The production of free radicals increases from the fourth decade of life onwards, and the amount of antioxidant enzymes such as superoxide dismutase (SOD) and glutathione peroxidase (GPX) decreases (1). Reactive oxygen species (ROS) lead to oxidative damage in lipid membranes and DNA through programmed cell death (2). Lipid peroxidation produces substances such as malondialdehyde (MDA) (3), and DNA damage is measured through 8-hydroxydeoxyguanosine (8-OHdG) (4). One of the factors that plays an important role in the loss of an active lifestyle is the progressive reduction of muscle mass or sarcopenia (5). Muscle mass forms more than 50% of the body weight of young people, while this amount reaches approximately 25% in older adults (6).

Cumulative damage to skeletal muscle and nerve cells in sarcopenia may result from oxidative stress. Sarcopenia could be caused by an increase of endogenous ROS formation in skeletal muscle but the source of ROS in sarcopenic muscle is still relatively unknown. However, an age-associated increase of ROS levels in muscle mass, as a consequence of an upregulation of NADPH oxidase 2 enzyme (NOX₂), has been reported (7). Moreover, a study by Sullivan-Gunn and Lewandowski (8) has highlighted the role of NOX₂ enzyme in a healthy mouse model of aging, suggesting that elevated levels of H₂O₂ from NOX₂, as well as the lack of antioxidant protection from catalase and glutathione peroxidase (GPX), carry out a key role in the onset of sarcopenia. The lack of SOD₁ also causes a reduction of skeletal muscle mass, impairment of neurotransmitter release, and neuronal degeneration in mice (9).

Moreover, irrespective of the mechanism, oxidative stress causes the onset of many types of disease such as cardiovascular disease (CVD) and cancer (10, 11) as well as modulation of cancer treatment-related outcomes (12, 13). Excessive ROS levels have been linked to tumor initiation, growth and progression (14). As mentioned before, the production of ROS increases with age. Therefore, the possibility of getting diseases related to ROS increases in older adults. Therapeutic benefits of creatine supplementation (CS) in some diseases associated with oxidative stress have been confirmed (15, 16).

In the body as a whole, creatine is synthesized in the kidney and in the liver (17). Specifically, the kidney accomplishes the first step of the synthesis, forming guanidinoacetic acid from arginine and glycine. Guanidinoacetic acid is then transported to the liver, where it is converted into creatine with the intervention of the methyl donor S-adenosyl-methionine (17). Creatine monohydrate is a common and popular supplement used by many athletes to improve strength, endurance and athletic performance (18). The antioxidant properties of creatine might be due to the presence of arginine, which disintegrates nitric oxide (19). The NO formed undergoes oxidative degradation to the stable inorganic nitrogen oxides, nitrite (NO₂), and nitrate (NO₃), which are detectable in plasma and urine (20).

Resistance training (RT) has the beneficial effects of preventing the complications of aging and leads to improved health through a variety of mechanisms (21). RT has been shown to reduce MDA and hydrogen peroxidase, while boosting GPX and SOD activity (22). On the other hand, in aging, we face a phenomenon called anabolic resistance which reduces the response of muscles to RT (23).

Long-term creatine supplementation along with moderate-intensity resistance and endurance training can probably reduce oxidative stress and increase the antioxidant defense system; however, in the short-term, creatine consumption and its effect on oxidative stress due to endurance exercise is not well known, although it seems that the short-term creatine ingestion possibly reduces oxidative stress due to intense resistance exercise. Considering the antioxidant effects of regular physical activity and creatine, it seems that the combined effect of physical activity and creatine consumption can reduce oxidative stress (12).

Stefani et al. (24) noted that creatine consumption combined with resistance exercise could reduce oxidative stress (reduced lipoperoxidation in plasma, heart and liver, and gastrocnemius). Moreover, this supplement had positive effects on the SOD activity in all groups. Creatine consumption possibly have a synergistic effect with resistance training in modulating SOD activity in the heart (24). Additionally, Rahimi stated that consuming 20 g of creatine per day for 7 days reduces MDA and 8-hydroxy-20 -deoxyguanosine (8-OHdG) after resistance training. Additionally, the antioxidant effects of creatine may be related to its compounds (arginine, glycine and methionine) (25).

