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Journal of Sports Sciences Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/rjsp20
Repeated monitoring of blood parameters for evaluating strain and overload in elite football players: is it justified? a
a
Steffen Meister , Karen aus der Fünten & Tim Meyer
a
a
Institute of Sports and Preventive Medicine, Saarland University, Saarbrücken, Germany Published online: 07 Jul 2014.
Click for updates To cite this article: Steffen Meister, Karen aus der Fünten & Tim Meyer (2014) Repeated monitoring of blood parameters for evaluating strain and overload in elite football players: is it justified?, Journal of Sports Sciences, 32:13, 1328-1331, DOI: 10.1080/02640414.2014.927070 To link to this article: http://dx.doi.org/10.1080/02640414.2014.927070
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Journal of Sports Sciences, 2014 Vol. 32, No. 13, 1328–1331, http://dx.doi.org/10.1080/02640414.2014.927070
POINT – COUNTERPOINT
Repeated monitoring of blood parameters for evaluating strain and overload in elite football players: is it justified?
STEFFEN MEISTER, KAREN AUS DER FÜNTEN & TIM MEYER
Downloaded by [New York University] at 11:00 12 February 2015
Institute of Sports and Preventive Medicine, Saarland University, Saarbrücken, Germany (Accepted 19 May 2014)
Keywords: blood parameters, strain and overload, football
Background Venous blood sampling is repeatedly conducted in many elite athletes to screen for deficits and earlystage illness. Another motivation for frequent blood sampling is monitoring physiological stress and fatigue to assess recovery needs and prevent performance decrements. However, there is some uncertainty about the existence of sufficient scientific evidence for these procedures and an appropriate selection of parameters. During a typical football season, it is noteworthy that for a given blood sample acute effects of training and competition (from the days before) cannot be safely discerned from chronic changes (due to the cumulation of exercise loads from the weeks or months before). Therefore, an overlap of acute exercise-induced and chronic changes is possible. Besides other aspects, this has to be taken into account for the correct interpretation of blood values. Acute and chronic effects of exercise on blood parameters Acute exercise effects Exercise leads to profound acute changes, i.e. within hours after training, in several blood parameters. Haemoconcentration due to sweat loss and due to fluid shifts from blood vessels to interstitial spaces has been considered one important mechanism of exercise-induced alterations (El-Sayed, 1998; Gillen
et al., 1991). A further effect of acute endurancetype exercise is leucocytosis and a mobilisation of leucocyte and lymphocyte subpopulations (Gabriel, Schwarz, Born, & Kindermann, 1992). A humoural immune reaction can be found after anaerobic exercise: C-reactive protein (CRP) was shown to be elevated as part of an acute-phase response after repeated short bouts of high-intensity cycling (Meyer, Gabriel, Ratz, Muller, & Kindermann, 2001). Serum enzymes like creatine kinase (CK), aspartate-aminotransferase (AST) and urea can also be affected by prolonged exercise (Haralambie & Berg, 1976; Noakes, 1987). CK has even been established as serum marker to quantify training- and competition-induced muscle damage in sports (Brancaccio, Maffulli, & Limongelli, 2007). In cases of high (eccentric) biomechanical strain, CK typically peaks 24–48 h after exercise and can be elevated up to several days (Newham, Jones, & Edwards, 1986; Noakes, 1987). Apart from mechanical strain and microtrauma in skeletal muscle, serum CK levels are strongly affected by genetically determined muscle fibre distribution (Wong et al., 1983) and muscle cell permeability (Haralambie, 1973; Nicholson, Morgan, Meerkin, Strauss, & McLeod, 1985; Schwartz, Carroll, & Douglas, 1971). Additionally, the type of training and individual response to exercise can significantly alter CK. Thus, knowledge of baseline levels and individual responsiveness of CK activity seems to be necessary for an appropriate interpretation.
