Effect of High-Intensity Intermittent Hypoxic Training on 3-on-3 Female Basketball Player’s Performance

Abstract

Purpose
To investigate the effects of 4 weeks high-intensity interval training in hypoxia on aerobic and anaerobic performance of 3-on-3 basketball players.

Methods
In a randomised controlled trial, 15 female basketballers completed eight 1-h high-intensity training sessions in either normobaric hypoxia (hypoxic group n = 8, altitude 3052 m) or normoxia (normoxic group n = 7, sea-level).

Results
After training, the hypoxic group increased their 1-min all-out shuttle run distance by 2.5% ± 2.3% (mean ± 95% CI, d = 0.83, P = 0.04), compared to the normoxic group 0.2% ± 2.3% ( d = 0.06, P = 0.8), with the difference between groups being clinically worthwhile but not statistically significant ( d = 0.77, P = 0.1). Distance covered in the Yo-Yo intermittent recovery test tended to increase in the hypoxic (32.5% ± 39.3%, d = 1.0, P = 0.1) but not normoxic group (0.3% ± 24.5%, d = 0.08, P = 0.9), with a non-significant change between groups ( d = 0.9, P = 0.2). Compared to normoxia, the hypoxic group significantly increased subjective markers of stress ( d = 0.53, P = 0.005), fatigue ( d = 0.43, P = 0.005), and muscle soreness ( d = 0.46, P = 0.01), which resulted in a lower perceived training performance in the hypoxic compared to the normoxic group ( d = 0.68, P = 0.001).

Conclusion
High-intensity interval training under hypoxic conditions likely improved 1-min all-out shuttle run ability in female basketball 3-on-3 players but also increased subjective markers of stress and fatigue which must be taken into consideration when prescribing such training.

Full text

Vol.:(0123456789)
1 3
Journal of Science in Sport and Exercise
https://doi.org/10.1007/s42978-022-00163-3
ORIGINAL ARTICLE
Effect ofHigh‑Intensity Intermittent Hypoxic Training on3‑on‑3
Female Basketball Player’s Performance
H.K.Smith1· M.J.Hamlin1,2 · C.A.Elliot1
Received: 24 November 2021 / Accepted: 6 March 2022
© The Author(s) 2022
Abstract
Purpose To investigate the effects of 4weeks high-intensity interval training in hypoxia on aerobic and anaerobic perfor-
mance of 3-on-3 basketball players.
Methods In a randomised controlled trial, 15 female basketballers completed eight 1-h high-intensity training sessions in
either normobaric hypoxia (hypoxic group n = 8, altitude 3052m) or normoxia (normoxic group n = 7, sea-level).
Results After training, the hypoxic group increased their 1-min all-out shuttle run distance by 2.5% ± 2.3% (mean ± 95%
CI, d = 0.83, P = 0.04), compared to the normoxic group 0.2% ± 2.3% (d = 0.06, P = 0.8), with the difference between groups
being clinically worthwhile but not statistically significant (d = 0.77, P = 0.1). Distance covered in the Yo-Yo intermittent
recovery test tended to increase in the hypoxic (32.5% ± 39.3%, d = 1.0, P = 0.1) but not normoxic group (0.3% ± 24.5%,
d = 0.08, P = 0.9), with a non-significant change between groups (d = 0.9, P = 0.2). Compared to normoxia, the hypoxic group
significantly increased subjective markers of stress (d = 0.53, P = 0.005), fatigue (d = 0.43, P = 0.005), and muscle soreness
(d = 0.46, P = 0.01), which resulted in a lower perceived training performance in the hypoxic compared to the normoxic
group (d = 0.68, P = 0.001).
Conclusion High-intensity interval training under hypoxic conditions likely improved 1-min all-out shuttle run ability in
female basketball 3-on-3 players but also increased subjective markers of stress and fatigue which must be taken into con-
sideration when prescribing such training.
Keywords 1-min all-out shuttle run· Anaerobic performance· Aerobic performance· Altitude training
Introduction
Over the past twodecades, due to increased interest in
team sport performance where any small improvement may
enhance the chances of winning, the use of training tech-
niques such as altitude training has increased [11, 12, 14,
19]. Modern technology enables the use of hypoxic expo-
sure without the cost and distraction of having to travel to
altitude, making this type of training available to many sport
teams. A popular type of living low-training high altitude
training is interval hypoxic training where athletes receive
relatively short episodes of hypoxic exposure (< 2h) while
completing training intervals at high-intensity interspersed
with similar or shorter duration recovery periods [29].
Adding the stress of systemic hypoxia during aerobic or
anaerobic interval training is thought to potentiate greater
performance improvements compared to similar training at
sea level. However, the effectiveness of altitude training,
including intermittent hypoxic training (IHT) in males is
contentious [27]. Moreover, such research into the effects of
IHT in females is almost non-existent, even though previous
research indicated male and female athletes benefit equally
from traditional altitude training [38].
Adding hypoxia to interval training has not always
resulted in improved performance at sea level. Faiss etal.
[11, 12] found that two repeated sprint training sessions per
week for 4weeks had little effect on overall power output
during a repeat sprint cycling test. Nevertheless, such train-
ing increased the number of all-out 10s cycling sprints able
to be completed prior to exhaustion in the hypoxic compared
* M. J. Hamlin
mike.hamlin@lincoln.ac.nz
1 Department ofTourism, Sport andSociety, Lincoln
University, Christchurch, NewZealand
2 Faculty ofHealth andEnvironmental Science, Sports
Performance Research Institute New Zealand (SPRINZ),
Auckland University ofTechnology, Auckland, NewZealand

