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Activity profile and physical demands of football referees and assistantreferees in international gamesPeter Krustrup a; Werner Helsen b; Morten B. Randers a; Jesper F. Christensen a; ChristopherMacDonald a; Antonio Natal Rebelo c; Jens Bangsbo a

a Department of Exercise and Sport Sciences, Section of Human Physiology, University of Copenhagen,Copenhagen, Denmark b Department of Biomedical Kinesiology, Katholieke Universiteit Leuven,Leuven, Belgium c Faculdade de Desporto, Universidade do Porto, Porto, Portugal

To cite this Article Krustrup, Peter, Helsen, Werner, Randers, Morten B., Christensen, Jesper F., MacDonald, Christopher,Rebelo, Antonio Natal and Bangsbo, Jens'Activity profile and physical demands of football referees and assistant refereesin international games', Journal of Sports Sciences, 27: 11, 1167 — 1176To link to this Article: DOI: 10.1080/02640410903220310URL: http://dx.doi.org/10.1080/02640410903220310

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Activity profile and physical demands of football referees and assistantreferees in international games

PETER KRUSTRUP1, WERNER HELSEN2, MORTEN B. RANDERS1,

JESPER F. CHRISTENSEN1, CHRISTOPHER MACDONALD1,

ANTONIO NATAL REBELO3, & JENS BANGSBO1

1Department of Exercise and Sport Sciences, Section of Human Physiology, University of Copenhagen, Copenhagen, Denmark,2Department of Biomedical Kinesiology, Katholieke Universiteit Leuven, Leuven, Belgium, and 3Faculdade de Desporto,

Universidade do Porto, Porto, Portugal

(Accepted 30 July 2009)

AbstractTime-motion analyses and physiological measurements were performed to investigate the physiological demands of footballreferees (n¼ 15) and assistant referees (n¼ 15) in international games and to examine whether high-intensity running (HIR)correlates to the referees’ ability to keep up with play. Total distance covered (10.27+ 0.90 vs. 6.76+ 0.83 km) and HIR(1.92+ 0.58 vs. 0.97+ 0.22 km) was higher (P5 0.05) for referees than assistant referees, while sprinting distance was notdifferent. Referees covered 0.89+ 0.37 km by backwards running and assistant referees covered 1.54+ 0.66 km bysideways running. Mean heart rate was higher (P5 0.05) for referees than assistant referees (150+ 3 vs. 123+ 3 b.p.m.),whereas blood lactate was not different. Backwards/sideways running decreased (P5 0.05) from the first to the last 15-minperiod for referees (49%) and assistant referees (42%), whereas HIR was unaltered. HIR was inversely correlated with thefive highest distances from infringements in both halves (r¼70.60 and 70.58, P5 0.05). In conclusion, internationalmatch officials carry out an important amount of HIR throughout games, while low-intensity and unorthodox runningactivities are reduced during games. Referees performing the most high-intensity work are better to keep up with play. Thematch activities differ significantly between referees and assistant referees, which should be considered in training and testingprocedures.

Keywords: Time-motion analysis, high-intensity running, heart rate, blood lactate, distance from infringements

Introduction

The activity profile and physical demands of football

refereeing have been examined in a number of

studies (Asami, Togari, & Ohashi, 1988; Castagna,

Abt, & D’Ottavio, 2002a,b, 2004; Catterall, Reilly,

Atkinson, & Goldwells, 1993; Da Silva & Fernandez,

2003; D’Ottavio & Castagna, 2001; Helsen &

Bultynck, 2004; Johnston & McNaughton, 1994;

Krustrup & Bangsbo, 2001; Krustrup, Mohr, &

Bangsbo, 2002; Weston, Bird, Helsen, Nevill, &

Castagna, 2006). In one study, top class association

football referees were evaluated in national league

games by computerised time-motion analyses as well

as by measurements of heart rate and blood lactate

(Krustrup & Bangsbo, 2001). It was observed that

the referees had a significant aerobic energy produc-

tion throughout the match and episodes of consider-

able anaerobic energy turnover. Furthermore, it was

found that the ability to perform high-intensity

running (HIR) and backwards running was reduced

towards the end of a match. Similar decrements were

observed for Australian referees (Johnston &

McNaugthon, 1994), whereas Italian referees only

had a reduction in backwards running towards the

end of Serie-A games (D’Ottavio & Castagna, 2001).

