Seasonal Changes in Stress Indicators in High Level Football

Transcription

1 Training & Testing 259 Seasonal Changes in Stress Indicators in High Level Football Authors O. Faude 1, 2, M. Kellmann 3, 4, T. Ammann 2, R. Schnittker 2, T. Meyer 1, 2 Affiliations 1 Institute of Sports and Preventive Medicine, Saarland University, Saarbr ü cken, Germany; FIFA Medical Centre of Excellence 2 Institute of Sports Medicine, Department of Sports and Health, University of Paderborn, Germany 3 Ruhr-University of Bochum, Faculty of Sport Science, Germany 4 The University of Queensland, School of Human Movement Studies, Australia Key words soccer overreaching fatigue performance match exposure recovery Abstract This study aimed at describing changes in stress and performance indicators throughout a competitive season in high level football. 15 players (19.5 ± 3. years, 181 ± 5 cm, 75.7 ± 9. kg) competing under professional circumstances were tested at baseline and 3 times during the season 28 / 9 (in-season 1, 2, 3). Testing consisted of the Recovery-Stress Questionnaire for Athletes (Total Stress and Recovery score), vertical jump tests (counter movement and drop jump (DJ)), and a maximal ramp-like running test. Average match exposure was higher during a 3-weeks period prior to in-season 3 compared to in-season 1 and 2 (1.5 vs. 1 h / week, p =.5). Total Stress score was elevated at in-season 1 and 2 compared to baseline (p <.1) with a further increase at in-season 3 (p <.3; generalized eta squared ( η 2 g ) =.37). Total Recovery score was decreased at in-season 1 and 3 compared to baseline (p <.5; η 2 g =.21). Maximal running velocity (V max ) and jumping heights were not significantly affected ( η 2 g.4). Changes in DJ height and V max between baseline and inseason 3 were correlated with the corresponding changes in Total Stress score (r =.55 and r =.61, p <.3). Usual match exposure during a professional football season does not induce relevant changes in performance indicators. Accumulated stress and a lack of recovery towards the end of a season might be indicated by psychometric deteriorations. accepted after revision November 13, 21 Bibliography DOI /s Published online: January 26, 211 Int J Sports Med 211; 32: Georg Thieme Verlag KG Stuttgart New York ISSN Correspondence Dr. Oliver Faude, PhD Saarland University Institute of Sports and Preventive Medicine Campus Bldg. B Saarbr ü cken Germany Tel.: 49 /681 / Fax: 49 / 681 / o.faude@mx.uni-saarland.de Introduction Due to the high frequency of regular matches in modern high level football it is often assumed that there is danger of too little time remaining for adequate recovery during intensive competition periods. Such high demands may have a negative impact on match performance and injury risk [5, 7]. In particular, this might be true for highly demanding competition phases towards the end of a football season [7]. Monitoring of the recovery-stress state and performance may be warranted to avoid an imbalance between stress and recovery and, thus, to prevent excessive fatigue or overtraining [9]. While many studies have been conducted which evaluated a large number of physiological correlates for the timely diagnosis of overreaching and overtraining, no single valid marker has been established yet [3]. Therefore, it seems worthwhile to approach the problem of diagnosing fatigue by a multi-dimensional test panel which is easily applicable in practical settings. Up to now, there are only a few studies which evaluated the psychological and physiological responses throughout a competitive football season. Naessens et al. [28] analysed psychological measures together with nocturnal urinary noradrenalin excretion 6 times throughout one season. Based on the finding that changes in fatigue rate (subscore of the Profile of Mood States (POMS) questionnaire) was related to changes in urinary noradrenalin excretion it was suggested that these means may be useful to monitor overtraining and overreaching in highlevel football players. Those authors also claimed that overreaching is not uncommon in football. A detailed analysis of training and competition exposure, however, was not conducted in that study. Filaire and colleagues [9, 1] reported changes in some haematological, immunological, hormonal and psychological variables over the course of one complete season (including a highintensity training period) in male professional football players. They concluded that a combined psychological (POMS) and physiological moni-

