To achieve maximum performance, athletes often face high-intensity, and/or high-volume physical training loads. Though this workout regime leads to high performance, it can also expose athletes to a non-functional risk of overreaching or overtraining. In such situations, an athlete's body cannot assimilate the training load and will show no improvement in performance or a sharp decline associated with neuro-immune endocrine disorders that affect athletes' health (Smith, 2004). In fact, it is estimated that even in young athletes, at least 20–30% have already experienced non-functional overreaching or signs of overtraining (Winsley and Matos, 2011).

Physical training naturally promotes damage of muscle tissues, which is accompanied by local inflammation. In the recovery period, muscle tissue repair and improvement of trained physical abilities occurs through the well-known phenomenon of general adaptation syndrome, which comprises non-specific systemic reactions of the body to continuous exposure to stress (Goldstein and Kopin, 2007; Aptekmann and Cesar, 2010; Winsley and Matos, 2011). However, if training loads are of high intensity and/or volume or the recovery period is inadequate, there may be an evolution from local muscle inflammation to systemic inflammation and oxidative stress, which evolves into neuroendocrine and behavioral disorders (Miranda-Vilela et al., 2009). Moreover, previous studies have shown minimization of muscle fatigue, systemic inflammation (Miranda-Vilela et al., 2009), and oxidative stress (Toscano et al., 2015) in athletes who received nutritional intervention with orange juice, pequi-fruit pulp oil, or grape juice, foods known for their antioxidant properties.

Sesame cultivar (Sesamum indicum L.) has high nutritional value due the significant amounts of dietary fiber, protein, natural antioxidants, unsaturated fatty acids, vitamins, and mineral constituents present in its composition (Anilakumar et al., 2010). The lipid fraction of sesame seeds shows good oxidative stability, which is attributed to the essential fatty acids, such as oleic, linoleic, and arachidonic present in its composition, as well as to antioxidant compounds (e.g., sesamin, sesamolin, and sesamol) that may act in synergism (Namiki, 2007; Kanu et al., 2010).

Previous study have demonstrated the antioxidant effects of sesame in hypertension model (Kamal-Eldin et al., 2011). Furthermore, the anti-inflammatory and antioxidant effects of sesame the anti-inflammatory and antioxidant effects of sesame via decreases in lipid peroxidation, C-reactive protein (hs-CRP), and interleukin-6 (IL-6) have also been shown (Haghighian et al., 2015). To date, whether soccer players would benefit from the antioxidant and anti-inflammatory effects of sesame has not been investigated. The aim of this study was to test the effect of a supplementation protocol with white sesame seeds (S. indicum L. cultivar BRS silk) on muscle damage markers, systemic inflammation, oxidative stress and aerobic capacity in soccer players exposed to routine training that includes loads of heavy training in the final half of the season.

Athletes in the experimental and placebo groups presented no differences regarding the assessed anthropometric variables (Table 1). The CK, LDH, MDA, and hs-CRP values obtained before the experimental intervention suggested physiological imbalances in the athletes included in the study, but no differences between groups were observed for any of these variables. SOD values were significantly lower in the experimental group than in the control group (Table 1).

The weekly 24-h recalls showed that the two groups were similar with respect to nutritional intake (Table 2), and no differences were observed in the consumption of calories or of compounds recognized as antioxidants, such as vitamin C (±77 mg/day), vitamin E (±11 mg/day), or vitamin A (±790 mg/day). However, both groups demonstrated an initial deficiency in intake of vitamin A and vitamin E based on the recommendations of the DRI (Institute of Medicine, 2004).

There were no reports of adverse symptoms such as bloating, cramping, nausea, vomiting, or diarrhea during the intervention, and no changes occurred in body mass index and body fat of the athletes, as assessed by skinfold measures.

The intake of sesame paste caused a significant decrease in serum CK levels of ~19% in the experimental group relative to the initial values. At the end of the assessed period, serum CK in the experimental group was 5% lower than in the placebo group (P < 0.0001; Figure 1A). CK levels were higher in the placebo group at the end of the experiment (515.2 ± 15.81 U/L) than at the beginning (584.3 ± 10.48 U/L). Athletes who consumed the sesame paste showed a significant decrease in LDH enzyme at the end of the intervention period with P = 0.0184 (37% lower than baseline; Figure 1B). The placebo group showed no change in this variable, but the final values for the experimental group were only descriptively lower than the values found in the placebo group. Both groups showed a significant reduction in hs-CRP between the beginning and end of the study (experimental group P = 0.0006; placebo group P = 0.0020), with no differences between the groups at the end of the study (Figure 1C). MDA levels in the experimental group decreased significantly compared to baseline (P = 0.0144; Figure 2A). The placebo group also showed a significant reduction of MDA (P = 0.0091), but the reduction observed in the experimental group was greater (~55 vs. 21%), and supplemented athletes completed the study with values significantly lower than in the placebo group (0.7 ± 0.07 μmol/L for experimental group and 1.3 ± 0.04 μmol/L for placebo). SOD increased significantly after supplementation (~14%; P = 0.0022), while no change occurred in the placebo group (Figure 2B). The improvement in oxidative stress markers and antioxidant capacity observed in the experimental group was accompanied by significant increases in both serum vitamin A (25%) and vitamin E (65%). Vitamin A did not change in the placebo group, and vitamin E showed a significant increase in this group (~14%). However, this increase was much lower than that observed in the experimental group. Thus, the final vitamin A and E values were significantly higher in the experimental group than in the placebo group (P = 0.0009 and P = 0.0005 to vitamin A and E, respectively; Figures 2C,D).

