JOURNAL OF SPORTS SCIENCE & MEDICINE
SEASON-TO-SEASON VARIATIONS OF PHYSIOLOGICAL FITNESS WITHIN A SQUAD OF PROFESSIONAL MALE SOCCER PLAYERS
Niall A. Clark1, Andrew M. Edwards2,3, R. Hugh Morton4 and Ronald J. Butterly3
1Charlton Athletic FC, London, UK, 2UCOL Institute of Technology, Applied Health Sciences, New Zealand, 3Leeds Metropolitan University, Carnegie Research Institute, Leeds, UK, 4Massey University, Institute of Food, Nutrition and Human Health, New Zealand.
© Journal of Sports Science and Medicine (2008) 7, 157 - 165
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|The purpose of this study was to examine season-to-season variations
in physiological fitness parameters among a 1st team squad of professional
adult male soccer players for the confirmatory purposes of identifying normative
responses (immediately prior to pre-season training (PPS), mid-season (MID),
and end-of-season (EOS)). Test-retest data were collected from a student
population on the primary dependent variables of anaerobic threshold (AT)
and maximal aerobic power (VO2 max) to define meaningful measurement
change in excess of test-retest technical error between test-to-test performances.
Participants from a pool of 42 professional soccer players were tested over
a set sequence of tests during the 3-year period: 1) basic anthropometry,
2) countermovement jump (CMJ) tests 3) a combined AT and VO2
max test. Over the 3-year period there were no test-to-test changes in mean
VO2 max performance exceeding pre-defined limits of test agreement
(mean of eight measures: 61.6 ± 0.6 ml·kg-1·min-1).
In contrast, VO2 at AT was significantly higher at the MID test
occasion in seasons 2 (+4.8%; p = 0.04, p < 0.05) and 3 (+6.8%; p = 0.03,
p < 0.05). The CMJ tests showed a test-to-test improvement of 6.3% (best
of 3 jumps) (p = 0.03, p < 0.05) and 10.3% (20-s sustained jumping test)
(p = 0.007, p < 0.01) between PPS2 and MID2 and thereafter remained stable.
Anthropometrics were unaffected. In summary, despite some personnel changes
in the elite cohort between test-to-test occasions, VO2 max values
did not vary significantly over the study which supports previous short-term
observations suggesting a general 'elite' threshold of 60 ml·kg-1
min. Interestingly, AT significantly varied where VO2 max was
stable and these variations also coincided with on- and off-seasons suggesting
that AT is a better indication of acute training state than VO2
Key words: Aerobic power, anaerobic threshold, countermovement jump, elite athletes.
There have been numerous studies conducted which have evaluated the physiological
characteristics of soccer players (e.g. Brewer and Davis, 1992;
Reilly et al., 2000;
Stølen et al., 2005)
and the physical demands of playing the game (e.g. Reilly and Thomas, 1976;
Edwards and Clark, 2006;
Krustrup et al., 2003).
However, there are few longitudinal reports on adult male professional soccer
players (Casajús, 2001;
Edwards et al., 2003a;
Reilly and Thomas, 1980)
and no studies have reported normative data from a pool of elite players
across more than one season. The absence of these basic data is problematic
when establishing appropriate 'threshold' levels of fitness among homogenous
groups of well-trained professional soccer players. This omission from the
current scientific literature is probably due to a combination of factors,
such as a reluctance of professional teams to release performance test results
to the scientific community, issues surrounding the absence of comparative
control groups, but also the limited opportunities for repeated testing
of the same players in well-controlled laboratory conditions during the
competitive season (Reilly, 2005).
The maintenance of fitness during a season is a key target for every team (Koutedakis, 1995) but this is a complex process reflecting the diverse physical demands of the game. The mean intensity of exercise during a soccer match has been estimated to approximate ~80% of maximal aerobic power (VO2 max) (Reilly et al., 2000; Stølen et al., 2005) and this intensity broadly resembles typical values of anaerobic threshold measurements in professional players (Edwards et al., 2003a). The association between VO2 max and distance covered during match play (Reilly and Thomas, 1976) has further been used to suggest that the predominant metabolic pathway during professional soccer is aerobic (Bangsbo, 1994). However, although elite soccer performance is, in part, dependent on a high cardiopulmonary fitness, VO2 max has not been correlated with high-intensity exercise during a game (Krustrup et al., 2003).
Several researchers have proposed that a VO2 max of ~60 ml·kg-1·min-1 is a minimal threshold for elite professional male soccer players (Helgerud et al., 2001; Reilly et al., 2000), but there is currently a lack of elite level normative data to support this observation and beyond the identification of a minimum 'elite performer' threshold, it is unclear whether cardiopulmonary fitness is of direct value to performance. In addition, it has yet to be established whether or not this variable is susceptible to seasonal variations among a homogenous population of elite players where changes in personnel are common, thus affecting the levelness of fitness among the squad; and also whether or not it is influenced both by long- and short-term factors such as: on- and off- seasons, training methods, frequency of match-play, and injuries.