2 26 Training & Testing toring (catabolic and anabolic hormones, uric acid) is appropriate to monitor training stress in relation to performance (winning percentage) in team sports. With regard to psychometric testing the Recovery-Stress Questionnaire for Athletes enables a detailed analysis of individual recovery-stress state and has previously been used to monitor the influence of intense training periods on psychological variables in different sports [4, 2, 21]. Coutts et al. [2, 3] observed decrements in strength, speed, power and maximal running capacity in semi-professional rugby players after an intensive 6-weeks training period. Similar changes in sprint times and jumping height were reported by Kraemer and colleagues [24] in 11 collegiate football (soccer) players competing in 19 matches during an 11-week period. As Coutts et al. [2, 3] intended to induce a state of overreaching and Kraemer et al. [24] analysed changes over a short season with extraordinary high match exposure, data on performance changes throughout a usual football season are still lacking. In light of the described gaps in the existing scientific literature, the present study aimed at describing changes in stress and performance variables throughout one competitive season in high level football players by means of a multi-dimensional panel of diagnostic tools (Recovery-Stress Questionnaire for Athletes (RESTQ-Sport), lower leg explosive power, maximal running capacity). To adequately simulate elite football, the study was conducted within a professional setting. Materials and Methods Study design and employed procedures are in accordance with the Declaration of Helsinki as well as the ethical standards of the IJSM [16]. The study was approved by the Ethics Committee of the Medical Faculty of the University of M ü nster (Northrhine- Westphalia, Germany). Each athlete gave his written informed consent before the start of the study. Participants and General Design Two football teams (32 field players) competing under professional circumstances on a national level (3 rd German league as well as highest national U-19 league including 4 U-2 and U-19 national team members) conducted a total of 5 tests throughout one complete season (July 28 to May 29 including a short winter break (2 3 weeks in December) and a second short preparation period (4 weeks in January), 44 weeks in total). Tests were performed before the onset of pre-season conditioning as well as evenly distributed throughout the season (September, November, February, April). There was at least one day between the tests and the last match and no intensive training session on the days prior to testing. Testing was conducted in the following sequence: RESTQ-Sport, vertical jump testing, and a ramp-like maximal exercise field test. Players who were injured for more than 2 consecutive weeks (N = 6) as well as players who changed the team during the season (N = 5) or missed at least 2 tests for other reasons (private obligations, minor acute injuries or infections, N = 6) were excluded. A total of 15 players (19.5 ± 3. years, 181 ± 5 cm, 75.7 ± 9. kg, including 2 national team players) performed a test at baseline (before pre-season preparation) as well as 3 times (in-season 1, 1 weeks after baseline, in-season 2 after 21 weeks, in-season 3 after 36 weeks) during the season. There were no significant differences at baseline between drop outs and players who were analysed (p >.16). Due to testing schedule some players conducted the in-season test 2 before and the remaining players after the winter break. There were no significant differences between those tests (p >.2). Individual exposure times in training and matches (regular and friendly matches) were recorded