Satellite cells (SCs) are the most abundant skeletal muscle stem cells. They are widely recognized for their contributions to maintenance of muscle mass, regeneration and hypertrophy during the human life span. These cells are good candidates for cell therapy due to their self-renewal capabilities and presence in an undifferentiated form. Presently, a significant gap exists between our knowledge of SCs behavior and their application as a means for human skeletal muscle tissue repair and regeneration. Both physiological and pathological stimuli potentially affect SCs activation, proliferation, and terminal differentiation - the former category being the focus of this article.Activation of SCs occurs following exercise, post-training micro-injuries, and electrical stimulation. Exercise, as a potent and natural stimulus, is at the center of numerous studies on SC activation and relevant fields. According to research, different exercise modalities end with various effects. This review article attempts to picture the state of the art of the SCs life span and their engagement in muscle regeneration and hypertrophy in exercise.

Introduction: The aim of this study was to investigate the role of resistance training on hormones involved in muscle hypertrophy. Methods: 30 professional athletes randomly into three groups of high intensity resistance training, traditional resistance training and controls were divided. After initial sampling, the intervention groups were active for 12 weeks. Blood samples were taken 48 hours after the last training session to remove the response to the last training session. All data were analyzed at the significant level P 0. 05. Results: The results showed that cortisol, testosterone, weight, fat percentage and body mass index in the high intensity resistance training group had a significant change compared to the control group and traditional resistance training (P<0. 05). The results also showed that the strength of the upper body and lower torso in the intervening groups increased significantly compared to the control group (P<0. 05). Low trunk strength is also a significant difference between the intervention groups and the control group. But there is no significant difference between the traditional and high intensity resistance training group (P>0. 05). However, these incremental changes have been more pronounced in the periodic resistance group. No significant change was observed in insulin, insulin resistance, glucose and glucagon (P>0. 05). Conclusion: The intensity of training seems to be an important and influential factor in the rate of change in factors related to athletes' performance. But it did not change the hormonal status of the athletes. Of course, more research is needed in the future to reach a definitive conclusion.

The experiments were carried out on the muscle spindle (MS) that located onto the soleus muscle (SM) in the anaesthetized rats. After applying a mechanical slow stretch (SS) on the SM, the MS wasn't influenced by this stimulant and it was in a slack status. On the other hand, the MS has showed a dysfunction. The slack status of MS, it means, without electro-mechanical activity for MS that was observed in isolating MS. And this slack status of MS also was occurred by insufficient of γ-motor stimulation. With using the passive stimulating vibration on the MS-SM, again, the slack status of MS was observed. Of course, in this experiment, before that the MS was made up with passive vibration, firstly, the activation of MS was clearly observed by gs-activity. On contrary of the positive effect of  gs into MS, there wasn't a positive effect with gd-activity into MS. But, it's stated that, there was the resting discharge (RD) in the MS during slack status and the RD scale has been significantly acceptable. The MS-RD was created with both of the SS and especially by γs stimulation, though not with gd stimulation.However, it was concluded that, the changing of MS-activity could be caused with the changing length of SK.M. In this process, the MS respond was pertinent to gs-activity. Meanwhile, the activation of γs was followed by activity of MS- chain- afferent. It's seemed that, in this loop of nervo-muscular wasn't any place for activating of MS-bag fiber.