Time of Exercise, As a New Identified Zeitgeber for Modulating the Molecular Clocks in Skeletal Muscle

Since last decades, knowledge regarding health and physical performance has progressively developed and scientists try to find a variety of ways for their maintenance and specially promotion. Therefore, it is necessary to focus on interaction between environmental condition and responses of body tissues such as skeletal muscle. Environment is fundamental determinant for possible changes in our body comprised of temperature, humidity, wind, darkness, lightness, feeding, exercise and etc. that all of them are stressor. In this text we focus in exercise and light, components of environment stress. On the other hand, our body stability requires homeostasis that means maintenance of internal physiologic balance of body. An important part of this vital task is performed by skeletal muscle. Muscles play roles with contractile activity via different actions (concentric, eccentric and isometric). The actions of muscles lead to locomotion that it is necessity of daily life. But, internal stability isn’t kept forever and adaptations for better encountering body to environment need to transient disturbance in homeostasis. External stress from out of body Impose shock on related organs and consequently, induce short term imbalance. Physical and mental performance declines below baseline in these conditions. However, body responds to forced stress through opening and promotion of series events in cellular levels to compensate induced turbulence and imbalance. Thus, if these shocks continue regularly, sum of responses will bring adaptations and in result of them, stressed body will develop up to higher level of performance. Collectively, body strengthens and previous stress is tolerated by organs comfortably. One of these environmental stressors is exercise. Everybody needs to do exercise for health or physical performance. Until recent years, health organizations such as American College of Sport Medicine (ACSM) only emphasis on frequency, duration and intensity of exercise for exercise prescription [1] and hasn’t been considered time of doing exercise as a probable effective factor. Also, evidence and studies regarding the effect of circadian rhythms and time of exercise on biochemical and metabolic reactions in cells specifically striated muscle fibers are rare.