Most studies on the effect of resistance training (RT) and creatine supplementation (CS) on oxidant/antioxidant equilibrium have focused on young people (25). To date, the effects of regular RT alone and with CS on various oxidative markers and antioxidant defense system in older adults have not been studied.

There was no significant difference (p > 0.05) between the three groups regarding any of the research variables in the pre-test.

There were significant main effect of time (F = 127.38, p = 0.001, and F = 468.47, p = 0.001) and group × time interaction (F = 21.98, p = 0.001, and F = 106.21, p = 0.001) respectively for malondialdehyde (MDA) and 8-hydroxydeoxyguanosine (8-OHdG). These serum indices of oxidative damage were significantly reduced in both experimental groups (RT + CS and RT + P) after 10 weeks of RT (in all cases, p = 0.001) and there was no difference between the training groups (p > 0.05; Figures 2A,B).

In relation to the glutathione peroxidase (GPX), there was a significant main effect of time (F = 155.32, p = 0.001), group × time interaction (F = 37.47, p = 0.001) and main effect of group (F = 5.39, p = 0.009). Serum concentrations of GPX was higher in both training groups (RT + CS and RT + P) compared with the control group in the post-test (p = 0.001 and p = 0.006, respectively). Indeed, in the post-test, the levels of this enzyme in the RT + CS was higher than the RT + P group (p = 0.004). GPX substantially increased in the RT + CS and RT + P groups after the 10-week intervention compared with the pre-test (p = 0.001, eta = 0.87 and p = 0.001, eta = 0.86; Figure 2C).

In regards total antioxidant capacity (TAC), there was a significant main effect of time (F = 41.77, p = 0.001) and group × time interaction (F = 15.51, p = 0.001). This index of antioxidant capacity also had an interesting rise in both training groups after 10 weeks (in both cases, p = 0.001), while no significant difference was observed between the groups in the post-test (p > 0.05; Figure 2D).

Regarding body mass index (BMI), there was a significant main effect of time (F = 3.68, p = 0.049) and group × time interaction (F = 23.93, p = 0.001). Intragroup changes showed that the body mass index decreased (p = 0.001) only in the RT + P group in comparison with the pre-test (Figure 2E).

However, with regard to creatinine, the interaction of time and group was significant (F = 6.40, p = 0.004). Creatinine levels elevated only in the RT + CS group after 10 weeks of supplementation (p = 0.014). No significant difference was observed between the groups in the post-test (p > 0.05; Figure 2F).

There was also a significant main effect of time (F = 1831.58, p = 0.001), group × time interaction (F = 441.69, p = 0.001) and main effect of group (F = 111.97, p = 0.001) for quality of life (Figure 2G). This index in the experimental groups (RT + CS and RT + P) improved after 10 weeks of intervention (in both groups, p = 0.001). Indeed, there was a difference between the groups in the post-test so much so that the quality-of-life index in the training groups was better than in the control group (Table 2).

Changes in muscle strength in all seven resistance movements including leg extension and leg curl machine, barbell bench press, lateral pulldown, barbell curl, overhead press, and triceps extension machine indicated that the training groups (RT + CS and RT + P) had a sharp increase compared to the pre-test (p < 0.05) as well as compared to the control groups in the post-test (p < 0.05). In addition, the increase in muscle strength of the RT + CS group was greater than that of the RT + P group (p < 0.05; Table 2).

Findings of the present study showed that 10 weeks of RT reduced the oxidative damage indices in older adults by strengthening the antioxidant defense system. In fact, after 10 weeks of regular RT, MDA and 8-hydroxydeoxyguanosine (8-OHdG) in the training groups decreased, while the amount of GPX and total antioxidant capacity (TAC) increased. An interesting result is that creatine supplementation did not have an incremental effect on reducing oxidative damage. However, the rate of increase in GPX enzyme in the supplement group was higher than the placebo group demonstrating the synergistic effect of creatine supplementation on the levels of this antioxidant enzyme.

