Effect of caffeinated gum on a battery of rugby-specific tests in trained university-standard male rugby union players

Caffeine is one of the most commonly consumed ergogenic aids as evidenced by a study of elite athletes, which detected caffeine in 74% of urine samples collected at doping controls [1]. The popularity of caffeine among athletes is understandable, because it has been shown to enhance: endurance performance [2], high intensity activity (1–60 min duration) [3], and performance during stop-and-go activities [4, 5] that typify team sports [6]. Caffeine is believed to exert its ergogenic effects largely as a result of blocking adenosine receptors in the central nervous system [7]. Evidence indicates that this enhances performance through increasing central drive and alertness and reducing muscle pain and rating of perceived exertion [7, 8].

Caffeine has multiple performance enhancing effects. It has been shown to reduce reaction time [9] and increase: anaerobic power [5], sprint speed [10] and endurance. Rugby is a sport that may benefit from the multiple ergogenic effects of caffeine. A rugby match is characterised by high-intensity running interspersed with bouts of low activity, multiple changes of direction and technical skills [11]. Strength and power are also key requirements especially when players are engaged in tackles, scrums, rucks and mauls [12]. Rugby players cover between 4000 and 7000 m during a typical match, so considerable endurance is also needed to ensure performance is maintained during game defining moments [13–15].

Previous studies have investigated the effects of caffeine on rugby-related performance measures such as sprints and impacts [16], and on rugby specific test protocols [17]. Del Coso et al. reported beneficial effects of a caffeine containing commercial energy drink (3 mg·kg^− 1 of body weight) on running pace and pace at sprint velocity during 3 games of rugby sevens and on power output in a 15 s jump test performed after the last game. Similarly, Stuart et al. found that 6 mg·kg^− 1 of caffeine (in a capsule) improved performance across a range of rugby specific tests (sprint speed, first and second drive power and passing accuracy) during a 2 × 40 min simulated rugby performance test.

Traditionally, caffeine has been provided in a capsule or beverage approximately one hour prior to exercise [3, 18–20]. However, chewing gum offers a novel alternative vehicle for the delivery of caffeine. The absorption of caffeine from chewing gum is more rapid than from capsules (5–10 min versus 45–60 min) [21]. This is because caffeine absorption from chewing gum initially occurs through the buccal mucosa [22], an accepted route for accelerating drug absorption [23]. Because drug action is limited by absorption rate, caffeine gum would be expected to have a faster onset of action than capsules [22]. The use of caffeine gum may therefore have practical applications to rugby, where limited time for nutritional interventions exist (e.g., the end of the warm-up, at half-time, or for substitutes required to enter competition with limited notice).

Despite the potential practical benefits of caffeine gum, few studies have investigated its effect on team sports. In a study of professional academy rugby players, 400 mg of caffeine delivered in gum failed to rescue the decrement in performance across two sprint tests (6 × 40 m) separated by a 15 min simulated half time period [24]. This lack of effect may have been because the rugby players had a mean habitual intake of caffeine of 191 ± 138 mg·d^− 1 [25, 26]. Evans et al. reported that caffeine gum reduced the decrement in repeated sprint performance in team sports players with a low caffeine intake but not in those with an intake greater than 130 mg·d^− 1. In contrast, despite supplying a lower dose of caffeine (200 mg) Ranchordas et al. [4] found small, but statistically significant positive effects of caffeine gum on two soccer specific performance tests (Yo-Yo Intermittent Recovery Test Level 1 and countermovement jump) in university-standard soccer players. The disagreement between studies may be explained by differences in study design, performance tests and characteristics of the participants. Given the possible practical benefits of delivering caffeine rapidly during competitions, further studies are needed to clarify the effects of caffeine gum on team sport specific performance tests. Therefore, this study was conducted to determine the effect of caffeine gum on a battery of rugby-specific performance tests. The effect of a low 200 mg dose of caffeine was investigated because: (i) it had previously been shown to be adequate to improve performance in soccer players [4]; (ii) to minimize the risk of adverse effects and (iii) to be consistent with the manufacturer’s recommendation for use.

The main findings of this study were that a low dose of caffeine supplied in gum enhanced performance on the CMJ by 3.6%, increased resistance to fatigue during a 6 × 30 m repeated sprint test, and improved performance on the Yo-Yo IR2 by 14.5%. However, caffeine gum failed to significantly improve performance in the Illinois agility test. Consistent with a number of previous studies there was evidence of variability in the response to caffeine among the participants. In 11 of 17 participants, caffeine supplementation improved CMJ, FI and the Yo-Yo IR2 test. For 5 participants, caffeine improved performance on two of the tests and for one participant, caffeine worsened performance in all the tests (see Fig. 5).

In the present study, caffeine evoked a small, statistically significant 3.6% increase in CMJ height. This magnitude of effect is consistent with previous studies using a similar dose of caffeine [4, 33] Clarke et al. [33] found that CMJ height during a rugby league simulation protocol was approximately 2% higher in elite rugby league players when they ingested 3 mg·kg^− 1 of body weight of caffeine alongside 40 g of carbohydrate in comparison to carbohydrate alone. Del Coso et al. reported that 3 mg·kg^− 1 of body weight of caffeine delivered in a commercial energy drink increased total muscle power output by 9% during a 15 s jumping test, in women from the Spanish rugby sevens national team. In contrast, in a couple of studies, caffeine has failed to exert a statistically significant effect on jumping ability [34, 35]. Tucker et al. [34] found no statistically significant effect of 3 mg·kg^− 1 of caffeine on 10 vertical rebound jumps in male basketball players, although the sample size was very small (n = 5). Also, Stanjanovic et al. [35] found that in female basketball players, caffeine (3 mg·kg^− 1) had no statistically significant effect on CMJ performed with and without an arm swing, although the effect sizes were slightly larger than the present study (0.29 and 0.30 versus 0.22).