Krustrup and Bangsbo (2001) demonstrated a

significant increase in the distance top Danish

referees are away from play infringements towards

the end of match play, thereby indicating accumu-

lated fatigue. Following a 12-week period of high-

intensity interval training it was demonstrated that

these same referees significantly improved maximal

oxygen uptake by 7% and their sport-specific test

performance based on a Yo-Yo IR1 test by 31%. In

addition, it was demonstrated that these referees

Correspondence: Peter Krustrup, Department of Exercise and Sport Sciences, The August Krogh Building, Universitetsparken 13, DK-2100 Copenhagen Ø,

Denmark. E-mail: pkrustrup@ifi.ku.dk

Journal of Sports Sciences, September 2009; 27(11): 1167–1176

ISSN 0264-0414 print/ISSN 1466-447X online � 2009 Taylor & Francis

DOI: 10.1080/02640410903220310

Downloaded By: [B-on Consortium - 2007] At: 22:13 17 November 2009

increased their total high-intensity running activity

during matches by 23%, and reduced their distance to

play infringements in the attacking zone by 15%.

Finally the pre-training increased distance to play

infringements towards the end of match play was no

longer present following the high-intensity training

programme. All of these results indicate a clear

improvement in referee performance after high-

intensity training. Accordingly, Weston, Helsen,

MacMahon, and Kirkendall, (2004) observed a 47%

improvement in the Yo-Yo IR1 test during a 16-

months training period consisting of intense inter-

mittent-exercise training. It should be expected that

the physical demands of referees in international

matches are higher than in national league games, as

observed for players (Di Salvo et al., 2007; Mohr,

Krustrup, & Bangsbo, 2003). However, the available

results are contradictory (Asami et al., 1988; Castagna

et al., 2004), which may be related to the standard of

the investigated national leagues, and it is unclear

whether referees in such games have a decrease in

high-intensity work towards the end of the game. It

would also be valuable to obtain information on

whether the distance from infringements is related to

the amount of HIR in order to understand the

importance of the physical capacity of the referee.

The physical demands of assistant referees have

been examined (Krustrup et al., 2002; Mallo,

Navarro, Garcıa-Aranda, Gilis, & Helsen, 2008).

Assistant refereeing in association football is charac-

terised by brief intense bouts of forward and sideways

running interspersed with long low-activity periods. It

has been observed that sprint performance of the

assistant referees was reduced towards the end of a

game in association with a reduced ability to keep up

with the off-side line. Furthermore, the assistant

referees’ performance of repeated sprints was corre-

lated to the amount of HIR in a game. However, no

information exists about the physical demands of

assistant referees during senior international games.

Every referee and assistant referee at national top-

level has to pass obligatory performance tests.

Traditionally, referees and assistant referees have

performed a 12-min continuous running test at a

minimum average speed of 13.5 km/h. Furthermore,

they are required to carry out two 50-m sprints and

two 200-m sprints within a 7.5- and 32-s time

standard, respectively (Eissmann, 1995). However,

referees’ ability to run as far as they can in 12 min

has been shown to correlate poorly with physical

match performance in national league games

(Krustrup & Bangsbo, 2001) and international

games (Castagna et al., 2002b). Similarly, it has

been shown that 200-m sprint performance is

neither correlated to total distance nor HIR distance

during international games (Mallo, Navarro, Garcıa-

Aranda, Gilis & Helsen, 2007). In some countries

the 12-min run has been replaced by the Yo-Yo

intermittent recovery level 1 test (Castagna et al.,

2002b; Castagna, Abt, & D’Ottavio, 2005; Krustrup

et al., 2003), which has been shown to be a good

predictor of HIR during match play for football

players and referees (Castagna et al., 2005, Krustrup

& Bangsbo, 2001; Krustrup et al., 2003; Krustrup,

Mohr, & Bangsbo, 2005). In addition, a test con-

sisting of repeated short sprints has been suggested

for assistant referees as the repeated sprinting

performance has been correlated with the ability to

keep up with play during national league games

(Krustrup et al., 2002). Recently, FIFA has intro-

duced a new test including intense intermittent

running and multiple short sprints. One test consists

of 20 (150 m) runs at high speed interspersed with

active recovery periods (50 m) lasting 35 s for

referees and 40 s for assistant referees. In addition,

referees and assistant referees are required to per-

form a repeated sprint test consisting of 6640 m

separated by a 1.5-min recovery period. The referees

and assistant referees have to cover each 40-m sprint

within 6.2 and 6.0 s, respectively. Thus, the same

‘‘fitness variables’’ are evaluated for referees and

assistant referees, whereas the required standards are

different. On that basis, it would be of interest to

compare the physical demands of referees and

assistant referees during an international game.

Thus, the aims of the present study were to

examine the physical performance of referees and

assistant referees throughout an international soccer

match and to compare the physical demands of

referees and assistant referees.

