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Yo-Yo IR2 testing of elite and sub-elite soccer players:Performance, heart rate response and correlations toother interval testsJørgen Ingebrigtsen a , Mads Bendiksen b , Morten Bredsgaard Randers c , Carlo Castagna d ,Peter Krustrup b & Andreas Holtermann ea Centre of Practical Knowledge, Department of Sports, University of Nordland, Bodø,Norwayb Department of Exercise and Sport Sciences, August Krogh Institute, Copenhagen, Denmarkc Department of Exercise and Sport Sciences, University of Copenhagen, Denmarkd Technical Department, Football Training and Biomechanics Laboratory, Italian FootballFederation (FIGC), Coverciano, Florence, Italye National Research Centre for the Working Environment, Copenhagen, Denmark
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To cite this article: Jørgen Ingebrigtsen, Mads Bendiksen, Morten Bredsgaard Randers, Carlo Castagna, Peter Krustrup &Andreas Holtermann (2012): Yo-Yo IR2 testing of elite and sub-elite soccer players: Performance, heart rate response andcorrelations to other interval tests, Journal of Sports Sciences, DOI:10.1080/02640414.2012.711484
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Yo-Yo IR2 testing of elite and sub-elite soccer players: Performance,heart rate response and correlations to other interval tests
JØRGEN INGEBRIGTSEN1, MADS BENDIKSEN2, MORTEN BREDSGAARD RANDERS3,
CARLO CASTAGNA4, PETER KRUSTRUP2, & ANDREAS HOLTERMANN5
1Centre of Practical Knowledge, Department of Sports, University of Nordland, Bodø, Norway, 2Department of Exercise and Sport
Sciences, August Krogh Institute, Copenhagen, Denmark, 3Department of Exercise and Sport Sciences, University of Copenhagen,
Denmark, 4Football Training and Biomechanics Laboratory, Italian Football Federation (FIGC), Technical Department,
Coverciano, Florence, Italy, and 5National Research Centre for the Working Environment, Copenhagen, Denmark
(Accepted 9 July 2012)
AbstractWe examined performance, heart rate response and construct validity of the Yo-Yo IR2 test by testing 111 elite and 92 sub-elite soccer players from Norway and Denmark. VO2max, Yo-Yo IR1 and repeated sprint tests (RSA) (n ¼ 51) and match-analyses (n ¼ 39) were also performed. Yo-Yo IR2 and Yo-Yo IR1 performance was 41 and 25% better (P 5 0.01) for elitethan sub-elite players, respectively, and heart rate after 2 and 4 min of the Yo-Yo IR2 test was 20 and 15 bpm (9 and 6%HRmax), respectively, lower (P 5 0.01) for elite players. RSA performance and VO2max was not different betweencompetitive levels (P 4 0.05). For top-teams, Yo-Yo IR2 performance (28%) and sprinting distance (25%) during matchwere greater (P 5 0.05) than for bottom-teams. For elite and sub-elite players, Yo-Yo IR2 performance was correlated(P 5 0.05) with Yo-Yo IR1 performance (r ¼ 0.74 and 0.76) and mean RSA time (r¼70.74 and 70.34). We concludethat the Yo-Yo IR2 test has a high discriminant and concurrent validity, as it discriminates between players of differentwithin- and between-league competitive levels and is correlated to other frequently used intermittent elite soccer tests.
Keywords: Yo-Yo IR1, repeated sprint test, VO2max, heart rate, discriminant validity, convergent validity
Introduction
The physiological demands of elite soccer have been
studied extensively (Bangsbo, Nørregaard, &
Thorsoe, 1991; Mohr, Krustrup, & Bangsbo, 2003;
Stølen, Chamari, Castagna, & Wisløff, 2005). Top-
level soccer is characterised by repeated sprinting
and multiple high-intensity activities interspersed
with periods of low intensity (Bloomfield, Polman,
& O’Donoghue, 2007; Bradley et al., 2009; Stølen
et al., 2005; Svensson & Drust, 2005). Several tests
have been designed to understand and monitor
soccer players’ ability to cope with these demands.
Aerobic power, lactate thresholds and muscle
strength are commonly tested in laboratories
(Svensson & Drust, 2005). However, most of these
tests have a poor ecological validity compared with
soccer-specific field tests and are also time consum-
ing and expensive (MacDougall & Wenger, 1991;
Svensson & Drust, 2005). Additionally, field tests are
often more applicable for coaches, as large numbers
of players can be tested on the training ground at the
same time. As a result, more recently coaches
have used field tests for monitoring player fitness
(Bangsbo, Iaia, & Krustrup, 2008).
