Spero Karas, MD, assistant professor of orthopaedics in the division of sports medicine at Emory University, says that testosterone, the male hormone responsible for muscle growth, maxes out between the ages of 16 and 18. It reaches a plateau during the 20s and then begins to decline. As a result, muscle building after the adolescent years can be challenging, he says.
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]
A previous meta-analysis [28] reported an overall creatine supplementation effect size (ES) of 0.24 ± 0.02 for activities lasting ≤30 s. (primarily using the ATP- phosphocreatine energy system). For this short high-intensity exercise, creatine supplementation resulted in a 7.5 ± 0.7% increase from base line which was greater than the 4.3 ± 0.6% improvement observed for placebo groups. When looking at the individual selected measures for anaerobic performance the greatest effect of creatine supplementation was observed on the number of repetitions which showed an ES of 0.64 ± 0.18. Furthermore, an increase from base line of 45.4 ± 7.2% compared to 22.9 ± 7.3% for the placebo group was observed. The second greatest ES was on the weight lifted at 0.51 ± 0.16 with an increase from base line of 13.4 ± 2.7% for the placebo group and 24.7 ± 3.9% for the creatine group. Other measures improved by creatine with a mean ES greater than 0 were for the amount of work accomplished, weight lifted, time, force production, cycle ergometer revolutions/min and power. The possible effect of creatine supplementation on multiple high intensity short duration bouts (<30 s) have shown an ES not statistically significant from 0. This would indicate that creatine supplementation might be useful to attenuate fatigue symptoms over multiple bouts of high-intensity, short duration exercise. The ES of creatine on anaerobic endurance exercise (>30 – 150s), primarily using the anaerobic glycolysis energy system, was 0.19 ± 0.05 with an improvement from baseline of 4.9 ± 1.5 % for creatine and -2.0 ± 0.6% for the placebo. The specific aspects of anaerobic endurance performance improved by creatine supplementation were work and power, both of which had a mean ES greater than 0. From the findings of this previous meta-analysis [28] it would appear that creatine supplementation has the most pronounced effect on short duration (<30s) high intensity intermittent exercises.
In fact, in one new study comparing the effects of aerobic exercise versus resistance training on the psychological health of obese adolescents, researchers found that people in the resistance group experienced significantly greater self-esteem and perceived strength over four weeks. But what’s most interesting is that the feeling of getting stronger — rather than any measurable gains — was all it took to give them a boost.
The maximum amount of creatine the body can store is about 0.3 gram per kilogram of body weight [6]. The creatine content of skeletal (voluntary) muscles averages 125 millimoles per kilogram of dry matter (mmol/kg/dm) and ranges from about 60 to 160 mmol/kg/dm. Approximately 60% of muscle creatine is in the form of PCr. Human muscle seems to have an upper limit of creatine storage of 150 to 160 mmol/kg/dm. Athletes with high creatine stores don't appear to benefit from supplementation, whereas individuals with the lowest levels, such as vegetarians, have the most pronounced increases following supplementation. Without supplementation, the body can replenish muscle creatine at the rate of about 2 g/day [7].
In particular situations, a coach may advise performing the valsalva maneuver during exercises which place a load on the spine. The vasalva maneuver consists of closing the windpipe and clenching the abdominal muscles as if exhaling, and is performed naturally and unconsciously by most people when applying great force. It serves to stiffen the abdomen and torso and assist the back muscles and spine in supporting the heavy weight. Although it briefly increases blood pressure, its is still recommended by weightlifting experts such as Rippetoe since the risk of a stroke by aneurysm is far lower than the risk of an orthopedic injury caused by inadequate rigidity of the torso.[10] Some medical experts warn that the mechanism of building "high levels of intra-abdominal pressure (IAP)...produced by breath holding using the Valsava maneuver", to "ensure spine stiffness and stability during these extraordinary demands", "should be considered only for extreme weight-lifting challenges — not for rehabilitation exercise".[11]
The process of phagocytosis (a macrophage consuming a pathogen) in macrophages appears to be associated with an acute reduction in creatine phosphate stores (45%)[436] and an increase in creatine kinase activity,[290] although prolonged stimulation is met with an increase in creatine phosphate (20%).[290] The creatine kinase activity does not appear to be altered based on creatine availability,[290] but since ATP seems to be preserved in these instances,[436][290] the increase in phosphocreatine may be explained by an overall creatine pool paralleling that found in medium.[290]

Side-Effects: While the signs of a great body may make one think that there cannot be anything wrong with bodybuilding supplements, the facts speak otherwise. Bodybuilding supplements do have side-effects and you must listen to your trainer before giving in to the thoughts of buying one. Creatine can cause heart problems, kidney problems, dehydration, diarrhoea and muscle cramping. You must also discuss your medical history with the trainer. 
