Soccer is a metabolically demanding sport involving different types of high-intensity actions, interspersed with lower intensity activities and passive recovery (3). During a soccer game at elite level, players cover a total distance of 9–12 km, including 220 high-intensity efforts, whereas the activity type changes every 4–6 seconds and heart rate (HR) averages 85% of maximal values (3). Because of this high physiological load, an activation of the immune system is expected, but only a limited number of studies examined the immune responses after a soccer match, using measurements mainly in saliva (23,37) and less frequently in blood (2,7,20). During intense exercise, skeletal muscle is the primary contributor to circulating cytokines, such as interleukin 6 (IL-6) in the blood, whereas IL-6 concentration is influenced by the intensity and duration of exercise (12,36). Tumor necrosis factor alpha (ΤNF-α) is mainly produced by macrophages infiltrated along with other inflammatory cells into the injured muscle which, in turn, contributes to further TNF-α increase (32,33), whereas C-reactive protein (CRP) is secreted by the liver cells and is mainly regulated by IL-6 and TNF-α (30).
In recent years, women's soccer has become very popular and an increasing level of participation is observed both in recreational and professional teams. However, the physiological responses to a match or training have not been studied as extensively in females compared with males (1,19,22,31). From those studies, it is evident that females cover less total distance as well as less distance at high intensity (2,31). This is due to the lower maximal oxygen uptake, muscle power, and sprint ability of females compared with males (18). In addition, females, due to their different hormonal profile, may have different inflammatory responses compared with males (25).
Several blood biomarkers have been used as indicators of systemic inflammation, including IL-6, TNF-α, and CRP (27). Cytokine response to soccer has been explored by only a few studies (2,7) providing contradictory results regarding postexercise cytokines' kinetics and performance (15,34). Thus, the aim of this study was to evaluate and compare the inflammatory responses of male and female soccer players for 48 hours after an official game.
Experimental Approach to the Problem
To investigate possible gender differences in inflammatory responses after a soccer match, 22 elite male and 21 elite female soccer players completed an official match. Venous blood samples were taken before and immediately after the soccer game, whereas the third and fourth samples were taken 24 and 48 hours after the match. Diet was controlled during the week before the match, and a pregame meal was taken 4.5 hours after the match. The control group consisted of 20 male and 20 female inactive individuals, and blood samples for the control group were taken at the same times of the day after similar dietary patterns with the players. The following dependent variables were measured: average HR during the game, TNF-α, IL-6, and CRP and compared across gender, training experience, and sampling time.
A total of 83 subjects took part in this study. The 2 experimental groups included 22 male elite soccer players and 21 female elite soccer players, whereas the 2 control groups included 20 males and 20 females (Table 1). The playing positions of the male and female players were balanced. Of the male players, 9 were midfielders, 4 were attackers, 5 were full-backs, and 4 were central defenders. Of the female players, 9 were midfielders, 4 were attackers, 5 were full-backs, and 4 were central defenders. No subjects were under 18 years of age.
As part of their yearly medical check, they had been subjected to a routine clinical assessment (electrocardiogram, measurement of arterial pressure, chest x-ray, and blood tests), which showed no evidence of any pathological condition. Subjects were informed about the procedures of the study and the possible risks involved and signed a written informed consent form before participation. The study was approved by the local Institutional Review Board, and all procedures were in accordance with the Helsinki declaration of 1975, as revised in 1996.
All players trained 5–7 times per week. Each training session lasted 75–90 minutes and included small-sided games, speed, power, strength and agility drills, as well as technical and tactical skill development drills. All players were playing 1 match every week. The control group consisted of subjects with an average level of physical activity, and their selection was done randomly from a population of the same age as the players. All participants did not smoke and did not consume any alcohol.
Standing height was measured to the nearest 0.5 cm (Stadiometer; Seca, Birmingham, United Kingdom), and nude body weight was measured to the nearest 0.1 kg (Beam balance 710, Seca, United Kingdom). Body fat was estimated from 7 skinfold measurements (16). Anthropometric measurements were performed during a preliminary visit.
