Nicotine supplementation enhances simulated game performance of archery athletes

Eleven healthy, male nonsmokers were recruited in 2018 through printed advertisements and by word of mouth from archery sport teams of both the National Taiwan University of Sport and the National Chung Cheng University in Taiwan. The participants were required to meet the following criteria: (1) they were archers who used a recurve bow; (2) their archery performances were at the national level; and (3) they had been continually training for a minimum of 2 h ≥ three times per week for at least 3 years. Participants were excluded if they had cardiac disease histories, were injured or were unable to participate in normal training (n = 0). Therefore, the recruited archers were all qualified and included in this study (n = 11). The sample size was calculated by G*power 3.1.9.4 (available at http://​www.​gpower.​hhu.​de). One of our aims was to evaluate the effects of nicotine use on HRV using two-way repeated measures analysis of variance (ANOVA) (within factors). Type 1 error (alpha) was set at the level of 5% (p = 0.05), and the power was set at 80%. The effect size f was determined by partial eta squared (η_p²) based on previous research (η_p² = 0.34) [31]. The results showed that at least 6 participants were required; thus, the sample size in this study was sufficient. The mean age of the participants was 20.3 ± 0.3 years, the mean body weight was 71.1 ± 9.2 kg, and the mean body height was 174.4 ± 4.5 cm. All participants were advised to abstain from stimulants such as coffee or energy drinks for 12 h. Each participant was fully informed of all potential risks and experimental procedures, after which informed written consent was obtained. All experimental procedures and protocols were approved by the Institutional Human Ethics Committee of Jen-Ai Hospital, Taichung, Taiwan.

The experimental protocol (schematized in Fig. 1) was a randomized, placebo-controlled crossover design, which was conducted across a period of 1 week. On arrival at the laboratory, the participants were fitted with a heartrate strap and monitor (Polar V800, Polar Electro Oy, Kempele, Finland) and seated for 5 min, after which baseline HR measurements were individually taken in stages 1–5. First, they were asked to remain in the seated position, and saliva samples were collected (stage 1, S1). For experimental trials, the participants chewed 2-mg nicotine gum (NIC group) or flavor-matched placebo gum (PLA group) for 30 min while seated, followed by the participants’ saliva being collected again (stage 2, S2). Then, they completed cognitive tests (Vienna Test System (VTS)–Cognitrone test (COG) and the grooved pegboard test (GPT)) (stage 3, S3) [39]. Furthermore, their archery performance was measured in a simulated game (stage 4, S4). Then, saliva samples were collected (stage 5, S5). Experimental trials were conducted at the same time of day, and the day of and prior to any experimental trial was marked by abstinence from alcohol, any exercise and only habitual caffeine use (as abstinence would in itself have confounding withdrawal-related effects). Additionally, the participants were asked to replicate their diet during the first experimental visit for subsequent trials to ensure a similar metabolic state.

The participants were instructed to consume the gum according to the manufacturer’s recommendations: one piece of 2-mg mint-flavored nicotine gum or placebo gum (Nicorette Icy Mint, Johnson & Johnson Pacific, Auckland, New Zealand) was introduced into the mouth followed by the instructions “chew until there is a strong taste, then place between your cheek and gums, and chew again when the taste has faded”; this stage lasted for 30 min.

All participants completed the cognitive outcome measures including the VTS–Cognitrone test (COG) and grooved pegboard test (GPT). The COG test measures attention and concentration through the comparison of figures regarding their congruence on a computer screen. The participants were presented with an abstract figure, and they were asked to match the figure to a model. The mean time for “correct rejections” made within the total working time of 7 min was recorded [39]. The GPT is a test of manual dexterity, speed of processing, and hand-eye coordination, which has been used in previous studies [39, 40]. The GPT includes 25 holes with randomly positioned slots. Participants were asked to put the pegs in the board in a fixed order and in the correct direction with only one hand being used. They were encouraged to perform the task as quickly as possible. The total time to completion was recorded in seconds. In this study, each participant was tested twice with his dominant and nondominant hands. Then, the average time was calculated to give an overall score.

The performance for the archery assessment was assessed according to the rules of national archery competition in outdoor areas. The participants used their own bow and arrow equipment. Before the experiment, they all had adequate warm-up and corrected the sighting position. Briefly, each player fired 72 arrows, 36 arrows for a game. In each single day, they had 2 games. Every participant fired six arrows for a round, and each round time limit was 4 min. Each arrow was worth up to 10 points; therefore, a single game overall had a possible score of 360 points. They rested for 15 min after the end of the first game. After the end of each round, the arrows were pulled, and the same person recorded the scores to verify the accuracy. Any guidance was excluded during the exercise. The same archery test was performed on three different days in a week to obtain the average archery assessment in each group.

