International Journal of Sports Physiology and Performance, 2015, 10, 401-403 http://dx.doi.org/10.1123/ijspp.2014-0046 © 2015 Human Kinetics, Inc.
www.IJSPP-Journal.com BRIEF REPORT
Prematch Salivary Secretory Immunoglobulin A in Soccer Players From the 2014 World Cup Qualifying Campaign Ryland Morgans, Adam Owen, Dominic Doran, Barry Drust, and James P. Morton Purpose: To monitor resting salivary secretory immunoglobulin A (SIgA) levels in international soccer players during the short-term training period that precedes international match play. Methods: In a repeated-measure design, saliva samples were obtained from 13 outfield soccer players who participated in the training camps preceding 7 games (5 home and 2 away) of the 2014 FIFA World Cup qualifying campaign. Samples were obtained daily for 4 d preceding each game (and analyzed for SIgA using the IPRO oral-fluid-collection system) at match day minus 1 (MD-1), minus 2 (MD-2), minus 3 (MD-3), and minus 4 (MD-4). Results: SIgA displayed a progressive decline (P = .01) during the 4-d training period (MD-4, 365 ± 127 μg/mL; MD-3, 348 ± 154 μg/mL; MD-2, 290 ± 138 μg/mL; MD-1, 256 ± 90 μg/mL) such that MD-1 values were significantly lower (P = .01) than both MD-4 and MD-3. The 95% confidence intervals for the differences between MD-1 and MD-4 were –191 to –26 and between MD-1 and MD-3 were –155 to –28. Conclusions: Data demonstrate that a short-term soccer-training camp in preparation for international competition induces detectable perturbations to mucosal immunity. Future studies should monitor SIgA (as a practical and noninvasive measure of immunity) alongside internal and external measures of training load in an attempt to strategically individualize training and nutritional strategies that may support optimal preparation for high-level competition. Keywords: immune response, intermittent exercise, training load The organization of preparation strategies for international soccer games is very different from preparation for domestic-league competition. For international competition involving countries of the United Kingdom, players typically report for duty 4 to 5 days before the game and subsequently participate in a short training camp that is designed to tactically and physically prepare them for the upcoming match. In relation to physical preparation, players are likely to report for international duty with varying degrees of soccer-specific fitness based on their recent game schedules, injury history, and the training culture of their particular club. As such, a major challenge for the fitness and science staff of international squads is to strategically manage training load so that players receive the necessary training stimulus (while simultaneously preventing symptoms of fatigue and overreaching) to optimally prepare for the game itself. Alongside measurements of training load (eg, GPS, heart rate, and ratings of perceived exertion), assessments of well-being can also be used to assist the individualized response to training and subsequent training modifications if necessary. In this regard, assessment of salivary secretory immunoglobulin A (SIgA) (the predominant immunoglobulin expressed in mucosal fluids) is potentially useful given that it not only inversely correlates with the onset of respiratory illness symptoms but also is sensitive to physical stress and appears to vary in accordance with exercise intensity and duration.1–3 Indeed, high-intensity and prolonged endurance exercise typically induces greater decrements in SIgA levels than moderate-intensity exercise protocols that are shorter in nature.3–5 Morgans is with the Faculty of Life Sciences and Education, University of South Wales, Upper Glyntaff, UK. Owen is with the Center for Research and Innovation in Sport, Université de Lyon, Villeurbanne, France. Doran, Drust, and Morton are with the Research Inst for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK. Address author correspondence to James Morton at [email protected].
In relation to soccer-specific exercise, the stress of an acute soccer-training session induces a transient fall in SIgA (albeit it when expressed as SIgA/total protein) in English Premier League soccer players that returns to basal levels within 18 hours.6 In addition, acute soccer-specific exercise (in the form of futsal) also induces acute decrements in SIgA when expressed as an absolute concentration.7 In both athletic populations8 and military personnel,9 resting SIgA also displays a chronic fall during times of intensified training, thereby demonstrating the potential of SIgA as a practically applicable and noninvasive marker of physiological well-being in response to increased training loads. To our knowledge, however, no researchers have yet examined the variation in basal SIgA levels in elite soccer players during a period of soccer-specific training. The aim of this case study was to therefore monitor resting SIgA levels in international soccer players during the training-camp period that precedes game day. We studied elite players of an international soccer team for 4 days before 7 games of the 2014 FIFA World Cup qualifying campaign. On the basis that fitness and coaching staff typically reduce training loads in the days leading up to games (ie, physical stress is progressively reduced), we hypothesized that SIgA would show no measurable change.