Methods

Participants

Fifteen referees and 15 assistant referees participated

in the study, all FIFA licensed with more than 4

years of experience with international games. The

referees had a mean age of 42 (range: 32–45) years,

an average height of 188 (176–191) cm, an average

body mass of 82.5 (76.1–93.4) kg and a body mass

index of 23 (20–27), with corresponding values for

the assistant referees of 43 (34–45) years, 181 (168–

192) cm, 77.8 (71.3–96.6) kg and 24 (22–28). The

match officials were fully informed about experi-

mental procedures and possible discomforts asso-

ciated with the study before giving their informed

consent to participate.

Match analysis

All the 15 referees were analysed during international

games, that is six A-team international games, two

U-21 international games, five Champions league

1168 P. Krustrup et al.

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games and two UEFA Cup games. Each of the referees

was video-filmed by two cameras to determine his

locomotor activities and to evaluate his ability to keep

up with play. The filming was performed by VHS

movie cameras (NV-M50, Panasonic, Germany)

positioned at the side of the pitch, at the level of the

mid line, at a height of 10–20 m and at a distance of

20–30 m from the touch-line. One camera filmed the

referee closeup for later computerised time-motion

analysis (n¼ 15), whereas the other camera filmed the

referee at a broad angle for later video analysis of his

distance from infringements (n¼ 14), using the pre-

markers in the grass as a distance measurement tool

(see Krustrup & Bangsbo, 2008). Four of the referees

were analysed in the 1999–2000 season and the

remaining 10 referees were analysed in the period

from 2004 to 2008, with no systematic differences

between the time-periods. All the 15 assistant referees

were analysed during international games over a

5-year period (2003–2008), that is eight A-team inter-

national games, five U-21 international games and two

Champions League games. All the assistant referees

were analysed in games where the referee was also

investigated. Each of the assistant referees was video

filmed by a camera positioned at the stadium stand, at

a height of 10–20 m and at a distance of 15–30 m

from the touch-line at the level of the penalty arch.

The assistant referees were filmed closeup for later

computerised analyses of the locomotor activities.

Nine locomotive categories were chosen for the

time-motion analysis, that is standing (0 km � h71),

walking (6 km � h71), jogging (8 km � h71), low-

speed running (12 km � h71), moderate-speed run-

ning (15 km � h71), high-speed running (18 km �h71), sprinting (25 km � h71), sideways running

(10 km � h71) and backwards running (10 km � h71).

The locomotive categories were chosen in accor-

dance with Krustrup and Bangsbo (2001) and

Krustrup et al. (2002), except that the speed of the

sideways running was corrected based on detailed

studies of the videotapes. The match activities were

subsequently divided into four locomotive categories:

(1) standing, (2) walking, (3) low-intensity running,

defined as jogging, low-speed running, sideways

running and backwards running and (4) HIR,

defined as moderate-speed running, high-speed

running and sprinting. The frequency and duration

of each activity were recorded and the data presented

in 5-, 15- and 45-min intervals. The distance covered

by each locomotion activity within each interval was

determined as the product of total time and mean

velocity for the activity. Reproducibility of results

obtained by time-motion analysis has previously

been shown to be in the range of 1–5% for each of

the individual activity categories (Bangsbo, Nørre-

gaard, & Thorsøe, 1991; Krustrup & Bangsbo, 2001).

All time-motion analyses included in the present

study were performed by the same experienced

observer.

Heart rate and blood samples

All referees and assistant referees had heart rate

recorded in 5-s intervals throughout the games. A

heart rate monitor (Polar Vantage NV, Kempele,

Finland) was placed around the chest of the match

officials *60 min before kick-off. The match offi-

cials were allowed to drink water ad libitum before

and during the game. For eight referees and eight

assistant referees, finger-prick blood samples were

taken 1–2 min after the end of the first and second

half, respectively. By the use of a 20–200 ml

Finnpipette (Labsystem, UK), 100 ml of blood was

haemolysed within 10 s of sampling in an ice-cold

100 ml Triton X-100 buffer solution and stored on

ice. Later on the same day, the samples were

analysed for lactate and glucose using an YSI 2300

lactate analyser (Yellow Spring Instruments, Yellow

Springs, OH, USA; Foxdal, Bergqvist, Eckerbom, &

Sandhagen, 1992).

Statistics

Distances covered and heart rate values in 15-min

periods were tested for significant within-group and

between-group differences by the two-way analysis of

variance (time period and group) with repeated

measures (RM ANOVA). When a significant inter-

action was detected, data were subsequently analysed

using a Newman-Keuls post-hoc test. Differences in

match activities, heart rate and blood lactate between

halves were tested by Students’ paired t-test, using

Bonferoni corrections. Between-group differences in

the total time spent, the average duration and total

number of occurrences within each activity category

were tested by Students’ unpaired t-test, using

Bonferoni corrections. Correlation coefficients were

determined and tested for significance using the

Pearson’s regression test. A significance level of 0.05

was chosen. Data are presented as means+ standard

deviation, unless otherwise stated.