Maximal oxygen uptake (
) and maximal HR were measured only for the players, during an incremental treadmill running test to exhaustion on a Technogym Runrace treadmill (Technogym, Gambettola, Italy), using a portable gas exchange analyzer (K4b2; Cosmed, Rome, Italy). Heart rate was measured telemetrically, using an HR monitor (Polar FT1 Model; Polar Electro Oy, Kempele, Finland). The protocol consisted of running at 7 km·h−1 for 1 minute and 8 km·h−1 for 30 seconds. Thereafter, treadmill speed was increased by 0.5 km·h−1 every 30 seconds until exhaustion. Individual
and maximal HR were determined as the peak values reached in a 15- and 5-second period, respectively, during the last part of the incremental test. Criteria for attainment of
included 2 of the following: Respiratory Exchange Ratio (RER) >1.1, maximal HR within 10 b·min−1 of the estimated value based on age, a rating of perceived exertion equal to, or higher than 18, or a leveling off in oxygen uptake (
<2 ml·kg−1·min−1) with an increase in treadmill speed.
The study was carried out during 3 official matches of the regular season in men's and 3 official matches of the regular season in women. The environmental conditions and the level of competition were similar in all matches (temperature: 17–20° C; relative humidity: 40–50%). During the week before matches, participants were advised to follow a balanced diet with daily consumption of 55% carbohydrates, 30% fat, and 15% protein. On the competition day, participants followed their typical pregame dietary pattern, that is, meal high in carbohydrate (60–65% of total calories), consumed 4.5 hours before the start of the game. Players were asked to replicate their prerecorded normal diet during the 48 hours after the match. Fluids were consumed ad libitum before, during half-time, and at the end of the match. Due to the fact that games were official, we could not measure the amount of fluids consumed during half-time.
Heart rate was recorded continuously during the game using the Polar Team 2 pro System (Polar Electro Oy, Kempele, Finland), and the average HR was calculated for each player.
Blood Sampling and Analyses
Four blood samples were drawn from the basilic or mesobasilic vein with the subject in a seated position. Samples (10 ml) were collected in vacutainers without anticoagulant. Tubes were mixed by gentle inversion, kept at 37° C for 1 hour to allow for clotting and then were centrifuged for 15 minutes at 4° C and 2,250g. The plasma samples were separated from the packed red cells, transferred to Eppendorf tubes, and immediately frozen and stored at −70° C.
The baseline sample was taken immediately before the game. The second sample was taken immediately after the soccer game, whereas the third and fourth samples were taken 24 and 48 hours after the match. Blood samples for the control group were taken at the same times of the day following similar dietary patterns with the players.
All the samples were measured in duplicate. The determination of IL-6 and TNF-α were made by commercial available ELISA kit (R&D Systems Inc., Minneapolis, MN, USA) according to the manufacturer's instructions on a standard ELISA reader. Levels of CRP were determined by an immunonephelometric assay on biochemistry analyzer (COBAS) according to the manufacturers' directions (ROCHE Diagnostics GmbH, Mannheim, Germany). The TNF-α and IL-6 values are presented in picograms per milliliter and CRP in milligrams per liter. The sensitivity for IL-6, TNF-α, and CRP was 0.11 pg·ml−1, 0.5 pg·ml−1, and 0.21 mg·ml−1, respectively. Plasma creatine kinase (CK) activity was determined spectrophotometrically using a test kit at a stable temperature of 37° C (Hitachi 917 analyzer; Roche Diagnostics GmbH, Mannheim, Germany).
Statistical analyses were performed with Statistica v. 8 (Statsoft Inc., Tulsa, OK, USA). Three-way analyses of variance (GROUP [trained vs. untrained] × GENDER [males vs. females] × TIME [blood sampling time]) with repeated measures on 1 factor (blood sampling time) were used to analyze differences in IL-6, TNF-α, and CRP concentrations, and CK activity. Tukey's post hoc tests were performed when a significant main effect or interaction was obtained (p ≤ 0.05) to locate differences between mean values. Effect size for main effects and interaction was estimated by calculating partial eta squared (η2) values. Effect sizes were classified as small (0.06), medium (0.14), and large (>0.14). Statistical significance was accepted at p ≤ 0.05.
was higher in male compared with the female players (57.9 ± 2.2 vs. 52.0 ± 1.8 ml·kg−1·min−1, p < 0.01). However, maximal HR was similar in male and female players (199 ± 7 vs. 198 ± 5 b·min−1, p = 0.59).
Heart Rate During Match Play
The average HR during the match was similar for the male and female players (173 ± 7 and 169 ± 5 b·min−1), which corresponded to 86.9 ± 4.3 and 85.6 ± 2.3% of maximal HR (p = 0.23).
