Jour nal of Sports Sciences, 1997, 15, 257 -263
Energetics of high-intensity exercise (soccer) with
particular reference to fatigue
T. R E IL LY
C entre for Sport and Exercise Sciences , School of H uman Science s , Liver pool John M oores U niversity, B yrom
Street , Liver pool L3 3A F, UK
Accepted 16 Septem ber 1996
Soccer entails intermittent exercise with bouts of short, intense activity punctuating longer periods of low-level,
m oderate-intensity exercise. High levels of blood lactate may sometim es be observed during a match but the
active recovery periods at subm aximal exercise levels allow for its removal on a continual basis. While anaerobic
efforts are evident in activity with the ball and shadowing fast-moving opponents, the largest strain is placed on
aerobic m etabolism.
On average, competitive soccer corresponds to an energy expenditure of about 75% maximal aerobic power.
The energy expenditure varies with playing position, being highest among mid® eld players. M uscle glycogen
levels can be reduced towards the end of a gam e, the level of reduction being re¯ ected in a decrease in work
rate. Blood glucose levels are generally well-m aintained, although body tem perature may rise by 2¡C even in
temperate conditions.
The distance covered by players tends to under-re¯ ect the energy expended. Unorthodox m odes of motion
- running backwards and sideways, accelerating, decelerating and changing direction - accentuate the
m etabolic loading. These are compounded by the extra requirements for energy associated with dribbling the
ball and contesting possession. The overall energy expended is extreme when players are required to play extratime in tournaments. Training, nutritional and tactical strategies may be used to reduce the effects of fatigue
that may occur late in the game.
K eywords : Aerobic metabolism , anaerobic metabolism, glucose, lactate, muscle glycogen.
Introduction
Soccer is probably the m ost popular sport worldwide,
w ith about 120 m illion registered players (Ekblom,
1986). It is played in all continents and participation is
especially increasing at underage (youth and under),
wom en’s and veteran’s levels. Its popularity is m ost
notable at a spectator level by the huge television audiences for the m ajor com petitions. At this professional
level, there are many physiological stresses associated
w ith competitive play that call for high levels of physical
® tness on the part of the players. T his review is focused
on the exercise intensity of playing soccer and the factors that m ay cause performance to fall off in the later
stages of the gam e. T his decline in perform ance characterizes fatigue.
The exercise intensity during soccer play can be indicated by the overall distance covered by each player
(Reilly, 1996). This is a global m easure of work rate,
w hich represents a com pilation of discrete actions or
m ovements for the whole m atch. These activities can be
classi® ed according to type of action or m ovement,
0264 -0414/97
©1997 E. & F.N. Spon
intensity (quality), duration (distance) and frequency.
The activities m ay be aligned to a tim e-base so that
average work:rest ratios can be determ ined. T hese
work:rest ratios can provide m odels for laboratory
investigations of fatigue in exercise conditions such as
soccer play, and can also be included as elem ents in
soccer players’ training program m es. The disclosure of
work-rate pro® les can be com plem ented by m onitoring
physiological responses to increase understanding
about the stresses that com petitive play entails. They
also allow for identifying decrem ents in performance as
the game progresses.
Work-rate pro® les
The energy expended during soccer play is a function
of the total distance covered throughout the 90 m in of
a m atch (Reilly, 1994). M ethods of m onitoring m ovem ents of players during com petition have included
tape-recorded com m entaries, video-recordings, ® lm
analysis, synchronized trigonom etric techniques and
258
com puter-aided video analysis (Reilly, 1996). W hatever
m ethod is adopted, it m ust com ply with quality control
criteria and provide valid, objective and reliable
observations.
There is a consensus in the literature that out® eld
players cover 8 -12 km during a gam e (Reilly, 1996).
T his encom passes over 1000 different activities, with a
change in the type or level of activity occurring about
once every 6 s (Reilly and T hom as, 1976). T he relative
distances covered in the different positions in a team
are shown for out® eld players in F ig. 1. M asked within
these categories are sideways and diagonal m ovem ents
and skills within the game that have energetic consequences, such as jum ping to w in possession of the ball,
kicking it, tackling, and so on. T he broad m ovem ent
categories neglect the frequent changes in pace that are
called for - runs to follow opponents, to m aintain
defensive or offensive lines, as well as chase the ball.