The Yo-Yo Intermittent Recovery tests, level 2
(Yo-Yo IR2) and level 1 (Yo-Yo IR1), are among the
most applied and studied field tests in soccer
(Bangsbo et al., 2008). The tests are based on
similar constructs, and both are specific and practical
to use when testing players’ ability to perform and
repeat high-intensity exercise (Bangsbo et al., 2008).
The tests consist of 20-m shuttle runs with progres-
sively increasing speed, interrupted by a 10 second
active rest period, and continue until the players are
unable to keep up with the required speed (Krustrup
et al., 2006). The Yo-Yo IR2 test starts with four
running bouts of 13–16 km � h71, seven bouts of
16.5–17 km � h71, and after that continues with
stepwise increases of 0.5 km � h71 every eight
running bouts. The Yo-Yo IR1 consists of four
running bouts at 10–13 km � h71, seven at
Correspondence: Jørgen Ingebrigtsen, Centre of Practical Knowledge, Department of Sports, University of Nordland, Bodø, Norway.
E-mail: [email protected]
Journal of Sports Sciences, 2012; 1–9, iFirst article
ISSN 0264-0414 print/ISSN 1466-447X online � 2012 Taylor & Francis
http://dx.doi.org/10.1080/02640414.2012.711484
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13.5–14 km � h71, and thereafter stepwise 0.5 km �h71 speed increments every eight running bouts.
This difference results in three-fold longer exercise
times in the Yo-Yo IR1 test (see Bangsbo et al.,
2008). Both the Yo-Yo IR1 and the Yo-Yo IR2 have
been shown to maximally stimulate aerobic energy
turnover (Bangsbo et al., 2008). Additionally, a
significant proportion of muscle fibres experience
reduced glycogen levels after finishing the tests
(Bangsbo et al., 2008; Krustrup et al., 2003).
Furthermore, the Yo-Yo IR2 has been shown to
involve a considerable anaerobic energy production,
leading to markedly reduced levels of creatine
phosphate (CP) and high muscle and blood lactate
at the end of the test (Bangsbo et al., 2008; Krustrup
et al., 2006). The Yo-Yo IR1 also depends on
anaerobic energy production, although the average
rate of muscle and blood lactate accumulation is
about 1/5 of what is observed in the Yo-Yo IR2 test
(Bangsbo et al., 2008; Krustrup et al., 2006).
Multiple sprint tests are observed to put considerable
stress on the anaerobic energy production, but also
aerobic energy production is speculated to play a
significant role for the ability to recover between the
sprints (Bangsbo, 1994; Bishop, Girard, & Mendez-
Villanueva, 2011; Girard, Mendez-Villanueva, &
Bishop, 2011; Glaister, 2005; Rampinini et al.,
2007; Svensson & Drust 2005).
Although the Yo-Yo IR2 is widely used, important
information for both coaches and scientists concern-
ing application and interpretation of the test perfor-
mances is lacking. Firstly, the ability of the Yo-Yo
IR2 test to differentiate between top-, mid-, and
bottom-team players of the same league as well as
between elite and sub-elite players from different
leagues remains uncertain, and it is unknown
whether sub-maximal heart rate values differ be-
tween elite and sub-elite players. Secondly, it is still
to be elucidated how Yo-Yo IR2 test results correlate
to the Yo-Yo IR1 and other field and laboratory tests
for elite and sub-elite soccer players. Together, such
evaluations would provide valuable information
about the discriminant and concurrent validity of
the Yo-Yo IR2 test.
Therefore, the main aims of this study were 1) to
examine performance of the Yo-Yo IR2 test for elite
and sub-elite players in two countries as well as
successful and unsuccessful players of the same
league, 2) to correlate the Yo-Yo IR2 test per-
formance to other frequently used tests in elite
soccer.
Methods
Participants
A total of 203 Norwegian (n ¼ 76) and Danish
(n ¼ 127) soccer players participated in the study.
One-hundred and eleven (111) participants were
elite players from the best Norwegian (n ¼ 38) and
Danish league (n ¼ 74), 92 participants were sub-
elite players from the third best Norwegian (n ¼ 39)
and Danish league (n ¼ 53). Body mass, stature,
body mass index (BMI) and age of the Norwegian
and Danish elite and sub-elite players are presented
in Table I. All players, as well as the clubs involved,
approved the use of the depersonalised data, and the
study was conducted in accordance with the Helsinki
declaration. The study was accepted by the Privacy
Ombudsman for Research, the Norwegian Social
Science Data Service.
