Most athletes participating in sports with specific weight categories (judo, wrestling, boxing, etc.) compete in a class that is 5-10% below their usual weight (4). Many athletes rely on weight loss achieved through a combination of excessive dietary and fluid restrictions and sweating through intensive exercise training. However, such weight loss might be harmful to the health and performance of athletes by decreasing muscular strength, anaerobic capacity (14), and simultaneously impairing endocrine (4) and immune functions (31). Reportedly, 64% of wrestlers have experienced poor physical conditions during a weight loss period (WL) as junior wrestlers (1). Accordingly, conditioning during a WL presents important implications for many athletes.
Upper-respiratory tract infection (URTI) incurs sore throat, headache, runny nose, coughing, fever, fatigue, or emesis, leading to impairment of conditions in athletes (22,24). Actually, URTIs are particularly common among athletes because of chronic immunosuppression during intensive exercise training and major competition (23). It is also well established that severe deficiency of energy and nutrients impairs immune function, thereby decreasing resistance against infection (7). Some athletes undergoing weight loss are known to suffer from infections. Results of our previous study showed that elite wrestlers experienced URTI symptoms during weight loss (24).
The human body protects itself against pathogens using different mechanisms including innate and acquired immunity. Elements of innate immunity exist before microbe exposure; its agents include phagocytes such as monocytes and neutrophils, and natural killer (NK) cells. Acquired immunity is triggered by exposure to foreign substances (antigens) with pathogens and involves an integrated system of host defenses. Acquired immunity features humoral and cell-mediated immune responses as a result of complex cross-talk between T and B lymphocytes, antigen-presenting cells (monocytes, macrophages, dendritic cells, and B lymphocytes), and immunoglobulins and lymphocyte-derived cytokines. Toll-like receptors (TLRs) play an important role in detecting pathogens (18). Actually, TLRs control the activation of innate immunity through the induction of antimicrobial activity (29) and generation of acquired immunity through induction of antigen-presenting and costimulatory molecules such as CD80 (19). On the surface of T cells, CD28 regularly expresses. Ligation of CD28 with its cognate receptor (CD80) on antigen-presenting cells is both necessary and sufficient, concomitantly with T-cell receptor signaling, to induce T-cell proliferation (12). Reportedly, TLR-4-deficient mice exhibit higher susceptibility to infection by tuberculosis than do wild-type mice (3). The CD28-deficient mice are also susceptible to Pneumocystis infection (2). Therefore, decreasing expressions of TLRs and CD28 might contribute to the increased incidence of infectious diseases. Reportedly, acute intensive exercise decreases TLRs expression on monocytes (16) and CD28 expressing T cells (5). Moreover, nutrient deficiency also decreases expressions of TLRs (10) and CD28 (15). Results of several studies have suggested adverse effects of weight loss including intensive training and energy restriction on immune parameters in athletes. Weight loss reportedly reduces neutrophil phagocytic activity (27), T-cell proliferation, cytokine production such as interferon-γ (11), and leukocyte counts (31). However, no report has described a study of the influences of weight loss on TLRs and CD28 expression.
The purpose of this study was to determine the influence of weight loss on immune parameters in judo athletes: TLR expression on monocytes, CD28 expression on T cells, and URTI symptoms. We hypothesized that the weight loss program for judo athletes conducted as usual might decrease TLR- and CD28-expressing cells and increase the appearance of URTI symptoms.
Experimental Approach to the Problem
Many athletes participating in sports with specific weight categories rely on weight loss achieved through a combination of excessive dietary and fluid restrictions and sweating through intensive exercise training. This study evaluates lymphocyte subsets such as CD28-expressing T cells and TLR-expressing monocytes and appearance of URTI symptoms in response to usual weight loss programs during 2 weeks preceding an actual competition in judo athletes.