The experimental group showed significant increases in aerobic capacity (~17%) and VO₂ peak speed (~10%), as shown in Figures 3A,B. No change was observed in the placebo group. However, the final values for these two variables did not differ between groups.

Biochemical markers commonly used for diagnosis of physiological state (Meeusen et al., 2013) and laboratorial reference parameters indicated physiological imbalance at the beginning of the study for the status of CK and LDH baseline levels. The athletes were already in the final months of a season, which explains the wear found present at the start of this study. This wear is commonly observed at the end of the season in soccer players (Handziski et al., 2006; Silva et al., 2014).

The observed deficiency in intake of vitamins A and E is probably related to the deficient intake of foods considered good sources for these vitamins by Brazilian adolescents (Tureck et al., 2013). After 28-day supplementation with the sesame paste, these two antioxidant vitamins (A and E) increased in the serum of the athletes, supporting the reported nutritional benefits of sesame (Anilakumar et al., 2010). The increase of serum vitamin E after sesame seed supplementation has been reported in rats (Yamashita et al., 1995; Hanzawa et al., 2013). It has been suggested that sesame lignans regulate vitamin E metabolism by inhibiting tocopherol catabolism (Uchida et al., 2007; Hanzawa et al., 2013). However, other factors related to the effects of training on athlete's metabolism could have influenced the increase of vitamin E, once it was also observed in placebo group.

The antioxidant activity of sesame seeds has been attributed to a synergistic effect of vitamin E with lignans that act to detoxify the hydroxyl radicals, inducing a reduction in lipid peroxidation and, consequently, in MDA level (Namiki, 2007; Askari et al., 2012). At the present time, we do not have explanations to justify the reduction of MDA serum levels in placebo group at the end of the study period. However, considering that this reduction was accompanied by an increase in vitamin E, it could be related to a decrease in lipid peroxidation. The inversely proportional relation among vitamins A and E and lipid peroxidation is well-known. The modulation of oxidizing agents production by intake of antioxidant vitamins (e.g., vitamins A and E) was previously described (Peuchant et al., 1997).

The reduction of the inflammation marker hs-CRP could be related to the antioxidant activity because the oxidative stress directly associated with the inflammatory response (Haddad, 2002). Finally, ROS formation plays an important role in the etiology of muscle injury and the lipid peroxidation due to increased production of ROS can lead to the release of muscle constituents (Taghiyar et al., 2013). This set of interactions between inflammatory processes, oxidative stress, and muscle damage could partially explain the changes in markers of oxidative stress and muscle damage markers observed in athletes supplemented with sesame paste. Further studies with larger number of participants and additional markers could help to clarify these interactions.

Interestingly, the increase in maximal aerobic capacity occurred even without any aerobic-focused training; the athletes were in the final stage of the season, when training focuses on strength, speed and technical-tactical elements. In fact, reduced aerobic capacity or absence of gains (but no increase) is expected in the final half of a soccer season (Kalapotharakos et al., 2011). Previous study reported an improved aerobic capacity concomitant with reduction of oxidative stress markers in runners supplemented with grape juice (Toscano et al., 2015). However, here it is not yet clear by which mechanisms reducing oxidative stress or systemic inflammation contributes to better aerobic capacity.

The results suggest that sesame consumption could be a nutritional strategy to improve the aerobic capacity of soccer players and to reduce important markers of oxidative stress and muscle damage.

This study was carried out in accordance with the recommendations of Resolution 196/96 of the Brazilian National Health Council (CNS) with written informed consent from all subjects. All subjects gave written informed consent in accordance with the Declaration of Helsinki. The protocol was approved by the Committee on Ethical Research Involving Humans Beings of the Federal University of Paraíba (João Pessoa, Brazil) under the Process Number 04308612.2.0000.5183.

CB participated in elaboration, execution and writing of the study. CO fulfilled the analyzes of MDA and CK, and has participated in the implementation of dietary survey. NM helped to prepare the products and monitoring of training. YS, WC, and RC performed the physical-chemical and microbiological characteristics of the product. ACS offered all technical and scientific support about cultivating sesame that was used in the study. MM, ASS, PD, and VB participated in the elaboration, coordination or writing of the study.