Experimental design
All participants performed the Yo-Yo IR2 test during
which heart rate was monitored. Discriminant
validity of the Yo-Yo IR2 test was evaluated by
comparing Yo-Yo IR2 performances for the elite and
sub-elite players as well as for 39 Danish elite players
in top- (rank 1–2, n ¼ 13), mid- (rank 5–8, n ¼ 13)
and bottom-teams (rank 10–12, n ¼ 13), that also
had their match activities recorded during competi-
tive games. The convergent (i.e. Concurrent and
Criterion) validity of the Yo-Yo IR2 test was
evaluated by correlating the Yo-Yo IR2 test perfor-
mance to the performance of other frequently used
tests in elite and sub-elite football. Therefore, 53
Norwegian players also performed the Yo-Yo IR1, a
Table I. Subject characteristics of the Norwegian and Danish elite and sub-elite players.
Norwegian players Danish players
Variables Elite (n ¼ 38) Sub-elite (n ¼ 39) Elite (n ¼ 74) Sub-elite (n ¼ 53)
Body mass (kg) 76.4 + 5.9 74.9 + 7.4 74.8 + 6.3 79.2 + 7.1**
Stature (m) 1.83 + 0.05 1.81 + 0.05 1.82 + 0.06 1.81 + 0.05
Body mass index (kg �m72) 22.9 + 1.5 22.8 + 1.8 23.2 + 1.7 24.2 + 2.1**
Age (y) 26 + 7 20 + 3* 25 + 5 24 + 5
Data are presented as means + s. *Significantly (P 5 0.01) lower than Norwegian elite players. **Significantly (P 5 0.05) higher than
Danish elite players.
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repeated sprint test (RSA) and a VO2max treadmill
test. All tests were performed at the start of the
competitive season. The full test battery including
Yo-Yo IR2, Yo-Yo IR1, repeated sprint test and
VO2max testing was carried out within a two week
period, with at least 24 hours of recovery between the
tests. The match recordings were carried out 3–21
days after the Yo-Yo IR2 test.
Instruments
Body mass was measured using an electronic scale
(A&D Company Limited, Tokyo, Japan). Stature
was measured by using a stadiometer (KaWe
Medizintecknik, Asperg, Germany). BMI was later
calculated from these measurements (Nevill, Holder,
& Watts, 2009). The Yo-Yo IR tests were conducted
on an indoor artificial turf using previously described
procedures (Krustrup et al., 2003, 2006). A Denon
CD-player (DC 1015, Denon Brand Company,
Japan) with a Sony amplifier (F590ES) and Sony
loudspeakers (SS-E420, Sony Corporation, Japan)
was used to play the Yo-Yo IR tests. Sprint times
were measured and recorded by a wireless Brower
Speed Trap II (Brower Timing Systems, Utah,
USA). Mean sprint time and fatigue index, as
described by Svensson and Drust (2005) were later
calculated by the use of Microsoft Excel (Microsoft
Corp., USA). During all field tests, heart rate was
recorded at 5-s intervals (Polar team 2, Polar,
Kempele, Finland). Data were later read with the
appurtenant software (Polar Team2software) in-
stalled on a personal computer (Dell XPS M1330,
Dell Products, USA). The treadmill used in this
study was a Rodby model RL 3500 (Rodby Innova-
tion AB, Hagby, Sweden). Each participant’s oxygen
consumption was measured every 20 s with a Sensor
Medics apparatus (VMAX 29, USA). Digital video
cameras (GR-D23E, JVC, Japan) were used for close
up video filming of individual players throughout a
competitive game (see below).
Testing procedures
Yo-Yo IR tests, level 2 and 1. All players were familiar
with the test procedure of both Yo-Yo IR tests. Both
levels of the Yo-Yo IR test consist of 26 20-m
shuttle-runs at increasing velocities with 10 s of
active recovery between shuttles (Krustrup et al.,
2003, 2006). While level 1 starts at an average
running speed of 10 km � h71, level 2 starts at
13 km � h71. Stepwise speed increments followed
until all participants either failed to reach the line
(objectively evaluated by experienced fitness coa-
ches) twice or felt too exhausted to continue at the
required speed (subjectively evaluated). Prior to the
Yo-Yo testing, all players conducted a standardised
warm up consisting of various running exercises with
increasing intensity towards the test start.
Repeated sprint test. The two first steps of the warm up
were similar to the procedure prior to the Yo-Yo IR
tests. Additionally, as a part of the warm up the
players ultimately performed three 40-m sprints at
near maximum speed separated by 2 min of rest. The
repeated sprint test then consisted of seven max-
imum 35-m sprints interspersed with 25 s of active
recovery. The percentage decrement (fatigue index;
%) and mean sprint time were calculated as both
have been described as reliable and useful measures
(Glaister, Howatson, Pattison, & McInnes, 2008;
Impellizzeri et al., 2008) for evaluating repeated
sprint ability.