Six male students of the University of Tsukuba, elite Japanese judo athletes (20.3 ± 0.4 years) were enrolled in this study. Three of them attended the All Japan Championship. Their mean period of practicing judo was 12.3 ± 2.2 years. The subjects' technical levels were second and third Dan black belts. They competed in categories between −60 and −73 kg. Based on results of a self-reported questionnaire, no subject had been treated with any drug that is known to affect immune function, had experienced acute illness from infection during the prior 3 months, or had smoked tobacco regularly. All subjects regularly trained for 16.5 hours per week. The training session consisted of 40 minutes of running in the morning and standing-technique and groundwork-technique judo trainings in the evening. The standing techniques training consisted of 30 minutes of uchikomi-keiko (judo-specific skills and drills) and 60 minutes of randori-keiko (fighting practice). The groundwork technique training consisted of 5 minutes of uchikomi-keiko and 30 minutes of randori-keiko. The exercise intensity during the judo match corresponds to approximately 92% V̇o2max (9). Potential subjects were given a detailed explanation of the risks, stress, and potential benefits of the study before they signed an informed consent form. This study, which conforms to the principles outlined in the Declaration of Helsinki, was approved by the Ethics Committees of the Institute of Health and Sport Sciences and the Institute of Clinical Medicine of University of Tsukuba. Moreover, this study conforms to the policy statement regarding the use of human subjects and written informed consent, as the American College of Sports Medicine's policies.
All subjects took part in the Divisional College Judo Championship, Classed by Weight. They conducted self-determined weight loss programs (dietary energy restriction, fluid restriction, bicycle exercise in the dry room, wearing sauna suits during training, and sauna) in addition to usual judo training during the 2 weeks preceding a competition. Assessments (anthropometric measurements, blood samples, and appearance of URTI symptoms) were measured in the morning (8:00) at their normal weight during periods designated as the baseline period (BL, 40 days before a competition), the WL (3 days before a competition), and after the competition (AC, 1 day after the competition). During the BL, subjects performed their regular regimens of judo and interval training, and resistance training normally for 2.5-3.0 hours. Judo training sessions involved stretching, judo-specific skills and drills, and high-intensity randori (fighting practice), at approximately 60-80% V̇o2max and 80-85% HRmax (21).
Assessment of Nutritional Intake
Values for nutritional intake were obtained from a straight 3-day food record kept during the BL and WL, and AC. Subjects were asked to be as accurate as possible in recording the amounts and types of food and fluid consumed. Values of daily nutritional intake were calculated using dietary assessment software (Excel Nutrition ver. 2.3; Kenpakusha, Tokyo, Japan).
Appearance of Upper-Respiratory Tract Infection Symptoms
We asked the subjects “Do you have URTI symptoms (sore throat, headache, runny nose, coughing or fever) now?” at BL, WL, and AC, and “Have you experienced URTI symptoms during the weight loss period?” at WL using a questionnaire, as described in a previous report (23).
The body mass, % fat, fat mass, fat-free mass, and body water were recorded using a digital scale (bioelectrical impedance analysis, BC-118; Tanita Corp., Tokyo, Japan) with each subject wearing light clothing and no footwear.
Subjects refrained from any exercise for at least 12 hours before blood sampling; they came to our experimental laboratory without eating breakfast. Samples were collected in vacutainers containing sodium ethylenediaminetetraacetic acid (EDTA). We quantified total leukocytes, lymphocytes, and monocytes from whole-blood samples using a multichannel hemocyte analysis system (SE-9000; Sysmex Corp., Hyogo, Japan).
