Greco-Roman wrestling style is to aim athletes gain superiority over the opponent by holding only the upper body of the opponent with their upper body, whereas freestyle wrestler can use their whole body in the competition [1]. The wrestling rules emphasize aggressive wrestling and scoring by exhibiting repetitive bouts of high-intensity moves (e.g., attacks and counterattacks) instead of blocking or holding the opponent [2,3]. In wrestling competition, such characteristics as aerobic capacity [4], anaerobic power and maximal strength are required for success [5]. Wrestlers have to produce high-level maximal strength for defense or offense [6-8]. In wrestling competitions, the upper and lower body maximal strength is one of the most crucial factors to obtain scores by applying the needed technique [9-11]. Studies have emphasized that successful wrestlers are capable of produce higher muscle strength than their less successful counterparts [2,10-14]. Therefore, increasing muscle strength can help be one of the key factors for wrestlers [1].

Acute dietary supplementation (with beetroot juice) supplementation has been primarily examined in endurance-based exercise and conflicting results have been found. Compared with endurance-based exercise, beetroot juice (BRJ) effects’ on strength were less studied [15]. Studies have shown that BRJ supplementation can affect different muscle fiber types in different level [16]. Since the percentages of skeletal muscle fiber distribution in the body are different [17], it is hypothesized that the effect of BRJ supplementation on lower and upper body strengths in the same individual may be different. To author’s knowledge, there are limited studies in the literature investigating acute dietary supplementation to increase wrestlers’ muscular strength. BRJ has recently been examined in the literature on different athletes for its potential effects on aerobic capacity, anaerobic power and muscle strength [18].

Beetroot juice, which has a high amount of inorganic nitrate (NO${}^{3-}$), has complete attention in sports fields [19]. This NO${}^{3-}$ in the BRJ is transformed to nitrite (NO${}^{2-}$) and then to the nitric oxide (NO) through the loss of oxygen [20]. NO is affecting some physiological processes related to exercise (i.e., regulating blood flow and producing muscle strength) [21]. NO can stimulate the conversion of cyclic guanosine monophosphate (cGMP) that resulting in dilating blood vessels [21], so the amount of blood flow to the muscle tissues increases [22]. Furthermore, the increase of cGMP increases the rate of contraction of muscle fibers and thus may affect maximal strength [21].

The increased NO in blood after drinking BRJ may support the improved type 2 skeletal muscle fiber contractile ability [16] and improved calcium (Ca${}^{2+}$) handling 23, decrease ATP cost of force production [23]. Bender et al. [24] found an increased maximal strength in the mid-tight pull. Coggan et al. [25] found increased strength in isokinetic dynamometry. Rodríguez-Fernández et al. [26] reported that BRJ increased eccentric contractions besides concentric contractions.

The isokinetic dynamometer has high reliability and can measure peak torque at different velocities and throughout the complete range of motion [27-29]. Given that isokinetic dynamometer has been shown as a gold standard strength assessment method [30,31], isokinetic dynamometry was used in this study. There are studies on the effects of BRJ on the isokinetic strength of the knee [23,25,32-40]. The BRJ supplementation effect on isokinetic strength is not well established for the upper and lower body together. However, there are no studies on Greco-Roman wrestlers’ upper and lower body isokinetic strength does not exist. Thus, the present study aims to examine the effects of acute BRJ supplementation on upper and lower isokinetic strength parameters in trained Greco-Roman wrestlers.

Peak torque data are shown in Table 2. As intended, BRJ supplementation improved muscle contractile function. Peak torque of knee extension and flexion improved with BRJ ingestion but not statistically. Shoulder internal (P = 0.048) (ES = 0.84) and external peak torque (P = 0.024) (ES = 1.01) increased significantly in favor of BRJ (large effect size).

Average torque data are shown in Table 3. Average knee strength significantly increased in BRJ trial (extension P = 0.023 (ES = 1.02) and flexion P = 0.027 (ES = 0.98)). In addition, shoulder internal (P = 0.023) (ES = 1.02) and external average torque (P = 0.021) (ES = 1.04) increased significantly in favor of BRJ.