Treadmill test. Some of the Norwegian players (elite
n ¼ 12; sub-elite n ¼ 13) also completed a progres-
sive treadmill test for determination of maximal
oxygen consumption (VO2max). VO2max is de-
scribed as the highest rate of the aerobic energy
turnover and is one of the most valid indications of
aerobic capacity (Bassett & Howley, 2000; Duncan,
Howley, & Johnson, 1997). The specific test-proto-
col used in this study was a continuous incremental
protocol with a total duration of five to six minutes
with increasing load every 30 seconds. The treadmill
elevation during the test was 5% for all players, while
the start speeds were individually adapted according
to the maximum speed of their previously performed
tests (all within the range of 10 to 13 km � h71). The
average of the two highest oxygen uptake values was
defined as VO2max. A plateau was reached for all
players, defined as an unaltered VO2 despite an
increase in running velocity (Svensson & Drust,
2005).
Match analyses. A total of 39 Danish Premier League
players were video filmed during competitive
matches. The analysis included 5 central defenders,
5 midfield players and 3 attackers from 2 top-teams
(ranked 1–4), 3 middle-teams (ranked 5–8) and 3
bottom-teams (ranked 9–12). Each player was filmed
close up during the entire match by digital video
cameras (GR-D23E, JVC, Japan) positioned at the
side of the pitch, at the level of the midline, at a
height of about 15 m and at a distance of 30–40 m
from the sideline. The recordings were later replayed
on a monitor for computerised coding of the activity
pattern. The following locomotor categories were
chosen in accordance with the study by Mohr et al.
(2003): standing (0 km � h71), walking (6 km � h71),
jogging (8 km � h71), low-speed running (12 km �h71), moderate-speed running (15 km � h71), high-
speed running (18 km � h71), sprinting (30 km � h71),
and backward running (10 km � h71). The amount of
Yo-Yo IR2 testing in elite and sub-elite soccer 3
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high-intensity running was calculated as the sum of
moderate-speed running, high-speed running and
sprinting. The frequency and duration of each
activity were recorded in pre-determined 5-, 15-
and 45-min intervals. The distance covered for each
activity was determined as the product of the total
time and mean speed for that activity. The total
distance covered during a match was calculated as
the sum of the distances covered during each type of
activity. Additionally, for each individual player, the
peak 5-min period was determined as the 5-min
period when the most high-intensity running was
performed. The peak 5-min value of high-intensity
running has previously been shown to differ mark-
edly between top-class and high-level male players
(Mohr, Krustrup, Andersson, Kirkendal, & Bangs-
bo, 2008) and also for the same female elite players
competing in international and domestic tourna-
ments (Andersson, Randers, Heiner-Møller, Krustr-
up, & Mohr, 2010).
Statistics
All statistical analysis was carried out with SPSS 14.0
(SPSS Inc., Chicago). Results are reported as
mean+ standard deviations (s), and 95% confidence
intervals (95% CI) were calculated for all measures.
Differences between Norwegian and Danish players
as well as Danish top-, mid- and bottom-team
players were evaluated by one-way analyses of
variance (ANOVA) tests. Determination of between
group differences was done by using the independent
samples t-test. Coefficients of correlation were
determined and tested for significance by using the
Pearson’s product-moment test. The magnitude for
correlation coefficients were considered as trivial
(r 5 0.1), small (0.1 5 r 5 0.3) moderate
(0.3 5 r 5 0.5), large (0.5 5 r 5 0.7), very large
(0.7 5 r 5 0.9), nearly perfect (r 4 0.9), and per-
fect (r ¼ 1.0), in accordance with Hopkins’ defini-
tions (Hopkins, 2000). Significance level was set to
P � 0.05 for all analyses.
Results
Yo-Yo IR2 test performance and heart rate response
Yo-Yo IR2 performance was 41% higher for elite
players (n ¼ 111) than for sub-elite players (n ¼ 92)
(965 + 251 (+s) vs 685 + 217 m) (Figure 1). The
Yo-Yo IR2 performance of the Norwegian and
Danish elite players were 65% (941 + 278 vs
571 + 155 m) and 27% (977 + 205 vs
769 + 199 m), respectively, higher (P 5 0.05)
than their sub-elite counterparts (Figure 1). The
Danish sub-elite players performed 35% better than
the Norwegian sub-elite players (Figure 1).