Flow Cytometry Analysis
We used a whole-blood staining method (25) to label the lymphocytes and monocytes with fluorescent dye: fluorescein isothiocyanate (FITC), phycoerythrin (PE), and allophycocyanin (APC). Three-color flow cytometry (FACSCalibur, BD Biosciences, NJ, USA), with antibodies (CD3, CD8; DakoCytomation, Glostrup, Denmark/CD4, CD14, CD56; Immunotech, Marseille, France/TLR-4; MBL, Nagoya, Japan) to appropriate clusters of differentiation, was used to identify total quantities of T cells (CD3+), CD4+, CD8+, CD28+CD4+, and CD28+CD8+ T-cell subpopulations, NK (CD56+CD3−) cells, and TLR-4+CD14+ monocytes. The primary recognition molecule of the monocyte in response to lipopolysaccharide (LPS) of gram-negative bacteria is TLR-4, which, in conjunction with CD14 (LPS receptor), mediates the production of inflammatory cytokines and activation of innate immunity (30). Two microliters of FITC-conjugated, 2 μL of PE-conjugated, and 2 μL of APC-conjugated antibody were pipetted into a tube, and 100 μL of whole blood was added and incubated for 15 minutes in the dark at room temperature. After incubation, 1 mL of lysing solution (0.15 M NH4Cl, 10 mM KHCO3, 0.1 mM EDTA-2Na) was added to each of the tubes and incubated for 10 minutes in the dark at room temperature for erythrocyte lysing. The tubes were centrifuged for 5 minutes at 3,000 rpm, the supernatant was vacuum aspirated, the cell pellet was washed with 1 mL of 0.1% bovine serum albumin (BSA)/0.1% NaN3/phosphate-buffered saline (PBS), centrifuged, and vacuum aspirated again. The pellet was suspended in 300 μL of 0.1%BSA/0.1% NaN3/PBS. Labeled cells were analyzed by flow cytometry using a fluorescence-activated cell sorter analyzer (FACSCalibur, BD Biosciences). Immunophenotyping by flow cytometry has become standard practice for identification of human leukocyte subpopulations. With regard to this method, previous study showed repeatability and reliability (6). The usual quantity of cells scanned was 10,000 cells per sample. The data were analyzed using the CELLQuest software (BD Biosciences), to determine proportions of fluorescent-labeled lymphocytes. Absolute numbers of cells in specific cell subsets were calculated using the total number of cells multiplied by the percentage of positive cells within the subset of interest.
All data are represented as mean ± SE. For all analyses, p ≤ 0.05 was inferred as statistically significant. All variables were analyzed using 1-way repeated-measures analysis of variance (ANOVA). A Fisher's protected least significant difference (PLSD) post hoc test was performed whenever significant effects were found using ANOVA. Furthermore, effect size (ES) was calculated as the difference between each means. An ES of 0.2 is considered small, 0.5 is moderate, and 0.8 is large (8). A power analysis was conducted by using actual values obtained from this study to verify of the null hypothesis.
A significant decrease in body mass at the weight loss phase (3.6% average loss) was found for all subjects compared to the baseline phase (p ≤ 0.05; ES: 0.84; power: 0.55) (Table 1). Percentages of body fat (ES: 0.96; power: 0.65), fat mass (ES: 0.94; power: 0.63), fat-free mass (ES: 0.73; power: 0.46), and body water (ES: 0.73; power: 0.46) were significantly lower after weight loss (p ≤ 0.05) (Table 1). The body mass (ES: 0.84; power: 0.55), percentage of body fat (ES: 0.95; power: 0.64), and fat mass (ES: 0.97; power: 0.65) remained significantly lower at AC (p ≤ 0.05).
The respective intakes of calories (ES: 0.92; power: 0.62), protein (ES: 0.94; power: 0.63), and fat (ES: 0.93; power: 0.62) during the WL were significantly lower than during the BL (p ≤ 0.05) (Table 2). After the competition, intakes of calorie, protein, and fat reverted to baseline values.
Although 1 instance of a runny nose was reported during the baseline phase, 1 case of headache, 3 runny noses, and 1 coughing instance were reported during the WL. At WL, single reports of a headache and 1 runny nose were given. After the competition, 1 athlete reported a runny nose.
Leukocytes (ES: 0.86; power: 0.57), lymphocytes (ES: 0.79; power: 0.51), and monocytes (ES: 0.87; power: 0.58) during the WL were significantly fewer than during the BL (p ≤ 0.05) (Table 3). The erythrocyte count (ES: 0.95; power: 0.64) and hemoglobin concentration (ES: 0.97; power: 0.65) during the WL were significantly lower than baseline values (p ≤ 0.05) (Table 3). After the competition, the absolute number of monocytes remained significantly lower (p ≤ 0.05; ES: 0.89; power: 0.59), although lymphocytes recovered to their baseline value.