Reilly
W hile the total am ount of work, as indicated by the
distance covered, m ay var y from gam e to gam e for any
individual player, the am ount of high-intensity exercise
appears to be m ore constant (Bangsbo, 1994a).
C ruising and sprinting m ay be com bined to represent high-intensity activity during soccer play. T his
would m ean that the ratio of low-intensity to highintensity exercise is approxim ately 2:1 if indicated by
the distance covered (Reilly and T hom as, 1976). W hen
referred to a tim e-base, the calculated ratio is about
7:1. This indicates a predom inant reliance on aerobic
energy. O verall, the rest periods average 3 s every 2
m in, although the low-activity movem ents (and rest
periods) increase towards the end of the gam e when
players cannot m aintain their running in support of
team m ates or covering for them . As only about 2% of
the total distance covered is in possession of the ball,
the majority of activity is perform ed `off-the-ball’ in
positional m anoeuvres on the periphery of the actions
`on the ball’ .
W hile the m ajority of the exercise associated with
com petitive soccer is at subm axim al intensities, the
im portance of the all-out efforts should not be discounted. Sprints are noted to occur about once ever y 90 s
and high-intensity efforts (cruises plus sprints) once
every 30 s (Reilly and Thom as, 1976; Reilly, 1994).
The tim ing and direction of these runs, whether in possession of the ball or `off-the-ball’ , are m ore im portant
than the velocity. These activities at high intensity constitute the anaerobic com ponents of soccer play and
often their successful execution determ ines the result of
a gam e.
Fatigue
F igure 1 Distance covered (mean ± S . D .) according to playing position in soccer matches (modi® ed from Reilly and
Thomas, 1976).
The distance covered in the second half of a gam e
tends to be less than in the ® rst half. T his is a m anifestation of fatigue, de® ned as a decline in perform ance
due to the need to continue perform ing. An overall
drop of 5% over the second half com pared with the
total distance covered in the ® rst half has been reported
by Bangsbo et al. (1991) for D anish players. T he corresponding difference covered was about 450 m in Belgian university players (Van G ool et al., 1988).
N evertheless, aerobic ® tness does seem to allow players
to continue at a high work rate, as an inverse relation
Ç
between m axim al aerobic power ( VO
2 m ax) and decrem ent in work rate has been noted (Reilly and T hom as,
1976). Fatigue is m ost pronounced in centre-backs and
strikers, and less apparent in m id® eld players and fullÇ 2 m ax values.
backs, who tend to have the higher VO
Although m id® eld players cover the greatest distances
am ong players in out® eld roles, their superior aerobic
259
Energetics of high-intensity exercise
® tness levels enable them to m aintain a high exercise
intensity throughout the gam e.
The level of m uscle glycogen stores pre-m atch is also
likely to delay the onset of fatigue. Saltin (1973) ® lm ed
soccer players during a com petitive gam e, sam pling
each subject’s activity for 3 m in at a tim e. He reported
that the soccer players with low glycogen content in the
quadriceps m uscles before the m atch covered 25% less
distance than the other players. T he m ost striking consequence was in running speed, since the players with
initially low glycogen stores covered 50% of the total
distance walking and 15% at top speed, in contrast to
27% walking and 27% sprinting for players who started
with high m uscle glycogen concentrations. It would
seem that attention to dietary m eans of boosting glycogen stores pre-m atch and avoiding hard training the
day beforehand would help in delaying fatigue, especially in m atches w here extra-tim e is possible.
The occurrence of fatigue m ay be linked with a host
of physiological factors. Bangsbo (1994a) attem pted to
identify the intram uscular factors causing fatigue in a
series of laboratory-based investigations. It proved difficult to identify any single factor (e.g. hydrogen ions,
lactic acid, potassium im balance, am m onia or energy
depletion) or precise com bination of factors that would
exp lain fatigue de® nitively.