by the coaches. Exposure was expressed as cumulative individual exposure (training and match exposure [in hours] from baseline test to specific test day) and acute individual exposure (training and match exposure [in hours] in the 3 weeks prior to testing). Material and Procedures Recovery-Stress Questionnaire for Athletes The RESTQ-Sport was developed with particular regard to the requirements of high performance sports [2, 22, 23]. The RESTQ-Sport has been used in various sports (e. g., triathlon, swimming, football, rugby) to monitor the impact of training or competitive seasons in athletes [2]. The version used in this study consists of 52 items which can be aggregated to 19 scales. The items have to be self-rated on a 7-point Likert scale ranging from (never) to 6 (always) indicating how often the subject has participated in various activities during the past 3 days / nights. The scale values are calculated by taking the mean of the item values (2 or 4 per scale). This enables a detailed, multi-dimensional analysis of the individual recovery-stress state. The RESTQ-Sport consists of 1 stress-associated scales (Total Stress score, sum of scales 1 7 and 13 15, see Table 1 ) and 9 recovery-associated scales (Total Recovery score, sum of scales 8 12 and 16 19, see Table 1 ). The questionnaire shows good reliability as well as construct validity [2, 22, 23]. Players received detailed instructions prior to the first test and were asked to complete the RESTQ-Sport at the beginning of all testing sessions prior to all other tests and warm-up. Vertical jump testing Lower limb explosive power was assessed using a vertical counter movement jump (CMJ) and a drop jump (DJ) from a drop height of.35 m. Flight times (t [s]) and contact time were measured using a contact mat ( m). The electrical signal was transmitted to a PC and flight time was recorded (NTG 2., Haynl electronics, Sch ö nebeck, Germany). Jumping height (h) was calculated according to the formula: h = ⅛ *9.81 m /s2 *t2. Jumps were performed with the hands placed on the hips. During CMJ players were advised to dip from a standing position and immediately jump as high as possible. The take off had to be done as a continuous movement with no observable pause between downward and upward phases [31]. The drop jumps had to be performed aiming at maximum height with minimum contact time [31]. Since the flight time method can be biased by methodological flaws (e. g. landing with leg or hip flexion, jumping in horizontal direction), an experienced investigator validated each trial visually. Subjects were instructed to land in a fully extended position. When a jump deviated from that instruction, it was not included in the analysis. Both jumps were performed several times (5 7) and the best 4 trials were recorded and averaged for statistical analyses. Reliability of drop jump height and contact time has previously been shown to be high (ICC.98) [11]. Within-subject variation has been shown to be about 2 % for the CMJ [27].

3 Training & Testing 261 Table 1 Results of the Recovery-Stress Questionnaire for Athletes throughout the season. Data as mean ± SD. N = 15 baseline in-season 1 in-season 2 in-season 3 ANOVA η 2 g 1 general stress.7 ±.4 * 2.1 ± ± ± 1.1 < emotional stress 1.4 ±.5 * 2.7 ± ± ± 1.3 < social stress 1.8 ±.5 * 2.9 ± ±.9 3. ± 1. < conflicts / pressure 1.7 ± ±.9 ( ) 2.4 ± ±.9 < fatigue 1.8 ± ± ± ± lack of energy 1.6 ± ± ± ± physical complaints 1. ± ±.8 ( ) 1.7 ± 1.,# 2.4 ± 1.2 < success 2.6 ± ± ± ± social recovery 4. ± ± ± 1.1 ( ),(#) 3.2 ± physical recovery 3.5 ± ± ± ± general well-being 4.4 ± ± ± ± sleep quality 4.3 ± ± ± ± disturbed breaks 1.3 ± ± ±.7,#,( ) 2.3 ± emotional exhaustion.8 ±.7 * 1.8 ± ± ±.9 < injury 2.2 ± ± ±.8 (#), 3. ± being in shape 3.7 ± ± ± ± personal accomplishment 3.5 ± ±.8 3. ± ± self-efficacy 4.4 ± ± ± 1.,( ) 3.4 ± self-regulation 4.9 ± ± ± 1.,( ) 3.7 ±.7 <.1.23 η 2 g = generalized eta squared; * = baseline vs. all other tests, = sign. different from baseline, # = sign. different from in-season 1, = sign. different from in-season 2, (in parentheses:.5 < p <.1); scales 1 7 and are stress-associated