The absolute numbers of CD3+ cells (ES: 0.81; power: 0.53), CD4+ cells (ES: 0.72; power: 0.38), and CD8+ cells (ES: 0.88; power: 0.49) in the WL were significantly lower than the baseline values (p ≤ 0.05); they reverted to baseline values at AC (Figure 1). During the study period, no significant change was found in absolute quantities of CD56+CD3− cells (Figure 1).
The CD28+CD4+ cells counted during the WL were significantly fewer than the baseline (p ≤ 0.05; ES: 0.70; power: 0.37) (Figure 2). After the competition, CD28+CD4+ cells reverted to baseline values (p ≤ 0.05; ES: 0.80; power: 0.44). No significant changes were found for CD28+CD8+ cells during the study period (Figure 2).
The absolute number of TLR-4+CD14+ cells during the WL was significantly lower than the baseline value (p ≤ 0.05; ES: 0.93; power: 0.62); it remained lower at AC (p = 0.06; ES: 0.63; power: 0.38) (Figure 3).
The primary finding of our investigation was that −3.6% of weight loss during 2 weeks decreased the number of TLR-4 expressing monocytes and CD28-expressing Th cells in parallel with increasing URTI symptoms in judo athletes. These results suggest that weight loss in judo athletes can induce high susceptibility to URTI because of impairment of monocyte function and T-cell-mediated immune function, thereby depressing the athlete's physical condition.
In this study, because subjects pursued weight loss programs for 2 weeks. their body mass during the WL decreased by 3.6 ± 1.1% compared to the baseline value. In this study, all subjects conducted self-determined weight loss programs including “dietary energy restriction,” “fluid restriction,” “bicycle exercise in the dry room,” “having on sauna suits during training,” and “sauna,” in preparation for the judo competition. Previous reports describing methods of weight loss in junior wrestlers showed that “dietary energy restriction,” “fluid restriction,” “increased training volume,” and “wearing on sauna suits during training” topped the list of weight loss methods (1). Therefore, the weight loss methods used by athletes in this study appear to be generally used.
An important role is played by TLRs in the detection and recognition of microbial pathogens and the induction of antimicrobial activity by both innate and acquired immune systems. Results of this study show that TLR-4+CD14+ monocytes were significantly fewer during the WL. To our knowledge, the data presented herein are the first to show that expression of TLRs is degraded in athletes pursuing a weight loss program. In an earlier study, a single bout of prolonged aerobic exercise was shown to decrease expression of TLR-4 on CD14+ monocytes in human blood (16). Protein deficiency decreased expression of TLR-4 on peritoneal monocytes (10); also, calorie restriction decreased the TLR-4 expression and phagocytic capacity of peritoneal macrophages in mice (26). Accordingly, weight loss including intensive exercise training and nutritional restriction might downregulate monocyte functions of pathogens' detection and recognition, in addition to phagocytic capacity in athletes. In this study, TLR-4+CD14+ cells remained at a lower level at AC, although T-cell subpopulations recovered. Previous report in the literature describes that the phagocytic capacity of monocytes was impaired by a weight loss program involving nutritional restriction (2-kg loss during 2 weeks) in athletes, although lymphocyte response to mitogens remained unchanged (13). These findings raise the possibility that monocyte function is more influenced by nutritional status than other cellular functions are.
Activation of TLRs engenders the induction of antimicrobial activity, the production of inflammatory cytokines and the upregulation of costimulatory molecules (28). The upregulation of costimulatory signals between CD80/CD86 on monocytes and CD28 on T cells is critical for the generation of adaptive immune responses. Results show that CD28+CD4+ cells were significantly fewer and that TLR-4+CD14+ cells were fewer during the WL. To date, no report in the relevant literature has described examination of the changes in CD28 expression during athletes' weight loss programs. Previous reports have explained that acute intensive exercise decreases CD28+CD4+ cells (5). Furthermore, altered CD28 expression has been related to a low nutrient condition. Particularly, iron deficiency has been well documented to downregulate CD28 expression (15), although we did not measure it. The CD28 molecule plays a critical role in orchestrating immune responses, including upregulation of various cytokine syntheses and T-cell proliferation. Imai et al. (11) showed that weight loss decreased T-cell proliferation and production of interleukin-2 and interferon-γ, whose cytokines induce T-cell activation and proliferation in wrestling athletes. Therefore, weight loss in athletes might impair T-cell activation and proliferation through decreased CD28 expression, thereby downregulating the function of immune system modulation.