The behaviour of players and m atch phenomena
attest to the occurrence of fatigue. The distribution of
goals scored during football m atches shows a bias
towards m ore goals than predicted being scored towards the end of the gam e (Reilly, 1996). T his cannot
be attributed to a fall in work rate, which should affect
both team s equally. N or can it be attributed to a fall in
blood glucose, as the liver releases enough glucose during a m atch to m aintain euglycaem ia (Bangsbo,
1994a). Its exp lanation is likely to be accounted for by
a com plex of phenom ena, including increased risktaking by the team that is behind, a change in tactics
due to the proxim ity of the end of the gam e, and lapses
in concentration or m ental fatigue. D eterioration in
m ental perform ance related to soccer-speci® c decisionm aking is evident only in less-skilled players (M arriott
et al., 1993).
The style of play can in¯ uence the physiological
demands on players. The `direct m ethod’ of play, characterized by the national team s of Ireland and N orway,
m aintains the gam e at a high pace (Reilly et al., 1992).
T his style has a levelling effect on the work rate of out® eld players, since they are all expected to work at a
high intensity `off-the-ball’ . There are particular
demands on forwards to pressurize defenders and thus
prevent a slow, methodical attack being built up. T he
tactics of both these national team s were m odi® ed in
the 1994 World C up, where the hot conditions pre-
vailed against the maintenance of a consistently high
work rate through out the gam e.
Physiological responses to match-play
Energy exp enditure during soccer m atch-play m ay be
indicated by direct means using D ouglas bags or portable telem etric devices such as Cosm ed K2 or Metam ax. Both m ethods have limitations in that their use is
only feasible in sim ulations of m atch-play and they
inhibit full involvement in the gam e. M easurem ents of
blood lactate periodically at intervals during a `friendly’
gam e and measurem ent of the rise in core tem perature
provide indications of the m etabolic processes engaged,
but lack precision for calculating energy expenditure.
The m ost widely used strategy has been to m easure
heart rate during m atch-play and juxtapose the obserÇ
vations on heart rate - VO
2 regression lines determ ined
during increm ental running on a treadm ill. The estiÇ 2 from obser vations of heart rate is likely to
m ate of VO
overstate the actual O 2 consumption due to the factors
(heat, emotional stress, static exercises) that cause
Ç
heart rate but not VO
2 to rise. The error is though t to
be sm all, since it is only for short periods that the relaÇ
tion between heart rate and VO
2 in the gam e differs
from that obtained in laborator y conditions (Bangsbo,
1994a). T he heart rate in itself provides a useful index
of overall physiological strain, quite apart from its use
Ç
in estim ating VO
2 (Reilly and Thom as, 1979).
A representative sam ple of results from studies of
heart rate during actual soccer m atches is given in
Table 1. H eart rates average around 165 beats m in -1 ,
which corresponds to a relative m etabolic loading of
Ç
about 75% VO
2 m ax. The resultant energy exp ended
for a player with 75 kg body m ass is 70 kJ m in -1 . This
is in excess of the energy requirem ents of locom otion
over 11 km because of the extra energetic demands
associated with soccer activities. T hey include jum ping,
changing direction, accelerating and decelerating, tackling, perform ing other gam es skills, and so on.
O bservations on blood lactate responses to exercise
are used to indicate anaerobic glycolysis. T he data are
variable, possibly being an artefact of the tim ing of the
sam ple. Values are generally not high, although concentrations approaching 10 m m ol l-1 m ay be noted. Blood
lactate concentrations tend to be higher at the more
intense levels of com petition (Ekblom , 1986) and in
sam ples obtained at the end of the ® rst half com pared
to the end of the second half. W hile lactate concentration in blood underestim ates m uscle lactate production, it is likely that the overall anaerobic energy yield
from this source during a gam e is sm all. This is because
the total duration of high-intensity exercise during a
m atch (including cruising and sprinting) accounts for
260
Reilly
Table 1 M ean heart rate during soccer matches
M atch situations
M odel 10 m in game
Sam ple 10 m in gam e
Friendly 90 min match
Friendly 90 min match
Competitive 90 min gam e
Competitive 90 min gam e
Heart rate
(beats m in -1 )
Source
160
165
161
169
161
171
Seliger (1968a)
Seliger (1968b)
Ogushi et al. (1993)
Ali and Farrally (1991)
Florida-Jam es and Reilly (1995)
Bangsbo (1994b)
only about 8% of gam e tim e and the average sprint is
for a distance of about 14 m. The vast majority of effort
is at low to m oderate intensity and engages aerobic
processes.
