 
V̇O2max. However, this cannot be concluded considering 
that the change in V̇O2max only exhibited a tendency for 
a correlation with the change in 3000- m performance 
(r  =  −0.32, p  =  0.08). For SIT 8 × 20 s, the enhanced 
performance may be explained by changes in both V̇O2max 
and MAOD. To our knowledge, the latter finding is the 
first to show how this SIT format affects long- distance 
time trial performance.
Although a smaller improvement than HIIT 4 × 4 min 
and SIT 8 × 20 s, the contributing factors to improved 
long- distance endurance performance following SIT 
10 × 30 s are elusive, since neither V̇O2max, CR, LT nor 
anaerobic capacity improved in this group. However, 
the SIT 10 × 30 s group did improve the rate of increase 
in V̇O2 during the supramaximal posttest (Table  3). 
This adaptation should enable a slightly increased ve-
locity during the 3000- m time- trial without attaining a 
larger oxygen debt or [la−]b and may thus explain the 
result. It has been shown that CR deteriorates when 
[la−]b is elevated,38 and a faster rate of increase in V̇O2 
TABLE 3 Data from pre- and posttests of maximal accumulated oxygen deficit.
HIIT 4 × 4 min (n = 10)
SIT 8 × 20 s (n = 12)
SIT 10 × 30 s (n = 9)
Pre
Post
Pre
Post
Pre
Post
MAOD
L
6.10 ± 0.59
6.11 ± 0.65
6.26 ± 1.41
7.02 ± 1.67** c
7.07 ± 1.95
6.70 ± 1.42
ml kg−1
83.6 ± 8.2
81.8 ± 6.0
83.2 ± 11.9
92.7 ± 16.8* c
88.0 ± 18.0
83.1 ± 12.9
L (curvilinear)
6.91 ± 0.68
6.89 ± 0.69
6.83 ± 1.28
7.78 ± 1.56** c
8.07 ± 2.17
7.83 ± 1.46
ml kg−1 (curvilinear)
93.5 ± 8.9
92.1 ± 3.7
91.3 ± 12.4
103.3 ± 17.8* c
98.9 ± 20.3
97.0 ± 17.0
Velocity % MAS
121 ± 10
117 ± 5
120 ± 7
123 ± 8c
120 ± 8
126 ± 9* cc
Velocity (km h−1)
16.2 ± 1.3
17.3 ± 1.4***
16.1 ± 1.3
17.3 ± 1.3**
16.2 ± 1.4
17.4 ± 1.5***
Time (s)
162 ± 37
145 ± 18
153 ± 34
150 ± 21
164 ± 21
142 ± 12*
V̇O2 response
Rate (ml kg−1 s−1)
0.70 ± 0.07
0.77 ± 0.09* b
0.75 ± 0.10
0.77 ± 0.10
0.69 ± 0.09
0.79 ± 0.12** b
Sec 90% V̇O2peak
95 ± 11
92 ± 8
92 ± 12
88 ± 9
96 ± 11
85 ± 10*
Sec pre- 90% V̇O2peak
86 ± 8*
89 ± 12
83 ± 13** b
Note: Data are presented as mean ± SD. 4 × 4 min, 4 × 4 min running at ~95% of maximal aerobic speed (MAS) interspersed by 3 min active recovery; 8 × 20 s, 
8 × 20 s exhaustive running at ~150% of MAS interspersed by 10 s passive recovery; 10 × 30 s, 10 × 30 s maximal running (average of ~175% MAS) interspersed 
by 3.5 min active recovery; MAOD, maximal accumulated oxygen deficit; curvilinear, calculation based on a curvilinear relationship between velocity and 
oxygen uptake; V̇O2peak, peak oxygen uptake; MAS, maximal aerobic speed; Rate, maximum rate of increase in V̇O2 during 60 continuous seconds; Sec 90% 
V̇O2peak, seconds to reach 90% of V̇O2peak. Significant different change from pre-  to posttest; within group (*p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001), compared to 8 × 20 s 
(bp ≤ 0.05), compared to 4 × 4 min (cp ≤ 0.05, ccp ≤ 0.01).
TABLE 4 Hematological variables
HIIT 4 × 4 min (n = 10)
SIT 8 × 20 s (n = 12)
SIT 10 × 30 s (n = 9)
Pre
Post
Pre
Post
Pre
Post
Erythrocytes (1012 L−1)
5.06 ± 0.21
5.14 ± 0.32
5.09 ± 0.31
5.14 ± 0.29
5.25 ± 0.28
5.28 ± 0.32
Hemoglobin (g dl−1)
15.11 ± 0.29
15.20 ± 0.82
15.28 ± 0.48
15.18 ± 0.44
15.47 ± 0.78
15.48 ± 0.79
Hematocrit (%)
44.1 ± 1.7
44.7 ± 2.8
44.4 ± 1.8
45.1 ± 1.9
45.8 ± 1.8
46.2 ± 2.0
MCV (fL)
87 ± 2
87 ± 2
87 ± 3
88 ± 3
87 ± 3
87 ± 3
MCH (pg)
29.9 ± 1.4
29.6 ± 0.9
30.1 ± 1.1
29.6 ± 1.0*
29.5 ± 1.1
29.4 ± 0.9
Bicarbonate (mM)
26.71 ± 0.95
28.57 ± 1.72** aa,bb
28.00 ± 1.41
28.25 ± 1.16
28.56 ± 1.42§
27.78 ± 1.92
Note: Data are presented as mean ± SD. 4 × 4 min, 4 × 4 min running at ~95% of maximal aerobic speed (MAS) interspersed by 3 min active recovery; 8 × 20 s, 
8 × 20 s exhaustive running at ~150% of MAS interspersed by 10 s passive recovery; 10 × 30 s, 10 × 30 s maximal running (average of ~175% MAS) interspersed by 
3.5 min active recovery; MCV, mean corpuscular volume; MCH, mean corpuscular hemoglobin. Significant different change from pre-  to posttest; within group 
(*p ≤ 0.05, **p ≤ 0.01), compared to 10 × 30 s (aap ≤ 0.01), compared to 8 × 20 s (bbp ≤ 0.01). Significantly different from 4 × 4 at baseline §p ≤ 0.05.