In highly trained athletes, URTIs are common reported illness (17). It has been hypothesized that performing prolonged, high-intensity exercise or periods of strenuous exercise training is associated with impairment of immune function and a high risk of URTI. In this study, decreases of TLR-4 and CD28 expression occurred along with the appearance of URTI symptoms during the WL. The respective deficiencies of TLR-4 and CD28 expression might be related to susceptibility to infection (2). Weight loss program including intensive exercise training and energy restriction, etc. might impair monocyte function and T-cell-mediated immune function, leading to the appearance of URTI symptoms in judo athletes. Results of our previous study showed that a rapid weight loss program (4.4% weight loss during 1 week) also induced URTI symptoms in elite wrestlers (24). A weight loss program achieving 3.6% weight loss during 2 weeks might adversely influence immune functions and contribute to the appearance of URTI symptoms in athletes. We therefore recommend that athletes conduct longer-term weight loss programs. Future studies must examine the influence of a gradual weight loss program on immunocompetence and infectious diseases in athletes.
In this study, the absolute numbers of CD3+, CD4+, CD8+, and CD28+CD4+ cells reverted to baseline values at AC. Rehydration in addition to nutritional intakes after the weigh-in might contribute to recoveries of them. However, there has been no study examining the relationship between rehydration and lymphocyte subsets. Previous study reported that hydrated state during exercise did not affect the absolute number of CD3+, CD4+, and CD8+ cells at normal environment (22°C) (20). Future studies need to examine closely the influences of hydrated status on immunocompetence such as lymphocyte subsets and monocytes. Additionally, the hot environment (38°C) caused more decrease of CD3+, CD4+, and CD8+ cells in dehydrated condition compared with euhydrated conditions (20). In turn, fluid deficits associated with intensive exercise particularly in hot environments might be at least partly responsible for decreases of lymphocyte subsets associated with intensive exercise. Therefore, athletes should avoid weight loss methods such as bicycle exercise in the dry room and wearing sauna suits during training, which lead to hyperthermia.
This study has limitations. There was a smaller sample size of subjects that limited our power to perform analyses. In addition, no control subjects without weight loss and without psychological stress related to an upcoming competition participated in this study. We examined the influence of weight loss before an actual competition on immune function clinically, which presented the difficulty of finding judo athletes without weight loss and who are participating in competition, and defied classification of the influences of each stress (exercise stress, nutrient deficiency, dehydration, and competitive psychological stress) on immune parameters. Additional studies must use proper number of weight loss and control subjects who are expending energy similar to that used for judo (e.g., wrestling) but who are not participating in competition, who are not pursuing weight loss such as open-category class athletes (e.g., >100-kg class in judo), and who perform either fluid restriction program or dietary energy restriction program. In addition, we did not measure direct dehydration status such as urine specific gravity. Future study needs to examine the influences of weight loss on immune parameters in parallel with hydration status.
In conclusion, we conclude that 2-week weight loss programs undertaken in preparation for competition might degrade cell-mediated immune functions and foster the appearance of URTI symptoms in male judo athletes. Although conducting weight loss activities to achieve an advantage in competition, the consequent weight loss might impair immune functions and biophylactic functions, thereby depressing the overall physical condition. Therefore, it is necessary for athletes to develop safer and more effective weight loss programs.
Many judo athletes conduct weight loss program. However, weight loss might be harmful to the health and performance of athletes. In this study, a weight loss program achieving 3.6% weight loss during 2 weeks engendered appearance of URTI symptoms and impairment of T-cell and monocyte-mediated immune function in judo athletes. We recommend that athletes schedule longer-term (e.g., over 2 weeks) and gradual weight loss programs in preparation for competition to avoid having to rapidly lose weight. Because protein deficiency (10) and iron deficiency (15) downregulate TLR-4 expression on monocytes or CD28 expression on T cells, we recommend that athletes supplement these nutrients during the WL. Above all, TLR-4-expressing monocytes might be difficult to reverse to baseline values after the weight loss program. Therefore, athletes should avoid protein deficiency during weight loss programs as far as possible. In addition, recovery of monocyte function might require more long-term recovery period (e.g. over a day) including rehydration and nutritional intakes. Coaches, support staff, and athletes should monitor athletes' body weight, hydrated status, appearance of URTI symptoms, and immunocompetence such as lymphocytes and monocytes to prevent their physical condition from becoming worse.
