Long popular among bodybuilders, casein protein absorbs slowly into the bloodstream, meaning it keeps your muscles fed with amino acids for longer compared to other types of protein such as whey and plant proteins. In one Medicine and Science in Sports and Exercise study, consuming casein protein immediately before bed boosted young men’s levels of circulating amino acids for 7.5 hours; they built muscle all night long while they slept.
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^ Southren AL, Gordon GG, Tochimoto S, Pinzon G, Lane DR, Stypulkowski W (May 1967). "Mean plasma concentration, metabolic clearance and basal plasma production rates of testosterone in normal young men and women using a constant infusion procedure: effect of time of day and plasma concentration on the metabolic clearance rate of testosterone". The Journal of Clinical Endocrinology and Metabolism. 27 (5): 686–94. doi:10.1210/jcem-27-5-686. PMID 6025472.

Phosphocreatine is known to be a major source of energy for cardiac tissue alongside fatty acids, which are dominant under periods of normoxia (normal oxygen) while phosphocreatine becomes more important in periods of hypoxic stress.[281][282][283] The entire CK system plays a role in the recovery of the heart following ischemic/hypoxic stress, since blocking CK activity impairs recovery[284][285] and overexpressing CK activity promotes it.[286] This is due to the heart tissue needing high energy phosphate groups at this time, and the ischemic stress reduces CK activity and the ability of CK to donate these groups.[287][288]
These complete proteins include all of the essential amino acids that the body cannot produce itself. Different proteins, such as whey and casein, egg and soy have different absorption rates. Whether you should favor one over another for muscle building is still a subject of popular and scientific debate, although whey protein isolate, a more rapidly absorbed protein, has some support from various scientific studies. For protein powders, assess the value by checking out the protein listed on the label. Combined with resistance training, sufficient protein consumption along with an appropriate diet can lead to increased muscle and reduced body fat. You should read more about The Bodybuilding Diet for supplement timing issues before and after training. 
Some of these athletes take it to an unhealthy — and in some cases illegal — extreme with anabolic steroids, prohormones, diuretics, and potentially harmful substances. In addition to their potential performance-enhancing attributes, many of these substances also can have serious and significant side effects. A telling example of this is the story of ephedra — a once widely-used supplement for bodybuilding that has since been banned and removed from the market due to multiple reports of life-threatening side effects and death after its use.
The benefits of weight training overall are comparable to most other types of strength training: increased muscle, tendon and ligament strength, bone density, flexibility, tone, metabolic rate, and postural support. This type of training will also help prevent injury for athletes. There are benefits and limitations to weight training as compared to other types of strength training. Contrary to popular belief, weight training can be beneficial for both men and women.
Nitrate-rich foods like beets, radishes, and pomegranates are a great way to boost the production of nitric oxide (NO). Although there's very limited research examining the effects of beet root juice and pomegranate extract on resistance training, these ingredients have previously been shown to increase skeletal muscle blood flow and lead to reduced soreness, which may ultimately lead to improvements in strength and performance.[9,10]
Studies of so-called "smart drugs" have also been taken out of context. Some "smart" nutrients, available over the counter, are marketed as a way to "increase mental focus and concentration during training." The problem is that the studies they're based upon involved either animals or people with brain pathology. In normal people the effects of smart drugs remain unproven, except anecdotally.
Any type of running will help strengthen your glutes, but sprinting at a very fast speed is even more effective. You can perform sprints as part of a HIIT workout or simply increase your speed while running or briskly walking for a short distance. Start out with about 15–20 minutes of HIIT intervals and work your way up to 25–30 minutes if you’d like.  To perform intervals alternate slower running or resting for 1–2 minutes with 30–90 seconds of sprinting as fast as you can. Most experts recommend practicing HIIT workouts 2–3 times per week.
The general strategy adopted by most present-day competitive bodybuilders is to make muscle gains for most of the year (known as the "off-season") and, approximately 12–14 weeks from competition, lose a maximum of body fat (referred to as "cutting") while preserving as much muscular mass as possible. The bulking phase entails remaining in a net positive energy balance (calorie surplus). The amount of a surplus in which a person remains is based on the person's goals, as a bigger surplus and longer bulking phase will create more fat tissue. The surplus of calories relative to one's energy balance will ensure that muscles remain in a state of anabolism.
If there are any benefits for swimming performance from creatine supplementation, they appear to be limited to a 50 meter sprint or a handful of 50 meter sprints with short intermissions. Excessive sprinting (over six sprints with short breaks) or too long of a break (five minutes rather than two) seem to not be associated with the benefits of creatine supplementation.
Mitochondrial myopathies are a subgroup of mitochondrial cytopathies in which the skeletal muscle is negatively influenced. They are characterized by weaknesses in muscular function and energy metabolism.[547] These particular myopathies are thought to benefit from creatine supplementation, since creatine can help with some of the dysregulated energy production.[548]
There’s no need to go overboard on creatine intake, though, in search of crazy muscle growth: “The maximum amount of creatine that you can hold depends on the amount of muscle mass you have,” explains Bates. “So if you have more muscle, then your body can store more creatine. In general, the muscle can hold about 2 to 3 g of creatine per kilogram of muscle mass. So the amount of creatine you use will depend on the amount of muscle mass you have.” (7)