Methods Subjects Thirteen male subjects (age 25 ± 3 y, body mass 73.9 ± 6.5 kg, height 1.77 ± 0.06 m) from the Wales national soccer team gave informed consent to participate in this study. Although no formal institutional ethical approval was received, all players provided written consent to adhere to all fitness, science, and medical-screening/monitoring procedures (inclusive of SIgA assessment) that were associated with their national-team duties. 401
402 Morgans et al
Design In a repeated-measures design, saliva samples were obtained from 13 outfield soccer players who participated in training camps for 7 games (5 at home and 2 away) of the 2014 FIFA World Cup qualifying campaign. Samples were obtained daily for the 4 days preceding each of the 7 games and are referred to hereafter as match day minus 1 (MD-1), minus 2 (MD-2), minus 3 (MD-3), and minus 4 (MD-4).
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SIgA Analysis All saliva samples were collected between 8:30 and 9:00 AM (before breakfast). Participants were provided with an oral fluid collector (IPRO Interactive, Oxfordshire, UK) consisting of a synthetic polymer-based material on a polypropylene tube. The oral fluid collector contains a volume-adequacy indicator, providing a clear color change (changing from white to dark blue) when 0.5 mL (± 20%) is collected. Participants were instructed to swallow any saliva present in the oral cavity before they placed the collection device on top of the tongue. SIgA concentration was analyzed according to a real-time lateral-flow device in accordance with the manufacturer’s guidelines (IPRO Interactive, UK). This method has previously been validated against ELISA (R2 = .78) in 208 samples collected from a cohort of English Premier League soccer players with a range of SIgA concentrations from 28 to 628 μg/mL.10
Figure 1 — Salivary secretory IgA concentration during the 4-day training period that preceded match day. Data are representative of 7 training camps. Abbreviations: MD-1, match day minus 1; MD-2, match day minus 2; MD-3, match day minus 3; MD-4, match day minus 4. *Significant difference from MD-4 and MD-3, P < .05.
Statistical Analysis Changes in SIgA were analyzed using a 1-way repeated-measures general linear model (SPSS, version 17, Windows). Where a significant main effect of time was observed (ie, P < .05), differences between specific time points were located using Bonferroni post hoc analysis. The 95% confidence intervals (95% CI) for the differences between specific time points were also calculated, and inferences on the magnitude of differences were reported according to Batterham and Hopkins.11 All data are presented as mean ± SD, with P values 40% (see Figure 2).
Discussion Contrary to our hypothesis, we provide novel data by demonstrating that SIgA in elite soccer players significantly declines during a shortterm training camp that precedes international-standard competitive match play. Given the relevance of SIgA to immune function,1 these data suggest that to maintain SIgA at near basal levels, alterations to the current training-camp structure may be required. It is difficult to readily determine the reason for the fall in SIgA levels during 4 days of soccer training, as, unfortunately, we were unable to collect any detailed and consistent measures of training load in this study. We acknowledge, therefore, that future studies
Figure 2 — Salivary secretory IgA levels on MD-3, MD-2, and MD-1 when expressed as a percentage of MD-4 values. Each circle represents an average of each individual player’s values from the 7 training camps. Abbreviations: MD-1, match day minus 1; MD-2, match day minus 2; MD-3, match day minus 3; MD-4, match day minus 4.
should attempt to ascertain potential measures of training load that contributed to the fall in SIgA levels observed here. However, if the mechanism of decline is indeed related to physiological loading, these data suggest that the current training prescription is of sufficient intensity and duration to induce perturbations to mucosal immunity. Indeed, recent data from our group support this hypothesis, as we observed that high-intensity soccer-specific training sessions are associated with greater decrements in SIgA than lowintensity training, as observed in professional soccer players from the Scottish Premier League.3
Salivary IgA and Professional Soccer 403
Alternatively, the mechanisms of decline in SIgA may not be related to physical loading but, rather, could be psychological in nature given the importance of the games in question (ie, FIFA World Cup qualifying games), as well as the potential sleep and travel stress12 associated with training-camp environments and international competition. However, given that 5 of the 7 games were played at home and that 1 of the away games was also against another country of the United Kingdom (hence could also be technically classified as a home fixture), we were unable to evaluate the potential effects of travel on SIgA responses.