Sub-maximal and peak heart rates during all tests
are seen in Table II. For the elite players, the heart
rate after 2 and 4 min of the Yo-Yo IR2 test was 20
and 15 bpm (9 and 6% HRmax) lower (P 5 0.01)
than for sub-elite players, whereas the corresponding
values during Yo-Yo IR 1 were 21 and 24 bpm (10
and 12% HRmax) (Table II).
For elite players, the heart rate after 2 and 4 min of
the Yo-Yo IR2 were 21 and 23 bpm higher
(P 5 0.05) than in the Yo-Yo IR1 test for elite
players. Corresponding values were found for sub-
elite players with 19 and 14 bpm (P 5 0.01),
respectively.
The peak heart rate for sub-elite players during
the Yo-Yo IR2 test (193 + 8 bpm) was not
significantly different from the Yo-Yo IR1 and
the incremental treadmill test, but higher than
during the repeated sprint test (189 + 7 bpm;
Table II). The Yo-Yo IR2 test peak heart rate
(182 + 7 bpm) for elite-players was not different
from the Yo-Yo IR1 test and the repeated sprint
test, but was lower than during the incremental
treadmill test (189 + 8 bpm; Table II).
Other test performances
The data for all test performances of the Norwegian
players are presented in Table III. The elite players
performed 25% better (P 5 0.05) in Yo-Yo IR1
than sub-elite players. However, no differences were
observed for mean 35-m sprint time (P ¼ 0.81),
repeated sprint ability fatigue index (P ¼ 0.26) or
VO2max (P ¼ 0.19).
Figure 1. Yo-Yo IR2 performance for Danish elite players
(n ¼ 74), Danish sub-elite players (n ¼ 53), Norwegian elite
players (n ¼ 37) and Norwegian sub-elite players (n ¼ 39). Data
are presented as means+ s. x denotes significant difference from
Danish sub-elite players. ¤ denotes significant difference from
Norwegian sub-elite players.
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Test performance correlations
Very large correlations were found between the Yo-
Yo IR2 and Yo-Yo IR1 performance within both
elite (r ¼ 0.74, P 5 0.01) and sub-elite players
(r ¼ 0.76, P 5 0.01) (Figure 2). A moderate corre-
lation was observed for sub-elite players between
Yo-Yo IR2 performance and VO2max (r ¼ 0.48,
P 5 0.01, n ¼ 13), whereas no significant correla-
tion was observed for the elite players (r ¼ 0.59,
P 5 0.10, n ¼ 12). Further, between the Yo-Yo IR2
performance and mean 35-m sprint time (s) in the
RSA test a very large negative correlation was
observed for the elite players (r¼70.84, P 5 0.01,
n ¼ 12), and a moderate correlation was observed
for the sub-elite players (r¼70.34, P 5 0.05,
n ¼ 39).
Very large correlations were observed between
Yo-Yo IR1 performance and VO2max for elite
players (r ¼ 0.76, P 5 0.01) as well as sub-elite
players (r ¼ 0.73, P 5 0.01). Very large and large
negative correlations were found between Yo-Yo IR1
performance and mean 35-m sprint time for elite
(r¼70.80, P 5 0.01) and sub-elite players
(r ¼ 70.51, P 5 0.05), respectively. No significant
relationship was observed between mean 35-m
sprinting time and VO2max in elite (r¼70.55,
P 5 0.10) and sub-elite players (r¼70.46,
P 5 0.10).
A large negative correlation was observed between
HR after 2 min of Yo-Yo IR2 (%HRmax) and Yo-Yo
IR2 performance for sub-elite players (r¼70.54,
P 5 0.01), but not for HR after 4 min (r¼70.26,
P ¼ 0.18). No significant correlations were observed
between sub-maximal Yo-Yo IR2 HR and Yo-IR2
performance for elite players. A moderate negative
correlation was found between HR after 4 min of Yo-
Yo IR1 (%HRmax) and Yo-Yo IR1 performance for
sub-elite players (r¼70.45, P 5 0.05), whereas no
significant correlation was observed for elite players
(r¼70.60, P ¼ 0.06).
Top-, mid- and bottom teams of the Danish League
Yo-Yo IR2 performance was 12% (118 m) and 28%
(235 m) better (P 5 0.001) for players in top-teams
Table II. Heart rate responses during field tests and a treadmill test for Norwegian elite and sub-elite players.