There was no statistically significant effect of caffeine gum on performance in the 6 × 30 m sprint test. However, there was a statistically significant reduction in an index of fatigue indicating a more sustained capacity for repeated sprint performance. At the time of data collection there was only one study that had reported on the effect of caffeine gum on performance of a repeated sprint protocol. Russell et al. [24] investigated the effect of caffeine gum (400 mg of caffeine) in professional academy rugby players undertaking 2 x repeated sprint protocols (6 × 40 m) separated by a 15 min passive recovery period (to simulate half-time). Caffeine gum failed to attenuate the decrement in performance from the first set of sprints to the second. Direct comparison with the present results is difficult because Russell et al. [24] did not report a fatigue index and their protocol was designed to investigate the ability of caffeine to rescue the decrement in performance that accompanies passive recovery between bouts of high intensity exercise. After the current study was completed, Evans et al. [26] reported that 200 mg of caffeine delivered in gum did not significantly improve performance of team sport players (soccer, rugby and hockey) completing a 10 × 40 m sprint test. However, a secondary data analysis revealed that the gum exerted a significant beneficial effect in those participants with a low intake of caffeine (< 40 mg·d^− 1), but not in those with a higher habitual intake (> 130 mg·d^− 1). Interestingly, the group with a higher habitual intake of caffeine had a mean intake lower than the rugby players in the null study of Russell et al. [24]. Others have reported benefits of caffeine when it is administered using traditional modes of delivery [36, 37]. For example, Del Coso et al. [5] found a beneficial effect of a caffeinated energy drink (3 mg·kg^− 1 of body weight) on mean peak running speed (+ 2.7%) in semi-professional soccer players completing 7 × 30 m sprints. Similarly, Carr and colleagues [37] reported that caffeine (6 mg·kg^− 1 of body weight) improved short sprint performance (20 m with an 180^o turn at 10 m) in team sport players when recovery time between sprints was 5.5 s or 20 s. The findings of a more sustained capacity for repeated sprint performance observed in this trial agrees with these studies.

This is the first study to show that a low dose of caffeine (200 mg) supplied in gum can improve performance (+ 14%) on the Yo-Yo IR-2 test. Ranchordas et al. [4] previously reported a marginal 2% improvement in performance in soccer players undertaking a different version of the Yo-Yo test (IR-1) after the same dose of caffeinated gum. The magnitude of effect observed in the current study is very similar to Mohr and colleagues [38] who found a 16% increase in distance covered on the Yo-Yo IR-2 in team sport players administered a moderately high dose of caffeine (6 mg·kg^− 1 of body weight) in capsule form.

Caffeine gum failed to significantly improve agility. In agreement with this null finding, Lorina et al. [39] reported that 6 mg·kg^− 1 caffeine failed to enhance performance on The Pro Agility Run test in young adult males. Similarly, Astorina et al. [40] found that a low dose of caffeine (80 mg in a drink of Red Bull) and Lee et al. [41] found that a moderate dose of caffeine (6 mg·kg^− 1) failed to improve performance of female team sports players in the repeated agility T test. In contrast, Duvnjak-Zaknich et al. [42] reported that in male team-sport athletes, 6 mg·kg^− 1 of caffeine had potential benefits on reactive agility tests conducted before, during and after a simulated team sport fatiguing protocol. It should be noted that Duvnjak-Zaknich et al. [42] found limited evidence of a treatment effect using traditional statistical approaches, and clearer effects were only detected when their data was analysed using magnitude-based inferences (a contemporary statistical approach [43]).

It is likely that the improvements observed after caffeine gum in this study were mediated through antagonism of adenosine receptors [7]. Adenosine receptor antagonism may have improved jumping performance by enhancing motor unit recruitment and rate coding in lower body muscle groups as a result of excitatory effects in the supraspinal region [44]. Blocking the actions of adenosine also increases arousal and reduces the perception of pain [45] which may a have contributed to the greater distance covered in the Yo-Yo IR2 and resistance to fatigue during the sprint test.

The improvements observed in this study may transfer into match play. The increase in jump height, although small, may determine who wins possession during a line-out or when catching a ball after it has been kicked. A more sustained capacity for repeated sprint performance could allow rugby players to maintain sprint speeds towards the end of a match, when fatigue may impair performance. Rugby matches are characterised by high intensity bursts with short recovery times, so the increased total distance covered in the Yo-Yo IR2 test could translate into benefits during match play. An important consideration when using caffeine gum is that it should not be used during pre-, mid- and end-season testing to enhance performance on the testing battery, because this could influence the interpretation of the data for the coaching and conditioning staff.

This study demonstrated that a low dose of caffeine (200 mg) supplied in gum enhances performance of university standard male rugby players undertaking a battery of rugby specific tests. Moreover, the onset of action was rapid, occurring in performances tests that commenced 5 min after the gum was chewed. This rapid onset of action aligns with the pharmacokinetic study of Kammiori et al. and very recent work in the authors’ laboratory [46]. Such a rapid onset of action has practical application to rugby (and other team sports), because there is often limited time for nutrition intervention during matches such as at half-time and before substitutes enter play. The finding that a low dose of caffeine enhanced performance is practically important, because low doses are less likely to produce adverse effects, which may limit the use of higher doses. Caffeine gum may be less likely to cause gastric irritation than capsules, because a substantial proportion of the dose is absorbed across the buccal mucosa. Accordingly, gum may be useful for players who cannot tolerate caffeinated beverages or capsules before kick-off, because of gastrointestinal distress.