This study examined the effects of BRJ supplementation on isokinetic strength in trained wrestlers of the upper and lower body. The isokinetic knee extension (P = 0.13) and flexion (P = 0.34) strength of the wrestlers did not change significantly in both trials, but average strength increased in the BRJ trial than the PLA trial (extension 9.57% and flexion 12.94%). Furthermore, the peak isokinetic strength of the shoulder increased in favor of the BRJ trial (internal 15.06% and external torque 13.39%). The average isokinetic shoulder internal (19.61%) and external (12.81%) strength of the wrestlers improved significantly.

The supplementation of BRJ increases NO availability in metabolism [37]. Literature shows that NO affects contractile properties in animals, also in human muscle [23-25,33,37,48]. However, the present study found no significant increased knee isokinetic strength in both extension and flexion parameters at 60${}^{\circ }$ sec${}^{-1}$ (slow angular velocity), consistent with Jonvik et al. [21] and Kokkinoplitis et al.’s findings [39]. In addition, studies showed that peak isokinetic strength of the knee values performed at 90${}^{\circ }$ sec${}^{-1}$ angular velocity (moderate angular velocity) was not significantly affected by NO${}^{-3}$ supplementation [25,37,40]. Inconsistent with the present study, Jonvik et al. [21] found significant improvement in knee flexion at 60${}^{\circ }$ sec${}^{-1}$ angular velocity, but their participants were formed by recreationally active individuals. Individuals with more training benefit less from NO${}^{-3}$ supplementation [41,49], which could be the underlying reason why isokinetic leg flexor peak strength was not significant in our study. In this study, BRJ supplementation did not significantly affect the peak isokinetic strength of the lower body but increased the peak isokinetic strength of the upper body significantly. NO${}^{3-}$ can be more effective at type 2 muscle fiber contraction [50]. Horswill et al. [51] reported that Greco-Roman wrestlers could generate more anaerobic power by the upper body than lower due to type II muscle fiber distribution. It can be hypothesized that type 2 muscle fiber distribution can be dominant in the shoulder muscle group than leg muscle, therefore, shoulder internal and external peak torque increased significantly in this study. To the author’s knowledge, although there is no study on upper extremity and isokinetic BRJ-strength in the literature, Williams et al. [15] reported that bench press power positively increased. Similar to our findings obtained in this study, there are studies in the literature that emphasized that lower extremity average strength outputs improved after ingestion of BRJ [26,35,52]. BRJ supplementation reported declining the ATP cost of force production [21,52]. Since local perfusion, fatigue resistance, increasing the intracellular release of calcium in the muscle and contractility of fast-twitch muscle fibers, in particular, can be improved by BRJ supplementation [53], the isokinetic strengths outputs were thought to increase in this study.

Due to the nature of wrestling, wrestlers should have advanced maximal strength, strength endurance, aerobic capacity and anaerobic power levels in addition to technical and tactical skills [1,5]. To perform a proper technique during the wrestling match, it is often necessary to move with high maximal strength and be able to repeat that movement at the highest strength possible [1]. Furthermore, the wrestlers should maintain maximal strength when they eat less for rapidly losing weight because studies stated that the muscle strength [54] and power [55] of the wrestlers could be affected by the rapid weight loss [56]. Thus, increasing maximal strength and strength endurance with acute BRJ supplementation can help wrestler’s performance in competition and training.

This study was conducted with limited resources, and it only provided insights into the strength of the lower and upper body of Greco-Roman wrestlers. Another limitation of the present study can be said as the number of participants was eight.

The data obtained by this study indicates that BRJ supplementation increased peak and average isokinetic strength of the lower and upper body of trained Greco-Roman wrestlers. These results suggest that beetroot juice can be used as an ergogenic aid before competition for increasing muscle strength performance in trained Greco-Roman wrestlers.

The study was approved by the local ethics committee (Protocol number 79, 19.10. 2020, Ethics Committee of Selcuk University, Faculty of Sports Science, Konya, Turkey). Before the assessment, every participant received the same detailed information about the testing procedure. Every participant signed the informed consent.

Thanks to all the peer reviewers for their opinions and suggestions.

This research received no external funding.

The author declares no conflict of interest.