Introduction
Rugby sevens took part of the Olympic Games in Rio 2016 for the first time. In the rugby sevens, the rules and field dimensions are the same as in the 15-player rugby union, except for the fact that the game is played by 7 players per team, in 2 halves with a duration of 7-minute each, and with a 2-minute half-time interval. Remarkably, it has been shown that the average velocity maintained during the rugby sevens matches is higher than in rugby union (7,26). Therefore, because of the high-intensity efforts demanded throughout these games (12,14,30), athletes are required to excel in speed, muscle power, and aerobic and anaerobic capacities to efficiently cope with the specific sport demands. In addition to physical fitness development, maintenance of nutritional and hydration status throughout the tournaments is fundamental for athletes to deal with rugby sevens match demands (8).
Rugby sevens tournaments are generally contested over 2 consecutive days, comprising 5–7 matches with ≈3-hour intervals between successive games. The sequential matches may lead to fatigue accumulation and reduced match performance (i.e., distance covered in different intensities) across the tournament. Although only trivial-to-small decrements in the match performance of rugby sevens players have been reported from the first to the second halves (12,30), between-match comparisons are less prevalent in the literature. One study analyzing match-to-match performance variations showed unclear-to-moderate differences in movement patterns (i.e., number of accelerations performed and distance covered in different intensities) between the first pool match on day 1 and the last knock out finals match on day 2 in international level male players (13), whereas in female players it seems that match performance is largely reduced in similar competition settings (3). However, it is currently unknown whether rugby sevens players experience physical performance impairments during the first day of competition, leading to deterioration of the neuromuscular/physiological traits and, consequently, hampering the athletes' performance on the second day. To date, a recent study (37) with female national and state level players showed moderately attenuated vertical jump performance, a large increase in muscle soreness, and a very large increase in circulating creatine kinase (CK) by the end of the tournament. Accordingly, decrements in countermovement jump (CMJ) performance related to prolonged neuromuscular fatigue and muscle damage were reported for up to 7 days' posttournament stages (37). As such, previous studies have shown that high physical demands of high-intensity running, disputes, and collisions acutely induce significant increases in postgame circulating muscle damage markers (e.g., CK) and inflammatory mediators (e.g., neutrophils and interleukin [IL]-6) immediately after 2 consecutive rugby sevens matches (31), and between 14- and 48-hour after rugby union (5) and soccer matches (28).
Confirming the existence of signs of neuromuscular fatigue (i.e., reduced vertical jump and sprint performances and decreases in the rate of force development [RFD]) and muscle damage (i.e., increased level of CK activity) at the start of the second day of competition in rugby sevens players would highlight the necessity of implementing nutritional interventions trying to maintain glycogen levels and hydration status (8); to use effective recovery strategies at the end of day 1 (e.g., cold water immersion) (6); and to develop more effective training strategies aiming to enhance the physical fitness components necessary to allow players to better cope with the high match demands (15). Furthermore, these “physical impairments” from the first to the second day could be a criterion to spare a player from full-match participation on the second day of competition. Therefore, the aim of this study was to analyze the match performance (i.e., distance covered in different intensities and body load [BL]), signs of muscle damage (i.e., CK activity and RFD), inflammatory status (assessed by means of IL-6, tumor necrosis factor [TNF]-α, and IL-10), and neuromuscular fatigue (i.e., vertical jump and sprint performances, maximum isometric force, and RFD) after 3 single-day simulated matches performed by rugby sevens players from the Brazilian National team.
Methods
Experimental Approach to the Problem
This observational study was designed to simulate the first day of a rugby sevens tournament played over 3 consecutive matches. Figure 1 displays the schematic representation of the study scheme. On the day before the matches (in the afternoon), the athletes performed a 40-m sprint, a vertical jump assessment (squat jump [SJ] and CMJ), and a maximal isometric force test in the half-squat exercise (baseline physical testing). On the day of the matches, in the morning (at 8:00 am), blood samples were collected (baseline measurements). Afterward, 3 simulated rugby sevens matches were performed with 2-hour intermission periods. The match performance (encompassing total distance and distance covered in different velocity ranges and BLs) was obtained from global positioning system (GPS) units. Before physical testing on day 1 and day 3 and before each match, a 10-minute standardized warm-up involving self-selected low-intensity runs for 5 minutes followed by active stretching and submaximal jumps and runs was supervised by the coaching staff. The matches were played in accordance with the rules of the World Rugby (Institutional Review Board) and under the control of an experienced referee. All the players participated in the entire 3 matches. Finally, on the next day, the athletes returned to the testing facilities between 8:00 am and 12:00 pm. Blood samples were drawn and the physical tests were repeated following the same order as used in the baseline measurements. All assessments were performed between 15- and 17-hours after the final simulated match (“post” measurements). The same experienced person performed all physical assessments, and the athletes were not allowed to use any recovery method or substance capable of affecting the study outcomes.
