The creatine kinase (CK) enzyme in rat heart tissue appears to have a KM around 6mM of creatine as substrate.[280] and is known to positively influence mitochondrial function as higher cytoplasmic phosphocreatine concentrations (not so much creatine per se) increase the oxidative efficiency of mitochondria[280] This is thought to be due to the transfer of high energy phosphate groups.[280]
Bodybuilders do cardio training such as running and using a StairMaster StepMill to burn fat and make their muscles more visible. “Do cardio throughout the year at least three days a week for at least 30-40 minutes, whether it be first thing in the morning on an empty stomach or after a post-workout protein shake,” says Heath. “Cardio won’t kill your gains as much as you think, you’ll see how much muscle you really have.” Break a sweat to stay lean ’round the clock. 

Lung disease (Chronic obstructive pulmonary disease). Early research on the effects of creatine in people with chronic obstructive pulmonary disease (COPD) is inconsistent. Some research suggests that taking creating daily does not improve lung function. However, other research suggests that taking creatine may improve lung function or exercise capacity.
Under most circumstances, sports drinks do not offer a physiological benefit over water during weight training.[18] However, high-intensity exercise for a continuous duration of at least one hour may require the replenishment of electrolytes which a sports drink may provide.[19] Some may maintain that energy drinks, such as Red Bull that contain caffeine, improve performance in weight training and other physical exercise, but in fact, these energy drinks can cause dehydration, tremors, heat stroke, and heart attack when consumed in excess.[20] 'Sports drinks' that contain simple carbohydrates & water do not cause ill effects, but are most likely unnecessary for the average trainee. More recently, people have been taking pre-workout before working out to increase performance. The main ingredients in these pre-workouts are: beta-alanine, creatine, BCAAs (branched chain amino acids) and caffeine.[21]
Creatine supplementation at 300mg/kg for one week (loading with no maintenance) in youth subject to six repeated 35m sprints (10s rest, known as the Running-based Anaerobic Sprint Test or RAST) noted that the increased average and peak power output seen in creatine was not met with a reduction in fatigue, although there was an attenuation in inflammation from exercise (TNFα and CRP).[299]
I’m glad you found some good information from this article. For any of these supplements, I would suggest talking to your doctor and pharmacist. I would suggest thinking about why you are interested in taking testosterone. Are you looking to increase muscle size? Bulk up? Knowing your fitness goals will help you determine which products are appropriate for you.
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]
That pump is tangible, real-time biofeedback to let you know that blood is flowing to your muscle cells, beginning a chain of events that stimulates protein synthesis. Maybe that'’s why it's easy to overlook how important good nutrition is in the mass-building equation. When you choose to eat, say, chicken instead of ice cream, there'’s no immediate muscle gratification -- no pump to keep you motivated.
Kornblum, C., Schroder, R., Muller, K., Vorgerd, M., Eggers, J., Bogdanow, M., Papassotiropoulos, A., Fabian, K., Klockgether, T., and Zange, J. Creatine has no beneficial effect on skeletal muscle energy metabolism in patients with single mitochondrial DNA deletions: a placebo-controlled, double-blind 31P-MRS crossover study. Eur J Neurol 2005;12:300-309. View abstract.
Creatine supplementation often causes weight gain that can be mistaken for increase in muscle mass. Increasing intracellular creatine may cause an osmotic influx of water into the cell because creatine is an osmotically active substance [10]. It is possible that the weight gained is water retention and not increased muscle. The retention of water may be connected to reports of muscle cramps, dehydration, and heat intolerance when taking creatine supplements. It would be prudent to encourage proper hydration for creatine users. Further research is needed to investigate these and other possible side effects.

Creatine citrate is creatine bound to citric acid, or citrate. Creatine citrate does not differ greatly from monohydrate in regard to absorption or kinetics.[83] Note that creatine citrate is more water-soluble than monohydrate,[84] but creatine absorption is generally not limited by solubility. The increased water solubility may play a factor in palatability.
One pilot study using 150mg/kg creatine monohydrate for a five day loading phase followed by maintenance (60mg/kg) for the remainder of the five weeks noted that supplementation was associated with fewer muscle symptoms and complaints alongside improved muscular function,[572] yet a later trial trying to replicate the obsevations using 150mg/kg daily for five weeks noted the opposite, that creatine supplementation exacerbated symptoms.[573]