Journal of Science in Sport and Exercise
1 3
to the normoxic trained groups [11, 12]. Galvin etal. [13],
had rugby league players complete 12 sessions of repeated
sprint training over 4weeks in either hypoxia or normoxia
and showed a significantly greater improvement in Yo-Yo
intermittent recovery test level 1 performance in the hypoxic
(33% ± 12%) compared to the normoxic group (14% ± 10%),
but no differences were found in the repeated sprint ability
between groups [13]. In a more recent study, male rugby
union players completed repeated sprint training for 3weeks
in either normobaric hypoxia or normobaric normoxia [20].
Compared to baseline, both the hypoxic and normoxic play-
ers similarly lowered fatigue in a repeated sprint test 1week
after the intervention (− 1.8% ± 1.6%, − 1.5% ± 1.4%, mean
change ± 90% confidence interval in hypoxic and normoxic
groups, respectively), but fatigue continued to improve in the
hypoxic compared to the normoxic group over the follow-
ing 2–4weeks [20]. Similarly, James and Girard [25] found
significantly improved repeated treadmill sprint performance
after 8 repeated sprint training sessions in hypoxia in hockey
players [25].
Basketball is considered an intermittent high-intensity
sport that requires a high level of anaerobic metabolism
[37], however, because the game duration is 40min, players
also require a high level of aerobic fitness [15] and there-
fore deeming it a sport that interval hypoxic training may
be effective at improving performance determinants such as
improved glycolysis and buffering capacity. Compared to
traditional basketball, a relatively new modification of the
sport that was played for the first time at the Toyko Olympic
Games was 3-on-3 basketball (3 × 3), where only 3 players
are permitted on each team on a reduced size court at once.
The demands of 3 × 3 basketball are different in that it is
significantly more anaerobic than traditional 5 × 5 basketball
[9, 31, 32] given the shorter court and quicker transitions of
the ball between possessions.
Czuba found that 5 × 5 basketball athletes who
trained for 3weeks (2500m, 4–5 sets of 4min bouts at
90% VO2max running velocity in hypoxia) significantly
improved running distance by 9.7% and relative VO2max by
7.8% compared to normoxic controls completing the same
training (4.0% and 2.1% respectively) [10]. Given that
the non-specific training programme used in the Czuba
etal. [10] study was effective at improving aerobic perfor-
mance in basketball athletes, we hypothesize that a more
specific training programme that accounts for the work-
to-rest ratios of the higher paced 3 × 3 basketball game
may prove beneficial at improving anaerobic and possibly
aerobic performance, both of which are required in the
3 × 3 game. Indeed recently, Lapointe etal. [26] showed
that more sport-specific training on 5 × 5 basketball ath-
letes (repeated sets of 6s sprints with a 24s recovery)
under hypoxic conditions likely improved repeated sprint
ability compared to normoxic controls [26]. To date, very
little research on the effects of hypoxic training in female
athletes exists, and no research using IHT has been con-
ducted on female 3 × 3 basketball players where repeated
running ability, anaerobic power, and aerobic endurance
play a substantial role in game performance. Therefore,
the purpose of this study was to investigate if the addition
of hypoxia to 4weeks of high-intensity training improved
maximal aerobic performance, shuttle run performance
and muscular power in female 3 × 3 basketball players
compared to a normoxic condition.
Methods
Study Design
This research was a single-blind controlled trial conducted
during the player’s preparation-early competition phase of
training (September–October). Players were familiar with
the test protocols and given a familiarisation session on
all protocols and procedures two days before the baseline
testing. To aid in the blinding, all players were under the
impression that they would be receiving altitude training.
The players were asked to arrive at training and testing in
a fully rested and hydrated state and to refrain from alco-
hol for 24-h, and avoid eating a heavy meal or consuming
caffeine containing beverages or food for 4-h prior to all
testing. Players were also asked to record all of their train-
ing, performance and perceived subjective ratings of stress
and sleep on training days throughout the study.
Participants
Fifteen female representative basketball players from Can-
terbury, New Zealand participated in this study. Players
were non-professionals who had over 10years’ experi-
ence each in both regional and national level competitions.
Subjects were randomly divided into a hypoxic (n = 8) or
normoxic group (n = 7), by way of a random number gen-
erator in Microsoft Excel. The study was approved by the
Lincoln University Human Ethics Committee (reference
# 2019-57) with written informed consent gathered from
all participants prior to the start of the study. The study
was carried out in accordance with the ethical standards as
laid down in the 1964 Declaration of Helsinki and its later
amendments. All players were healthy, free from injury,
lived at sea level and had not resided at altitude within
the previous 6months. Players were asked to maintain
their usual basketball training sessions throughout the
study which consisted of 2 team trainings per week and to
maintain their normal diet.