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Figure 1.:
Schematic illustration of the study design.
Subjects
Ten male rugby sevens players (mean ± SD: 25.2 ± 3.6 years; 88.7 ± 7.1 kg; 182.2 ± 6.3 cm) from the Brazilian National team participated in the study. The players competed at professional level and trained 10–12 hours per week. Although athletes did not train in the same place on a daily basis, they trained under the same training regime, supervised by the coaching staff of the Brazilian National team. In addition, they took part in several training camp weekends throughout the season to develop their technical and physical abilities equally. From the 10 players, 7 comprised one team and the other 3 formed part of the other team. To complete the second team, 4 players of the same competitive level participated solely in the simulated matches, and did not take part in any other experimental testing. From the 14 players involved in the matches, only 10 were monitored due to the availability of the GPS units. The 2 teams were formed by the coaching staff, matching the athletes in terms of physical and technical performances. Before commencing the study, participants were briefed about the experimental design and signed an informed consent form. The study was approved by the Anhanguera-Bandeirante University Ethics Committee.
Procedures
Match Performance
The game movement patterns of the rugby matches were obtained from the GPS units, sampling at 5-Hz (SPI Elite; GPS ports Systems, Canberra, Australia). The equipment was fitted to the upper back of each player using an adjustable neoprene harness. The GPS contained a triaxial accelerometer system (sampling at 100-Hz) which was used to quantify body accelerations. The units were turned on during the warm-up, to allow satellite detection, and placed in the harness immediately before the kick-off.
The velocity ranges were selected based on a previous study (30). The match activities were divided into the following categories: walking (0–6.0 km·h−1), jogging (6.1–12.0 km·h−1), cruising (12.1–14.0 km·h−1), striding (14.1–18.0 km·h−1), high-intensity running (18.1–20.0 km·h−1), and sprinting (>20.1 km·h−1).
The acceleration vector magnitude (AVM) as a function of time (i) was obtained from x (lateral), y (frontal/back), and z (vertical) axis components (i.e., acx, acy, and acz, respectively) obtained from the 100 Hz accelerometer system, using the following equation:
Finally, the BL was calculated as the accumulated sum of all AVM values obtained across the matches. Because the distance covered in different intensities could underestimate the actual physical demands of the match due to the incapacity of the GPS system (5-Hz) in detecting short, but intense movements, such as accelerations/decelerations and collisions, the BL has been used as an important tool for match performance monitoring that quantifies all kind of movements performed by players during the matches (10,11). The BL results were divided by 100 to simplify the expression and presentation.
Neuromuscular Fatigue
The neuromuscular fatigue was assessed by means of 3 different physical measures: (a) the vertical jumping height, (b) the 40-m linear speed, and (c) the maximal isometric force and the RFD applied in the half squat exercise.
The vertical jump height was assessed through SJ and CMJ. The athletes performed 5 attempts, with a 15-second interval between each jump. In the SJ, a static position with a 90° knee-flexion angle was maintained for 2 seconds before a jump attempt without any preparatory movement. In the CMJ, athletes were instructed to execute a downward movement followed by a complete extension of the legs. To avoid changes in the jumping coordination pattern, the amplitude of the countermovement was freely determined. All jumps were executed with the hands on the hips. The jumps were performed on a contact platform (Smart Jump; Fusion Sport, Coopers Plains, Australia) with the recorded flight time (t) being used to estimate the height (h) of the rise of the body's center of gravity during the vertical jump (i.e., h = gt2/8, where g = 9.81 m·s−2). The best attempt was retained for data analysis.
Before the execution of the maximum speed test, 2 pairs of photocells (Smart Speed; Fusion Sport, Coopers Plains, Brisbane, Australia) were positioned at distances of 0- and 40-m. The athletes sprinted twice, starting from a standing position, 0.5-m behind the start line. A 5-minute rest interval was allowed between the 2 attempts, and the fastest time was retained for analysis.