scales and summed up to the Total Stress score; scales 8 12 and are recovery-associated scales and summed up to the Total Recovery score Maximal exercise field test Maximal running speed (V max ) was assessed using an incremental ramp-like exercise test until volitional exhaustion (mod. Montreal Track Test [29] ). The test was completed on a 2-m track marked by cones placed every 5 m on a regular soccer pitch. An artificial turf surface was chosen to minimise the influence of changing climatic conditions during the season compared to natural grass. Players ran with cleated shoes. Following an acoustic signal, the subjects performed the incremental field test, starting from 8. km *h 1 with speed then increasing by 1. km *h 1 every minute. The test was terminated when the participant failed to reach a marked 5 m zone before the next cone within the required time for 2 successive 5 m intervals or if he felt unable to cover another interval at the given speed. During the test, athletes were verbally encouraged by the technicians and by their coach. If the last step was not completed, V max was calculated according to: V max = V compl (t /6 s) [km /h] with V compl [km / h] being the last completed step and t [s] the elapsed time of the uncompleted step. V max during the ramp test has been shown to correlate well with distances covered at various speeds (total distance, high intensity running, very high intensity running; correlation r ~.6) during a football match in professional players and, thus, can be regarded as a valid estimate of football-specific endurance capacity [29]. Test-retest reliability for the original version of the Montreal Track test has been reported to be r =.97 [25]. Withinsubject variation for peak performance in incremental exercise tests has been reported to be about 2 % [17]. Heart rate was continuously recorded by means of a heart rate monitor (Polar S61 and S81, Polar Electro, Kempele, Finland). The highest heart rate before termination was taken as maximum heart rate (HR max ). Capillary blood samples (2 μl) were taken before, directly after termination as well as 2, 4 and 6 min after cessation from the hyperemized earlobe for determination of maximal blood lactate concentrations ([bla] max, enzymaticamperometric method, EBIO Plus, Eppendorf, Hamburg, Germany; CV = 2.9 % for lactate values of 7 mmol *L 1 ). Statistical procedures Exposure times were not normally distributed and, thus, are presented as medians. To compare exposure data, non-parametric statistical procedures were used (Friedman test for seasonal time course, post hoc: Wilcoxon test). All other variables were normally distributed. To analyse the time course of changes in all dependent variables during the whole season a repeated measures analysis of variance was calculated. In case of a significant global time effect, the Scheffé test was applied post hoc. Pearson s product moment correlation was calculated to analyse absolute changes in performance and psychological parameters between baseline and in-season test 3. Spearman s rank correlation was used to compare absolute changes in stress indicators with exposure times. To assess effect sizes generalized eta squared ( η 2 g ) was calculated as this measure has recently been considered most appropriate for repeated measures designs [1]. However, up to now η 2 g is not very common in exercise science research. These values will gain meaning when compared with other findings from similar, future studies [1] and, thus, are mainly reported to develop a sense for typical strength and responsiveness of the various variables used in this study. An α level of p <.5 was accepted as statistically significant. Results There was a continuous increase in exposure times throughout the season ( Fig. 1 ). When analysing the 3 weeks period prior to the tests, there was a tendency for higher exposure times in regular matches (p =.52) and significantly lower training exposure (p =.7) at in-season 3 compared to in-season 1 and 2. Total exposure (matches and training) was not significantly different during the 3 weeks prior to all tests (p =.15).