Downloaded by Australian Catholic University on 09/27/16, Volume 10, Article Number 3
Practical Applications From a practical perspective, data suggest that monitoring SIgA provides a noninvasive assessment that may be useful alongside additional internal and external markers of training load to assess how soccer players respond to short-term training. Notably, our data demonstrate that SIgA displayed a progressive decline in the days before game day and thereby provides objective evidence for the administration of appropriate interventions to prepare players for the physical stress of game day itself. Future studies should attempt to correlate SIgA levels and secretion rates to specific markers of training load, as well as report SIgA data on game day and recovery days to verify the efficacy of any strategy put in place, for example, reduction of training load, sleep strategies, nutritional interventions. Furthermore, prior measurement of players’ SIgA levels during their habitual training environment (ie, domestic clubs) would also provide a more definitive assessment of each player’s true baseline SIgA profile (as opposed to the MD-4 values per se that are reported here), thus providing further evidence as to how players adapt to the demands of international training and competition.
Conclusions We conclude that a soccer-training camp in preparation for international competition induces detectable perturbations in markers of mucosal immunity. Monitoring SIgA (as a practical and noninvasive measurement tool) may therefore be useful alongside additional internal and external measures of training load to strategically tailor training and nutritional strategies that optimally prepare players for high-level competition. Acknowledgments The authors acknowledge the support of the coaching staff and players for adhering to data-collection procedures.
References 1. Neville V, Gleeson M, Folland JP. Salivary IgA as a risk factor for upper respiratory infections in elite professional athletes. Med Sci Sports Exerc. 2008;40:1228–1236. PubMed doi:10.1249/ MSS.0b013e31816be9c3 2. Gleeson M, Pyne DB. Exercise effects on mucosal immunity. Immunol Cell Biol. 2000;78:536–544. PubMed doi:10.1111/j.1440-1711.2000. t01-8-.x 3. Owen AL, Wong DP, Dunlop G, et al. High intensity training and salivary immunoglobulin-A responses in professional top level soccer players: effect of training intensity [published online ahead of print January 19, 2014]. J Strength Cond Res. PubMed 4. Nieman DC, Henson DA, Fagoaga OR, et al. Change in salivary IgA following a competitive marathon race. Int J Sports Med. 2002;23:69– 75. PubMed doi:10.1055/s-2002-19375 5. Mackinnon LT, Hooper S. Mucosal (secretory) immune system responses to exercise of varying intensity and during overtraining. Int J Sports Med. 1994;15:S179–S183. PubMed doi:10.1055/s-2007-1021134 6. Fredericks S, Fitzgerald L, Shaw G, Holt DW. Changes in salivary immunoglobulin A (IgA) following match play and training among English Premiership footballers. Med J Malaysia. 2012;67:155–158. PubMed 7. Moreira A, Arsati F, de Oliveira Lima-Arsati YB, de Freitas CG, de Araujo VC. Salivary immunoglobulin A responses in professional top-level futsal players. J Strength Cond Res. 2011;25(7):1932–1936. PubMed doi:10.1519/JSC.0b013e3181e7fbc0 8. Gleeson M, McDonald WA, Cripps WA, Pyne DB, Clancy RL, Fricker PA. The effect on immunity of long term intensive training in elite swimmers. Clin Exp Immunol. 1995;102:210–216. PubMed doi:10.1111/j.1365-2249.1995.tb06658.x 9. Whitham M, Laing SJ, Dorrington M, et al. The influence of an arduous military training program on immune function and upper respiratory tract infection incidence. Mil Med. 2006;171:703–709. PubMed 10. Dunbar J, Jehanli A, Skelhorn S. Investigating the use of a point of care SIgA test in the sporting environment. Paper presented al: International Society of Exercise and Immunology; July 11–13, 2011; Oxford, UK. Abstract P.85. Available at: www.isei.dk. 11. Batterham AM, Hopkins WG. Making meaningful inferences about magnitudes. Int J Sports Physiol Perform. 2006;1:50–57. PubMed 12. Walsh NP, Gleeson M, Shephard RJ, et al. Position statement part one: immune function and exercise. Exerc Immunol Rev. 2011;17:6–63. PubMed
www.IJSPP-Journal.com BRIEF REPORT