Maximal isometric force and RFD in the half-squat exercise were determined using a Smith-machine (Technogym Equipment, Cesena, Italy), positioned over a force platform with custom-designed software (AccuPower; AMTI, Graz, Austria), sampling at a rate of 400-Hz (36). The initial position of the test was validated by an experienced test administrator, who set and fixed the bar on the safety pins at a height corresponding to ≈90° of knee flexion (to maximize the force application) (8). After an initial command, subjects were instructed to push as hard and fast as possible against a fixed pre-set bar, sustaining the muscle contraction for 5 seconds. The maximal isometric force represented the maximum force output (peak force) achieved/collected over the force-time curve during the course of 5 seconds. Rate of force development was determined as the slope of the isometric force-time curve over the time-intervals of 0–100 milliseconds (RFD100) and 0–200 milliseconds (RFD200) (1,34). In addition, the variation in the RFD in the 100–200 milliseconds (RFD100-200) interval was calculated because Peñailillo, et al. (24) reported that this interval is a sensitive marker of exercise-induced muscle damage and neuromuscular fatigue. Strong verbal encouragement was provided during the tests.
Muscle Damage Markers and Cytokines
Blood samples (5-ml) were collected from an antecubital arm vein into evacuated tubes containing EDTA. Plasma was separated by centrifugation (1,500g, 4°C, 10 minutes). Samples were collected before and between 15 and 17 hours after the final match. The time for blood sample collection was determined in accordance with the timetable defined by the technical staff. Plasma concentrations of IL-6, TNF-α, and IL-10 were determined by enzyme-linked immunosorbent assay, using commercial kits (Becton and Dickinson, Franklin Lakes, USA) according to the manufacturer's instructions. Creatine kinase activity was determined using a commercial kit in an automated biochemical analyzer (Dimension EXLTM Chemistry System, Siemens, Munich, Germany). All cytokines and CK analyses were performed with duplicate.
Statistical Analyses
The Shapiro-Wilk test was used to check the data normality. To compare the CK activity and cytokines and the performance in the physical tests (at baseline and after the simulated matches), a paired t-test was used. A linear mixed model analysis was used to compare the distance covered in different ranges of velocities and also to compare the BL accumulated between match halves (during each of the 3 matches and between matches). This approach is used in general linear models with repeated measures and has the ability to compare the slope among curves (i.e., rate of change in the distance covered across the matches) (35). Accordingly, 2 factors were included for analyses: match number and period (i.e., first and second halves). The Tukey's post hoc test identified where the possible differences occurred. The level of statistical significance was set at p ≤ 0.05. Finally, the magnitudes of the differences for the comparisons in all variables were analyzed using the Cohen's d effect size (ES) and its confidence intervals (CIs) (4). The magnitudes of the ESs were qualitatively interpreted using the following thresholds: <0.2, trivial; 0.2–0.5, small; 0.5–0.8, moderate; and >0.8, large (4).
Results
Table 1 demonstrates the comparisons of the total distance and the distance covered in the different velocity ranges among the 3 consecutive matches. The distance covered in the 0–6 and 6–12 km·h−1 velocity ranges in match 3 was significantly shorter than in matches 1 and 2, respectively (16.2 and 9.2% of difference; p ≤ 0.05). During match 2, athletes covered greater distances in the 6–12 km·h−1 and 12–14 km·h−1 velocity ranges in relation to match 1 (15.8 and 19.2% of difference, respectively; p ≤ 0.05), while covering shorter distance in sprinting (>20 km·h−1) than during match 1 (50.5% of difference; p ≤ 0.05). No differences in BL were observed comparing the 3 matches (match 1: 977.8 ± 26.8 a.u.; match 2: 975.6 ± 27.3 a.u.; match 3: 973.4 ± 18.6 a.u., p > 0.05).
Table 1.:
Total distance (TD) and distance covered in different velocity ranges in the three rugby sevens matches.*
Figure 2 shows the comparisons between the first and second halves for total distance and distance covered in the different velocity ranges. The athletes covered a shorter total distance and shorter distances in jogging (6–12.0 km·h−1), cruising (12.0–14.0 km·h−1), and striding (14.0–18.0 km·h−1) in the second half compared with the first half (ES [90% CI] % of difference: −1.30 [−2.02 to −0.42] 9.6%, −1.33 [−1.86 to −0.29] 20.7%, −1.52 [−2.40 to −0.72] 31.8%, and −0.92 [−1.65 to −0.11] 21.4%, respectively; p ≤ 0.05). The distance covered walking (0–6 km·h−1) was significantly greater in the second half than in the first half (ES: 1.72 [0.69–2.36] 19.1%; p ≤ 0.05). No difference was observed in the distance covered at high-intensity (18.0–20.0 km·h−1) and sprinting (>20 km·h−1) between the 2 halves (ES: −0.43 [−1.20 to 0.29], −0.04 [−0.77 to 0.70], respectively; p > 0.05). Figure 3 shows the comparison of the BL between the first and second halves. The second half presented a significantly lower BL compared with the first half (ES: −1.28 [−2.00 to −0.40] 3.5%; p ≤ 0.05).