An obvious use case is injury rehabilitation. Creatine has sometimes (not always) been shown to improve responses to rehabilitation protocols. Related to this, a very rigorous review of all studies that explored effects of creatine in treating skeletal muscle disorders unambiguously showed that creatine improves muscle strength and quality of life in muscular dystrophy patients.

A testicular action was linked to circulating blood fractions – now understood to be a family of androgenic hormones – in the early work on castration and testicular transplantation in fowl by Arnold Adolph Berthold (1803–1861).[182] Research on the action of testosterone received a brief boost in 1889, when the Harvard professor Charles-Édouard Brown-Séquard (1817–1894), then in Paris, self-injected subcutaneously a "rejuvenating elixir" consisting of an extract of dog and guinea pig testicle. He reported in The Lancet that his vigor and feeling of well-being were markedly restored but the effects were transient,[183] and Brown-Séquard's hopes for the compound were dashed. Suffering the ridicule of his colleagues, he abandoned his work on the mechanisms and effects of androgens in human beings.
Entry into neural tissues in general is mediated by the secondary creatine transporter (CrT-2) known as SLC6A10,[186] which is the same transporter that is active in a male’s testicles.[145] CrT-2 belongs to the family of SLC6 transporters that act to move solutes across the membrane by coupling transport with sodium and chloride.[187][188] Genetic deletions in the 16p11.2 region, which encodes both SLC6A8[189] and SLC6A10[186] can result in severe mental retardation in humans and is one of the causes of “Creatine Deficiency Syndrome.” Creatine Deficiency Syndrome is not only caused by lack creatine transporter expression, however, as creatine synthesis is also critical for neural function.[190].[189] Retardation caused by defective creatine synthesis[31] can be reversed with creatine supplementation and dietary changes.[191]
Unlike women, who experience a rapid drop in hormone levels at menopause, men experience a more gradual decrease of testosterone levels over time. The older the man, the more likely he is to experience below-normal testosterone levels. Men with testosterone levels below 300 ng/dL may experience some degree of low T symptoms. Your doctor can conduct a blood test and recommend treatment if needed. They can discuss the potential benefits and risks of testosterone medication, as well.
Even human studies can be misinterpreted or manipulated. A few years ago a then-esoteric trace mineral called boron was found to increase testosterone, but only in older women, as it turned out. When boron was tested in young men engaged in weight training, it proved worthless for increasing testosterone. That doesn't mean boron is useless; it helps the body use the minerals calcium and magnesium, and it appears to increase mental alertness.
The rise in testosterone levels during competition predicted aggression in males but not in females.[90] Subjects who interacted with hand guns and an experimental game showed rise in testosterone and aggression.[91] Natural selection might have evolved males to be more sensitive to competitive and status challenge situations and that the interacting roles of testosterone are the essential ingredient for aggressive behaviour in these situations.[92] Testosterone produces aggression by activating subcortical areas in the brain, which may also be inhibited or suppressed by social norms or familial situations while still manifesting in diverse intensities and ways through thoughts, anger, verbal aggression, competition, dominance and physical violence.[93] Testosterone mediates attraction to cruel and violent cues in men by promoting extended viewing of violent stimuli.[94] Testosterone specific structural brain characteristic can predict aggressive behaviour in individuals.[95]
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