Journal of Science in Sport and Exercise
1 3
Hypoxic andNormoxic Training
On 8 separate occasions over 4weeks (with at least 2days
rest between each occasion), subjects completed 60min of
high-intensity interval training on a variety of devices posi-
tioned inside an altitude room (Vertex Altitude, Christch-
urch, NZ). Players initially completed a 5min slow jog
(6–8km/h) as a specific treadmill warm-up inside the room,
then performed a series of dynamic movement warm-up
patterns which included the following areas: chest, side
abdomen, back, hip flexors, groin, quadriceps, hamstrings,
gluteal and calves for a further 5min. Following that, 6
sets of 6 repetitions of 6 exercises with 30s maximal exer-
tion and 30s of passive recovery between repetitions, were
completed on the following pieces of equipment; a rowing
ergometer (Concept 2, Model C, Concept 2 Inc., USA), a
motorised treadmill (Star Trac E-TRx, USA), battle ropes,
a ski ergometer (Concept 2, SkiErg PM5, Concept2 Inc.,
USA), an assault bike (Assault Air Bike Classic, LifeCORE,
USA) and finally another treadmill run (Star Trac E-TRx,
USA). We used the 30s-on and 30s-off protocol because it
aligns with the reported exercise work:rest periods of 3 × 3
players (for example, periods of 15–30s makes up about
45% of all measured intervals during play in a 3 × 3 game,
whereas bench time of a player is between 0 and 30s [31,
32]. The exercise modes used in this study are not entirely
sport specific but most have some cross-over with the bas-
ketball game in that they use similar muscle groups in a
similar movement pattern (apart from perhaps the rower and
assault bike). In addition, the varied exercise modes gave
some variety to the programme, helped to reduce monotony
in the athletes and reduced their on-feet training load which
was a concern with these players after a long 8-month 5 × 5
playing season. A 2-min active recovery (walking inside the
hypoxic room) was given between sets with a 5min walk
and 5min stretch for a cool-down given at the end of the
exercises inside the hypoxic room. All exercises were an all-
out effort and players were constantly encouraged to reach
maximal intensity during the exercises. The entire training
session was completed within the single room with players
breathing either normobaric hypoxia (altitude of 3052m)
or normobaric normoxia (0m or sea level) delivered via a
Pressure Swing Adsorption Hypoxicator (Vertex Altitude
Training, Christchurch).
Performance Testing
Prior to performance testing, player’s height was measured
to the nearest 0.1cm barefoot using a portable stadiometer
(Seca 213, Hamburg, Germany) and body mass to the near-
est 0.1kg (Tanita BWB-800, Tokyo, Japan). Before perfor-
mance testing, players completed a warm-up consisting of a
5min slow jog, followed by a series of standardised dynamic
movements utilising the lower and upper body.
Squat Jump
Explosive power (peak power) and velocity (peak velocity)
during a squat jump was determined using a wooden dowel
connected to a linear position transducer (LPT) (GymAware;
Kinetic Performance Technologies, Canberra, Australia) and
an iPad (Apple Inc., USA running GymAware App, Aus-
tralia) using previously reported protocols [39]. Players com-
pleted three jumps with at least 5min between efforts and
the best jump was used for analysis.
Countermovement Jump Test
After 5min rest a countermovement jump was determined
by using a contact mat (Smart Jump, Fusion Sport, Aus-
tralia) and an iPad (Apple Inc., USA running Fusion Sport
Smart Speed App, Australia). Players completed three jumps
with at least 2min rest between efforts and the best jump
was used for analysis.
Shuttle Run Test
After a 10min passive rest, the players undertook the 1-min
all-out shuttle run test, which consisted of completing as
many shuttle sprints as possible over a 17-m distance for
a timed period of 1min. The National Basketball Associa-
tion (NBA), Division 1, 2 and 3 college basketball teams in
the United States of America use a similar test called the
3min run (colloquially known as the ‘Boston Marathon’),
where players must sprint as fast as they can from baseline to
baseline (28m) as many times as they can within the 3min
period. However, as this test is used on 5 × 5 players and
court dimensions are comparatively different (i.e. 28m long
compared to 14m in 3 × 3), an abbreviated version of this
test was used. Players were instructed to sprint maximally
for every sprint and pacing was discouraged. From a stand-
ing stance, 0.4cm behind the starting line, when instructed
to start, player’s sprinted in-line for 17m, touched a line
on the floor with any part of the foot and then completed a
180° change of direction and sprinting back to the starting
line to also touch this line with any part of the foot. This
sprinting continued for 1min without any rest after which
time players were instructed to stop immediately and stand
in position. The total achieved distance(to the nearest 1.0m)
was recorded using marked cones. Observers were present
at both ends of the court ensuring players touched the line
with their foot and counted the number of laps completed.
The reproducibility of the test (measured as a coefficient
of variation between the baseline and post-test) was 1.8%.