4 262 Training & Testing 3 weeks exposure time [h] total exposure time [h] 35 3 regular matches friendly matches training in-season 1 in-season 2 in-season 3 Fig. 1 Total exposure until tests (top) as well as during the 3 weeks period prior to tests (bottom). * = training exposure significantly different from in-season 1 and 2; Data as medians with lower and upper quartiles. score # * Recovery-Stress Questionnaire for Athletes Several stress scales of the RESTQ-Sport (General Stress, Emotional Stress, Social Stress, Emotional Exhaustion) were significantly elevated throughout the whole season compared to baseline ( Table 1 ). Furthermore, results from in-season 3 were significantly deteriorated in 5 scales (Conflicts /Pressure, Lack of Energy, Sleep Quality, General Well-Being, Personal Accomplishment) compared to baseline and in 6 scales (Physical Complaints, Injury, Disturbed Breaks, Social Recovery, Self-Regulation, Self- * (*) * Total Stress score Total Recovery score baseline in-season 1 in-season 2 in-season 3 Fig. 2 Total Stress score and Total Recovery score of the Recovery-Stress Questionnaire for Athletes throughout the season. # = Total Stress score significantly different from all other tests; * = Total Recovery score significantly different between marked tests; (in parentheses:.5 < p <.1). Data as mean ± SD. # Efficacy) compared to both other in-season tests. The remaining 4 scales (Fatigue, Success, Physical Recovery, Being in Shape) showed no significant changes throughout the season. There was a significant main time effect for Total Stress (p <.1, η 2 g =.37) and Recovery score (p =.1, η 2 g =.21). Post hoc testing revealed that Total Stress score was significantly enhanced at all in-season tests when compared to baseline (p <.1) with a further increase at in-season 3 (p <.3, Fig. 2 ). In addition, Total Recovery score was decreased at in-season 1 (p =.5) and 3 (p <.1) compared to baseline values and at in-season 3 compared to test 2 (p =.6). Performance Tests Jumping heights were not significantly affected throughout the whole season ( Table 2 ). However, DJ contact time continuously decreased with significantly lower values at in-season 2 (p =.2) and 3 (p <.1) compared to baseline. There was a significant main time effect for the maximal velocity in the ramp test (p =.4). However, post hoc analysis revealed a tendency for a decrease in V max from in-season 1 towards in-season 3 (p =.8, Table 2 ). No significant changes in HR max and [bla] max were observed. Individual reductions in DJ height and V max between baseline and in-season test 3 were significantly correlated with corresponding absolute increases in Total Stress score ( Fig. 3 ). In addition, cumulative individual exposure until in-season 3 was significantly related to absolute changes in Total Stress score between baseline and in-season 3 ( Fig. 3 ). Changes in all other parameters were not significantly related to exposure times (p >.4). Discussion The present study aimed at describing changes in stress indicators during the competitive season in high level football players. Our data suggest an increase in stress parameters after the preparation period which is mainly displayed by changes in the recovery-stress state. No relevant effects on physiological performance could be observed throughout the competition period. Further deteriorations in mood states parameters were apparent towards the end of the season indicating accumulated stress and a lack of recovery. Meeusen et al. [26] recently defined different stages on the (over)training continuum. Accordingly, overload training is usually designed to induce relevant adaptations leading to improved performance but results also in reversible acute fatigue. If training (or competition) stress is continued (possibly together with further non-sport-specific stressors), temporary performance decrements can occur. This state has been called functional overreaching. Further disruptions of the balance between training or competitive stress and recovery will result in prolonged performance decrements accompanied by severe changes in psychological or hormonal parameters (non-functional overreaching or overtraining syndrome) [26]. A decreased maximal performance capacity during incremental exercise tests has been observed in several overtraining studies in endurance athletes [3]. Coutts et al. [2, 3] reported reductions in maximal oxygen uptake, maximal aerobic velocity and performance in a multi-stage fitness test after 6 weeks of over-