Results

Activity profile

Match activities. The number of occurrences, mean

duration and percentage of total time in each of the

nine activity categories are summarised in Table I.

Briefly, the total number of activities and the

occurrence of jogging, low-speed, moderate-speed

and backwards running was higher (P5 0.05)

for referees than assistant referees, whereas the

Physical demands of international match officials 1169

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occurrence of sideways running was lower

(P5 0.05) for referees than assistant referees (Table

I). The mean duration of the high-intensity activities

was *2 s both for referees and assistant referees

(Table I). The time spent on unorthodox directional

modes of running (i.e. sum of backwards and

sideways running) was lower (P5 0.05) for referees

than assistant referees; 5.8+ 2.2 (1.9–8.4) vs.

10.2+ 4.4 (3.6–17.1)% of total time (Table I).

Match distances. The total distance covered was

10.27+ 0.90 (8.88–11.92) km for referees and

6.76+ 0.83 (5.20–8.21) for assistant referees

(P5 0.05), of which HIR accounted for 1.92+0.58 (0.97–3.03) and 0.97+ 0.22 (0.71–1.28) km

for referees and assistant referees, respectively (P50.05). Distance covered by sprinting was similar

for referees and assistant referees (0.22+ 0.13

[0.0870.54] and 0.26+ 0.10 [0.1170.45] km)

(Figure 1). Referees covered 0.89+ 0.37 (0.44–

1.33) km by backwards running, but essentially no

sideways running, whereas assistant referees covered

as much as 1.54+ 0.66 (0.50–2.50) km by sideways

running (Figure 1).

For referees, no significant difference was ob-

served in the total distance running and HIR

between the two halves (P4 0.05), whereas the

amount of backwards running was 24% lower

(P5 0.05) in the second compared to the first half

(0.38+ 0.19 vs. 0.50+ 0.21 km). The total distance

covered was 9, 11 and 10% lower (P5 0.05) from

30 to 45, 60 to 75 and 75 to 90 min, respectively,

compared to the first 15-min period (Figure 2a). The

amount of HIR was 27 and 28% lower (P5 0.05)

Tab

leI.

Mat

chac

tivi

ties

for

refe

rees

(n¼

14

)an

das

sist

ant

refe

rees

(n¼

14

)in

inte

rnat

ion

alm

atch

es.

Sta

nd

ing

Wal

kin

gJo

ggin

gL

Sru

nM

Sru

nH

Sru

nS

pri

nt

Bac

kw

ard

sS

idew

ays

To

tal

%o

fto

tal

tim

e,R

efer

ees

21

.9+

4.7

(13

.6–2

9.9

)

40

.2+

5.1

(33.6

–4

4.7

)

15

.8+

2.9

(10.9

–2

1.0

)

9.3+

1.5

(7.0

–1

1.9

)

4.8+

1.5

(2.6

–7

.4)

2.1+

0.9

(0.8

–4

.0)

0.4+

0.2

(0.2

–0

.8)

5.3+

2.4

(1.9

–8

.4)

0.2+

0.2

(0.0

–0

.7)

10

0

(100

–1

00

)

Ass

ista

nt

refe

rees

45

.8+

5.4

#

(36

.0–5

5.1

)

29

.7+

2.8

#

(25.4

–3

3.8

)

6.3+

1.8

#

(3.5

–8

.8)

4.0+

0.9

#

(2.6

–5

.2)

1.9

+0

.3#

(1.6

–2

.4)

1.2+

0.3

#

(0.8

–1

.7)

0.6+

0.2

(0.3

–0

.9)

0.3+

0.4

#

(0.0

–1

.0)

10.2

+4

.5#

(3.3

–1

6.1

)

10

0

(100

–1

00

)

Occ

urr

ence

s(n

),R

efer

ees

17

8+

37

(114

–2

33

)

42

8+

75

(316

–5

50

)

329+

60

(24

1–4

05

)

209+

51

(15

1–3

18

)

11

4+

37

(69–1

90

)

51+

19

(24–8

7)

13+

4

(7–2

0)

86+

33

(42

–1

28

)

5+

9

(0–22

)

14

12+

15

2

(119

8–1

58

3)

Ass

ista

nt

refe

rees

25

6+

45

(209

–3

56

)

37

1+

31

(326

–4

30

)