Journal of Science in Sport and Exercise
1 3
Aerobic Test
Finally, after another passive rest of 15min players com-
pleted the Yo-Yo intermittent recovery test level 1 (YYIR1,
BangsboSport, Denmark), which was undertaken according
to previously-published protocols [1]. The YYIR1 finishing
shuttle number was converted to a distance and then used in
the analysis. At the end of each test, the players were asked
to rate their perceived exertion using the 6–20 Borg scale
[4]. All tests were completed indoors on a FIBA measured
wooden basketball court in normoxic conditions under simi-
lar climatic conditions (19.4 ± 0.4 °C). Players also wore
basketball court shoes.
Physiological Measures
At the end of each set during the training sessions, heart rate
(FT1; Polar, Kemple, Finland) and arterial oxygen saturation
(SpO2) (Sport-Stat; Nonin Medical, Minneapolis, Minne-
sota, USA) were recorded by the researchers while keeping
the data blind to the players. However due to missing data
and recording problems the heart rate data have not been
used in this study.
Subjective Measures
Due to time restrictions, our research group decided to
incorporate elements of established measures into our own
customised, brief, easy-to-use, self-report measure. For this
study, we asked a series of questions used successfully in a
number of other studies [17, 18, 20] which were modelled on
previous research [28] and based on a five-point Likert scale
to record athletes subjective ratings of stress, fatigue, sleep
quality, muscle soreness and training performance. Players
were asked to input their subjective training data after each
training. Furthermore, player’s RPE during training was
recorded at the end of each set and at the end of training
with the Borg scale (6–20) [4].
Statistical Analysis
Changes in the measurement variables from baseline to
post-training along with standard deviations representing
the between-and within-subject variability were estimated
using a mixed modelling procedure (Proc Mixed) in the
Statistical Analysis System (Version 9.3, SAS Institute,
Cary, NC, USA). For the performance data, we analyzed
the natural logarithm of each measure to reduce any effects
in non-uniformity of error and to obtain changes in measures
and errors as percentages [22] but analyzed the raw vari-
ables for non-performance data. The fixed effects were test
time (pre and post for performance data and training day for
non-performance data), group (hypoxic, normoxic) and their
interaction. The random effects were subject and residual
variance. Chances that the true effects were substantial were
estimated with a published spreadsheet [24], when a value
for the smallest worthwhile effect was entered. We used a
value of 1% for performance measures [34]. For non-perfor-
mance measures, we chose 0.20 standardised units (change
in the mean divided by the between-subject SD at baseline)
as the smallest worthwhile change [8]. To make decisions
about the true (population) values of the effect of training in
hypoxia we used both hypothesis testing (an alpha level of
P < 0.05 for significance was used) and clinical-based infer-
ences [2, 24] along with Cohen’s effect sizes where > 0.2 is
small, > 0.5 is moderate and > 0.8 is large. We used a spread-
sheet [23] to calculate the number of participants required
in the study with the smallest worthwhile change in per-
formance being 1.0% [34] and the typical error or within-
subject SD in similar tests of 0.7% [36]. Using a type I error
of 0.5% and a type II error of 25% the number of participants
in a pre-post parallel-groups controlled trail was calculated
to be 7 per group.
Results
Physical Performance
At baseline, the two groups were similar in all charac-
teristics apart from the 1-min all-out shuttle run and
body mass (Table1). For shuttle run ability, the nor-
moxic players were able to cover more distance at
baseline, compared to the hypoxic group (6.3 ± 5.8m,
mean ± 95% CI, P = 0.03). The normoxic players also had
a lower body mass compared to the hypoxic players at
Table 1 Physical and performance characteristics of the two training
groups at baseline
Data are mean ± SD
Squat PP Squat jump peak power, Squat PV Squat jump peak veloc-
ity, Shuttle run 1-min all out shuttle run, CMJ Countermovement
jump, YYIR1 YoYo Intermittent Recovery teat level 1
*Statistically significant difference (P < 0.05)
^ Clinically substantial difference between groups
Parameters Normoxic
(n = 7)
Hypoxic
(n = 8)
Age (year) 20.6 ± 2.0 20.8 ± 1.9
Height (cm) 174.4 ± 4.8 173.5 ± 6.8
Body mass (kg) 68.4 ± 4.1 74.2 ± 7.4^
Squat PP (W) 3411.3 ± 598.3 3561.9 ± 785.0
Squat PV (m/s) 2.6 ± 0.2 2.7 ± 0.2
CMJ (cm) 37.1 ± 5.3 35.1 ± 4.9
Shuttle run (m) 238.6 ± 1.0 232.3 ± 8.5*^
YYIR1 (m) 933.3 ± 228.6 868.6 ± 392.4