Correspondence: Steffen Meister, Institute of Sports and Preventive Medicine, Saarland University, Saarbrücken, Germany. E-mail: [email protected] © 2014 Taylor & Francis
Repeated blood monitoring in football players
Downloaded by [New York University] at 11:00 12 February 2015
Chronic exercise effects As a result of long-term regular training (e.g. longer than 21 days), some training-induced adaptations of blood parameters can be observed too (Sawka, Convertino, Eichner, Schnieder, & Young, 2000). These “chronic” changes mainly consist of a haemodilution due to an increase of plasma volume, which can exceed the gain in red blood cell mass. After a 9-month endurance training for a marathon in 16 leisure sportsmen, Schmidt and Prommer (2008) reported a considerable expansion of plasma volume by 11.6%, whereas total haemoglobin increased only by 6.4%. Plasma volume-enhancing endurance effects might even contribute to “athletes’ pseudoanaemia”, particularly when it is pronounced by some degree of exercise-induced intravascular haemolysis (Carlson & Mawdsley, 1986). However, the existence of real sports anaemia has recently been controversially discussed (Ottomano & Franchini, 2012). Potential of professional football to alter blood values Professional football is characterised by high muscular demands including neuromuscular activity with sprints, jumps, stop-and-go actions, tacklings and other forceful muscle contractions (Stolen, Chamari, Castagna, & Wisloff, 2005). Players undergo frequent, usually daily training and competition during 10–11 months of the year. For this reason and on the basis of the above-mentioned physiological processes, some serological and haematological blood values might be susceptible to interference from repeated intense football-specific loads. For instance, upper reference limits for CK were six times higher in football players than in an inactive population (Mougios, 2007). Furthermore, a high-intensity football training programme induced a significant increase in uric acid and cortisol in elite French football players (Filaire, Lac, & Pequignot, 2003). In other professional football players, long-term training periods led to an increase of total leucocyte and neutrophil numbers and some lymphocyte subpopulations at the end of the season compared to pre-season values (Rebelo et al., 1998). Thus, some serological and haematological parameters seem to be responsive to football training and, thus, potential candidates for a monitoring of the training load as well as individual strain and possible overload. Evidence for the usefulness of blood parameters for monitoring purposes Studies over a whole season or over large parts of one season Few studies are available in which different routine blood parameters were repeatedly analysed in
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professional football players during the period of a half or an entire season (Filaire et al., 2003; Heisterberg et al., 2013; Meyer & Meister, 2011; Ostojic & Ahmetovic, 2009; Rebelo et al., 1998). In a study of routine blood parameters in more than 400 elite players of Germany’s elite football players from the two highest leagues, only an increase of plasma volume (with a decrease of haematocrit) and an increase of CK reached a relevant size over a 1-year football season (Meyer & Meister, 2011). A decrease of haematocrit was similarly found from a pre-season collection to two in-season measurements in 35 Serbian football players (Ostojic & Ahmetovic, 2009). This is likely due to the mentioned changes in plasma volume during training and competition periods that typically accompany an increase in endurance capacity (Brun, 2002; Kargotich, Goodman, Keast, & Morton, 1998; Oscai, Williams, & Hertig, 1968; Sawka et al., 2000). An increased haematocrit (not haemoglobin), accompanied by a small decrease of mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC), at the end of the season was reported in a 6-month study in 27 players of Denmark’s highest football league (Heisterberg et al., 2013). This increase of haematocrit at the end of the season with its blood viscosity-enhancing effect and the decrease of MCH and MCHC was associated with performance decrements. It was observed that VO2max decreased slightly (2.3%; 11 of 12 measured players with lower values compared to pre-season). A slight increase of haematocrit at the very end of the season compared to the first weeks of the season was also found in a Serbian study of 35 professional players, which examined indicators of iron status four times during the course of an entire season (Ostojic & Ahmetovic, 2009). In contrast to the results of Meyer and Meister (2011) and the physiological expectations, such observations might indicate worsened drinking behaviour at the end of the season or simply accompany a loss of endurance capacity (Schmidt & Prommer, 2008). Concerning parameters of immunological function, Rebelo et al. (1998) reported an increase of total leucocyte number (and some leucocyte subpopulations) towards the end of a season. However, from a larger longitudinal study, there is no evidence that parameters of the immune system reliably indicate individual training and competitive strain of football players. White blood cells, CRP and the acute-phase and iron storage protein ferritin were not significantly altered during a whole season in elite football players (Meyer & Meister, 2011). Also, immunoglobulins IgA, IgG and IgM were not affected by training and competition during one season in the top French professional league (Filaire
