Other side effects include increased risk of heart problems in older men with poor mobility, according to a 2009 study at Boston Medical Center. A 2017 study published in JAMA found that treatments increase coronary artery plaque volume. Additionally, the Food and Drug Administration (FDA) requires manufactures to include a notice on the labeling that states taking testosterone treatments can lead to possible increased risk of heart attacks and strokes. The FDA recommends that patients using testosterone should seek medical attention right away if they have these symptoms:

As blood levels of testosterone increase, this feeds back to suppress the production of gonadotrophin-releasing hormone from the hypothalamus which, in turn, suppresses production of luteinising hormone by the pituitary gland. Levels of testosterone begin to fall as a result, so negative feedback decreases and the hypothalamus resumes secretion of gonadotrophin-releasing hormone. 


When creatine is increased in the fetus (from maternal supplementation of 5% creatine), the fetus has a greater chance of survival and increased growth rates to a level not significantly different than vaginal birth.[531] Protection from hypoxia has also been noted in the offspring’s diaphragm (through preserved muscle fiber size),[533] kidneys,[534] and neural tissue (due to less oxidation in the brain and less cellular apoptosis).[535]
While it'’s okay to chow down on the occasional fast-food choice for convenience, a mass-gain program isn'’t an excuse to gorge on pizza and chocolate sundaes. “"Rebuilding muscle tissue broken down by training requires energy -— in other words, calories,"” says bodybuilding nutritional guru Chris Aceto. "“But many people, including many nutritionists, overestimate the energy needs for gaining mass, encouraging extreme high-calorie intakes. This often leads to an increase in bodyfat, making you bigger, for sure, but also leaving you fat." In general, aim for 300-500 more calories every day than your body burns through exercise and normal functioning (multiply bodyweight by 17). And that'’s divided among six meals a day.
Extracellular creatine (creatine outside of a cell) appears to influence creatine uptake into a cell. It seems that prolonged and excessive levels of creatine actually suppress uptake (a form of negative regulation to prevent excessive influx).[180] In vitro studies in rat muscle cells have shown that including 1mM creatine into cell culture medium substantially reduces creatine uptake into cells. The inhibitory effect was partially negated by protein synthesis inhibitors, suggesting that high levels of creatine induce the expression of a protein that suppresses creatine transporter activity.[180] Similar findings were reported in a later study in cultured mouse myoblasts, which noted a 2.4-fold increase in intracellular creatine levels in the presence of the protein synthesis inhibitor cyclohexamide.[174]
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.
Extracellular creatine (creatine outside of a cell) appears to influence creatine uptake into a cell. It seems that prolonged and excessive levels of creatine actually suppress uptake (a form of negative regulation to prevent excessive influx).[180] In vitro studies in rat muscle cells have shown that including 1mM creatine into cell culture medium substantially reduces creatine uptake into cells. The inhibitory effect was partially negated by protein synthesis inhibitors, suggesting that high levels of creatine induce the expression of a protein that suppresses creatine transporter activity.[180] Similar findings were reported in a later study in cultured mouse myoblasts, which noted a 2.4-fold increase in intracellular creatine levels in the presence of the protein synthesis inhibitor cyclohexamide.[174]
To meet the demands of a high-intensity exercise, such as a sprint, muscles derive their energy from a series of reactions involving adenosine triphosphate (ATP), phosphocreatine (PCr), adenosine diphosphate (ADP), and creatine. ATP, the amount of which is relatively constant, provides energy when it releases a phosphate molecule and becomes ADP. ATP is regenerated when PCr donates a phosphate molecule that combines with ADP. Stored PCr can fuel the first 4-5 seconds of a sprint, but another fuel source must provide the energy to sustain the activity. Creatine supplements increase the storage of PCr, thus making more ATP available to fuel the working muscles and enable them to work harder before becoming fatigued [1].
In muscle cells, the creatine transporter is predominantly localized to the sarcolemmal membrane. Western blot analysis of creatine transporter expression revealed the presence of two distinc protein bands, migrating at 55kDa and 70kDa on reducing SDS-PAGE gels.[147][148] The 73kDa band has been reported to be the predominant band in humans, with no differences based on gender.[148] A more recent report demonstrated that the 55kDa creatine transporter variant is glycosylated, forming the 73 kDa protein. Therefore, the 55 and 75kDa protein bands are actually immature and mature/processed forms of the creatine transporter protein, respectively.[149]
Creatine is known to occur in highly concetrated levels in chicken photoreceptors, relative to other parts of the eye (10-15mM[466]) alongside high levels of creatine kinase.[466] The creatine transporter in human eyes also seems to be concentrated in the photoreceptors,[468] which are known to be susceptible to hypoxic cellular death[471][472] which, for humans, usually means retinal detachment.[473] 

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.
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