Journal of Science in Sport and Exercise
1 3
baseline (5.8 ± 6.3kg, P = 0.07). After 4weeks of train-
ing, the normoxic players showed a small non-significant
increase in their 1-min all-out shuttle run performance
of 0.2% ± 2.3% (Cohen’s d = 0.06, P = 0.88), however the
players that trained in hypoxia increased their 1-min all-
out shuttle run performance by 2.5% ± 2.3% (d = 0.83,
P = 0.04). The between-group difference in the 1-min
all-out shuttle run test (5.3m or approximately 2.3%) did
not meet statistical significance (P = 0.1) but exceeded
the smallest worthwhile clinical change with an effect
size of 0.77. The hypoxic players also showed an increase
in the distance covered in the YYIR1 after the training
intervention (32.5% ± 39.3%, d = 1.0) and while this
increase is greater than the smallest worthwhile clini-
cal effect, it was not statistically significant (P = 0.1)
(Table2). Performance change as a result of the 4-weeks
training varied considerably between individuals (Fig.1),
with larger increases indicated for the hypoxic compared
to the normoxic players in both the Yo-Yo IRT L1 and
1-min all-out shuttle run test. Player’s body mass and
jump performance showed non-significant and unclear
changes between training groups over the training period
(Table2).
Training Parameters
Oxygen saturation was consistently lower during each
training session in the hypoxic compared to the normoxic
group (Fig.2a), with the overall mean of the hypoxic group
(for all repetitions on all training days) significantly lower
(90.7% ± 3.6%) than the overall mean of the normoxic group
(95.4% ± 2.3%, P < 0.05). Player’s RPE taken immediately
after each repetition during training is shown in Fig.2b. The
hypoxic group’s RPE was significantly lower during the first
training day in sets 2, 4 and 6 compared to the normoxic
group. Although the RPE was also lower in the hypoxic
group in set 2 of the second training day, by the end of train-
ing day 2, both groups RPE was similar and continued that
trend for the remaining training sessions (Fig.2b).
Figure3 shows the subjective measures taken each
day from the players with significant differences between
groups on individual days indicated. We also analyzed the
pooled data from all days between groups and found that
the hypoxic group had significantly more overall stress
compared to the normoxic group over the training inter-
vention (mean overall stress level was 2.8 ± 0.9 for hypoxic
players and 2.3 ± 0.8 for controls, d = 0.53, P = 0.005).
Table 2 Body mass and performance changes in basketball players before (pre) and after (post) high-intensity training
Pre and post are mean ± SD of each group’s raw data with the difference within and between groups given as the log transformed mean % ± 95%
confidence interval along with the clinical inference for the between group change.
Squat PP Squat jump peak power, Squat PV Squat jump peak velocity, Shuttle run 1-min all out shuttle run test, CMJ Countermovement jump,
YYIR1 Yo-Yo intermittent recovery test level 1.
*Statistically significant (P < 0.05) change within groups
† Statistically significant change between groups
^ Clinically substantial change between groups
Parameters Normoxic Group Hypoxic group Between group
Pre-post % change
(± 95% Cl) and clinical
inference
Pre (n = 7) Post (n = 7) Normoxic
group
Pre–post %
change (± 95%
Cl)
Pre (n = 8) Post (n = 8) Hypoxic group
Pre–post %
change (± 95%
Cl)
Body mass (kg) 68.4 ± 4.1 68.7 ± 4.1 0.5% (8.9) 74.2 ± 7.4 73.9 ± 7.3 − 0.4% (8.5) − 0.9% (12.0)
Unclear
Squat PP (W) 3411.3 ± 598.3 3287.3 ± 472.1 − 3.4% (20.3) 3561.9 ± 785.0 3558.9 ± 530.0 − 0.0% (17.9) 3.3% (27.0)
Unclear
Squat PV (m/s) 2.6 ± 0.2 2.7 ± 0.2 3.2% (9.0) 2.6 ± 0.2 2.7 ± 0.2 2.0% (8.6) − 1.2% (12.6)
Unclear
CMJ (cm) 37.1 ± 5.3 36.3 ± 5.7 − 2.5% (14.7) 35.1 ± 4.9 35.1 ± 4.4 0.2% (9.2) 2.7% (20.6)
Unclear
Shuttle run (m) 238.6 ± 1.0 239.0 ± 2.2 0.2% (2.3) 232.3 ± 8.5 238.0 ± 5.7 2.5% (2.3)* 2.3% (3.5)^
Likely positive
YYIR1 (m) 933.3 ± 228.6 960.0 ± 326.9 0.3% (24.5) 868.6 ± 392.4 1188.6 ± 512.6 32.5% (39.3) 32.8% (59.4)
Unclear
YYIR1 RPE 17.5 ± 1.1 18.3 ± 1.2 4.6% (6.2) 18.3 ± 0.8 18.7 ± 0.8 2.3% (5.7) − 2.3% (8.5)
Unclear