Downloaded by [New York University] at 11:00 12 February 2015
1330
S. Meister et al.
et al., 2003). But this is in contrast to some findings from Heisterberg et al. (2013). For almost all of the tested routine parameters, a very low intraindividual variability was determined over the course of a season in the mentioned study within the two first German professional leagues (Meyer & Meister, 2011). Limited intraindividual variability for a given parameter reflects little spontaneous fluctuation (i.e. without underlying disease) over a whole season. Thus, it is advisable to limit the range of screening parameters to others than blood count, creatinine, uric acid, total cholesterol and electrolytes (CV ≤ 10% in Meyer & Meister, 2011) – at least in the absence of clinically suspicious signs. In case of a high clinical impact of a blood value (e.g. blood glucose and CRP), screening might be justified, although intraindividual variability is typically small or unknown. Studies about intensive periods of a season Under the assumption that the final weeks of the season or other highly demanding training and competition periods (including weeks with midweek matches) might lead to a specific pattern in blood values, one study focused on such periods (Meister, Faude, Ammann, Schnittker, & Meyer, 2013). The effects of a 3-week period with high vs. low training and competition on routine blood parameters were investigated in a population of 88 elite football players of Germany’s top football leagues (Meister et al., 2013). In this study, none of the investigated haematological (including erythrocyte indices) or serological routine blood parameters (e.g. CK, AST, urea, creatinine, uric acid, CRP, cholesterol and electrolytes) was affected by the difference in loads – and no alteration in any routine blood parameter was found at the end of the season (i.e. “crunch time”) in more than 400 football players (Meyer & Meister, 2011). No other such study was conducted with a population size comparable to the studies of Meyer and Meister (2011) and Meister et al. (2013). Thus, in a large population of players, highly demanding periods revealed no systematic difference in any routine blood parameter. Unfortunately, in most of the existing studies, information about training and match exposure is not given, which makes an assessment of real physiological strain difficult. At least differences in match exposure (training loads not available) were reported by Meister et al. (2013). However, it cannot be ruled out that coaches respond to a congested schedule with a reduction in the training load. Likewise, in the study of Filaire et al. (2003), players underwent weekly matches and more intensive training during the end of the season, but with reduced amount of training exposure compared to the start of
the season (20 vs. 27 h). Heisterberg et al. (2013) gave no information about differences in training, and matches were often performed twice a week during the end of the season. Training and match exposure were not given in the study of Ostojic and Ahmetovic (2009), either. Thus, it is unclear whether differences in exposure were high enough to cause differences in blood values. On the other hand, the studies reflect real exposure and, thus, have high ecological validity.
Significance of existing study results for justifying an evaluation of strain and overload in elite football players by means of repeated blood sampling There are few relevant studies available analysing blood values over a whole season (or at least over a period long enough to include differing training and competition load) in elite football players (Filaire et al., 2003; Heisterberg et al., 2013; Meyer & Meister, 2011; Ostojic & Ahmetovic, 2009; Rebelo et al., 1998). Slight alterations of few parameters (i.e. haematocrit, MCH and MCHC) at the end of the season were reported (Heisterberg et al., 2013; Ostojic & Ahmetovic, 2009; Rebelo et al., 1998). However, the significance of studies with only statistical trends, low sample sizes or other limitations like imprecise information about match exposure is questionable. Most studies were conducted with a population of about 20–40 football players. Only one study with half of all players of Germany’s two highest football leagues investigated a complete panel of routine blood parameters over the course of an entire season (Meyer & Meister, 2011). Furthermore, only this study reported detailed findings in relation to match exposure (Meister et al., 2013). Relevant in-season alterations of routine blood parameters that can be useful for monitoring load were neither present during the course of an entire season nor when contrasting highly demanding training and competition periods in more than 400 professional football players (Meister et al., 2013; Meyer & Meister, 2011). As chosen parameters seemed to be quite robust against the influences of football training and competition, repeated determination of routine blood parameters does not seem to be reasonable without suspicious complaints and without knowledge of intraindividual variability of each player. On these grounds, we recommend a single routine screening at the beginning of a season (and as appropriate in the preparation period of the second half of the season), if clinical symptoms are lacking. Repeated screening might lead to incidental findings primarily caused by intraindividual variability.
