Background and Aim: Tendon is the extracellular matrix of the muscle that mechanically and structurally adapts to the mechanical load. However, the cellular and molecular mechanisms of this adaptation are not known yet. The purpose of this study was to investigate the effect of 6 weeks of resistance training on expression of two Transforming Growth Factor Beta 1 (TGF-β1) and myostatin genes in the tendon of fast- and slow-twitch muscles including Extensor Digitorum Longus (EDL) and Soleus (SOL).
Methods & Materials: Twelve male Wistar rats with 8 weeks of age were randomly divided into two groups of exercise (n=6) and control (n=6). The exercise group performed resistance training (Carrying weights with 40-160% body weight on the ladder) for 6 weeks, 5 sessions per week. Forty-eight hours after the last training session, all rats were sacrificed and the tendons of SOL and EDL muscles were extracted. The mRNA expression level of TGF-β1 and myostatin genes was assayed using real time polymerase chain reaction. Independent t-test was used for statistical analysis. 
Ethical Considerations: All experiments on animals were according to the ethical guidelines of Research Ethics Committee of Islamic Azad University, Central Tehran Branch (ethical code: IR.IAU.PS.REC.1398.296)
Results: The expression of TGF-β1 gene in EDL (P≤0.001) and SOL (P≤0.01) muscle tendons significantly increased, while the expression of myostatin gene in EDL (P≤0.001) and SOL (P≤0.05) tendons were significantly reduced. 
Conclusion: Resistance training appears to up-regulate the basal levels of TGF-β1 gene and down-regulate the basal levels of myostatin gene in tendons of fast- and slow-twitch muscles, where these effects are significantly more pronounced in the tendon of fast-twitch muscle.

Background and Aim: Tendon, like the skeletal muscle, exhibits mechanical and morphological adaptations resulted from exercise training; however, little is known about the basic cellular and molecular mechanisms that regulate these responses. The aim of the present study was therefore to investigate the effect of 6 weeks of aerobic training on the TGF-β1, myostatin and MMP9 mRNAs expression in the tendon of fast- and slow-twitch muscles. 
Methods & Materials For this purpose, 12 male Wistar rats at 8 weeks of age were randomly divided into two groups: experimental (n=6) and control (n=6). The exercise group performed aerobic training for 6 weeks, 5 sessions per week. Forty-eight hours after the last training session, all rats were sacrificed and the tendons of soleus and Extensor Digitorum Longus (EDL) muscles were extracted. Expression of TGF-β1, myostatin and MMP9 mRNAs were assayed using RealTime-PCR. Independent t-test was also used for statistical analysis.
Ethical Considerations: All stages of the study were conducted according to the ethical guidelines and authorization of Research Deputy of Islamic Azad University, Central Tehran Branch No. IR.IAU.PS.REC.1398.296. 
Results: The results showed that the expression of TGF-β1 mRNA in EDL and soleus tendons significantly increased (P≤0.001), whereas the expression of myostatin in EDL tendon was significantly reduced (P≤ 0.001). Increased mRNA expression of MMP9 in the tendon of EDL and soleus muscles was not statistically significant (P>0.05).
Conclusion: It seems that aerobic exercise can modulate the expression of genes involved in the regulation of tendon collagen in a muscle type-dependent manner.