Introduction
The elderly population is increasing with an increasing mortality rate due to liver diseases [1]. Aging causes impairments in mitochondrial respiration and lipid profile. These conditions can ultimately increase the risks of metabolic syndromes [2], oxidative/antioxidant imbalances in the body, and liver disorders [3]. By enhancing hematological factors and cellular redox, physical exercises can increase mitochondrial biogenesis and transcription factors of genes in liver tissues [5, 6, 7, 8]. 
It has been recommended to use antioxidants such as resveratrol for the treatment of many diseases due to its antioxidant, anti-inflammatory, anti-apoptotic properties, which can enhance the metabolism of fats and glucose [11]. Since there is scant research on the combined effects of training and resveratrol use on expression of antioxidant genes, the present study aims to examine the combined effects of high-intensity intermittent swimming and resveratrol use on antioxidant markers and lipid peroxidation index in the liver tissue of older rats.
Methods 
In this experimental study, 32 elder male rats (Age: 18–20 months, weight: 350-70 grams) were randomly divided into four groups of control (methylcellulose use only), resveratrol, swimming, and swimming+resveratrol. During 6 weeks of intervention, the control group received only the inert solvent of resveratrol (based on previous studies). The swimming was performed at three sessions lasted 14-20 seconds with a 10-second interval between sets. The weight attached to the rats in the first week was equal to 9% of their weights, and 1% was added to their weights every week to apply the overload principle. The added weight in the last week reached 15% of their body weights [15]. Resveratrol was administrated by gavage daily as 100 mg/kg dissolved in 1% methylcellulose [16]. The rats were anesthetized 48 hours after the last training session and resveratrol consumption, and their liver tissues were carefully extracted.To measure the gene expression levels of superoxide dismutase (SOD) and glutathione peroxidase (GPx), real-time polymerase chain reaction method was used. The Malondialdehyde (MDA) level was measured by the sandwich ELISA method using a special MDA kit (ZellBio Co.). One-way analysis of variance (ANOVA) followed by Tukey’s post hoc test was used to compare the means between different groups. Data analysis was carried out in SPSS version 22 software (IBM Corp., Armonk, NY, USA).
Results
The GPx, MDA and SOD levels are compared in Figure 1. The results of one-way ANOVA showed no significant differences in SOD level among the study groups (P=0.92), but there were significant differences in GPx (P=0.001) and MDA (P=0.001) levels. The results of Tukey’s post-hoc test showed that GPx level in the swimming+resveratrol group were significantly higher than in the control (P=0.001), resveratrol (P=0.04), and swimming (P=0.002) groups. Moreover, the MDA level in the resveratrol (P=0.001), swimming (P=0.001), and swimming+resveratrol (P=0.001) groups were significantly lower than in the control group. Furthermore, MDA level in the swimming+resveratrol group were significantly lower than in the resveratrol (P=0.001) and swimming (P=0.009) groups (Figure 1).
Discussion
This study results indicated that high-intensity intermittent swimming and resveratrol supplementation simultaneously increased expression level of GPx and reduced expression level of MDA gene in the liver tissues of older rats. The swimming alone also increased GPx and reduced MDA levels. Hence, high-intensity training can increase catecholamines (epinephrine and norepinephrine), activate adenylate cyclase, improve cyclic adenosine monophosphate (AMP), and cause phosphorylation of protein kinase A and AMP-activated protein kinase, leading to the activation of the nuclear factor erythroid 2-related factor 1 and 2 and an increase in the intracellular expression of antioxidant enzymes in the liver tissues by the peroxisome proliferator-activated receptor gamma coactivator 1-alpha [7]. 
Studies have shown that endurance training (continuous and intermittent) depending on the type, intensity, and number of sessions per week at different ages can have various effects on oxidative stress. However, performing these exercises, especially high-intensity training, can boost the antioxidant capacity and strengthen the enzymatic and non-enzymatic antioxidant defense systems. In the present study, resveratrol supplementation alone increased GPx and reduced MDA expression levels in the liver tissues of older rats. Its consumption can improve the liver function and reduce oxidative stress through different mechanisms. In addition to the enzymatic antioxidant defense system, resveratrol can improve the enzymatic antioxidant system due to its flavonoids and ingredients. 

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of Marvdasht Branch, Islamic Azad University (Code: IR.IAU.M.REC.1399.036). 

Funding
This research is taken from the PhD thesis of Maryam Mahboudi, Department of Physical Education, Sports Physiology, Faculty of Physical Education, Islamic Azad University, Aliabad Katul Branch. This research received no specific funding from any funding organization in the public, commercial or non-profit sectors.

Authors' contributions
All authors contributed equally to preparing this article.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgements
The authors would like to thank the spiritual support of the Deputy for Research and Technology of Aliabad Katoul Branch, Islamic Azad University.



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