Alikhani and colleagues in line with the present study illustrated an improvement in MDA and TAC in older and younger people after 12 weeks of RT. (30) Consistent with the current findings, two other studies also confirmed the positive effects of regular exercise training on improving the activity of antioxidant enzymes such as catalase, superoxide dismutase and glutathione peroxidase in the older adults (31, 32). The effect of combined training (aerobic and resistance training) on DNA oxidative damage and antioxidant properties in middle-aged and older people was investigated by (33) which indicated the positive role of the above exercise program in improving antioxidant capacity and reducing 8-OHdG. Ghahramani Moghadam^’s study also demonstrated a reduction in 8-OHdG levels in older women after 8 weeks of exercise training (34). In another study by Padilha, three sessions of RT per week (for 12-weeks) reduced oxidative stress indices in older women (35). In a research conducted by Koechlin, the effect of RT with an intensity of 40% of 1-RM with N-acetylcystein supplementation on the older adults with chronic obstructive pulmonary disease was evaluated and indicated that the TAC index did not change (36). It appears that the low intensity of the exercise program, the type of supplement used and also the illnesses of the subjects are the reasons for the contradiction in the findings of the above research with the results of the present study.

Kinksly et al. examined the effect of cycling and creatine consumption on non-enzymatic indicators of antioxidant defense. The finding of the above study indicated that creatine had no effect on improving the antioxidant system (37). However, in a study conducted on young subjects stated that 7 days of creatine supplementation reduced MDA and 8-OHdG following acute RT. Candow et al. reported that creatine supplementation improved body composition and muscle strength in older adults without any adverse effects on the kidney (27). Canadow in another study illustrated that creatine supplementation had anti-sarcopenic effects and would improve bone mineral density (38). In addition, Deminice et al. stated that short-term creatine supplementation (for 7 days) had no effect on catalase and superoxide dismutase activity after an anaerobic test (39).

According to the results of previous research, it seems that short-term use of creatine supplementation has no effect on strengthening the antioxidant system. Available findings are limited and relatively contradictory in regards the long-term effects of this supplement which makes the final conclusion difficult. As mentioned, in the present study, 10 weeks of creatine monohydrate supplementation doubled the activity of GPX enzyme, while no synergistic effect of this supplement on TAC were observed. Therefore, further research is needed to prove the possible effects of creatine on boosting the antioxidant system. Nevertheless, it has been found that regular RT can be a logical approach for reducing exercise training-induced oxidative damage by enhancing the antioxidant capacity of older adults.

The finding of the present study regarding changes in muscle strength showed that after 10 weeks of RT and creatine supplementation, the average increase in muscle strength (mean of the seven muscle groups studied) in the training-placebo group was 35.9% and in the training-creatine group was equal to 57%. These findings generally indicate the positive effect of RT on increasing muscle strength in the older adults, and in particular the synergistic effects of creatine supplementation on elevating strength in these individuals. Moreover, the results of the current study demonstrated that there was a significant decrease in body mass index only in the training-placebo group. The present research finding have been confirmed by previous research on the effect of RT on upgrading muscle strength and body composition, as well as the dual role of creatine supplementation in improving muscle strength in older adults (27).

The present results showed an improvement of 79.9% and 89.2% of quality of life index in the training-placebo and training-creatine groups, respectively.

Regular resistance training can be recommended as a very suitable non-pharmacological approach to strengthen the body’s antioxidant system, muscle strength and quality of life in older adults. There are no definite findings on the role of creatine on the antioxidant system and quality of life in older adults, but the use of this supplement in addition to RT can double the amount of strength gained from resistance training. From a clinical viewpoint, our findings indicated that these results can be obtained using a modest exercise prescription for an aging population.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by the research design was approved by the Ethics Committee of the University of Kurdistan (IR.UOK.REC.1399.010). The patients/participants provided their written informed consent to participate in this study.

EA: writing original draft of the manuscript. DS-V: methodology, editing the manuscript, and supervision. EA and DS-V: data analysis and interpretation. All authors contributed to the article and approved the submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.