Beat-to-beat heart rate was recorded with 1-ms resolution using portable HR monitors. The HR, percentage of differences between adjacent normal RR intervals of more than 50 ms (pNN50), low-frequency normalized units (LFnu) and high-frequency normalized units (HFnu) were calculated from the 5-min recordings. LF/HF was calculated from the ratio of LFnu over HFnu. Spectral analysis was performed by the maximum entropy method, and autoregressive coefficients were estimated using the Burg algorithm. The power spectrum was calculated from 0.01 to 0.40 Hz with 0.01-Hz frequency resolution. LF and HF components were calculated through integration of the power spectra of 0.04 to 0.15 Hz and 0.15 to 0.40 Hz, respectively.

Unstimulated whole saliva was collected as previously described [41]. Briefly, all participants were seated and asked to thoroughly rinse their mouth with 30 ml of sterile distilled water before sample collection. The participants remained seated for 10 min until all saliva samples were collected into sterile plastic containers. Two ml saliva samples were collected at three time points: before gum administration (S1), after gum administration (S2), and after the archery test (S5). The saliva samples were immediately stored at − 80 °C until assay. Since the half-life of nicotine is short, cotinine, the major metabolite, was used as a reliable marker based on its longer half-life. The salivary cotinine level was determined using an enzyme-linked immunosorbent assay (ELISA) kit (Cozart Bioscience Ltd., Oxfordshire, UK). α-Amylase activity was determined using a kinetic reaction assay kit (Salimetrics LLC, State College, PA, USA) according to the manufacturer’s instructions. All samples were measured in triplicate. The intra-assay coefficients of variation (CVs) for the measurements of cotinine and α-amylase activity were 5 and 4%, respectively.

All data are expressed as the mean ± standard deviation (SD). Two-way (condition x time) repeated measures ANOVA with a Tukey post hoc test was used to determine differences between the conditions and time points. Statistical comparisons between the NIC and PLA groups were analyzed using paired t-tests. Partial eta squared (η_p²) values are reported as a measure of effect sizes, with demarcations of small (< 0.09), medium (> 0.09 and < 0.25) and large (> 0.25) effects [31]. Significant differences were set at p < 0.05.

Thirty minutes after chewing the nicotine gum, the participants performed the cognitive function tests. The mean “correct rejection” time in the NIC group was significantly shorter than that in the PLA group (7.29 ± 0.87 vs. 8.23 ± 0.98 msec, respectively, p = 0.038; Table 1), indicating that the NIC group had better concentration than the PLA group. In addition, the NIC group completed the GPT in a significantly shorter time than the PLA group (48.76 ± 3.18 vs. 53.41 ± 4.05 s, respectively, p = 0.003). These findings indicated that the NIC group had better cognitive performance than the PLA group. The participants’ archery performance was measured by calculating the mean score of 36 arrows for each game from three independent days. Each arrow was worth up to 10 points. The archery score in the NIC group was significantly higher than that of the PLA group (298.05 ± 8.56 vs. 290.58 ± 10.09, respectively, p = 0.009; Table 1).

After supplementation with nicotine (S2), the HR, LF and LF/HF ratio were significantly increased, whereas the pNN50 and HF significantly decreased and were lower than baseline (S1) (Table 2). When the participants were taking the cognitive function test (S3), all the HRV parameters were similar to those at baseline in both groups. During archery performance (S4), the HR, LF and LF/HF ratio were significantly higher, whereas the pNN50 and HF were significantly lower than their own baseline in both groups. In particular, HR in the NIC group was significantly higher than that in the PLA group during the archery test. All HRV parameters in both groups, with the exception of HR in the NIC group returned to baseline after the archery test (S5).

Saliva α-amylase activity was significantly decreased (39.64 ± 15.97 vs. 51.82 ± 19.09 U/ml, p < 0.01) after nicotine supplementation (S2) but increased immediately after the archery test (S5) and was higher than the basal level (S1) (72.36 ± 36.66 vs. 51.82 ± 19.09 U/ml, respectively, p < 0.05; Fig. 2). At S5, the NIC group showed significantly higher α-amylase activity than the PLA group (72.36 ± 36.66 vs. 50.74 ± 20.44 U/ml, respectively, p < 0.01). There was no difference at the three time points in the PLA group.