In situations where players are well-matched for cardiovascular fitness it is likely that other match-related factors such as sprinting and jumping performances are important. Studies of motion-analysis in match-play suggest that almost all (~96%) sprints during games are <30-m and the majority of these are <10-m (Reilly and Thomas, 1976; Bangsbo, 1994). However, few studies of professional players have reported longitudinal measures of explosive capability (Casajús, 2001; Reilly and Thomas, 1980). One study (Reilly and Thomas, 1980) demonstrated an improvement in vertical jump performance at the beginning of the competitive season but reported no further change. This suggests that anaerobic characteristics are well maintained over the course of the season, although the lack of substantial confirmatory data from elite populations to support seasonal variations in either aerobic or anaerobic characteristics remains problematic.
The repeated measurements of fitness variables in professional players can be heavily influenced by participation rates that are compromised by injuries, match commitments, inter-club transfers, and general player availability. This is a common difficulty where the objectives of the researcher are of secondary importance to the professional team. For example, Casajús, 2001 reported well controlled measurements of physiological fitness from Spanish League players on two occasions between September (following 5 weeks of training), and February (mid-season) and observed a non-meaningful change of +1.7% in maximal aerobic power. However, of the 16 players who began that study, only 12 were available for testing on the second occasion. Due to this high level of participant attrition, no other studies have reported mean test responses in elite players over an extended period, probably due to similar difficulties which are clearly exacerbated over time. This omission from the scientific literature poses substantial problems for investigators seeking to establish normative physiological responses in relatively homogenous groups.
The purpose of this study is to examine the season-to-season variations of physiological fitness among professional adult male soccer players over a 3-year period utilising a more frequent and repetitive view of seasonal variation than reported previously (immediately prior to pre-season training, mid- season, and end-of-season) and, where possible, identifying meaningful performance changes in the context of pre-defined limits of agreement derived from empirical test-retest data collected in our laboratory.
reliability of the cardiopulmonary fitness test protocol
data: test-retest reliability of cardiopulmonary fitness test measurements
jump (CMJ) performance tests
mass and composition
main observation of this study was that mean VO2 max remained
relatively stable among a homogenous population of elite soccer players
and, in contrast to AT, did not change with different phases of the off-
and on-seasons. Despite occasional test-to-test changes in personnel,
the significant differences observed in AT measurements compared with
VO2 max (in the same players) clearly identifies AT as the
more sensitive measure of training state. This observation confirms our
previous observations from single test off- and on-season (Edwards et
Although VO2 max and AT responded similarly over the duration
of the study, the magnitude of change according to our criteria was only
of biological meaning in AT and these observations are supported by several
generic laboratory investigations reporting increases in measures of the
anaerobic threshold without parallel changes in VO2 max (Denis
et al., 1982;
Edwards et al., 2003a;
Henritze et al., 1985).
Figure 2 illustrates the observation
that AT demonstrated both significant changes and these were also in excess
of the pre-set limits we identified as estimates of test-to-test measurement
error. Our finding also supports the use of this technique to infer an
element of control in elite athlete studies where it is not always possible
to include a comparative control group. This may encourage others to report
data from elite populations which would be of assistance to the further
understanding of high quality performances across different sports.
|In conclusion, this study is, to our knowledge, the first report of inter-seasonal variations among the physiological fitness parameters of adult male professional soccer players. The findings demonstrated that VO2 max test performances were reasonably stable when measured across off- and on-seasons as all test-to-test changes were within the pre-defined limits of agreement indicating that variation was trivial. This appears to confirm our earlier observations (Edwards et al., 2003a) but was in contrast to several measures of AT which demonstrated significant change of biological meaning according to both the pre-defined limits of agreement and ANOVA analysis. Interestingly, the optimal mean test responses of the soccer players in this study generally coincided with the mid-season measurements where significant gains in several fitness indices were consistently observed. This presumably reflects enhanced motivation, and the avoidance of accumulative fatigue that may be prevalent at the end of season. However, although players were drawn from the same squad, some changes in player personnel between test-to-test measurements may have contributed to the observations in this study. Consequently, additional confirmatory studies are required to further support these findings.|
Employment: Head of Sports Science at Charlton Athletic FC.
Research interests: The physiology of elite soccer performance.
Andrew M. EDWARDS
Employment: Assoc Professor at UCOL Institute of Technology (NZ) and Visiting Research Fellow of Leeds Metropolitan University (UK).
Research interests: Thermoregulatory and respiratory responses to elite sports performance.
R. Hugh MORTON
Employment: Assoc Professor of Sport Science and Biostatistics at Massey University (NZ).
Research interests: Sports data analyses, mathematical models of response to exercise.
Ron J. BUTTERLY
Employment: Principal Lecturer in Exercise Physiology at Leeds Metropolitan University (UK).
Research interests: Energetics and physiology of ball games.