Prematch Salivary Secretory Immunoglobulin A in Soccer Players From the 2014 World Cup Qualifying Campaign Ryland Morgans, Adam Owen, Dominic Doran, Barry Drust, and James P. Morton Purpose: To monitor resting salivary secretory immunoglobulin A (SIgA) levels in international soccer players during the short-term training period that precedes international match play. Methods: In a repeated-measure design, saliva samples were obtained from 13 outfield soccer players who participated in the training camps preceding 7 games (5 home and 2 away) of the 2014 FIFA World Cup qualifying campaign. Samples were obtained daily for 4 d preceding each game (and analyzed for SIgA using the IPRO oral-fluid-collection system) at match day minus 1 (MD-1), minus 2 (MD-2), minus 3 (MD-3), and minus 4 (MD-4). Results: SIgA displayed a progressive decline (P = .01) during the 4-d training period (MD-4, 365 ± 127 μg/mL; MD-3, 348 ± 154 μg/mL; MD-2, 290 ± 138 μg/mL; MD-1, 256 ± 90 μg/mL) such that MD-1 values were significantly lower (P = .01) than both MD-4 and MD-3. The 95% confidence intervals for the differences between MD-1 and MD-4 were –191 to –26 and between MD-1 and MD-3 were –155 to –28. Conclusions: Data demonstrate that a short-term soccer-training camp in preparation for international competition induces detectable perturbations to mucosal immunity. Future studies should monitor SIgA (as a practical and noninvasive measure of immunity) alongside internal and external measures of training load in an attempt to strategically individualize training and nutritional strategies that may support optimal preparation for high-level competition. Keywords: immune response, intermittent exercise, training load The organization of preparation strategies for international soccer games is very different from preparation for domestic-league competition. For international competition involving countries of the United Kingdom, players typically report for duty 4 to 5 days before the game and subsequently participate in a short training camp that is designed to tactically and physically prepare them for the upcoming match. In relation to physical preparation, players are likely to report for international duty with varying degrees of soccer-specific fitness based on their recent game schedules, injury history, and the training culture of their particular club. As such, a major challenge for the fitness and science staff of international squads is to strategically manage training load so that players receive the necessary training stimulus (while simultaneously preventing symptoms of fatigue and overreaching) to optimally prepare for the game itself. Alongside measurements of training load (eg, GPS, heart rate, and ratings of perceived exertion), assessments of well-being can also be used to assist the individualized response to training and subsequent training modifications if necessary. In this regard, assessment of salivary secretory immunoglobulin A (SIgA) (the predominant immunoglobulin expressed in mucosal fluids) is potentially useful given that it not only inversely correlates with the onset of respiratory illness symptoms but also is sensitive to physical stress and appears to vary in accordance with exercise intensity and duration.1–3 Indeed, high-intensity and prolonged endurance exercise typically induces greater decrements in SIgA levels than moderate-intensity exercise protocols that are shorter in nature.3–5 Morgans is with the Faculty of Life Sciences and Education, University of South Wales, Upper Glyntaff, UK. Owen is with the Center for Research and Innovation in Sport, Université de Lyon, Villeurbanne, France. Doran, Drust, and Morton are with the Research Inst for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK. Address author correspondence to James Morton at [email protected].
In relation to soccer-specific exercise, the stress of an acute soccer-training session induces a transient fall in SIgA (albeit it when expressed as SIgA/total protein) in English Premier League soccer players that returns to basal levels within 18 hours.6 In addition, acute soccer-specific exercise (in the form of futsal) also induces acute decrements in SIgA when expressed as an absolute concentration.7 In both athletic populations8 and military personnel,9 resting SIgA also displays a chronic fall during times of intensified training, thereby demonstrating the potential of SIgA as a practically applicable and noninvasive marker of physiological well-being in response to increased training loads. To our knowledge, however, no researchers have yet examined the variation in basal SIgA levels in elite soccer players during a period of soccer-specific training. The aim of this case study was to therefore monitor resting SIgA levels in international soccer players during the training-camp period that precedes game day. We studied elite players of an international soccer team for 4 days before 7 games of the 2014 FIFA World Cup qualifying campaign. On the basis that fitness and coaching staff typically reduce training loads in the days leading up to games (ie, physical stress is progressively reduced), we hypothesized that SIgA would show no measurable change.