The genealogy of lifting can be traced back to the beginning of recorded history[1] where humanity's fascination with physical abilities can be found among numerous ancient writings. In many prehistoric tribes, they would have a big rock they would try to lift, and the first one to lift it would inscribe their name into the stone. Such rocks have been found in Greek and Scottish castles.[2] Progressive resistance training dates back at least to Ancient Greece, when legend has it that wrestler Milo of Croton trained by carrying a newborn calf on his back every day until it was fully grown. Another Greek, the physician Galen, described strength training exercises using the halteres (an early form of dumbbell) in the 2nd century.
Side-Effects: While the signs of a great body may make one think that there cannot be anything wrong with bodybuilding supplements, the facts speak otherwise. Bodybuilding supplements do have side-effects and you must listen to your trainer before giving in to the thoughts of buying one. Creatine can cause heart problems, kidney problems, dehydration, diarrhoea and muscle cramping. You must also discuss your medical history with the trainer. 
Nephrotoxic drugs. Because taking high doses of creatine might harm your kidneys, there is concern about combining creatine with drugs that might damage the kidneys (nephrotoxic drugs). Potentially nephrotoxic drugs include nonsteroidal anti-inflammatory drug (NSAIDs) such as ibuprofen (Advil, Motrin IB, others) and naproxen sodium (Aleve, others), cyclosporine (Neoral, Sandimmune) and others.
Side-Effects: While the signs of a great body may make one think that there cannot be anything wrong with bodybuilding supplements, the facts speak otherwise. Bodybuilding supplements do have side-effects and you must listen to your trainer before giving in to the thoughts of buying one. Creatine can cause heart problems, kidney problems, dehydration, diarrhoea and muscle cramping. You must also discuss your medical history with the trainer. 
Bodybuilding developed in the late 19th century, promoted in England by German Eugen Sandow, now considered as the "Father of Bodybuilding". He allowed audiences to enjoy viewing his physique in "muscle display performances". Although audiences were thrilled to see a well-developed physique, the men simply displayed their bodies as part of strength demonstrations or wrestling matches. Sandow had a stage show built around these displays through his manager, Florenz Ziegfeld. The Oscar-winning 1936 musical film The Great Ziegfeld depicts the beginning of modern bodybuilding, when Sandow began to display his body for carnivals.
For many people in rehabilitation or with an acquired disability, such as following stroke or orthopaedic surgery, strength training for weak muscles is a key factor to optimise recovery.[35] For people with such a health condition, their strength training is likely to need to be designed by an appropriate health professional, such as a physiotherapist.
Prohormones are precursors to hormones and are most typically sold to bodybuilders as a precursor to the natural hormone testosterone. This conversion requires naturally occurring enzymes in the body. Side effects are not uncommon, as prohormones can also convert further into DHT and estrogen. To deal with this, many supplements also have aromatase inhibitors and DHT blockers such as chrysin and 4-androstene-3,6,17-trione. To date most prohormone products have not been thoroughly studied, and the health effects of prolonged use are unknown. Although initially available over the counter, their purchase was made illegal without a prescription in the US in 2004, and they hold similar status in many other countries. They remain legal, however, in the United Kingdom and the wider European Union. Their use is prohibited by most sporting bodies.
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