Figure 2.:
Comparisons between the first and second halves for total distance covered and distance covered in the different velocity ranges during the rugby sevens matches. TD = total distance. *P < 0.05.
Figure 3.:
Comparison of the body load between the first and second halves during the rugby sevens matches. *P < 0.05.
Table 2 shows the comparisons of the physical test results at baseline and following the 3 consecutive rugby sevens matches. The SJ and RFD measured in 0–100 milliseconds, 0–200 milliseconds, and 100–200 milliseconds were significantly lower in the posttests than in the baseline tests (5.7, 28.8, 26.7, and 23.1% of difference, respectively; p ≤ 0.05). No significant differences were observed in the CMJ, 40-m sprinting speed, or maximum isometric force comparing the baseline with the postassessments.
Table 2.:
Comparison of the physical tests at baseline (pre) and after (post) three consecutive rugby sevens matches.*
Table 3 displays the serum CK activity and cytokine concentration at baseline and 15 hour after the final match. The CK activity was significantly higher in the postmeasurements than in the baseline measurements (83.2% of difference; p ≤ 0.05). No significant differences were observed in the cytokine concentration comparing the 2 moments (i.e., baseline vs. postmeasurements; p > 0.05).
Table 3.:
Serum creatine kinase (CK) activity and cytokine concentration at baseline (pre) and 15 hours after three consecutive rugby sevens matches.*
Discussion
The main finding of this study was that the investigated players were capable of maintaining the activity profile and intensity of the match, between the first and last matches on the first day of a simulated rugby sevens tournament. Significant reductions with a large ES were demonstrated in the total distance and BL when comparing the second with the first half of all games combined. In the physical tests (performed 15-hours after the matches), there were decrements in the SJ height and in the RFD (assessed in 0–100, 0–200, and 100–200 milliseconds) obtained from the half-squat maximal isometric force test. The CK activity increased 15 hours after the matches, whereas inflammatory cytokines did not substantially change from baseline. These results suggest that the rugby sevens players experienced substantial levels of muscle damage and neuromuscular fatigue (i.e., increased CK activity and reduced RFD) which was accompanied by decreased performance in the vertical jump height 15-hours after 3 simulated rugby sevens matches.
The total distance (1,413.3-m per match on average) and the distance covered at high intensity (80.1-m per match on average) and sprinting (146.7-m per match on average) during matches reported herein are strictly in line with previous studies that analyzed national and international level rugby sevens players (13,27,30). For instance, Suarez-Arrones, et al. (30) demonstrated that during national level matches, these athletes might cover a total of 1,500-m, being 79.5-m at high-intensity efforts and 137.7-m at maximal sprinting speed. Furthermore, although using a slightly different threshold for detecting sprinting (i.e., 21.6 km·h−1), a previous study (13) demonstrated higher total distance (120 m·minute−1) and similar distance in sprinting (11.5 m·min−1) during domestic and international matches in comparison to those observed in our study (101 m·min−1 and ≈10.5 m·min−1, respectively). Meanwhile, Ross, et al. (27) revealed that sevens players could cover a total of 105 m·min−1, 9 m·min−1 being in sprinting, during provincial and international matches. Together, these data suggest that the intensity of the sevens matches investigated in this study is comparable with those already observed during top-level matches (13,27,30).
A previous study analyzing the profile of players' activities over a rugby sevens tournament showed only small reductions in the distance covered in low-intensity running (<12.6 km·h−1), comparing the first to the last match during official 2-day tournaments (13). Importantly, we did not find any meaningful difference across 3 consecutive matches (especially between the first and last matches). Therefore, the rugby sevens players of our study were able to “fully” recover between the successive matches, maintaining their physical performance throughout the first day of a simulated tournament, even with a game movement pattern equivalent to those found in international matches (13,27,30).
Conversely, when comparing the match halves, a significant reduction was detected in the total distance covered by the players and in the BL from the first to the second halves (Figures 2 and 3). This is in contrast with some previous studies (12,13,30) which did not show reductions in total distances after analyzing the first and second halves of sevens matches. Nevertheless, Suarez-Arrones, et al. (30) demonstrated that the time spent at >90% maximal heart rate increased in the second half (in comparison with the first half). Moreover, when compared with athletes who participated in the entire match, the substitute players covered greater distances while running at high intensities during the second half (13). From an applied standpoint, these results indicate that, despite the absence of signs of permanent fatigue throughout successive matches, temporary fatigue can be observed during each match. Although the mechanisms underlying fatigue experienced during the matches were not fully elucidated, some studies have already suggested that this could be caused by metabolic and neural disturbances, such as ionic imbalances and central fatigue (2,20,33). It is important to note that we did not permit substitutions of the monitored players during the 3 matches; as aforementioned, substitute players may cover higher distances when compared with players involved in the entire match, which could compromise the objectives of our investigation (14,26).