Journal of Science in Sport and Exercise
1 3
The hypoxic players also had significantly more fatigue
(3.3 ± 0.8 and 2.9 ± 0.8, d = 0.43, P = 0.005, for the
hypoxic and normoxic groups respectively), more mus-
cle soreness (3.1 ± 0.9 hypoxic and 2.8 ± 0.8 normoxic,
d = 0.46, P = 0.01) and lower perceived training perfor-
mance (2.9 ± 0.9 hypoxic and 2.4 ± 0.7 normoxic, d = 0.68,
P = 0.001, note the reverse scale for this subjective meas-
ure). There was little difference in sleep (3.0 ± 0.8 con-
trol and 2.9 ± 0.8 hypoxic, P = 0.595) or session RPE
(18.2 ± 1.3 normoxic and 18.4 ± 1.3 hypoxic, P = 0.552)
between groups.
Discussion
The major findings from this study indicated that eight
sessions of high-intensity intermittent hypoxic training
likely improved 1-min all-out shuttle run ability conducted
Fig. 1 Individual player’s performance change as a result of training
in the normoxic and hypoxic groups. a and b are the Yo-Yo Intermit-
tent Recovery Level 1 test results while c and d are the shuttle run
ability test results. Continuous lines are individual data while dashed
lines are group means

Journal of Science in Sport and Exercise
1 3
under normoxic conditions in female 3 × 3 basketball play-
ers. However, the hypoxic training was significantly more
stressful than normoxic training with subjective markers of
stress, fatigue and muscle soreness elevated in the hypoxic
players. Finally, the effect of intermittent hypoxic training
on muscular power and aerobic fitness was unclear.
The likely improved 1-min shuttle run performance in
the hypoxic compared to the normoxic group found in this
research supports an emerging body of evidence indicating
that repeated-sprint or high-intensity intermittent hypoxic
training may be an effective training modality for team sport
athletes [6, 20]. However, not all researchers have found ben-
eficial effects when adding hypoxia to this type of training
[13, 16], which may be due to a number of factors including
a mismatch between the hypoxic training protocols used for
the research trial and the performance tests used to measure
change after the trial. Other factors including differences
in fitness levels between players, degree and frequency of
hypoxic exposure, differing post-training testing times and
subsequent performance testing procedures. For example,
Galvin etal. [13], asked rugby players to complete 12 ses-
sions of 10 × 6-s all out sprints with a 30-s recovery under
hypoxic conditions, but used a performance test that did not
match the protocol used. Data obtained from the Galvin etal.
[13] study showed that the average time to run 20m was ∼
3s. Therefore, to match the training program to the perfor-
mance test used, these athletes should have been running ∼
40m during performance testing and not 20m. Such details
are important, as during training, these athletes would have
been stressing and subsequently adapting to more aerobic
Fig. 2 Saturated arterial oxygen
(a) and rating of perceived
exertion (b) during training in
the two groups on the 8 training
days. *Significant difference
between groups