Variables Elite (n ¼ 12) Sub-elite (n ¼ 39) Difference 95% CI
Yo-Yo IR2 – Submax HR, 2 min (bpm) 164.9 + 5.6 185.1 + 8.7 720.2 + 2.7* 725.6 to 714.7
Yo-Yo IR2 – Submax HR, 4 min (bpm) 175.6 + 6.5 190.3 + 7.7 714.7 + 2.5* 719.8 to 79.5
Yo-Yo IR2 – Peak HR (bpm) 181.5 + 6.9 192.6 + 8.0 11.1 + 2.6* 716.3 to 75.9
Yo-Yo IR1 – Submax HR, 2 min (bpm) 143.8 + 25.4 165.2 + 8.8 721.4 + 4.9* 731.3 to 711.5
Yo-Yo IR1 – Submax HR, 4 min (bpm) 153.1 + 20.1 177.1 + 8.4 724.0 + 4.2* 732.4 to 715.5
Yo-Yo IR1 – Peak HR (bpm) 183.7 + 5.8 192.5 + 8.1 78.8 + 2.5* 713.9 to 73.8
Repeated Sprint Test – Peak HR (bpm) 179.2 + 8.5 188.7 + 7.0 79.5 + 2.5* 714.5 to 74.4
Treadmill test – Peak HR (bpm) 189.5 + 7.9 194.5 + 6.4 75.1 + 2.9 711.2 to 1.0
Data are presented as means + s. *Significantly different (P 5 0.01). Dn ¼ 13 for VO2max in sub-elite players.
Table III. Field test performances and laboratory test results of Norwegian elite and sub-elite players.
Variables Elite (n ¼ 12) Sub-elite (n ¼ 39) Difference 95% CI
Yo-Yo IR2 (m) 747 + 201# 571 + 155 176 + 55* 65 to 287
Yo-Yo IR1 (m) 2033 + 416 1633 + 476 356 + 135** 85 to 629
Fatigue Index (%) 8.3 + 5.3 6.4 + 4.7 1.9 + 1.7 71.4 to 5.2
Mean 35-m time (s) 5.24 + 0.24 5.26 + 0.18 70.02 + 0.07 70.15 to 0.12
VO2max (ml � kg71 � min71) 59.2 + 3.9 61.5 + 4.5D 72.3 + 1.7 75.9 to 1.3
Data are presented as means + s. *Significantly different (P 5 0.01). ** Significantly different (P 5 0.05). #Yo-Yo IR2 performance for all
the Norwegian elite players (n ¼ 38) was 941 + 278 m. Dn ¼ 13 for VO2max in sub-elite players.
Figure 2. Relationships between Yo-Yo IR2 performances and Yo-
Yo IR1 performances in Norwegian elite (n ¼ 12, r ¼ 0.74,
P 5 0.01) and sub-elite players (n ¼ 39, r ¼ 0.76, P 5 0.01).
Yo-Yo IR2 testing in elite and sub-elite soccer 5
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than mid-teams and bottom-teams, and 14%
(117 m) better (P 5 0.05) for players in mid-teams
than for bottom-teams (Figure 3). In the most
intense 5-min match period players in the top- and
mid-teams sprinted 42–46% longer (P 5 0.001) and
ran 31–38% longer (P 5 0.05) at a high intensity
(�15 km � h71) than bottom-team players. During
the full game, top- and mid-team players sprinted
25–33% longer (P 5 0.001) than bottom-team
players, whereas total distance covered and amount
of high intensity running was not significantly
different.
Discussion
The present study demonstrated that Yo-Yo IR2 and
Yo-Yo IR1 performances were much higher for elite
than sub-elite players and that the heart rate after
2 and 4 min of the Yo-Yo IR2 was much lower for
elite players. Additionally, Yo-Yo IR2 test perfor-
mance, sprinting distance and peak 5-min high-
intensity running during match play were greater for
successful than for unsuccessful teams in the same
league. RSA performance and VO2max was not
different between elite and sub-elite players. The
study revealed large correlations between Yo-Yo IR2
performance and the Yo-Yo IR1 performance and
repeated sprinting ability and a moderate correlation
with VO2max.