Repeated blood monitoring in football players Conclusion
Downloaded by [New York University] at 11:00 12 February 2015
Repeated determination of a panel of routine laboratory parameters might sound reasonable for screening purposes in elite athletes. However, from the existing literature, frequent blood sampling does not contribute to an appropriate monitoring of high physical strain and overload in elite football players. The use of an intraindividual profile of an elite player including known baseline levels which have been repeatedly measured might be a more convincing approach. In line with Fallon (2008), on clinical grounds a repeated wide routine biochemical screening (without suspicious complaints or signs) cannot be recommended. References Brancaccio, P., Maffulli, N., & Limongelli, F. M. (2007). Creatine kinase monitoring in sport medicine. British Medical Bulletin, 81–82, 209–230. Brun, J. F. (2002). Exercise hemorheology as a three acts play with metabolic actors: Is it of clinical relevance? Clinical Hemorheology Microcirculation, 26(3), 155–174. Carlson, D. L., & Mawdsley, R. H. (1986). Sports anemia: A review of the literature. The American Journal of Sports Medicine, 14(2), 109–112. El-Sayed, M. S. (1998). Effects of exercise and training on blood rheology. Sports Medicine, 26(5), 281–292. Fallon, K. E. (2008). The clinical utility of screening of biochemical parameters in elite athletes: Analysis of 100 cases. British Journal of Sports Medicine, 42(5), 334–337. Filaire, E., Lac, G., & Pequignot, J. M. (2003). Biological, hormonal, and psychological parameters in professional soccer players throughout a competitive season. Perceptual and Motor Skills, 97(3 Pt 2), 1061–1072. Gabriel, H., Schwarz, L., Born, P., & Kindermann, W. (1992). Differential mobilization of leucocyte and lymphocyte subpopulations into the circulation during endurance exercise. European Journal of Applied Physiology and Occupational Physiology, 65(6), 529–534. Gillen, C. M., Lee, R., Mack, G. W., Tomaselli, C. M., Nishiyasu, T., & Nadel, E. R. (1991). Plasma volume expansion in humans after a single intense exercise protocol. Journal of Applied Physiology, 71(5), 1914–1920. Haralambie, G. (1973). Neuromuscular irritability and serum creatine phosphate kinase in athletes in training. Internationale Zeitschrift Für Angewandte Physiologie, 31(4), 279–288. Haralambie, G., & Berg, A. (1976). Serum urea and amino nitrogen changes with exercise duration. European Journal of Applied Physiology and Occupational Physiology, 36(1), 39–48. Heisterberg, M. F., Fahrenkrug, J., Krustrup, P., Storskov, A., Kjaer, M., & Andersen, J. L. (2013). Extensive monitoring through multiple blood samples in professional soccer players. Journal of Strength and Conditioning Research, 27(5), 1260–1271.