The 3-way analysis of variance for IL-6 revealed a significant main effect only for time (p < 0.001, η2 = 0.66), as well as an interaction effect for time × group (p < 0.001, η2 = 0.66). There was neither a time × gender interaction (p = 0.68, η2 = 0.006) nor a time × gender × group interaction (p = 0.88, η2 = 0.002). Thus, there was no gender difference in the IL-6 responses to the match. Post hoc analysis for time × group interaction showed that IL-6 peaked immediately after the end of the match, and this increase was 3- to 4-fold above the resting values (p < 0.001, Table 2). Interleukin 6 returned to baseline values 24 hours after the match and remained at this level at 48 hours (Table 2). There was no change in IL-6 concentration in the control group. Finally, IL-6 was higher in the control subjects than in players at all time points (Table 2).
Tumor Necrosis Factor Alpha
The 3-way analysis of variance for TNF-α revealed a significant main effect only for time (p < 0.001, η2 = 0.75), as well as the following interaction effects: time × gender (p < 0.001, η2 = 0.08), time × group (p < 0.001, η2 = 0.74), and time × gender × group (p < 0.001, η2 = 0.08). Post hoc analysis for time × gender × group showed that TNF-α peaked immediately after the end of the match, and this increase was ∼18% greater in males compared with females (p < 0.005; Table 3). Tumor necrosis factor alpha returned to baseline values 24 hours after the match and remained at this level at 48 hours (Table 3). There was no change in TNF-α concentration in the control group. Finally, TNF-α was higher in the control subjects than in players at all time points (Table 3).
The 3-way analysis of variance for CRP revealed a significant main effect only for time (p < 0.001, η2 = 0.42), as well as an interaction effect for time × group (p < 0.001, η2 = 0.41). There was neither a time × gender interaction (p = 0.16, η2 = 0.02) nor a time × gender × group interaction (p = 0.20, η2 = 0.02). Thus, there was no gender difference in the CRP responses to the match. Post hoc analysis for time × group interaction showed that CRP peaked 24 hours after the end of the match, and this increase was about 120% above the resting values (p < 0.001, Table 4). C-reactive protein returned to baseline values 24 hours after the match and remained at this level at 48 hours (Table 4). There was no change in CRP concentration in the control group. Finally, CRP was higher in the players compared with the control subjects 24 hours after the match (Table 4).
The 3-way analysis of variance for CK revealed a significant main effect for group (p < 0.001, η2 = 0.77) and for time (p < 0.001, η2 = 0.70). There was also a gender × group (p < 0.043, η2 = 0.05) and a time × group interaction effect (p < 0.001, η2 = 0.70). There was no time × gender × group interaction (p = 0.28, η2 = 0.016). Post hoc analysis for time × group interaction showed that CK was increased 2-fold compared with resting values immediately after the match, but peaked 24 hours later (Table 5). CK did not return to baseline values 48 hours after the match (Table 5). There was no change in CK concentration in the control group and resting CK did not differ between players and subjects in the control group (Table 5).
This study investigated the effect of playing a competitive soccer game on cytokines response in male and female athletes. One main finding was that IL-6 and TNF-α values increased significantly on game cessation, whereas they returned to resting levels within the following 24 hours. Interestingly, CRP and CK reached peak values at 24 hours after the match, and there was no difference between male and female players. The comparison between cytokine changes in male and female players showed that IL-6 responses were similar, but TNF-α immediately after the match was higher in males compared with female players.
Cytokines are involved in the control of the acute-phase response, in inflammatory reactions, and in tissue repair processes. Interleukin 6 is one of the initial cytokines in the respective cascade mainly released from the muscle (8,24). Muscle damage alone induces a repair response, including macrophage entry into the muscle causing further IL-6 production. As indicated by the indirect marker CK, the degree of possible muscle damage was similar in male and female players (Table 5). This may partially explain the lack of significant gender difference in IL-6 responses. However, there is evidence that IL-6 is secreted by muscle contraction per se (6), independently of muscle damage. Reduced glycogen availability, changes in calcium homeostasis, and increased formation of reactive oxygen species can activate transcription factors, which regulate the IL-6 synthesis (10,12). It seems that IL-6 plays a pivotal role in the regulation of metabolism during exercise since its plasma increase enhances skeletal lipolysis and glucose uptake as well as liver glucose production (40). Therefore, it has been suggested that the appearance of IL-6 into the circulation depends on exercise intensity and especially duration (13). As it has been shown in several studies, IL-6 shows a gradual increase with exercise duration, with the peak values observed at the end of the effort (9,12), followed by a fast decrease toward the resting levels during the recovery period. This pattern was also observed in this study, where IL-6 peaked immediately after the game and the values returned to baseline 24 hours later. This is in agreement with the 2 previous studies where IL-6 was measured after a soccer match (2,15).