15

5+

30#

(11

3–1

99

)

99+

19#

(74

–1

29

)

60+

9#

(50–7

7)

38+

10

(24–5

6)

17+

5

(9–2

5)

7+

10

#

(0–2

8)

16

0+

49

#

(73–2

23

)

11

64+

10

9

(948

–1

23

2)

Mea

nd

ura

tio

n(s

),R

efer

ees

7.0+

1.1

(5.6

–8

.6)

5.4+

1.3

(4.1

–8

.4)

2.8+

0.6

(2.3

–4

.2)

2.7+

0.5

(2.1

–4

.0)

2.4+

0.3

(1.9

–2

.8)

2.4+

0.2

(2.0

–2

.7)

1.9+

0.6

(1.1

–3

.0)

3.4+

0.5

(2.4

–4

.3)

1.5+

0.3

(1.3

–1

.8)

4.0+

0.1

(3.5

–4

.7)

Ass

ista

nt

refe

rees

10

.0+

1.6

#

(8.6

–1

1.1

)

4.5+

0.6

(3.6

–5

.1)

2.2+

0.4

(1.7

–2

.9)

2.2+

0.2

(1.9

–2

.5)

1.7

+0

.1#

(1.6

–1

.9)

1.7+

0.2

#

(1.4

–2

.0)

1.9+

0.2

(1.6

–2

.3)

2.4+

1.6

(0.0

–5

.6)

3.6+

0.8

(2.7

–5

.2)

4.9+

0.2

(4.2

–5

.9)

Val

ues

are

mea

ns+

sas

wel

las

ran

ges

.#

:D

eno

tes

sign

ifica

nt

dif

fere

nce

fro

mre

fere

es.

Figure 1. Distance covered in various locomotor modes for

referees (filled bars, n¼15) and assistant referees (open bars,

n¼ 15), that is standing (ST), walking (W), jogging (J), low-speed

running (LSR), moderate-speed running (MSR), high-speed

running (HSR), sprinting (SPR), backwards running (BR) and

sideways running (SR). Values are means+SD. xSignificant

difference (P50.05) between referees and assistant referees.

1170 P. Krustrup et al.

Downloaded By: [B-on Consortium - 2007] At: 22:13 17 November 2009

from 30 to 45 and 60 to 75 min, respectively,

compared to the first 15-min period, whereas no

difference was observed between the first and last

15-min period of the game (Figure 2b). The distance

covered by backwards running was 35% and 49%

lower (P5 0.05) from 60 to 75 and 75 to 90 min,

respectively, compared to the first 15-min period

(Figure 3).

For assistant referees, the distance covered by

sideways running decreased (P5 0.05) by 18%

(0.90+ 0.35 vs. 0.74+ 0.39 km) from the first to

the second half, whereas no differences were

observed in total distance covered, HIR or sprinting

between halves. The total distance covered was

lowered by 19% and 21% and sideways running by

37% and 42% from 60 to 75 and 75 to 90 min,

respectively, compared to the first 15-min period

(Figures 2 and 3). No significant changes were

observed in HIR and sprinting when comparing

15-min periods of the game (Figure 2b).

Physiological response

Heart rate. The mean heart rate during the match was

151+ 9 (141–170) beats �min71 for referees and

124+ 15 (105–157) beats �min71 for assistant re-

ferees (P5 0.05). For referees mean heart rate was

not significantly altered during the game, whereas

the mean heart rate was 11–13 beats �min71 lower

(P5 0.05) for assistant referees from 45 to 60, 60

to 75 and 75 to 90 min compared to 0 to 15 min

(Figure 4). The mean heart rate values corresponded

to 85+ 3% and 77+ 5% of peak heart rate reached

during the game for referees and assistant referees

(177+ 12 and 161+ 13 beats �min71, respectively,

P5 0.05).

Blood lactate and glucose. For referees (n¼ 8), blood

lactate concentration was 3.4+ 2.3 mmol � l71

after the first half and 4.6+3.3 mmol � l71 after the

second half (P4 0.05), with corresponding values for

assistant referees (n¼ 8) being 2.8+ 1.4 and

2.8+ 2.6 mmol � l71 (Figure 5a).

For referees (n¼ 8), blood glucose was 5.4+ 0.7

and 5.2+ 0.5 mmol � l71 (P4 0.05) after the first

and second half, respectively, and 4.9+ 1.5 and

4.9+ 0.8 mmol � l71 for assistant referees (n¼ 8)

(Figure 5b).

Distance from infringements

For referees (n¼ 14), the mean distance from

infringements during the game was 12+ 1 (9–13)

Figure 2. Total distance covered (a) and HIR (b) for referees

(filled bars, n¼ 15) and assistant referees (open bars, n¼15) in

international games, reported in 15-min intervals, as well as during

additional time in the first (1:05 min) and second half (2:45 min).