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Fig. 3 Levels of perceived stress (a), perceived muscle soreness (b),
perceived training performance (c), perceived fatigue (d), perceived
sleep quality (e), and whole of session rating of perceived exertion
(f) in the two groups on the 8 training days. *Significant difference
between groups. Filled circles are the normoxic group while open
diamonds are the hypoxic group

Journal of Science in Sport and Exercise
1 3
than anaerobic metabolic processes, yet during testing, these
athletes would have been relying more on their anaerobic
rather than aerobic metabolic systems. Unsurprisingly, these
authors reported substantial improvements in endurance
(aerobic) performance after training (∼15% improvement
in VO2max in the hypoxic compared to normoxic group),
which suggests the training was more conducive to endur-
ance performance than the anaerobic repetitive sprinting
performance adaptations for which they were testing. In
the current study we had participant’s complete 30s all-out
repetitions during training but we used a 60s all-out perfor-
mance shuttle run test. While there is a difference between
training and testing exercise durations which could result in
different aerobic and anaerobic energy demands, we were
confident that the 60s all-out effort in the shuttle run test
was short enough to elicit high levels of energy demand from
the anaerobic system [33], thereby giving us a reasonable
estimate of anaerobic energy production change.
The likely increased shuttle run ability in the hypoxic
compared to the normoxic group in this study along with
a less clear between-group change in the aerobic measure
(YYIR1) suggests improvement mainly in the anaerobic
rather than the aerobic metabolism involved with such train-
ing. It has been suggested that the work-to-rest ratios for
such training needs to be approximately 1:5 so that the gly-
colytic energy system does not “time-out” [3]. The longer
rest periods allow for recovery from strenuous work includ-
ing the restoration of intramuscular ATP levels, clearance of
lactic acid and return to equilibrium, permitting another very
high intensity work interval to be completed in a subsequent
repetitiom or set [3]. However, due to the intermittent nature
of the sport of 3 × 3 basketball where sprint bouts found
in real 3 × 3 basketball games are typically 30s work: 30s
rest [International Basketball Federation (FIBA), 2019], the
design of this study was tailored to suit the physical demands
required to play this sport. Typically, 1:1 work-to-rest ratios
target the aerobic metabolism, where timings range from
5min work: 5 rest. However, due to low duration of exercise
(i.e. 30s work: 30s rest), and high intensity, we hypothesize
that both anaerobic (i.e. 30s work) and aerobic (six sets of
6 repetitions of 30s) energy systems were involved. Simi-
lar improvements in sprint performance, when comparing
hypoxic to normoxic groups, were also observed by Bro-
cherie e al. (2015), where the authors applied a work-to-rest
ratio of 1:1 (15s: 15s). However, Jones etal. (2015) used
a 1:1.25 ratio (60s: 75s), while Hamlin etal. [20], used a
1:5 ratio (5s: 25s), which also showed significant benefi-
cial improvement in the hypoxic compared to the normoxic
group. Interestingly, Brechbuhl etal. [5], found no benefit
in repeated sprint performance in tennis players with a 1:4
ratio (6s: 24s) [5] while Galvin etal. [13], found no benefit
in rugby union and rugby league players with a 1:5 ratio (6s:
30s). To summarise, the smaller work-to-rest ratio, the less
recovery is given, which increases demand on the aerobic
system to aid in the recovery of muscular ATP-PC. In future
repeated sprint research studies, the work-to-rest ratio should
be established to allow maximal anaerobic stress and adapta-
tion responses to occur.
The addition of high-intensity intermittent running shut-
tles, and all-out efforts in normoxic training programs has
previously been shown to be effective for increasing aerobic
performance in team sport players [10, 13]. However, the
results in the current study showed positive but less clear dif-
ferences in the hypoxic compared to normoxic group. This
was expected as the total duration of hypoxic exposure was
probably too low for inducing any positive haematological,
capillary or mitochondrial adaptations [35]. Moreover, train-
ing intensities and work-to-rest ratios used in the current
study were not likely to elicit VO2 responses near VO2max. It
is more likely that such training would stimulate adaptation
in other central (i.e. ventilatory, hemodynamics, or neural
adaptations) or peripheral (i.e. muscle-buffering capacity,
economy, mitochondrial biogenesis, lactate transport, pH
regulation) factors [11, 12]. Team sport training stimulates
a myriad of metabolic and neuromuscular systems simulta-
neously, thus anaerobic glycolytic energy contribution and
neuromuscular load/musculoskeletal strain are likely the
more important variables to consider [7]. Although over-
all results showed unclear differences in the current study,
some individual’s YYIR1 benefited from this training (see
Fig.1b), therefore we would urge coaches and trainers to
test the effectiveness of such training individually on their
athletes before considering any implementation on the entire
team.
Overall, the hypoxic players perceived their training per-
formance to be significantly lower than the normoxic group
(Fig.3c). Further to this, when compared to the normoxic
group, the hypoxic group showed more subjective muscle
soreness, more fatigue and more stress. These results may
be explained by the fact that on the whole, the hypoxic play-
ers muscles were probably working harder during training.
According to Henneman’s size principle, motor units are
generally recruited in order of smallest to largest as the
contraction increases [21]. It is currently thought that in
general, type I (small, slow twitch oxidative) motor units
are recruited first, then type II (large, fast twitch glycolytic)
unitsare recruited as the force required to be generated is
increased. Therefore, during high-intensity intermittent
training, type II fibres have to take up much of the work.
There is evidence that breathing hypoxic mixtures during
training increases type II recruitment compared to normoxic
air [30]. Breathing hypoxic air during training may there-
fore cause earlier than normal fatigue of type I fibres (which
rely on oxygen and therefore fatigue early in a low oxygen
environment), which creates greater reliance on the type II
fibres which are required to complete a greater amount of the