Although TNF-α and IL-6 are tightly linked, since they are early mediators of inflammation, we have found an 18% higher peak in TNF-α in male compared with the female players. The fact that the peak of TNF-α was higher in male players may be due to several possible reasons. Based on average HR measurements performed in this study, the physiological load during the match was similar in male and female elite players, and this is also supported by the existing literature (3,19). However, the absolute workload is lower in female players, since they cover less total distance as well as less distance at high intensity during a match, compared with male players (2,31). This is due to the lower maximal oxygen uptake, muscle power, and sprint ability of females compared with males (21,22). Thus, it may be speculated that the lower peak in TNF-α in females may be related with the lower absolute load (i.e., distance run) during the match. Additionally, a possible suppressive effect of estradiol on TNF-α (25) may explain the lower peak in TNF-α in female players found in this study. All these factors may be related with the lower TNF-α in the female players of this study (26). Muscle damage does not seem to be the primary regulator of TNF-α concentration in the circulation. Andersson et al. (1) investigated changes in TNF-α in elite female soccer players after two 90-minute games separated by a 72-hour active or passive recovery. They found an increase of TNF-α after the first but not after the second soccer match (1), suggesting that its concentration in the blood is not regulated only from muscle damage. In agreement with this notion, there was no gender difference in CK responses, in this study, and thus, possible muscle damage seems to be similar. A number of studies indicated that TNF-α and its receptors are involved in muscle regeneration, rather than muscle damage, by a mechanism that involves a decrease in infiltrating neutrophils and macrophages and expression of myogenic regulatory factors, as shown in animal experiments (28,39). Furthermore, TNF-α increase has been also suggested as a regulatory factor of force generating capacity, aiming to minimize damage by reducing intensity of muscular contraction. Indeed, TNF-α administration to mice suppresses myofibrillar force production by 40% within 60 minutes (14). Likewise, Ispirlidis et al. (15) showed that maximal muscular strength is compromised up to 72 hours on game termination.
In this study, CRP reached peak values at 24 hours after the soccer match and was similar between genders. Thereafter, CRP returned to baseline 48 hours after the match. Also, CRP peak values were significantly lower in male and female soccer players than the subjects of the control group. The time course of CRP was similar to that reported individually for soccer (15), handball (4), and basketball (5), peaking in the next day after the match and returning to baseline 2 days later. C-reactive protein is synthesized primarily by the hepatocytes, and it is regulated by IL-6, IL-1, and TNF-α (11,17). Its concentration in plasma can increase several thousand-fold during injury and infection. During inflammation, increased circulating IL-6 acts on hepatocytes to stimulate the synthesis of acute-phase proteins, such as CRP. C-reactive protein has a role in inducing anti-inflammatory cytokines in circulating monocytes and in suppressing the synthesis of proinflammatory cytokines in tissue macrophages (29). Soccer induced a marked but transient CRP rise within 24 hours in both male and female players, as previously shown in other exercise protocols (7,15,34). Moreover, baseline values of CRP, IL-6, and TNF-α were lower in both male and female players compared with subjects in the control group. This is in accordance with the fact that chronic exercise improves the inflammatory profile by decreasing cytokine production by adipose tissue, skeletal muscles, endothelial and blood mononuclear cells, as well as CRP levels (13,27,35,38).
In conclusion, a soccer match caused significant inflammatory responses in both male and female players as shown by a 2- to 4-fold increase in inflammatory cytokines and CRP. Although the inflammatory responses to an official soccer match were similar in male and female players, TNF-α was 18% higher in males compared with females. The lower baseline values of IL-6, TNF-α, and CRP in male and female players compared with the control subjects are indicative of a positive effect of regular exercise training in reducing inflammatory markers at rest (17,27).
The results of this study show that a soccer match induces significant inflammatory responses in both male and female players, with IL-6 and TNF-α returning to baseline 24 hours later, whereas CRP decreases to resting values 48 hours after the match and CK remains elevated at 48 hours. With the exception of TNF-α, that was 18 % higher in male than in female players, the inflammatory responses to the match were independent of gender. The time course of those responses has implications for training volume and intensity after a soccer match. Because of the effects of inflammatory responses on performance and health of the players, it is suggested that coaches and trainers should adjust exercise training programs after a match to promote recovery and protect the athletes' health. Furthermore, this study provides evidence that exercise training for soccer reduces the resting levels of CRP, TNF-α, and IL-6.
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