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Kargotich, S., Goodman, C., Keast, D., & Morton, A. R. (1998). The influence of exercise-induced plasma volume changes on the interpretation of biochemical parameters used for monitoring exercise, training and sport. Sports Medicine, 26(2), 101–117. Meister, S., Faude, O., Ammann, T., Schnittker, R., & Meyer, T. (2013). Indicators for high physical strain and overload in elite football players. Scandinavian Journal of Medicine & Science in Sports, 23(2), 156–163. Meyer, T., Gabriel, H. H., Ratz, M., Muller, H. J., & Kindermann, W. (2001). Anaerobic exercise induces moderate acute phase response. Medicine & Science in Sports & Exercise, 33(4), 549–555. Meyer, T., & Meister, S. (2011). Routine blood parameters in elite soccer players. International Journal of Sports Medicine, 32(11), 875–881. Mougios, V. (2007). Reference intervals for serum creatine kinase in athletes. British Journal of Sports Medicine, 41(10), 674–678. Newham, D. J., Jones, D. A., & Edwards, R. H. (1986). Plasma creatine kinase changes after eccentric and concentric contractions. Muscle & Nerve, 9(1), 59–63. Nicholson, G. A., Morgan, G., Meerkin, M., Strauss, E., & McLeod, J. G. (1985). The creatine kinase reference interval. An assessment of intra- and inter-individual variation. Journal of the Neurological Sciences, 71(2–3), 225–231. Noakes, T. D. (1987). Effect of exercise on serum enzyme activities in humans. Sports Medicine, 4(4), 245–267. Oscai, L. B., Williams, B. T., & Hertig, B. A. (1968). Effect of exercise on blood volume. Journal of Applied Physiology, 24(5), 622–624. Ostojic, S. M., & Ahmetovic, Z. (2009). Indicators of iron status in elite soccer players during the sports season. International Journal of Laboratory Hematology, 31(4), 447–452. Ottomano, C., & Franchini, M. (2012). Sports anaemia: Facts or fiction? Blood Transfusion, 10(3), 252–254. Rebelo, A. N., Candeias, J. R., Fraga, M. M., Duarte, J. A., Soares, J. M., Magalhaes, C., & Torrinha, J. A. (1998). The impact of soccer training on the immune system. The Journal of Sports Medicine and Physical Fitness, 38(3), 258–261. Sawka, M. N., Convertino, V. A., Eichner, E. R., Schnieder, S. M., & Young, A. J. (2000). Blood volume: Importance and adaptations to exercise training, environmental stresses, and trauma/sickness. Medicine & Science in Sports & Exercise, 32(2), 332–348. Schmidt, W., & Prommer, N. (2008). Effects of various training modalities on blood volume. Scandinavian Journal of Medicine & Science in Sports, 18(Suppl. 1), 57–69. Schwartz, P. L., Carroll, H. W., & Douglas Jr., J. S. (1971). Exercise-induced changes in serum enzyme activities and their relationship to max V O2. Internationale Zeitschrift Für Angewandte Physiologie, 30(1), 20–33. Stolen, T., Chamari, K., Castagna, C., & Wisloff, U. (2005). Physiology of soccer: An update. Sports Medicine, 35(6), 501–536. Wong, E. T., Cobb, C., Umehara, M. K., Wolff, G. A., Haywood, L. J., Greenberg, T., & Shaw Jr., S. T. (1983). Heterogeneity of serum creatine kinase activity among racial and gender groups of the population. American Journal of Clinical Pathology, 79(5), 582–586.
Journal of Sports Sciences Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/rjsp20
Repeated monitoring of blood parameters for evaluating strain and overload in elite football players: is it justified? a
a
Steffen Meister , Karen aus der Fünten & Tim Meyer
a
a
Institute of Sports and Preventive Medicine, Saarland University, Saarbrücken, Germany Published online: 07 Jul 2014.
Click for updates To cite this article: Steffen Meister, Karen aus der Fünten & Tim Meyer (2014) Repeated monitoring of blood parameters for evaluating strain and overload in elite football players: is it justified?, Journal of Sports Sciences, 32:13, 1328-1331, DOI: 10.1080/02640414.2014.927070 To link to this article: http://dx.doi.org/10.1080/02640414.2014.927070
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Journal of Sports Sciences, 2014 Vol. 32, No. 13, 1328–1331, http://dx.doi.org/10.1080/02640414.2014.927070
POINT – COUNTERPOINT
Repeated monitoring of blood parameters for evaluating strain and overload in elite football players: is it justified?