Bangsbo (1994a) reported that the free fatty acid
concentrations in the blood increased during a soccer
m atch and m ore so during the second half of the
m atch. As glycerol showed only a m inor increase, this
was deemed to represent a signi® cant gluconeogenic
precursor during soccer play. Intram uscular lipolysis
probably also occurs and overall the contribution of fat
to total energy m etabolism is likely to be about 20%
(Bangsbo, 1994b). It will exceed this when a m atch
runs the full course of extra-tim e.
The energy expended during soccer play contributes
to a rise in body core tem perature and leads to sweating
to lose heat by evaporation to the environm ent. T he
elevation in body tem perature m ay be greater during
interm ittent exercise than during continuous exercise
of sim ilar overall work output (Cable and Bullock,
1996). Ekblom (1986) reported average rectal tem peratures of 39.5¡C in players at the end of a Swedish
First D ivision soccer m atch. The corresponding average for players of lower standard was 39.1¡C, re¯ ecting
a lower overall pace of play. Soccer players can lose 3
litres or m ore of ¯ uid during 90 m in of a com petition in
the heat. This ® gure is an average and varies with the
clim atic conditions as well as between individuals
(Reilly, 1996). T hose who sweat profusely are likely to
becom e dehydrated near the end of the gam e and
exp erience fatigue. A ¯ uid loss of 3.1% body m ass has
been reported during a m atch at 33¡C and 40% relative
hum idity. A sim ilar amount of ¯ uid was lost when the
am bient tem perature was 26.3¡ but hum idity was 78%
(M ustafa and M ahm ood, 1979). Acclim atization helps
to m aintain a desirable work rate during contests in hot
conditions: this m ay be an in¯ uential factor in dictating
the overall pace at w hich the gam e is played.
G am e-related activities
T he m ism atch in energy calculations based on values of
distance covered in a gam e and values obtained from
Ç
employing the heart rate - VO
2 relationship is due
largely to the energetic demands of gam e-related activities not accounted for in a crude m easure of locom otion such as overall distance. Som e attem pts have been
m ade to assess the m agnitude of the physiological
demands of gam e skills in excess of the energy cost of
m otion. D ribbling the ball is an exam ple of one skill
that has been isolated for study.
Reilly and Ball (1984) investigated the additional
energetic cost of dribbling a ball on a m otor-driven
treadm ill at speeds of 9, 10.5, 12 and 13.5 km h -1 .
Their protocol allowed players to control the ball, playing it against a rebound box at the front of the treadm ill
belt at a dictated rate. T he added cost of dribbling was
5.2 kJ m in -1 irrespective of the speed of m otion (Fig.
2). The elevation in m etabolism was paralleled by an
increase in rating of perceived exertion and in blood
lactate. The increased energy cost is partly attributable
to the extra m uscular activity required to control the
ball and propel it forward. There is also likely to be a
contribution due to the departure from an optim al
stride rate, which is increased in dribbling. A variation
in stride length occurs in a gam e when the player is
directly engaged in play or seeks to use this alteration in
stride pattern to outw it an opponent. K awakam i et al.
(1992) demonstrated the high oxygen cost of dribbling
in a ® eld setting; values ranged from 2.0 and 4.0 litres
m in -1 for drills such as 1 vs 1 and 3 vs 1 practices.
T he direction of m ovem ent also in¯ uences the
energy cost of exercise. Around 16% of the distance
covered by players is in m oving backwards, sideways or
`jockeying’ for position (Reilly, 1996). T his percentage
is highest in defenders. Running backwards and running sideways are sim ilar in term s of energy exp enditure but are elevated com pared to the energy used in
running normally (Table 2). T he extra cost of the unorthodox modes of motion increases disproportionately
with the speed of m otion (Reilly and Bowen, 1984).
Clearly, an im provem ent in m ovem ent economy in
running backwards and sideways would be of bene® t to
the player and should be incorporated into training
drills.
