Osteoblast cells are known to express creatine kinase.[39][417] Bone growth factors such as IGF-1,[418] PTH,[419] and even Vitamin D[420][421] seem to induce bone growth alongside increases in creatine kinase activity. Vitamin D has been noted to work indirectly by increasing the cellular energy state (these hormones increase creatine kinase in order to do so) in order to make bone cells more responsive to estrogen.[420] This evidence, paired with enhanced growth rates of osteoblasts in the presence of higher than normal (10-20mM) concentrations of creatine[422] suggest a role of creatine in promoting osteoblastic and bone growth, secondary to increasing energy availability.
Testosterone levels generally peak during adolescence and early adulthood. As you get older, your testosterone level gradually declines — typically about 1 percent a year after age 30 or 40. It is important to determine in older men if a low testosterone level is simply due to the decline of normal aging or if it is due to a disease (hypogonadism).
In 1912, Harvard University researchers Otto Folin and Willey Glover Denis found evidence that ingesting creatine can dramatically boost the creatine content of the muscle.[5][non-primary source needed] In the late 1920s, after finding that the intramuscular stores of creatine can be increased by ingesting creatine in larger than normal amounts, scientists discovered creatine phosphate, and determined that creatine is a key player in the metabolism of skeletal muscle. The substance creatine is naturally formed in vertebrates.[6]
Of the three, protein will of course play the most important role in the muscle building process (like calories, it’s one our required “supplies”), although fat and carbs will still be important for other reasons which range from optimizing hormone production (e.g. testosterone, the muscle building hormone) to enhancing training performance and recovery.
Hook a velcro cuff to a low cable pulley and then attach the cuff to your right ankle. Face the weight stack from a distance of about two feet, grasping the frame for support. Keep your knees and hips bent slightly and your abs tight, contract your right glutes to kickback the leg. Slowly bring your working leg forward, resisting the pull of the cable until you reach the starting position. Repeat for required reps, then switch legs.
Wilkinson, S. B., Tarnopolsky, M. A., MacDonald, M. J., MacDonald, J. R., Armstrong, D., & Phillips, S. M. (2007). Consumption of fluid skim milk promotes greater muscle protein accretion after resistance exercise than does consumption of an isonitrogenous and isoenergetic soy-protein beverage. The American Journal of Clinical Nutrition, 85(4), 1031-1040.

Genetic deficiencies in the creatine biosynthetic pathway lead to various severe neurological defects.[26] Clinically, there are three distinct disorders of creatine metabolism. Deficiencies in the two synthesis enzymes can cause L-arginine:glycine amidinotransferase deficiency caused by variants in GATM and guanidinoacetate methyltransferase deficiency, caused by variants in GAMT. Both biosynthetic defects are inherited in an autosomal recessive manner. A third defect, creatine transporter defect, is caused by mutations in SLC6A8 and inherited in a X-linked manner. This condition is related to the transport of creatine into the brain.[27]
Bodybuilders often split their food intake for the day into 5 to 7 meals of roughly equal nutritional content and attempt to eat at regular intervals (e.g. every 2 to 3 hours). This method can serve two purposes: to limit overindulging in the cutting phase, and to physically allow for the consumption of large volumes of food during the bulking phase. Contrary to popular belief, eating more frequently does not increase basal metabolic rate when compared to the traditional 3 meals a day. While food does have a metabolic cost to digest, absorb, and store, called the thermic effect of food, it depends on the quantity and type of food, not how the food is spread across the meals of the day. Well-controlled studies using whole-body calorimetry and doubly labeled water have demonstrated that there is no metabolic advantage to eating more frequently.[38][39][40]
Focus on form. Good form means you can reap all of the benefits of your workout and avoid injuries at the same time. To maintain proper form, pay attention to your posture (stand tall with chest lifted and abs held tight), move slowly (this ensures you're relying on muscles, not momentum, to do the lifting), and remember to breathe. Many people hold their breath while exerting, but exhaling during the hardest part of the exercise helps fuel the movement.