5 Training & Testing 263 N = 15 baseline in-season 1 in-season 2 in-season 3 ANOVA η 2 g CMJ height [cm] 36.4 ± ± ± ± DJ height [cm] 34.6 ± ± ± ± DJ contact time [ms] 217 ± 38 * 23 ± ± ± 28 <.1.8 V max [km* h 1 ] 18. ± ± ±.8 (#) 17.9 ± HR max [min 1 ] 194 ± ± ± ± [bla] max [mmol* L 1 ] 11.2 ± ± ± ± η 2 g = generalized eta squared; CMJ = counter movement jump, DJ = drop jump, V max = maximal velocity, HR max = maximal heart rate, # [bla] max = maximal blood lactate concentration. * = baseline vs. in-season 2 and 3, = sign. different from in-season 1, (in parentheses:.5 < p <.1) Table 2 Results of the performance tests throughout the season. Data as mean ± SD. DJ height [cm] V max [km h 1 ] Total exposure [h] r =.55, p = RESTQ-Sport Total Stress score r =.61, p = RESTQ-Sport Total Stress score r =.52, p = RESTQ-Sport Total Stress score Fig. 3 Correlations between absolute changes (baseline to in-season test 3) in RESTQ-Sport Total Stress score and absolute changes in drop jump height (DJ, top), maximal ramp test velocity (V max, middle) and cumulative total exposure (bottom). RESTQ-Sport = Recovery-Stress Questionnaire for Athletes. load training in semi-professional rugby players. Thus, a decreased maximal exercise capacity may also be useful as a marker of overreaching in team sport athletes. It seems, however, questionable, if the slight reduction in V max towards the end of the season, which was observed in the present study, is really indicative of overreaching. A slight decrease in endurance capacity seems also possible. A negative impact of excessive stress on power abilities has previously been reported in team sport athletes. For instance, Kraemer et al. [24] reported deteriorations in speed, jumping heights and strength parameters during a 11-weeks competitive period (including 19 matches) in 11 collegiate football (soccer) players. Those impairments were considered critical for football players, particularly during the latter stages of the season [24]. Similar changes in power parameters after an intensive training period in rugby players were reported by Coutts et al. [2, 3]. These studies either intended to induce a state of overreaching [2, 3] or analysed an 11-weeks period of extraordinary high match exposure on performance markers [24]. The exact reasons for the reported deteriorations in speed and power are unknown. In the present study jumping heights remained unaffected. A significant decrease in drop jump contact time from baseline to the first inseason test was observed. This improvement is likely due to the pre-season training which comprised plyometric training and football-specific movement pattern including stretch-shortening-cycle activities. During the season drop jump contact time remained nearly constant. To summarize, the slight changes in V max as well as in drop jump contact time during the season seem to be of minor practical relevance. Therefore, when comparing the results of Coutts et al. [2, 3] and Kraemer et al. [24] with our data, it seems justified to conclude that on a group average no relevant physiological signs of fatigue or overreaching were present over the course of the football season. More pronounced changes could be observed in the recoverystress state. The RESTQ-Sport has been used in different sports for monitoring the impact of training on mood states [4, 19 21]. Considerable differences in most RESTQ-Sport scales as well as in Total Stress and Total Recovery scores between baseline and in-season measurements may reflect increased stress during the season compared to a more recovered state after the transition period prior to the beginning of the season. However, no extraordinary in-season values were observed. Mean group values for all subscores were between 2 and 3 (according to sometimes ) for the stress scales and around 4 (according to often ) for the recovery scales on the 7-point Likert scale. Towards the end of the season further deteriorations in several areas were present. At in-season 3 players had the highest cumulated as well as the highest acute match exposition. A moderate correlation was observed between cumulated total football exposure and absolute changes in Total Stress score. Furthermore, both participating teams were involved in the struggle against relegation. It may be speculated that this could at least partly be responsible for the observed changes in the recovery-stress state. In particu-

6 264 Training & Testing lar, the observed deteriorations in scales like Self-Efficacy, Self- Regulation, Conflicts / Pressure, Emotional Exhaustion, Social Recovery and Personal Accomplishment might have been influenced by this fact. Psychological deteriorations are among the first signs of overreaching in endurance sports [3]. Thus, the observed changes might be interpreted as beginning overreaching, although no physiological impairments were present. Whereas the mean group scores are not extraordinary, individual players could be identified who showed a diminished recovery-stress state. Therefore, individual changes of the recovery-stress state might indicate which players are at risk for developing (non-functional) overreaching. In this regard the correlations between changes in Total Stress score and DJ height and V max are of interest. Individuals with the greatest increase in stress state showed also the most pronounced impairments in reactive power and maximal running capacity. In football deteriorations on a group level might have an important impact on team performance. However, the early recognition of individual impairments seems to be more relevant to identify players who are at risk of developing a state of (nonfunctional) overreaching. Both psychometric questionnaires (intentional manipulation, for instance because players fear that the coach will make substitutions [3] ) as well as maximal performance testing (repeated maximal effort necessary) are