Values are means+SD. xSignificant difference (P50.05) be-

tween referees and assistant referees. #Significantly different

(P50.05) from the first 15-min period.

Figure 3. Backwards running for referees (filled bars, n¼15) and

sideways running for assistant referees (open bars, n¼15) in

international games, reported in 15-min intervals, as well as during

additional time in the first (1:05 min) and second half (2:45 min).

Values are means+SD. xSignificant difference (P5 0.05) be-

tween referees and assistant referees. #Significantly different

(P5 0.05) from the first 15-min period.

Physical demands of international match officials 1171

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m in the middle zone and 16+ 3 (11–21) m in the

attacking zones. The mean distance from infringe-

ments in the attacking zones increased (P5 0.05)

from 14+ 3 to 18+ 4 m from the first to the last

15-min period of the game, whereas the distance

from infringements in the middle zone was unaltered

during the game (Figure 6).

The mean value of the five highest recorded

distances from infringements was 21+ 3 (15–25)

m in the middle zone and 28+ 5 (18–34) m in the

attacking zones. The amount of HIR in the first half

(r¼70.60) and second half (r¼70.58) was in-

versely correlated (P5 0.05) with the mean of the

five highest recorded distances from infringements

(Figure 7). The total distance covered was also

correlated to the mean of the five highest recorded

distances from infringements in the second half

(r¼70.60, P5 0.05), but not in the first half

(r¼70.42, P4 0.05).

Discussion

The major findings of the present study are that

international match officials are able to maintain a

significant amount of HIR towards the end of the

game, whereas low-intensity running and unortho-

dox running activities are reduced during the game

and that the amount of HIR is correlated to the

ability to keep up with play. Evidence was also

provided that the activity profile and physical

demands of games differ significantly between

referees and assistant referees, with higher heart

rates and more HIR and backwards running for

referees, while there was more sideways running for

assistant referees. These findings underline the

importance of performing intermittent HIR activities

in training and testing of international match officials

and emphasise that referees and assistant referees

should be considered as separate groups.

The referees in the international games covered a

similar total distance and amount of backwards

running as observed for international referees in

games in the Danish national league (Krustrup &

Bangsbo, 2001). Similarly, the referees in the present

study covered almost the same distance with HIR

during games as Danish national league referees

having carried out a 12-wk period of intense

intermittent training (Krustrup & Bangsbo, 2001).

Furthermore, the referees in the present study

performed more sprinting than observed previously,

and in accordance with findings from Italian national

league games, there was no significant reduction in

high-intensity exercise in the last 15-min period of

Figure 4. Mean heart rate for referees (filled bars, n¼15) and

assistant referees (open bars, n¼15) in international games,

reported in 15-min intervals during the games, as well as during

additional time in the first (1:05 min) and second half (2:45 min).

Values are means+SD. xSignificant difference (P5 0.05) be-

tween referees and assistant referees. #Significantly different

(P50.05) from the first 15-min period.

Figure 5. Blood lactate concentration (a) and blood glucose

concentration (b) after the first and second half of international

games for referees (n¼8) and assistant referees (n¼ 8). Means and

individual values are presented.

1172 P. Krustrup et al.

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the game (Castagna & Abt, 2004; D’Ottavio &

Castagna, 2001). One of the referees ran more than

3 km at high intensity, which is the longest distance

ever recorded, and he did not have an increase in the

distance from infringements during the game. Taken

together, these findings suggest that the fitness level

of referees in international matches is very high.

However, the present study demonstrated a signifi-

cant increase in the distance from play infringements

in the attacking zone during the last 15-min period of

the game (Figure 6), suggesting that the physical

requirements are high for referees the latter part of

international games. This can be explained by a

combination of player fatigue and tactical adjust-

ments, such as a shift towards a strategy of long

passes (Reilly & Gregson, 2006). The potential

elevation in work demands in the later stages of

match play for referees, combined with accumulating

fatigue, justifies creating and implementing specific

training programmes aimed at improving intermit-

tent high-intensity endurance capacity, to aid refer-

ees in coping with these unique physical demands

(Krustrup & Bangsbo, 2001).