STEFFEN MEISTER, KAREN AUS DER FÜNTEN & TIM MEYER
Downloaded by [New York University] at 11:00 12 February 2015
Institute of Sports and Preventive Medicine, Saarland University, Saarbrücken, Germany (Accepted 19 May 2014)
Keywords: blood parameters, strain and overload, football
Background Venous blood sampling is repeatedly conducted in many elite athletes to screen for deficits and earlystage illness. Another motivation for frequent blood sampling is monitoring physiological stress and fatigue to assess recovery needs and prevent performance decrements. However, there is some uncertainty about the existence of sufficient scientific evidence for these procedures and an appropriate selection of parameters. During a typical football season, it is noteworthy that for a given blood sample acute effects of training and competition (from the days before) cannot be safely discerned from chronic changes (due to the cumulation of exercise loads from the weeks or months before). Therefore, an overlap of acute exercise-induced and chronic changes is possible. Besides other aspects, this has to be taken into account for the correct interpretation of blood values. Acute and chronic effects of exercise on blood parameters Acute exercise effects Exercise leads to profound acute changes, i.e. within hours after training, in several blood parameters. Haemoconcentration due to sweat loss and due to fluid shifts from blood vessels to interstitial spaces has been considered one important mechanism of exercise-induced alterations (El-Sayed, 1998; Gillen
et al., 1991). A further effect of acute endurancetype exercise is leucocytosis and a mobilisation of leucocyte and lymphocyte subpopulations (Gabriel, Schwarz, Born, & Kindermann, 1992). A humoural immune reaction can be found after anaerobic exercise: C-reactive protein (CRP) was shown to be elevated as part of an acute-phase response after repeated short bouts of high-intensity cycling (Meyer, Gabriel, Ratz, Muller, & Kindermann, 2001). Serum enzymes like creatine kinase (CK), aspartate-aminotransferase (AST) and urea can also be affected by prolonged exercise (Haralambie & Berg, 1976; Noakes, 1987). CK has even been established as serum marker to quantify training- and competition-induced muscle damage in sports (Brancaccio, Maffulli, & Limongelli, 2007). In cases of high (eccentric) biomechanical strain, CK typically peaks 24–48 h after exercise and can be elevated up to several days (Newham, Jones, & Edwards, 1986; Noakes, 1987). Apart from mechanical strain and microtrauma in skeletal muscle, serum CK levels are strongly affected by genetically determined muscle fibre distribution (Wong et al., 1983) and muscle cell permeability (Haralambie, 1973; Nicholson, Morgan, Meerkin, Strauss, & McLeod, 1985; Schwartz, Carroll, & Douglas, 1971). Additionally, the type of training and individual response to exercise can significantly alter CK. Thus, knowledge of baseline levels and individual responsiveness of CK activity seems to be necessary for an appropriate interpretation.