Methods Subjects Thirteen male subjects (age 25 ± 3 y, body mass 73.9 ± 6.5 kg, height 1.77 ± 0.06 m) from the Wales national soccer team gave informed consent to participate in this study. Although no formal institutional ethical approval was received, all players provided written consent to adhere to all fitness, science, and medical-screening/monitoring procedures (inclusive of SIgA assessment) that were associated with their national-team duties. 401
402 Morgans et al
Design In a repeated-measures design, saliva samples were obtained from 13 outfield soccer players who participated in training camps for 7 games (5 at home and 2 away) of the 2014 FIFA World Cup qualifying campaign. Samples were obtained daily for the 4 days preceding each of the 7 games and are referred to hereafter as match day minus 1 (MD-1), minus 2 (MD-2), minus 3 (MD-3), and minus 4 (MD-4).
Downloaded by Australian Catholic University on 09/27/16, Volume 10, Article Number 3
SIgA Analysis All saliva samples were collected between 8:30 and 9:00 AM (before breakfast). Participants were provided with an oral fluid collector (IPRO Interactive, Oxfordshire, UK) consisting of a synthetic polymer-based material on a polypropylene tube. The oral fluid collector contains a volume-adequacy indicator, providing a clear color change (changing from white to dark blue) when 0.5 mL (± 20%) is collected. Participants were instructed to swallow any saliva present in the oral cavity before they placed the collection device on top of the tongue. SIgA concentration was analyzed according to a real-time lateral-flow device in accordance with the manufacturer’s guidelines (IPRO Interactive, UK). This method has previously been validated against ELISA (R2 = .78) in 208 samples collected from a cohort of English Premier League soccer players with a range of SIgA concentrations from 28 to 628 μg/mL.10
Figure 1 — Salivary secretory IgA concentration during the 4-day training period that preceded match day. Data are representative of 7 training camps. Abbreviations: MD-1, match day minus 1; MD-2, match day minus 2; MD-3, match day minus 3; MD-4, match day minus 4. *Significant difference from MD-4 and MD-3, P < .05.
Statistical Analysis Changes in SIgA were analyzed using a 1-way repeated-measures general linear model (SPSS, version 17, Windows). Where a significant main effect of time was observed (ie, P < .05), differences between specific time points were located using Bonferroni post hoc analysis. The 95% confidence intervals (95% CI) for the differences between specific time points were also calculated, and inferences on the magnitude of differences were reported according to Batterham and Hopkins.11 All data are presented as mean ± SD, with P values 40% (see Figure 2).
Discussion Contrary to our hypothesis, we provide novel data by demonstrating that SIgA in elite soccer players significantly declines during a shortterm training camp that precedes international-standard competitive match play. Given the relevance of SIgA to immune function,1 these data suggest that to maintain SIgA at near basal levels, alterations to the current training-camp structure may be required. It is difficult to readily determine the reason for the fall in SIgA levels during 4 days of soccer training, as, unfortunately, we were unable to collect any detailed and consistent measures of training load in this study. We acknowledge, therefore, that future studies
Figure 2 — Salivary secretory IgA levels on MD-3, MD-2, and MD-1 when expressed as a percentage of MD-4 values. Each circle represents an average of each individual player’s values from the 7 training camps. Abbreviations: MD-1, match day minus 1; MD-2, match day minus 2; MD-3, match day minus 3; MD-4, match day minus 4.
should attempt to ascertain potential measures of training load that contributed to the fall in SIgA levels observed here. However, if the mechanism of decline is indeed related to physiological loading, these data suggest that the current training prescription is of sufficient intensity and duration to induce perturbations to mucosal immunity. Indeed, recent data from our group support this hypothesis, as we observed that high-intensity soccer-specific training sessions are associated with greater decrements in SIgA than lowintensity training, as observed in professional soccer players from the Scottish Premier League.3
Salivary IgA and Professional Soccer 403
Alternatively, the mechanisms of decline in SIgA may not be related to physical loading but, rather, could be psychological in nature given the importance of the games in question (ie, FIFA World Cup qualifying games), as well as the potential sleep and travel stress12 associated with training-camp environments and international competition. However, given that 5 of the 7 games were played at home and that 1 of the away games was also against another country of the United Kingdom (hence could also be technically classified as a home fixture), we were unable to evaluate the potential effects of travel on SIgA responses.