The present study also revealed a large inter-

individual differences in the amount of HIR com-

pleted by referees, and this amount of high-intensity

running was negatively correlated to the greatest

distances from match play infringements, indicating

that those referees capable of sustaining the greatest

amount of high-intensity running are better to keep

up with play. These results taken together with the

previous finding that the amount of high-intensity

running performed during a game is related to the

referees’ fitness level and that physical training

results in attenuation of the relative aerobic loading

and cognitive stress (Castagna et al., 2002; Krustrup

& Bangsbo, 2001; Reilly & Smith, 1986), suggest

that the referees with the highest fitness capacity may

have the best possibility of evaluating the actions

occurring throughout an international game. The

previous finding that total distance covered is

correlated with optimal positioning for referees

(Hurley, Tozer, & Doust, 2002), was only partly

confirmed in the present study. This may be due to

the fact that the distances covered can be diminished

by clever positioning and anticipation of future

events (Castagna, Abt, D’Ottavio, & Weston, 2005;

Weston, Castagna, Impellizzeri, Rampinini, &

Breivik, 2008).

The referees in the international matches in the

present study had average and peak heart rates

similar to or lower than observed for referees in

national league games (Catterall et al., 1993;

D’Ottavio & Castagna, 2001; Johnston &

McNaughton, 1994; Krustrup & Bangsbo, 2001).

It is well known that the maximal heart rate differs

significantly within a group of 32–45-year-old match

officials (Krustrup & Bangsbo, 2001; Krustrup

et al., 2002) and it is therefore a study limitation

that only seven of the 15 referees had maximal heart

rate determined. However, for those referees the

maximal heart rates were lower than reported in the

study by Krustrup and Bangsbo, 2001 (179 vs. 190

beats �min71), resulting in rather similar average

heart rates when expressed in percentage of max-

imal heart rate. In other studies the average heart

rate has been expressed in percentage of peak heart

rate reached during the game, as it has been shown

that referees reach 95–100% of their maximal heart

rate during high-level games (Helsen & Bultynck,

Figure 6. Distance from infringements in the middle zone (filled

bars) and attacking zones (open bars) for referees in international

games, reported in 15-min intervals. Values are means+SD

(n¼ 15). *Significant difference (P5 0.05) between the distance

in the middle zone and the attacking zones. #Significantly different

(P50.05) from the first 15-min period.

Figure 7. Intra-individual correlation between the amount of HIR

in each of the two halves and the mean of the five highest recorded

distances from infringements in the attacking zones. The correla-

tion coefficients were r¼70.60 and r¼70.58 (n¼14, P5 0.05)

for the first and second half, respectively.

Physical demands of international match officials 1173

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2004; Krustrup & Bangsbo, 2001). When doing so,

the average heart rate for the international referees

in the present study was also very similar to values

reported for national league games (Catterall et al.,

1993; D’Ottavio & Castagna, 2001; Johnston &

McNaughton, 1994; Krustrup & Bangsbo, 2001). It

is also noteworthy that the average heart rates varied

significantly among the seven international referees

that had their maximal heart rate determined (72–

90% of HRmax), which could be due to differences

in the tempo of the games (Weston et al., 2006),

but it may also be due to differences in fitness level,

since a period of intermittent training resulted in a

significant lowering of heart rate during games for

Danish elite referees, despite the referees perform-

ing more high-speed running (Krustrup & Bangsbo,

2001). Blood lactate has previously been measured

for referees during national league games (Krustrup

& Bangsbo, 2001) and high-level friendly games

(Castagna, Abt, & D’Ottavio, 2002a), but not

during international games. In the present study,

the average values were 4 mM and ranged from 1.4

to 10.5 mM. These values are similar to competitive

games for Danish referees before and after a

training period (Krustrup & Bangsbo, 2001), and

demonstrate that the anaerobic system is highly

stimulated during the game. The observation that

seven of eight referees had higher blood lactate

values after the second half than after the first half,

illustrates that the physical demands are high

throughout the international games and emphasises

the need for physical training that focuses on HIR.

In the present study we also measured blood

glucose and demonstrated that values where main-

tained between 4 and 7 mM after both halves,

confirming the hypothesis that hypoglycaemia is not

a frequently occurring phenomenon during an

intermittent high-intensity activity such as refereeing

(see Bangsbo, Iaia, & Krustrup, 2007).

The assistant referees in the international games

observed in the present study covered the same total

distance, amount of HIR and sprinting as assistant

referees in national league games (Krustrup et al.,

2002). However, they performed 40% more side-

ways running and had lower heart rates compared

to observations for national league games (Krustrup

et al., 2002). Furthermore, they had no reduction in

HIR from the first to the last 15-min period of a

game which is in contrast to the 25% drop observed

for assistant referees in national league games.