Correspondence: Steffen Meister, Institute of Sports and Preventive Medicine, Saarland University, Saarbrücken, Germany. E-mail: [email protected] © 2014 Taylor & Francis
Repeated blood monitoring in football players
Downloaded by [New York University] at 11:00 12 February 2015
Chronic exercise effects As a result of long-term regular training (e.g. longer than 21 days), some training-induced adaptations of blood parameters can be observed too (Sawka, Convertino, Eichner, Schnieder, & Young, 2000). These “chronic” changes mainly consist of a haemodilution due to an increase of plasma volume, which can exceed the gain in red blood cell mass. After a 9-month endurance training for a marathon in 16 leisure sportsmen, Schmidt and Prommer (2008) reported a considerable expansion of plasma volume by 11.6%, whereas total haemoglobin increased only by 6.4%. Plasma volume-enhancing endurance effects might even contribute to “athletes’ pseudoanaemia”, particularly when it is pronounced by some degree of exercise-induced intravascular haemolysis (Carlson & Mawdsley, 1986). However, the existence of real sports anaemia has recently been controversially discussed (Ottomano & Franchini, 2012). Potential of professional football to alter blood values Professional football is characterised by high muscular demands including neuromuscular activity with sprints, jumps, stop-and-go actions, tacklings and other forceful muscle contractions (Stolen, Chamari, Castagna, & Wisloff, 2005). Players undergo frequent, usually daily training and competition during 10–11 months of the year. For this reason and on the basis of the above-mentioned physiological processes, some serological and haematological blood values might be susceptible to interference from repeated intense football-specific loads. For instance, upper reference limits for CK were six times higher in football players than in an inactive population (Mougios, 2007). Furthermore, a high-intensity football training programme induced a significant increase in uric acid and cortisol in elite French football players (Filaire, Lac, & Pequignot, 2003). In other professional football players, long-term training periods led to an increase of total leucocyte and neutrophil numbers and some lymphocyte subpopulations at the end of the season compared to pre-season values (Rebelo et al., 1998). Thus, some serological and haematological parameters seem to be responsive to football training and, thus, potential candidates for a monitoring of the training load as well as individual strain and possible overload. Evidence for the usefulness of blood parameters for monitoring purposes Studies over a whole season or over large parts of one season Few studies are available in which different routine blood parameters were repeatedly analysed in
1329
professional football players during the period of a half or an entire season (Filaire et al., 2003; Heisterberg et al., 2013; Meyer & Meister, 2011; Ostojic & Ahmetovic, 2009; Rebelo et al., 1998). In a study of routine blood parameters in more than 400 elite players of Germany’s elite football players from the two highest leagues, only an increase of plasma volume (with a decrease of haematocrit) and an increase of CK reached a relevant size over a 1-year football season (Meyer & Meister, 2011). A decrease of haematocrit was similarly found from a pre-season collection to two in-season measurements in 35 Serbian football players (Ostojic & Ahmetovic, 2009). This is likely due to the mentioned changes in plasma volume during training and competition periods that typically accompany an increase in endurance capacity (Brun, 2002; Kargotich, Goodman, Keast, & Morton, 1998; Oscai, Williams, & Hertig, 1968; Sawka et al., 2000). An increased haematocrit (not haemoglobin), accompanied by a small decrease of mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC), at the end of the season was reported in a 6-month study in 27 players of Denmark’s highest football league (Heisterberg et al., 2013). This increase of haematocrit at the end of the season with its blood viscosity-enhancing effect and the decrease of MCH and MCHC was associated with performance decrements. It was observed that VO2max decreased slightly (2.3%; 11 of 12 measured players with lower values compared to pre-season). A slight increase of haematocrit at the very end of the season compared to the first weeks of the season was also found in a Serbian study of 35 professional players, which examined indicators of iron status four times during the course of an entire season (Ostojic & Ahmetovic, 2009). In contrast to the results of Meyer and Meister (2011) and the physiological expectations, such observations might indicate worsened drinking behaviour at the end of the season or simply accompany a loss of endurance capacity (Schmidt & Prommer, 2008). Concerning parameters of immunological function, Rebelo et al. (1998) reported an increase of total leucocyte number (and some leucocyte subpopulations) towards the end of a season. However, from a larger longitudinal study, there is no evidence that parameters of the immune system reliably indicate individual training and competitive strain of football players. White blood cells, CRP and the acute-phase and iron storage protein ferritin were not significantly altered during a whole season in elite football players (Meyer & Meister, 2011). Also, immunoglobulins IgA, IgG and IgM were not affected by training and competition during one season in the top French professional league (Filaire