susceptible for methodological biases when frequent testing is intended. Thus, a combined assessment of psychological and performance measures might be recommended for practical purposes. Interestingly, deteriorations in the recovery-stress state towards the end of the season were particularly present in scales like Physical Complaints and Injury (indicating muscle stiffness and vulnerability to injury). Junge et al. [18] observed that nearly 8 % of football players from the 3 highest Czech divisions suffered from physical complaints with about half of those players reporting muscle / tendon pain. The authors concluded that the prevalence of such complaints should be considered in medical care of football players. In addition, Ekstrand et al. [7] observed that about 3 % of the players who played regularly in international matches during the end of the season were injured during the FIFA World Cup 22. An influence of accumulated stress and fatigue at the end of the season on injury proneness (in particular to muscle or overuse injuries) should, thus, be considered. This might be important because muscle injuries are the most common injury type in high level male football [6, 8, 14]. In accordance with Ekstrand et al. [7] it can be concluded that players may cope with high demands in the short-term (here: 3 weeks). However, negative impact of accumulated fatigue on performance and injury proneness in the long-term cannot be ruled out. Limitations of the Study Although our participants were playing at a national level, the question remains whether the present results can be easily transferred to professional football at the international level. Average match and training exposure of the players in the present study (1 to 1.5 match hours and 6 training hours per week) is comparable to that of professional football players competing at the highest level in the UEFA Champions League (41 match hours and 213 training hours during a 44 weeks season [6] ). Nevertheless, these are average values and in single players exposure times can be considerably higher [6, 7]. Moreover, no statement with regard to the influence of training and match intensity on the analysed parameters can be made from the present data. Additionally, further stressors (e. g. mass media, financial burdens, frequent travelling) have to be considered in elite players which necessitates careful transfer of our results. Further research is necessary for evaluating stress in more outstanding players. Otherwise, professional players are probably very carefully monitored while, for instance, high level youth players are also exposed to a high number of matches but medical and scientific support is less common. Thus, the present results are certainly of interest for this population, too. A further limitation might be seen in the choice of parameters which were assessed in the present study. Exercise-induced fatigue is a complex phenomenon resulting in symptoms of several organ systems. A huge amount of possible markers has been investigated during the past decades, including biochemical, immunological, vegetative, hormonal, physiological, and psychological parameters [12, 15, 26, 3]. The present study was not designed as a broad based analysis of a wide variety of parameters. In contrast, it was intended to assess stress and fatigue with a well-founded economical test panel which can be easily applied in daily practice. In addition to the chosen performance parameters, match analysis may be seen as the best indicator of real competition performance in football players and, thus, might be considered for future research in this area. Such an approach, however, is very complex and expensive. Moreover, as match performance characteristics of football players are dependent on the opponent and on tactical aspects and high-intensity activities during match play show high match-to-match variability [13], it seems questionable, whether such an approach would have benefit in detecting acute fatigue-induced performance decrements. Conclusions and Future Perspectives From the results of the present study it is concluded that usual match exposure under professional circumstances does not induce relevant physiological signs of overreaching in high level football players on a group level. Nonetheless, accumulated stress and a lack of recovery towards the end of a season might be indicated by deteriorations in the recovery-stress state. Combined psychological and performance testing is recommended to identify single players who are at risk for developing overreaching. Future research should be designed to focus on individual responses to excessive overload, on the transferability of the results to the elite level, on a possible link between overreaching and injury proneness as well as on appropriate interventions to avoid severe deteriorations. Acknowledgements We thank all players as well as the coaches of the participating clubs. Oliver Faude received a Jo ã o Havelange scholarship from FIFA (Federation International de Football Associations, Zurich, Switzerland) and the International Centre for Sports Studies (CIES, Neuchatel, Switzerland) for this project.

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