These findings suggest that the assistant referees

in the international games are better prepared than

the domestic assistant referees. Nevertheless, the

amount of low-intensity forward running and

sideways running was significantly reduced for the

international assistant referees towards the end of

the game, which could be taken as a sign of

accumulating fatigue. It has been observed that

assistant referees have a decrease in sprint perfor-

mance at the end of national games (Krustrup

et al., 2002). On the other hand, the international

assistant referees observed in the present study had

no reduction in the amount of HIR towards the end

of the game, and the lowering of the sideways

running may be due to a general reduction in the

match tempo in the last part of the game due to

fatigue of the players as observed in a number of

occasions (Mohr, Krustrup, & Bangsbo, 2005;

Mohr et al., 2003).

The findings in the present study show that the

physical demands of referees and assistant referees

are high in international games. Therefore, it is

important to evaluate the fitness level of the match

officials. The intermittent nature of the locomotor

activities of referees and assistant referees with a

change in activity every 4–5 s and performance of

multiple brief and intense running bouts should be

reflected in the testing protocols. The Yo-Yo

intermittent recovery test consists of repeated 20-m

shuttles at progressively increasing speed, separated

by 10-s recovery periods and this test has been shown

to provide valuable information about the match-

related physical fitness of referees (Castagna et al.,

2005; Krustrup & Bangsbo, 2001). In 2005, FIFA

introduced new tests to evaluate the physical capacity

of match officials. One of the tests consists of

repeated 150-m runs at an average velocity of

18 km/h separated by 35 and 40 s recovery periods

for referees and assistant referees, respectively. The

test is primarily challenging the aerobic power and

anaerobic capacity (see Bangsbo, Mohr, Poulsen,

Perez-Gomez, & Krustrup, 2006). Referees demon-

strate high average heart rates and many episodes of

high anaerobic energy turnover, which creates a

situation where both the aerobic and anaerobic

energy systems are simultaneously taxed. However,

the present study showed that each bout of intense

running during the game is much shorter than that

used during the test, and the stimulation of the

anaerobic system appears to be much higher in the

test than in actual match play. For assistant referees

the aerobic loading is low-to-moderate during inter-

national games and future research should explore

whether the test requirements are unnecessarily high

for assistant referees. In the optimisation of the tests

for referees and assistant referees, it may also be

taken into account that the referees and assistant

referees are performing a significant amount of

backwards and sideways running, respectively. The

referees and assistant referees are also performing a

repeated sprint test consisting of 6640 m separated

by a 1:30-min recovery period, each sprint to be

covered within 6.2 and 6.0 s for referees and

assistant referees, respectively. As both referees and

1174 P. Krustrup et al.

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assistant referees are performing repeated sprints in a

game, in some cases 2–3 within a few minutes, it

seems reasonable to perform such a test. High

standards for assistant referees should also be set,

since a significant correlation has been observed

between performance of repeated sprint and the

ability to keep up with the off-side line (Krustrup

et al., 2002). Moreover, the present study showed

that assistant referees in international games perform

on average 17 sprints at near-maximal or maximal

speed, whereas referees perform 13 sprints of which

few are maximal. However, the length of each sprint

(40 m) may have to be shorter, as the mean distance

of a sprint for referees and assistant referees was 12

and 14 m, respectively, and rarely longer than 25 m

(present study; Krustrup & Bangsbo, 2001; Krustrup

et al., 2002). Taken together the activity pattern in

games are better reflected in the new FIFA tests, and

fitness training that is aimed at fulfilling the require-

ments of the tests may result in a better performance

during a game. However, the test battery may be

further improved to include tests specifically targeted

at the demanding game activities of the referees and

the assistant referees. In this respect, it remains an

open question whether optimal physical tests for

match officials can be performed on athletic tracks,

which appears to be a FIFA priority.

In conclusion, the present study showed that

referees in international games are performing more

high-speed running than observed in domestic

games, and that there is an increase in the distance

from infringements towards the end of game,

despite a significant amount of HIR. The assistant

referees are performing much less HIR than the

referees, but as much sprinting and more sideways

running. They were able to maintain the same level

of high-intensity work throughout a game, but had a

drop in the amount of sideways running towards

the end of a game. The study also showed that

the amount of HIR is directly correlated to

referees’ ability to keep up with play in international

games.

Acknowledgements

This study was supported by Danish Football

Association and the European Football Association,

UEFA. We would like to thank the match officials

involved in the study for their committed participa-

tion. We would also like to acknowledge the great

effort of Per Hansen, Jan Malm-Hansen, Mihai

Ursta Relu, Jorge Perez-Gomez, Mads Bendixen,

Rasmus Bischoff, Thomas Gunnarsson, Therese

Hornstrup, Karina Thomsen and Lena Varntoft in

filming the referees. Practical assistance and much

good advice were provided by the Referee Commit-

tee of the Danish Football Association.

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