Energetics of high-intensity exercise
261
F igure 2 The added energy cost and elevation in blood lactate with dribbling a ball at different velocities of movem ent
(modi® ed from Reilly and Ball, 1984)
Strategies to reduce fatigue
Players w ho are aerobically well trained are better able
to m aintain their work rates towards the end of the
gam e than those of poorer aerobic ® tness (Sm aros,
1980; Reilly, 1994). A program m e of aerobic training
also speeds recovery following high-intensity efforts.
Active recover y at low to m oderate intensity accelerates
rem oval of lactate from the blood compared to standing
still (Gollnick and H erm ansen, 1973).
N utritional strategies can also be effective in decreasing the effects of fatigue. Saltin (1973) had demonstrated the im portance of pre-start m uscle glycogen
levels in players’ performance. K irkendall (1993) investigated the effects of a glucose polym er supplement on
work rate during soccer matches. Players were fed
either 400 m l of the polym er or a placebo pre-game
and at half-tim e. N o effect was evident in the ® rst half
but distance covered in the second half was 25%
Table 2 M ean (± S .D .) blood lactate concentrations
(mmol 1 -1 ) during soccer
First-half
5.1±
5.6±
4.9±
4.9
4.4±
1.6
2.0
1.9
1.2
Second-half
3.9± 1.6
4.7± 2.2
4.1± 1.3
3.7
4.5± 2.1
Source
Rohde and Espersen (1988)
Gerisch et al. (1988)
Sm aros (1980)
Bangsbo et al. (1991)
Florida-James and Reilly (1995)
greater and the distance covered at speed 40% greater
for the glucose polym er condition. Sim ilarly, Foster et
al. (1986) examined the effects of a glucose polym er
solution on perform ance in successive m atches of an
indoor tournam ent. Players com peted in a 50 m in
gam e, rested for 60 m in and then played again. In the
interm ission, they consum ed either a glucose polym er
solution or a placebo. Players supplem ented with the
glucose polym er ran further and faster in the second
gam e than players w ho were given the placebo.
T he energy provided in the glucose drinks delays
fatigue, partly by saving m uscle glycogen stores. Leatt
and Jacobs (1989) exam ined players who were given
either 500 m l glucose polym er solution or placebo 10
m in pre-gam e and at half-tim e. Glycogen reduction
was greater in the placebo group than in those subjects
given the glucose polym er, demonstrating that glucose
ingestion decreased the net m uscle glycogen utilization
during soccer.
T he bene® cial effects of carbohydrate ingestion m ay
not be m anifest in the execution of soccer skills late in
the game. Zeederberg et al. (1996) failed to show any
in¯ uence of ingesting a glucose polym er solution on
m otor skills such as tackling, heading, dribbling and
shooting during a gam e. N evertheless, youth professional soccer players have reported positive subjective
effects of consum ing a m altodextrin solution during a
long training session w here perform ance decrements
would otherwise be expected (M iles et al., 1992).
262
D ehydration can contribute towards fatigue, particularly w hen matches are played in the heat. A strategy
for rehydration for soccer players has been outlined
elsewhere (Maughan and Leiper, 1994). T he am eliorative effects of rehydration at half-tim e, and since the
1994 World Cup in the U SA at the sidelines when
breaks in play perm it, have been dem onstrated m ainly
in laboratory studies of 90 m in exercise (Reilly and
Lewis, 1985), rather than in soccer m atches w here conditions are m ore dif® cult to control.
A team w ith the superior tactical ability can dictate
the pace of the gam e so that the perform ance capabilities of out® eld players are not overtaxed. Alternatively,
players m ay share high-intensity bouts in turn so that
the overall pace of play is m aintained. In environm ental
conditions such as at altitude, the ability to pace the
total team effort econom ically is especially im portant.
O verview
T he gam e of soccer can be played at an intensity that
taxes both aerobic and anaerobic param eters. T he aerobic capacities determ ine the degree to which a high
work rate can be sustained throughout the entire
gam e.
Gam e-related activities im pose additional energetic
demands on players above those associated w ith running. Players have to be capable of optim al perform ance in these activities to contribute to a successful
m atch outcom e. Training and dietary strategies m ay be
used to m inim ize the effects of fatigue, particularly
those exp erienced in the late stages of a gam e.
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