We thank all subjects for participating in this study. We also thank K. Komata and T. Takezawa (University of Tsukuba) for critical comments. The authors have no conflict of interest related to this study.
1. Aizawa, K, Kukidome, T, Masujima, A, Nakajima, K, Sakamoto, S, Toda, Y, Nishimaki, K, Hosokawa, M, Aoyama, H, and Ohba, H. Weight loss methods of junior wrestlers. Jap J Clin Sports Med
13: 214-219, 2005.
2. Beck, JM, Blackmon, MB, Rose, CM, Kimzey, SL, Preston, AM, and Green, JM. T cell costimulatory molecule function determines susceptibility to infection with Pneumocystis carinii
in mice. J Immunol
171: 1969-1977, 2003.
3. Branger, J, Leemans, JC, Florquin, S, Weijer, S, Speelman, P, and Van Der Poll, T. Toll-like receptor
4 plays a protective role in pulmonary tuberculosis in mice. Int Immunol
16: 509-516, 2004.
4. Brownell, KD, Steen, SN, and Wilmore, JH. Weight regulation practices in athletes: Analysis of metabolic and health effects. Med Sci Sports Exerc
19: 546-556, 1987.
5. Bruunsgaard, H, Jensen, MS, Schjerling, P, Halkjaer-Kristensen, J, Ogawa, K, Skinhøj, P, and Pedersen, BK. Exercise induces recruitment of lymphocytes with an activated phenotype and short telomeres in young and elderly humans. Life Sci
65: 2623-2633, 1999.
6. Catellier, DJ, Aleksic, N, Folsom, AR, and Boerwinkle, E. Atherosclerosis risk in communities (ARIC) carotid MRI flow cytometry study of monocyte and platelet markers: Intraindividual variability and reliability. Clin Chem
54: 1363-1371, 2008.
7. Chandra, RK. McCollum award lecture: Nutrition and immunity: Lessons from the past and new insights into the future. Am J Clin Nutr
53: 1087-1101, 1991.
8. Cohen, J. Statistical Power Analysis for the Behavioral Sciences
(2nd ed.). New York, NY: Academic Press, 1988. pp. 75-95.
9. Degoutte, F, Jouanel, P, and Filaire, E. Energy demands during a judo match and recovery. Br J Sports Med
37: 245-249, 2003.
10. Fock, RA, Vinolo, MA, de Moura Sá Rocha, V, de Moura Sá Rocha, LC, and Borelli, P. Protein-energy malnutrition decreases the expression of TLR-4/MD-2 and CD14 receptors in peritoneal macrophages and reduces the synthesis of TNF-alpha in response to lipopolysaccharide (LPS) in mice. Cytokine
40: 105-114, 2007.
11. Imai, T, Seki, S, Dobashi, H, Ohkawa, T, Habu, Y, and Hiraide, H. Effect of weight loss on T-cell receptor-mediated T-cell function in elite athletes. Med Sci Sports Exerc
34: 245-250, 2002.
12. Jenkins, MK, Taylor, PS, Norton, SD, and Urdahi, KB. CD28
delivers a costimulatory signal involved in antigen-specific IL-2 production by human T cells. J Immunol
147: 2461-2466, 1991.
13. Kono, I, Kitano, H, Matsuda, M, Haga, S, Fukushima, H, and Kashiwagi, H. Weight reduction
in athletes may adversely affect the phagocytic function of monocytes. Phys Sportsmed
16: 56-65, 1988.
14. Kurakake, S, Umeda, T, Nakaji, S, Sugawara, K, Saito, K, and Yamamoto, Y. Changes in physical characteristics, hematological parameters and nutrients and food intake during weight reduction
in judoists. Environ Health Prev Med
3: 152-157, 1998.