Downloaded by [New York University] at 11:00 12 February 2015
1330
S. Meister et al.
et al., 2003). But this is in contrast to some findings from Heisterberg et al. (2013). For almost all of the tested routine parameters, a very low intraindividual variability was determined over the course of a season in the mentioned study within the two first German professional leagues (Meyer & Meister, 2011). Limited intraindividual variability for a given parameter reflects little spontaneous fluctuation (i.e. without underlying disease) over a whole season. Thus, it is advisable to limit the range of screening parameters to others than blood count, creatinine, uric acid, total cholesterol and electrolytes (CV ≤ 10% in Meyer & Meister, 2011) – at least in the absence of clinically suspicious signs. In case of a high clinical impact of a blood value (e.g. blood glucose and CRP), screening might be justified, although intraindividual variability is typically small or unknown. Studies about intensive periods of a season Under the assumption that the final weeks of the season or other highly demanding training and competition periods (including weeks with midweek matches) might lead to a specific pattern in blood values, one study focused on such periods (Meister, Faude, Ammann, Schnittker, & Meyer, 2013). The effects of a 3-week period with high vs. low training and competition on routine blood parameters were investigated in a population of 88 elite football players of Germany’s top football leagues (Meister et al., 2013). In this study, none of the investigated haematological (including erythrocyte indices) or serological routine blood parameters (e.g. CK, AST, urea, creatinine, uric acid, CRP, cholesterol and electrolytes) was affected by the difference in loads – and no alteration in any routine blood parameter was found at the end of the season (i.e. “crunch time”) in more than 400 football players (Meyer & Meister, 2011). No other such study was conducted with a population size comparable to the studies of Meyer and Meister (2011) and Meister et al. (2013). Thus, in a large population of players, highly demanding periods revealed no systematic difference in any routine blood parameter. Unfortunately, in most of the existing studies, information about training and match exposure is not given, which makes an assessment of real physiological strain difficult. At least differences in match exposure (training loads not available) were reported by Meister et al. (2013). However, it cannot be ruled out that coaches respond to a congested schedule with a reduction in the training load. Likewise, in the study of Filaire et al. (2003), players underwent weekly matches and more intensive training during the end of the season, but with reduced amount of training exposure compared to the start of
the season (20 vs. 27 h). Heisterberg et al. (2013) gave no information about differences in training, and matches were often performed twice a week during the end of the season. Training and match exposure were not given in the study of Ostojic and Ahmetovic (2009), either. Thus, it is unclear whether differences in exposure were high enough to cause differences in blood values. On the other hand, the studies reflect real exposure and, thus, have high ecological validity.
Significance of existing study results for justifying an evaluation of strain and overload in elite football players by means of repeated blood sampling There are few relevant studies available analysing blood values over a whole season (or at least over a period long enough to include differing training and competition load) in elite football players (Filaire et al., 2003; Heisterberg et al., 2013; Meyer & Meister, 2011; Ostojic & Ahmetovic, 2009; Rebelo et al., 1998). Slight alterations of few parameters (i.e. haematocrit, MCH and MCHC) at the end of the season were reported (Heisterberg et al., 2013; Ostojic & Ahmetovic, 2009; Rebelo et al., 1998). However, the significance of studies with only statistical trends, low sample sizes or other limitations like imprecise information about match exposure is questionable. Most studies were conducted with a population of about 20–40 football players. Only one study with half of all players of Germany’s two highest football leagues investigated a complete panel of routine blood parameters over the course of an entire season (Meyer & Meister, 2011). Furthermore, only this study reported detailed findings in relation to match exposure (Meister et al., 2013). Relevant in-season alterations of routine blood parameters that can be useful for monitoring load were neither present during the course of an entire season nor when contrasting highly demanding training and competition periods in more than 400 professional football players (Meister et al., 2013; Meyer & Meister, 2011). As chosen parameters seemed to be quite robust against the influences of football training and competition, repeated determination of routine blood parameters does not seem to be reasonable without suspicious complaints and without knowledge of intraindividual variability of each player. On these grounds, we recommend a single routine screening at the beginning of a season (and as appropriate in the preparation period of the second half of the season), if clinical symptoms are lacking. Repeated screening might lead to incidental findings primarily caused by intraindividual variability.
Repeated blood monitoring in football players Conclusion
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