The present study is the first to demonstrate a
difference in Yo-Yo IR2 test performance between
successful and unsuccessful teams of the same
Scandinavian league. We found that the top-teams
performed 28% better than the bottom-teams and
that the top-teams were sprinting 25% more during
games than the bottom-team players. Moreover, the
top-team players performed 38% more high-intensity
running and 42% more sprinting during the most
intense 5-min period of the game compared to the
bottom-team players. These findings are in line with
the previously shown association between physical
capacity and locomotor match performance (Krustr-
up et al., 2003, Krustrup, Mohr, & Bangsbo, 2005)
and the findings that the ability to perform high-
intensity interval exercise in the most intense periods
as well as throughout games could be of great
importance for the success of elite players (Krustrup
et al., 2003; Mohr et al., 2003; Pettersen, 2008;
Rampinini et al., 2009a). However, although only
small match-to-match variation in running distance
has been reported in studies using time-motion
analyses (coefficient of variation (CV) of 3.1–9.8%,
Mohr et al., 2003), we recognise the lack of multiple
matches to assess match locomotor performance of
the players as a possible weakness of the present
study. Further, it should be emphasised that the
findings of the present study that successful Danish
elite players performed more sprinting during
matches than unsuccessful players is different from
what was reported by Rampinini et al. (2009a) and
Di Salvo, Gregson, Atkinson, Tordoff, and Drust
(2009) in Premiership Italian and English competi-
tive matches. The reported inverse relation between
team success and match high-intensity coverage was
supposed a consequence of better team technical-
tactical efficiency of the higher ranked teams (Di
Salvo et al., 2009; Rampinini, Impellizzeri, Castag-
na, Coutts, & Wisløff, 2009b). Although fatigue in
top-level football has been shown to affect both
offensive and defensive high-intensity running (Brad-
ley et al., 2009) it may require more high-intensity
running to defend against technically superior teams
with better ball retention. However, previous re-
search has not examined the fatigue development
during games and the effect of team fitness level on
high-intensity running making comparison between
the present and previous studies difficult.
Another interesting finding of the present study
was that elite players had a 41% better Yo-Yo IR2
performance than sub-elite players. The absolute
values for the elite players were similar to or slightly
lower than previously observed for Danish, Swedish
and English Premier League players (Bangsbo et al.,
2008; Krustrup et al., 2006; Rampinini et al., 2010;
Thomassen, Christensen, Gunnarsson, Nybo, &
Bangsbo, 2010), whereas the Yo-Yo IR2 perfor-
mances of the Norwegian third-division players were
much lower than the present and previous reports on
Danish second division players (Krustrup et al.,
2011). It is well-known that Yo-Yo IR2 performance
is improved by high-intensity training such as speed
endurance training (Iaia et al., 2008; Mohr et al.,
Figure 3. Yo-Yo IR2 performance and running performance
during competitive matches for top-team players (rank 1–2,
n ¼ 13), mid-team players (rank 5–8, n ¼ 13) and bottom-team
players (rank, 10–12, n ¼ 13). # denotes significant difference
from bottom-team players. * denotes significant difference from
mid-team players.
6 J. Ingebrigtsen et al.
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2007) and it is likely that the intensity of matches and
training is much higher for the elite players than the
sub-elite players (Bangsbo, Mohr, Poulsen, Perez-
Gomez, & Krustrup, 2006; Mohr et al., 2003).
Actually, lack of high-intensity training may well be
one of the reasons for the poor Yo-Yo IR2
performances along with reasonably high VO2max
for the three investigated Norwegian third division
teams as their physical training focused on long-
duration moderate intensity training. However, it is
unknown whether these observations are representa-
tive for the whole of Norway. The construct validity
of the Yo-Yo IR2 test was also investigated through
correlation analyses with other frequently used
soccer-tests (convergent validity; Nelson, 2011).
The results of the present study show that the
concurrent validity was high for the Yo-Yo IR2 test
when comparing test results with other interval tests.
Thus, large correlations were observed between the
Yo-Yo IR2 test and the Yo-Yo IR1 test and the
repeated sprint test. Despite the high aerobic energy
contribution throughout the Yo-Yo IR2 test (Krustr-
up et al., 2006), only moderate correlates have been
found with VO2max (e.g. r2¼ 0.25, Bangsbo et al.,
2008; r2 ¼ 0.22, Rampinini et al., 2010, r2 ¼ 0.24,
Krustrup et al., 2006). Recent findings indicate that
muscular oxidative capacity and oxygen uptake
kinetics, along with running economy and anaerobic
capacity, are more important determinants of Yo-Yo
IR2 performance for elite soccer players than
VO2max (Aziz, Chia, & The, 2000; Christensen
et al., 2011; Rampinini et al., 2010). Accordingly, in
this study Yo-Yo IR2 performance was only moder-
ately correlated with VO2 max for the sub-elite
players with r2 ¼ 0.24 and not significantly corre-
lated for the elite players. However, these results
must be interpreted with caution because of the small
number of participants who completed the VO2max
test.