15. Kuvibidila, SR and Porretta, C. Iron deficiency and in vitro iron chelation reduce the expression of cluster of differentiation molecule (CD)28 but not CD3 receptors on murine thymocytes and spleen cells. Br J Nutr
90: 179-189, 2003.
16. Lancaster, GI, Khan, Q, Drysdale, P, Wallace, F, Jeukendrup, AE, Drayson, MT, and Gleeson, M. The physiological regulation of toll-like receptor
expression and function in humans. J Physiol
563: 945-955, 2005.
17. Mackinnon, LT. Chronic exercise training effects on immune function. Med Sci Sports Exerc
32: S369-S376, 2000.
18. Medzhitov, R. Toll-like receptors and innate immunity. Nat Rev Immunol
1: 135-145, 2001.
19. Medzhitov, R, Preston-Hurlburt, P, and Janeway, CA Jr. A human homologue of the Drosophilia
Toll protein signals activation of adaptive immunity. Nature
388: 394-397, 1997.
20. Mitchell, JB, Dugas, JP, McFarlin, BK, and Nelson, MJ. Effect of exercise, heat stress, and hydration on immune cell number and function. Med Sci Sports Exerc
34: 1941-1950, 2002.
21. Miyamoto, T, Oshima, Y, Shigematsu, R, Bar-Or, Y, and Miura, K. Intensity of randori exercise and anaerobic threshold in judo athletes. Mem Osaka Inst Tech Ser IV
42: 91-100, 1994.
22. Nieman, DC and Pedersen, BK. Exercise and immune function. Recent development. Sports Med
27: 73-80, 1999.
23. Shephard, RJ, Verde, TJ, Thomas, SG, and Shek, P. Physical activity and the immune system. Can J Sport Sci
16: 163-185, 1991.
24. Shimizu, K, Aizawa, K, Suzuki, N, Kukidome, T, Kimura, F, Akama, T, Mesaki, N, and Kono, I. Evaluation of condition during rapid weight loss using salivary level of secretory SIgA in elite wrestlers. Jap J Clin Sports Med
15: 441-447, 2007.
25. Shimizu, K, Kimura, F, Akimoto, T, Akama, T, Tanabe, K, Nishijima, T, Kuno, S, and Kono, I. Effect of moderate exercise training on T-helper cell subpopulations in elderly people. Exerc Immunol Rev
14: 24-37, 2008.
26. Sun, D, Muthukumar, AR, Lawrence, RA, and Fernandes, G. Effects of calorie restriction on polymicrobial peritonitis induced by cecum ligation and puncture in young C57BL/6 mice. Clin Diagn Lab Immunol
8: 1003-1011, 2001.
27. Suzuki, M, Nakaji, S, Umeda, T, Shimoyama, T, Mochida, N, Kojima, A, Mashiko, T, and Sugawara, K. Effects of weight reduction
on neutrophil phagocytic activity and oxidative burst activity in female judoists. Luminescence
18: 214-217, 2003.
28. Takeda, K, Kaisho, T, and Akira, S. Toll-like receptors. Ann Rev Immunol
21: 335-376, 2003.
29. Thoma-Uszynski, S, Stenger, S, Takeuchi, O, Ochoa, MT, Engele, M, Sieling, PA, Barnes, PF, Rollinghoff, M, Bolcskei, PL, Wagner, M, Akira, S, Norgard, MV, Belisle, JT, Godowski, PJ, Bloom, BR, and Modlin, RL. Induction of direct antimicrobial activity through mammalian toll-like receptors. Science
291: 1544-1547, 2001.
30. Triantafilou, M and Triantafilou, K. Lipopolysaccharide recognition: CD14, TLRs and the LPS-activation cluster. Trends Immunol
23: 301-304, 2002.
31. Umeda, T, Nakaji, S, Shimoyama, T, Kojima, A, Yamamoto, Y, and Sugawara, K. Adverse effects of energy restriction on changes in immunoglobulins and complements during weight reduction
in judoists. J Sports Med Phys Fitness
44: 328-334, 2004.