The increased blood CK activity suggests that substantial level of muscle damage may occur after 1-day of simulated competition. For instance, Takahashi et al. (31) demonstrated an increase of 42% in CK after 2 consecutive sevens matches. In this study, we showed an increase of 83% in the CK activity 15 hours after 3 consecutive matches. Despite the large increase in the CK activity reported herein, this increase is lower than that demonstrated by West et al. (37) (250 and 500% of increase after the first and second day of competition, respectively) and by Clarke et al. (3) (126% of increase) after official tournaments, in male and female sevens players, respectively. Possibly, the higher CK values demonstrated by Clarke et al. (3) are related to the fact that the athletes covered greater distances in sprinting than our players (13.5 vs. 10.5 m·min−1) (23). In addition, these studies were performed during official tournaments, which probably induced higher physical engagement in specific playing actions (e.g., collisions), consequently entailing greater signs of muscle damage (23,29,32). In this regard, it is essential to further examine the physical/physiological differences between “friendly” and competitive rugby sevens matches.
There was a moderate decrease of 5.7% in the SJ height, 4.8% in the CMJ height (nonsignificant), and a large decrease of 23% in the RFD100–200. This reduction in vertical jumping performance (SJ and CMJ) is in accordance with previous studies that demonstrated neuromuscular fatigue (i.e., measured by means of jump height) after professional rugby union (38), rugby league (21), and consecutive rugby sevens matches (37). Importantly, a previous study indicated that reductions in the RFD100–200 were highly associated with exercise-induce muscle damage and neuromuscular fatigue (24). Indeed, it has been shown that decreases in SJ height, CMJ height, and RFD100–200 (in association with increased levels of CK) might be related to significant impairments in the contractile machinery (24). From a physiological perspective, the decrement in the capacity to quickly apply/produce force and the symptoms associated with muscle damage and fatigue may be connected to the repetitive involvements in high-intensity efforts, such as collisions and maximum sprints during the matches (21,22). Although the SJ and CMJ height have been shown to be highly associated with sprinting speed (16,17), at least for this group of top-level rugby sevens players, the reductions in the vertical jumping performance were not accompanied by decreases in the maximal sprinting capacity. This suggests that the extent of muscle damage and fatigue induced in our sample was not able to affect/disturb the speed performance. However, the signs of muscle damage described here might compromise the ability of the players to perform maximally during the second day of competition, strongly indicating the necessity of implementing effective recovery methods during the transition from the first to the second day of competition during rugby sevens tournaments (6).
This study presented some inherent limitations, listed as follows: (a) Although players received similar meals and could ingest water ad libitum during the study duration, the exact composition of the food portions and the hydration status were not controlled; (b) The baseline physical tests on day 1 were performed in the afternoon, whereas the postmatch tests on day 3 were performed in the morning; (c) Since circadian variations are expected in some physical performance indices (9,25), our results could have been somewhat biased by this biological factor.
In summary, the rugby sevens players were able to maintain the game movement patterns across 3 successive matches simulating the first day of a tournament. In addition, the increased levels of CK and the decreases in the SJ and RFD100–200 suggest that substantial levels of muscle damage and neuromuscular fatigue occurred in the day after the matches. This probably causes significant physical performance impairments on the second day of competition. Finally, additional studies are needed to comprehensively examine the efficacy of different recovery methods for restoring the physical and physiological traits of these elite athletes between successive matches or training sessions. Certainly, these applied approaches will positively influence the competitive performance of these players throughout the rugby sevens' tournaments.
Practical Applications
Sevens' tournaments are typically executed over 2 consecutive days, with players performing up to 7 matches, interspersed with short recovery intervals (i.e., ≈3–4 hours). After examining the data collected in this study, it was revealed that these athletes could effectively maintain the game movement patterns during 3-successive sevens matches. However, on the second day, they experienced meaningful signs of muscle damage and a compromised capacity to produce explosive force (i.e., RFD). In this sense, coaches and scientists involved in this sport are strongly encouraged to implement and create specific strategies able to improve (and reduce the impairments) in the neuromuscular function of their athletes. Intrinsically, training components such as plyometric and eccentric exercises may be optimal alternatives to increase the “explosive muscle strength” (18) and enhance the protective effect against muscle damage (19) in sevens players.
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