Yo-Yo IR2 testing of elite and sub-elite soccer players: Performance, heart rate response and correlations to other interval tests

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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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