   | 157
HOV et al.
may therefore enhance long- distance endurance perfor-
mance. Another possible explanation is the lack of fa-
miliarization before the time trials, probably affecting 
tactical and technical aspects.
4.5 | HIIT, SIT, and 300- m sprint 
endurance performance
No differences between groups were observed for sprint 
endurance performance. Albeit, both SIT- groups exhib-
ited within- group improvements. The improved 300- m 
running performance following SIT 10 × 30 s is in close 
agreement to previous research demonstrating anaerobic 
performance improvements in the range of 5– 7% follow-
ing comparable protocols.19,37 Furthermore, we are not 
aware of previous research investigating the effects of SIT 
8 × 20 s or HIIT 4 × 4 min on 300- m running performance. 
However, mean power during a Wingate test increase fol-
lowing SIT 8 × 20 s.39 Therefore, although obvious differ-
ences exist between 300- m running and a Wingate test, 
the enhanced sprint endurance performance after SIT 
8 × 20 s may be in line with previous research.
4.6 | HIIT, SIT, and 
hematological variables
Bicarbonate concentration, an indicator of buffer capac-
ity, increased following HIIT 4 × 4 min compared with 
both SIT protocols, suggesting a superior buffer capac-
ity following HIIT. However, this finding contrasts with 
previous work,40 and whether bicarbonate concentration 
regularly increase with HIIT remains to be elucidated. 
Since neither hematocrit nor the concentration of eryth-
rocytes and hemoglobin did change in any of the groups, 
the increases in V̇O2max cannot be explained by improved 
oxygen carrying capacity of the blood, in accordance with 
previous research on well- trained males.8
4.7 | Perspective
The present study may guide the public, coaches, and 
athletes towards selecting the most suitable interval for-
mat for aerobically well- trained men, depending on the 
purpose of prescribing exercise. If the objective is to im-
prove V̇O2max, a pivotal parameter for aerobic endurance 
performance, HIIT protocols such as 4 × 4 min should be 
recommended. SIT with short recovery breaks, for exam-
ple, 8 × 20 s, may be a supplement for enhancing the an-
aerobic fraction of such events. Anaerobic capacity, and 
likely sprint endurance performance, are better enhanced 
applying SIT 8 × 20 s.
A noteworthy difference between HIIT 4 × 4 min and the 
SIT formats is that the former is not performed with a maxi-
mal effort while the latter are. Individuals reach absolute ex-
haustion during the SIT protocols, either at the end of each 
interval (SIT 10 × 30 s) or at the end of the last interval (SIT 
8 × 20 s). Anecdotally, we experienced several non- severe ad-
verse effects during the SIT interventions, such as nausea, 
vomiting, and dizziness. Therefore, it should be questioned 
if the extremely intense and fatiguing nature of SIT is ap-
propriate in many populations, such as elderly and patients.
5 | CONCLUSION
In conclusion, HIIT 4 × 4 min is superior for increas-
ing V̇O2max compared with SIT protocols, carried out as 
8 × 20 s and 10 × 30 s. Despite a lower overall intensity dur-
ing HIIT 4 × 4 min than SIT, the aerobic intensity is higher 
during the former. HIIT should be the recommended in-
terval format for aerobic performance.
ACKNOWLEDGEMENT
We thank the subjects for their time, effort, and coopera-
tion during this project. The authors declare no conflicts 
of interest. The results of this study are presented clearly, 
honestly, and without fabrication falsification, or inappro-
priate data manipulation. The study was funded by The 
Research Council of Norway.
FUNDING INFORMATION
The study was funded by The Research Council of Norway.
CONFLICT OF INTEREST
The authors declare no conflicts of interest.
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are avail-
able from the corresponding author upon reasonable 
request.
INFORMED CONSENT
Participants were informed with a written consent.
ORCID
Håkon Hov 
 https://orcid.org/0000-0003-2976-2079 
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How to cite this article: Hov H, Wang E, Lim YR, 
et al. Aerobic high-intensity intervals are superior 
to improve V̇O2max compared with sprint intervals 
in well-trained men. Scand J Med Sci Sports. 
2023;33:146-159. doi: 10.1111/sms.14251

Aerobic high-intensity intervals are superior to improve V̇O<sub>2max</sub> compared with sprint intervals in well-trained men.
Hov, Håkon,Wang, Eivind,Lim, Yi Rui,Trane, Glenn,Hemmingsen, Magnus,Hoff, Jan,Helgerud, Jan