Downloaded by Australian Catholic University on 09/27/16, Volume 10, Article Number 3
Practical Applications From a practical perspective, data suggest that monitoring SIgA provides a noninvasive assessment that may be useful alongside additional internal and external markers of training load to assess how soccer players respond to short-term training. Notably, our data demonstrate that SIgA displayed a progressive decline in the days before game day and thereby provides objective evidence for the administration of appropriate interventions to prepare players for the physical stress of game day itself. Future studies should attempt to correlate SIgA levels and secretion rates to specific markers of training load, as well as report SIgA data on game day and recovery days to verify the efficacy of any strategy put in place, for example, reduction of training load, sleep strategies, nutritional interventions. Furthermore, prior measurement of players’ SIgA levels during their habitual training environment (ie, domestic clubs) would also provide a more definitive assessment of each player’s true baseline SIgA profile (as opposed to the MD-4 values per se that are reported here), thus providing further evidence as to how players adapt to the demands of international training and competition.
Conclusions We conclude that a soccer-training camp in preparation for international competition induces detectable perturbations in markers of mucosal immunity. Monitoring SIgA (as a practical and noninvasive measurement tool) may therefore be useful alongside additional internal and external measures of training load to strategically tailor training and nutritional strategies that optimally prepare players for high-level competition. Acknowledgments The authors acknowledge the support of the coaching staff and players for adhering to data-collection procedures.
References 1. Neville V, Gleeson M, Folland JP. Salivary IgA as a risk factor for upper respiratory infections in elite professional athletes. Med Sci Sports Exerc. 2008;40:1228–1236. PubMed doi:10.1249/ MSS.0b013e31816be9c3 2. Gleeson M, Pyne DB. Exercise effects on mucosal immunity. Immunol Cell Biol. 2000;78:536–544. PubMed doi:10.1111/j.1440-1711.2000. t01-8-.x 3. Owen AL, Wong DP, Dunlop G, et al. High intensity training and salivary immunoglobulin-A responses in professional top level soccer players: effect of training intensity [published online ahead of print January 19, 2014]. J Strength Cond Res. PubMed 4. Nieman DC, Henson DA, Fagoaga OR, et al. Change in salivary IgA following a competitive marathon race. Int J Sports Med. 2002;23:69– 75. PubMed doi:10.1055/s-2002-19375 5. Mackinnon LT, Hooper S. Mucosal (secretory) immune system responses to exercise of varying intensity and during overtraining. Int J Sports Med. 1994;15:S179–S183. PubMed doi:10.1055/s-2007-1021134 6. Fredericks S, Fitzgerald L, Shaw G, Holt DW. Changes in salivary immunoglobulin A (IgA) following match play and training among English Premiership footballers. Med J Malaysia. 2012;67:155–158. PubMed 7. Moreira A, Arsati F, de Oliveira Lima-Arsati YB, de Freitas CG, de Araujo VC. Salivary immunoglobulin A responses in professional top-level futsal players. J Strength Cond Res. 2011;25(7):1932–1936. PubMed doi:10.1519/JSC.0b013e3181e7fbc0 8. Gleeson M, McDonald WA, Cripps WA, Pyne DB, Clancy RL, Fricker PA. The effect on immunity of long term intensive training in elite swimmers. Clin Exp Immunol. 1995;102:210–216. PubMed doi:10.1111/j.1365-2249.1995.tb06658.x 9. Whitham M, Laing SJ, Dorrington M, et al. The influence of an arduous military training program on immune function and upper respiratory tract infection incidence. Mil Med. 2006;171:703–709. PubMed 10. Dunbar J, Jehanli A, Skelhorn S. Investigating the use of a point of care SIgA test in the sporting environment. Paper presented al: International Society of Exercise and Immunology; July 11–13, 2011; Oxford, UK. Abstract P.85. Available at: www.isei.dk. 11. Batterham AM, Hopkins WG. Making meaningful inferences about magnitudes. Int J Sports Physiol Perform. 2006;1:50–57. PubMed 12. Walsh NP, Gleeson M, Shephard RJ, et al. Position statement part one: immune function and exercise. Exerc Immunol Rev. 2011;17:6–63. PubMed