Journal of Science in Sport and Exercise
1 3
work causing more muscle damage and subsequently fatigue
and muscle soreness. However this remains speculative until
further research can confirm such changes.
A limitation of this study is that we used well-trained
3 × 3 basketball players and therefore the results may not
reflect what may occur in untrained team sport athletes, or
even 5 × 5 basketballers. In addition, differences in shuttle
run ability between groups at baseline can be considered a
limitation as both groups were not similar in shuttle run per-
formance. The low participant numbers in this study suggest
caution is required when interpreting the results until our
findings can be substantiated by studies with larger sample
sizes. Some of the training modes used in this study (e.g.
battles ropes, ski erg, rowing machine) were not specific to
shuttle run performance, however were necessary to avoid
too much on-feet training load. Finally the hypoxic chamber
was set at 3052m, however we did not validate the cham-
ber FIO2 concentration at each training session. Therefore
absolute differences in hypoxia or changes from day-to-day
may have affected results. Taking these limitations into con-
sideration, the training protocols outlined in this study may
be of interest to coaches and athletes after considering the
many confounders that can influence player’s performance
in a team sport like 3 × 3 basketball.
In conclusion, a likely improvement in shuttle run ability
at sea level was found after high-intensity hypoxic interval
training in well-trained female 3 × 3 basketball players. How-
ever, this training protocol had unclear effects on muscular
power and aerobic performance and showedincreased levels
of subjective stress and fatigue and therefore should be fully
considered prior to use.
Acknowledgements We would like to thank the participants for their
time and effort in this study. Partial financial support was received
from a Faculty of Environment Society and Design Research Grant,
Lincoln University.
Author Contributions All authors conceived and designed the study.
All authors contributed to manuscript preparation, revisions and
approved the final version.
Funding Open Access funding enabled and organized by CAUL and
its Member Institutions. Funding to complete this study was received
from Lincoln University. Written informed consent was obtained from
all participants. The authors have no relevant financial or non-financial
interests to declare.
Data Availability The datasets generated and/or analysed during the
current study are available from the corresponding author on reason-
able request.
Declarations
Competing interests The authors have not disclosed any competing
interests.
Open Access This article is licensed under a Creative Commons Attri-
bution 4.0 International License, which permits use, sharing, adapta-
tion, distribution and reproduction in any medium or format, as long
as you give appropriate credit to the original author(s) and the source,
provide a link to the Creative Commons licence, and indicate if changes
were made. The images or other third party material in this article are
included in the article's Creative Commons licence, unless indicated
otherwise in a credit line to the material. If material is not included in
the article's Creative Commons licence and your intended use is not
permitted by statutory regulation or exceeds the permitted use, you will
need to obtain permission directly from the copyright holder. To view a
copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/.
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