Perhaps 1 to 2% of intramuscular creatine is degraded into creatinine each day, which is excreted in urine. Therefore, approximately 1 to 3 g of creatine needs replenishing daily to maintain basal levels. Some of this replacement is fulfilled by the liver and kidneys, which can use the amino acids arginine and glycine to synthesize creatine. A tiny minority of people has gene mutations that result in impaired creatine synthesis or transport. These unfortunate people experience severe neurodevelopmental problems beginning early in life and benefit from consuming more creatine in their diets.
In 1927, the University of Chicago's Professor of Physiologic Chemistry, Fred C. Koch, established easy access to a large source of bovine testicles — the Chicago stockyards — and recruited students willing to endure the tedious work of extracting their isolates. In that year, Koch and his student, Lemuel McGee, derived 20 mg of a substance from a supply of 40 pounds of bovine testicles that, when administered to castrated roosters, pigs and rats, remasculinized them.[184] The group of Ernst Laqueur at the University of Amsterdam purified testosterone from bovine testicles in a similar manner in 1934, but isolation of the hormone from animal tissues in amounts permitting serious study in humans was not feasible until three European pharmaceutical giants—Schering (Berlin, Germany), Organon (Oss, Netherlands) and Ciba (Basel, Switzerland)—began full-scale steroid research and development programs in the 1930s.
Depression is a common psychological disorder affecting millions of people around the world. It results in severe sadness, loss of interest in activities, and difficulty performing daily tasks. It may be caused by common factors such as life events, genetic predisposition, conflict, and other psychological problems. However, low testosterone remains an, often missed cause of depression. In persons with low testosterone levels and depression, treatment includes testosterone replacement therapy as well as supportive measures including dietary modifications, increased activity, and use of natural supplements such as Tongkat Ali.
Some other cytokines and hormones may increase the receptor activity. These include growth hormone (GH) which acts upon the growth hormone receptor (GHR)[166][167] to stimulate c-Src[168][169] which directly increases the activity of the CrT via phosphorylation. This is known to occur with the 55kDa version of c-Src but not the 70kDa version and requires CD59 alongside c-Src.[170]
There have also been concerns that creatine can cause kidney damage, and doctors warn that people with a history of kidney disease or conditions, such as diabetes, that increase the risk of kidney problems should steer clear of the supplement. Combining creatine with nephrotoxic drugs — drugs that might damage the kidneys — like nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (advil or motrin) and naproxen sodium (Aleve), should also be avoided, according to the U.S. Department of Health and Human Services. (1)
These terms combine the prefix iso- (meaning "same") with tonic ("strength") and plio- ("more") with metric ("distance"). In "isotonic" exercises the force applied to the muscle does not change (while the length of the muscle decreases or increases) while in "plyometric" exercises the length of the muscle stretches and contracts rapidly to increase the power output of a muscle.

If you are referring to how many pushups to do in one session, the short answer is as many as you can. Aim for a number that challenges you but is still realistic. Build up from day to day to increase muscle strength. If you are referring to how long you should do pushups as a form of exercise, that is up to you. Pushups are a good part of a long-term or permanent exercise regimen. Remember that if you stop doing them, your muscles will weaken.

Macrophages are known to express creatine kinase[290] and take creatine up from a medium through a sodium dependent mechanism (likely the creatine transporter) in a saturable manner,[435] with a second component that requires there to be no concentration gradient to work against (likely passive diffusion) but this effect tends to only account for up to 10% of total uptake in the physiological range (20-60µM).[435] Supraphysiological range was not tested.

Why less volume for the smaller muscle groups, you ask? Partially because they are smaller, but mostly because they get a ton of indirect volume while training the bigger muscle groups (e.g. your biceps get hit pretty hard while training back, triceps get hit pretty hard while training chest and shoulders, shoulders get hit pretty hard while training chest, etc.).
There is some research that suggests that creatine can help people with type 2 diabetes by improving insulin sensitivity, glucose uptake into the cells, and glycemic control. This has led many people with T2 to start supplementing their diets with pure creatine to try and reap the benefits. At this time there has been no conclusive research done into the effectiveness of creatine for type 1 diabetics.