Several studies have investigated the use of
frequent, sub-maximal versions of intermittent field
tests for elite soccer players, and it is evident that
heart rate recordings during sub-maximal versions of
the Yo-Yo IR1 test (Bangsbo et al., 2008; Krustrup
et al., 2003) and the Yo-Yo intermittent endurance
level 2 test (Bangsbo et al., 2006; Bradley et al.,
2011) can be used to detect adaptations to short-
term training interventions, provide information
about the maximal Yo-Yo test performances and be
a rough indicator of locomotor performance in a
soccer match. However, the present study is the first
to compare the sub-maximal heart rate responses of
the Yo-Yo tests for different competitive levels.
Interestingly, the present study revealed markedly
lower heart rates after 2 and 4 min of the Yo-Yo IR2
test (differences of 9 and 6% of HRmax, respec-
tively) as well as the Yo-Yo IR1 test (differences of
10 and 12%, respectively) for elite compared to sub-
elite soccer players. We interpret this finding to
provide further support of the discriminant validity of
the Yo-Yo IR2 test. Due to the higher exercise
intensity in the Yo-Yo IR2 test, heart rates were 20
bpm higher than in the Yo-Yo IR1 test after 2 min
and several sub-elite players had reached near-
maximal heart rate values after 4 min of the Yo-Yo
IR2 test. Additionally it was observed that heart
rate loading for sub-elite players after 2 min of the
Yo-Yo IR2 test, but not after 4 min, correlated
with a Yo-Yo IR2 performance. Together this
indicates that sub-maximal Yo-Yo IR2 testing
should last less than 4 min, which is shorter than
the established recommendations for sub-maximal
Yo-Yo Intermittent Endurance test 2 (IE2) and
Yo-Yo IR1 testing of 4–8 min (Bradley et al.,
2011; Krustrup et al., 2003). Further, as several
studies using other protocols have shown that sub-
maximal heart rate loading is a good indicator of
cardiovascular stress (Borresen & Lambert, 2007:
Buchheit, Voss, Nybo, Mohr, & Racinais, 2011;
Krustrup et al., 2010) it would be of value for
future studies to investigate whether measurements
of heart rate during the early phase of the Yo-Yo
IR2 test can provide information to physical
coaches about changes in aerobic intermittent
exercise ability for football players without applying
strenuous maximal tests. However, it should be
emphasised that the current evidence suggests that
the sub-maximal Yo-Yo IR1 heart rate response is
correlated closer to intermittent exercise capacity
than the sub-maximal Yo-Yo IR2 heart rate
response (Krustrup et al., 2003, 2006). Moreover,
when working with sub-maximal heart rate one
should be aware that its ability to reflect perfor-
mance decrements in young soccer players has
been questioned (Buchheit, Simpson, Al Haddad,
Bourdon, & Mendez-Villanueva, 2012).
Concerning the peak heart rates reached during
the various tests, the Yo-Yo IR2 test elicited higher
values than the RSA test for the 39 sub-elite players,
and equally high values as for the treadmill test and
the Yo-Yo IR1 test. This supports previous studies
showing that the peak heart rate reached during the
Yo-Yo IR2 test provides a good indication of the
maximal heart rate (Bangsbo et al., 2008; Krustrup
et al., 2006). For the 13 elite players, however, the
peak heart rate during the Yo-Yo IR2 test was similar
to the peak heart rate reached during the RSA and
the Yo-Yo IR1 test, but somewhat lower than values
obtained during the incremental treadmill test
(*96%). Further studies with a larger sample size
are required to elucidate whether the elite soccer
players can elicit their maximal heart rate during the
Yo-Yo IR2 test and to explore the full potential of
heart rate and blood lactate responses during a
Yo-Yo IR2 testing in elite and sub-elite soccer 7
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sub-maximal version of the Yo-Yo IR2 test for elite
soccer players. As the heart rate response during
controlled sub-maximal exercise is generally ac-
cepted as a good indicator of cardiovascular stress
(Borresen & Lambert, 2007), the above presented
findings also suggest that the aerobic loading during
the first part of the test affects the overall perfor-
mance of the test.
Conclusion
The present study demonstrates that the Yo-Yo IR2
test has high discriminant validity as Yo-Yo IR2
performance of elite players is superior to sub-elite
players and as Yo-Yo IR2 performance differentiates
physical fitness and intense match activities between
players of successful and unsuccessful teams of the
same Scandinavian league. Secondly, it can be
concluded that the heart rate after 2–4 min of a
sub-maximal version of the Yo-Yo IR2 test is
markedly lower for elite than sub-elite players, hence
strengthening our notion of discriminant validity of
the Yo-Yo IR2 test. Moreover, the concurrent
validity was established as very large correlations
were observed between the Yo-Yo IR2 test and other
intense intermittent tests such as the Yo-Yo IR1 and
35-m repeated sprint test and a moderate correlation
was observed with VO2max.
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