Introduction
Studies have shown that the use of anabolic androgenic steroids by athletes leads to increased strength and endurance by increasing protein production and improving muscle size; however, their abuse causes severe and irreversible damage to vital tissues of the body. One of the anabolic androgenic steroids is boldenone which is used by athletes [1].
The main function of L-carnitine in the body is to support metabolism and convert food into energy. Under the influence of exercise, more free fatty acids are transferred from the breakdown of triglycerides, leading to their further oxidation. The effectiveness of L-carnitine in reducing serum triglyceride levels is also due to increased excretion of acetyl carnitine [2].
Regular and moderate exercise has been shown to reduce the risk of infection, but the increase of the intensity and duration of exercise can cause damage to the immune system, followed by damage to most tissues in the body, including the lungs [3]. The present study aims to evaluate the effect of L-carnitine use combined with endurance training on structural damage to the lung tissue in male rats poisoned with boldenone.
Methods 
In this study, 30 male Wistar rats (Weight= 228.53±7.94 g) were randomly divided into five groups: Control, boldenone, boldenone+training, boldenone+supplementation, and boldenone+training+supplementation. Boldenone steroid (5 mg/kg) was injected into the biceps femoris once a week to induce poisoning. L-carnitine supplement (600 mg/kg) was administrated in gavage into the stomach three days per week [4]. The endurance training program consisted of running on treadmill for 6 weeks, three days per week, each for 30 minutes at a speed of 12 meters per minute which reached 60 minutes and 30 meters per minute in the last week [5]. Histopathological changes in bronchioles and alveoli were examined with a light microscope. Kolmogorov-Smirnov test was used to assess the normality of data distribution, and one-way ANOVA with Bonferroni post-hoc test was used to analyze the data in SPSS v. 25 software, considering a significance level of P≤0.05
Results 
The results of one-way ANOVA showed that 6 weeks of aerobic training combined with L-carnitine consumption had an effect on weight changes in rats poisoned by boldenone; a significant increase in the weight of two groups of supplementation and endurance training+supplementation was observed compared to the poisoned group (P=0.005). The destructive effects of boldenone in the group without endurance training showed moderate damage to bronchioles and alveoli and severe inflammation and hyperemia compared to the healthy control group. In the supplementation group, there was a mild damage, while in the endurance training+supplementation group, this damage improved significantly (P=0.001) (Table 1).


Discussion 
It has been shown that taking testosterone analogs can increase the risk of cholesterol deposition and hypertension; the aromatase enzyme is activated in the body, leading to the accumulation of water, salts, and fat in the body [6]. L-carnitine plays an important role in skeletal muscles in the transfer of free fatty acids to the mitochondrial matrix under beta-oxidation process [2]. Therefore, it is possible that aerobic exercise combined with L-carnitine consumption may produce better results in weight balance.
Anabolic androgenic steroids have been shown to cause liver inflammation, hyperemia, sinusoids, and fatty vacuole formation in liver tissue [7]. In the present study, it was observed that the consumption of L-carnitine along with endurance training greatly reduced the destructive effects of boldenone. In the acute phase of lung injury, the cells involved in swelling and inflammation are present in the tissues, and alveolar macrophages increase. Blood secretions fill the alveoli and the fibrin-containing hyaline membrane is expanded [8].

Ethical Considerations
Compliance with ethical guidelines
In this study, all ethical principles for the use of animals, including the availability of water and food, proper storage conditions, and no compulsion in training, were observed. An ethical approval was obtained from the ethics committee of Islamic Azad University, Shahrood Branch (SIAU) (Code: IR.IAU.SHAHROOD.REC.1396.9).

Funding
The study was funded by Islamic Azad University, Shahrood Branch (SIAU), Semnan, Iran

Authors' contributions
Research design and implementation: Seyyed Javad Ziaulhaq; Writing, editing and correction of the article: Maleeha Ardakanizadeh; Statistical method and data analysis: Narges Haj Abutalebi; Drafting: Majid Gholami.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgements
Thanks are given to all those who contributed to the implementation of this study.

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